Patent Application
20210128791
The invention disclosed herein generally relates to implantable devices.
Tissue integration is a major challenge in the field of implantable biomedical device. Efforts are made to achieve improved soft tissue integration and osteointegration in the biomedical fields that involve implantable devices, e.g., dental implants, stenting, or bone implants with success of some degree, but tissue integration remains a major challenge.
Additionally, implant-associated microbial infections are one of the most serious complications in orthopedic surgery because they are extremely difficult to treat and result in increased morbidity and substantially worse outcomes. Despite a recent focus on aseptic surgical and procedural techniques, catheter- and surgical implant-associated infections account for nearly half of the 2 million cases of nosocomial infections in the United States per year, representing a significant healthcare and economic burden. Devices and methods for imaging sub-millimeter-sized tumors that are embedded in tissues (e.g., at depths greater than 1-2 mm) are not available. Consequently, methods for treating such tumors are also lacking due to the inability in combining high specific and sensitive imaging with highly conformal radiation.’
Management of an implant-associated infection typically requires device removal, multiple debridement surgeries, and long-term systemic antibiotic therapy, despite the associated side effects and additional complications. However, these additional surgical procedures and medical therapies not only increase the healthcare costs, but also result in an increased rate of recurrence, particularly because it is difficult to clear the infection from devascularized bone and other necrotic tissues. Soon after introduction of an implant, a conditioning layer composed of host-derived adhesins (including fibrinogen, fibronectin, collagen, etc.) covers the surface of the implant. This layer promotes adherence of free-floating (planktonic) bacteria, which subsequently form an extracellular anionic polysaccharide 3 dimensional (3D) biofilm. Once a biofilm forms, it is extremely difficult to treat these infections because the biofilm blocks the penetration of both host immune cells (such as macrophages) and systemic antibiotics, promoting further bacterial survival. Given the difficulties in treating implant-associated infections, strategies aimed at preventing the infection and biofilm formation during surgery and in the immediate postoperative period may serve as more effective alternative that can prevent these infections altogether.
Prior studies have coated or covalently-linked antibiotics onto prosthetic materials to prevent bacterial infection during surgical implantation. Although this local antibiotic therapy may be effective, they are limited to certain bacterial species and these infections can be caused by a spectrum of bacteria, including Gram-positive Staphylococcus aureus, Staphylococcus epidermidis and Streptococci species, and Gram-negative Pseudomonas and Enterobacter species. Moreover, antibiotics used in this manner can contribute to the development of antibiotic resistance, which is especially relevant as there is an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE) strains.
What is needed in the art are implant with materials that can resist infection while simultaneously promoting tissue integration and/or regeneration, e.g., bone growth.
The embodiments described below address the above-identified issues and needs.
In one aspect of the present invention, it is provided an implantable device, comprising a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed,
wherein the galvanic redox system comprises a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the non-zero surface potential is a positive surface potential.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, a stainless-steel alloy, a titanium alloy, a cobalt-chromium alloy, amalgam, or combination thereof.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, or Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole in part with Graphite,
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the implantable device further comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention device, the second metal comprises silver (Ag).
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the implant device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In another aspect of the present invention, it is provided a method of fabricating an implantable device, comprising forming a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed,
wherein forming the galvanic redox system comprises forming a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and
the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the non-zero surface potential is a positive surface potential.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, or stainless-steel alloy, titanium alloy, cobalt-chromium alloy, amalgam, or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole or in part with graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal comprises silver (Ag).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In another aspect of the present invention, it is provided a method of treating or ameliorating a medical or cosmetic condition in a subject in need thereof, comprising applying an implantable device to the subject, the implantable device comprising a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed, wherein the galvanic redox system comprises a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and
the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the non-zero surface potential is a positive surface potential.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, a stainless-steel alloy, a titanium alloy, a cobalt-chromium alloy, amalgam, or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole or in part with graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal comprises silver (Ag).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the subject is a human being.
Those of skill in the art will understand that the drawings, described below, are for illustrative purposes only. The drawings are not intended to limit the scope of the present teachings in any way.
Unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.
As used herein, the term “device” encompasses any device that can be placed within a mammal (e.g., a human, a cow, a dog, etc.) via a surgical or otherwise invasive procedure. In some embodiments, the term device is used interchangeably with the term “scaffold”, “fixture” or “implant.”
As used herein, the term “nanoparticle” encompasses small particles having sizes that are often smaller than micrometers. Exemplary nanoparticle configurations include but are not limited to nanoclusters (e.g., having at least one dimension between 1 and 100 nanometers and a narrow size distribution); nanopowders (e.g., agglomerates of ultrafine particles, nanoparticles, or nanoclusters); nanocrystals (nanometer-sized single crystals, or single-domain ultrafine particles, or groups of crystals). In some embodiments, the size of a nanoparticle will be determined by its smallest dimension. It will be understood that the term nanoparticle does not imply that a spherical configuration. For example, silver nanoparticles do not necessarily suggest a spherical or ball-like shape. Indeed, silver nanoparticles can be spherical, fiber-like, branch-like, cluster-like, or of an irregular shape. In this application, the term “nanosilver” is used interchangeably as “silver nanoparticles.”
As used herein, the term “biocompatible” refers to a property of a material characterized by it, or its physiological degradation products, being not, or at least minimally, toxic to living tissue; not, or at least minimally and reparably, otherwise injurious living tissue; and/or not, or at least minimally and controllably, causative of an immunological reaction in living tissue. With regard to salts, both the cation and anion must be biocompatible.
As used herein, the term “biodegradation” includes all means by which a polymer can be disposed of in a patient's body, which includes bioabsorption, resorption, etc. Degradation occurs through hydrolysis, chemical reactions, or enzymatic reactions. Biodegradation can take place over an extended period of time, for example over 2-3 years. The term “biostable” means that the polymer does not biodegrade or bioabsorb under physiological conditions, or biodegrade or bioabsorb very slowly over a very long period of time, for example, over 5 years or over 10 years.
As used herein, the term “layout of the first metal” refers to a configuration of the first metal formed on the body substrate of the implantable device disclosed here, examples of such can be high density discontinuous dots or discrete deposits of the first metal or a thin layer. In this context, high density shall mean 100 or more dots or discrete deposits per 1 cm2 (for example, 100, 500, 1,000, 5,000, 10,000, 50,000, 100,000, 500,000, or 1,000,000 dots or discrete deposits per 1 cm2) and a thin layer can be a uniform thin layer or a layer formed by joined or substantially joined dots or deposits of the first metal.
As used herein, the term “coating” is broadly defined as a layer of substance or material that is deposited over a surface of a device (e.g., a scaffold or an implant). In some embodiments, a polymeric matrix comprising silver nanoparticles is deposited as a coating upon a metal or polymeric device. In some embodiments, the coating comprises one or more layers in any combination, with one or more of such layers comprising silver nanoparticles. In some embodiments, multiple layers including but not limited to a primer layer, which may improve adhesion of subsequent layers on the implantable substrate or on a previously formed layer; (b) a reservoir layer, which may comprise a polymer and nanoparticles in the presence or absence a therapeutic agent or, alternatively, a polymer free agent; (c) a topcoat layer, which may serve as a way of controlling the accessibility of the silver nanoparticles or the rate of release of the therapeutic agent; and (d) a biocompatible finishing layer, which may improve the biocompatibility of the coating. In some embodiments, the polymer matrix and polymer substrate can be completely absorbed by the body, preferably at different rate.
As used herein, the term “polymer material” and “polymeric material” can be used interchangeably.
As used herein, the term “is included” shall mean “is a part of or the whole of”.
Unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.
In one aspect of the present invention, it is provided an implantable device, comprising a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed,
wherein the galvanic redox system comprises a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the non-zero surface potential is a positive surface potential.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, a stainless-steel alloy, a titanium alloy, a cobalt-chromium alloy, amalgam, or a combination thereof.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole or in part with graphite.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the implantable device further comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention device, the second metal comprises silver (Ag).
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention device, optionally in combination with any or all the various embodiments disclosed herein, the implant device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In some embodiments, the polymeric material is biocompatible. In some embodiments, the polymeric material is bioabsorbable. In some embodiments, the polymeric material is biodegradable.
In some embodiments, one or more additional coatings can be deposited over the silver-containing nanoparticles or a coating comprising the silver-containing nanoparticles. The additional coating can be formed by one or more polymeric material that is biocompatible, bioabsorbable and/or biodegradable.
Nanoparticles (e.g., of silver or with silver embedded therein) of a wired range of sizes can be used to impart antimicrobial property to a medical device (e.g., an implantable device). In some embodiments, the nanoparticles have a mean size of about 1000 nm or smaller, about 900 nm or smaller, about 800 nm or smaller, about 700 nm or smaller, about 600 nm or smaller, about 500 nm or smaller, about 400 nm or smaller, about 300 nm or smaller, about 250 nm or smaller, about 200 nm or smaller, about 180 nm or smaller, about 150 nm or smaller, about 120 nm or smaller, about 100 nm or smaller, about 90 nm or smaller, about 80 nm or smaller, about 70 nm or smaller, about 60 nm or smaller, about 50 nm or smaller, about 45 nm or smaller, about 40 nm or smaller, about 35 nm or smaller, about 32 nm or smaller, about 30 nm or smaller, about 28 nm or smaller, about 25 nm or smaller, about 22 nm or smaller, about 20 nm or smaller, about 18 nm or smaller, about 15 nm or smaller, about 12 nm or smaller, about 10 nm or smaller, about 8 nm or smaller, about 5 nm or smaller, or about 2 nm or smaller. In some embodiments, the nanoparticles used have a size between 20 nm to 40 nm.
In some embodiments, about 10% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 20% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 30% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 35% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 40% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 45% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 50% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 55% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 60% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 65% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 70% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 75% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 80% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 85% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 80% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 95% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 98% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles. In some embodiments, about 99% or more of the nanoparticles have sizes that are comparable to the mean size of the population of nanoparticles.
In some embodiments, a device (e.g., with an antimicrobial coated on its surface or embedded within) provided herein is an osteoconductive scaffold that promotes osteoblastic cell ingrowth and at the same time prevents fibroblastic cell ingrowth. Advantageously, silver nanoparticles are preferentially toxic to fibroblasts rather than osteoblasts.
Exemplary polymeric material that can be used here include but are not limited to a biocompatible or bioabsorbable polymer that is one or more of poly(DL-lactide), poly(L-lactide), poly(L-lactide), poly(L-lactide-co-D,L-lactide), polymandelide, polyglycolide, poly(lactide-co-glycolide), poly(D,L-lactide-co-glycolide), poly(L-lactide-co-glycolide), poly(ester amide), poly(ortho esters), poly(glycolic acid-co-trimethylene carbonate), poly(D,L-lactide-co-trimethylene carbonate), poly(trimethylene carbonate), poly(lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(tyrosine ester), polyanhydride, derivatives thereof. In some embodiments, the polymeric material comprises a combination of these polymers.
In some embodiments, the polymeric material comprises poly(D,L-lactide-co-glycolide). In some embodiments, the polymeric material comprises poly(D,L-lactide). In some embodiments, the polymeric material comprises poly(L-lactide).
Additional exemplary polymers include but are not limited to poly(D-lactide) (PDLA), polymandelide (PM), poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), poly(L-lactide-co-D,L-lactide) (PLDLA), poly(D,L-lactide) (PDLLA), and poly(L-lactide-co-glycolide) (PLLGA), et al., or a combination thereof. With respect to PLLGA, the stent scaffolding can be made from PLLGA with a mole% of GA between 5-15 mol %. The PLLGA can have a mole% of (LA:GA) of 85:15 (or a range of 82:18 to 88:12), 95:5 (or a range of 93:7 to 97:3), or commercially available PLLGA products identified as being 85:15 or 95:5 PLLGA. The examples provided above are not the only polymers that may be used. Many other examples can be provided, such as those found in Polymeric Biomaterials, second edition, edited by Severian Dumitriu; chapter 4.
In some embodiments, polymers that are more flexible or that have a lower modulus that those mentioned above may also be used. Exemplary lower modulus bioabsorbable polymers include, polycaprolactone (PCL), poly(trimethylene carbonate) (PTMC), polydioxanone (PDO), poly(3-hydrobutyrate) (PHB), poly(4-hydroxybutyrate) (P4HB), poly(hydroxyalkanoate) (PHA), and poly(butylene succinate), and blends and copolymers thereof.
In exemplary embodiments, higher modulus polymers such as PLLA or PLLGA may be blended with lower modulus polymers or copolymers with PLLA or PLGA. The blended lower modulus polymers result in a blend that has a higher fracture toughness than the high modulus polymer. Exemplary low modulus copolymers include poly(L-lactide)-b-polycaprolactone (PLLA-b-PCL) or poly(L-lactide)-co-polycaprolactone (PLLA-co-PCL). The composition of a blend can include 1-5 wt % of low modulus polymer.
More exemplary polymers include but are not limited to at least partially alkylated polyethyleneimine (PEI); at least partially alkylated poly(lysine); at least partially alkylated polyornithine; at least partially alkylated poly(amido amine), at least partially alkylated homo- and co-polymers of vinylamine; at least partially alkylated acrylate containing aminogroups, copolymers of vinylamine containing aminogroups with hydrophobic monomers, copolymers of acrylate containing aminogroups with hydrophobic monomers, and amino containing natural and modified polysaccharides, polyacrylates, polymethacryates, polyureas, polyurethanes, polyolefins, polyvinylhalides, polyvinylidenehalides, polyvinylethers, polyvinylaromatics, polyvinylesters, polyacrylonitriles, alkyd resins, polysiloxanes and epoxy resins, and mixtures thereof.
Additional examples of biocompatible biodegradable polymers include, without limitation, polycaprolactone, poly(L-lactide), poly(D,L-lactide), poly(D,L-lactide-co-PEG) block copolymers, poly(D,L-lactide-co-trimethylene carbonate), poly(lactide-co-glycolide), polydioxanone (PDS), polyorthoester, polyanhydride, poly(glycolic acid-co-trimethylene carbonate), polyphosphoester, polyphosphoester urethane, poly(amino acids), polycyanoacrylates, poly(trimethylene carbonate), poly(iminocarbonate), polycarbonates, polyurethanes, polyalkylene oxalates, polyphosphazenes, PHA-PEG, and combinations thereof. The PHA may include poly(α-hydroxyacids), poly(β-hydroxyacid) such as poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-valerate) (PHBV), poly(3-hydroxyproprionate) (PHP), poly(3-hydroxyhexanoate) (PHH), or poly(4-hydroxyacid) such as poly poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanoate), poly(hydroxyvalerate), poly(tyrosine carbonates), poly(tyrosine arylates), poly(ester amide), polyhydroxyalkanoates (PHA), poly(3-hydroxyalkanoates) such as poly(3-hydroxypropanoate), poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate) and poly(3-hydroxyoctanoate), poly(4-hydroxyalkanaote) such as poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanote), poly(4-hydroxyheptanoate), poly(4-hydroxyoctanoate) and copolymers including any of the 3-hydroxyalkanoate or 4-hydroxyalkanoate monomers described herein or blends thereof, poly(D,L-lactide), poly(L-lactide), polyglycolide, poly(D,L-lactide-co-glycolide), poly(L-lactide-co-glycolide), polycaprolactone, poly(lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(dioxanone), poly(ortho esters), poly(anhydrides), poly(tyrosine carbonates) and derivatives thereof, poly(tyrosine ester) and derivatives thereof, poly(imino carbonates), poly(glycolic acid-co-trimethylene carbonate), polyphosphoester, polyphosphoester urethane, poly(amino acids), polycyanoacrylates, poly(trimethylene carbonate), poly(iminocarbonate), polyphosphazenes, silicones, polyesters, polyolefins, polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymers and copolymers, vinyl halide polymers and copolymers, such as polyvinyl chloride, polyvinyl ethers, such as polyvinyl methyl ether, polyvinylidene halides, such as polyvinylidene chloride, polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics, such as polystyrene, polyvinyl esters, such as polyvinyl acetate, copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers, polyamides, such as Nylon 66 and polycaprolactam, alkyd resins, polycarbonates, polyoxymethylenes, polyimides, polyethers, poly(glyceryl sebacate), poly(propylene fumarate), poly(n-butyl methacrylate), poly(sec-butyl methacrylate), poly(isobutyl methacrylate), poly(tert-butyl methacrylate), poly(n-propyl methacrylate), poly(isopropyl methacrylate), poly(ethyl methacrylate), poly(methyl methacrylate), epoxy resins, polyurethanes, rayon, rayon-triacetate, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, carboxymethyl cellulose, polyethers such as poly(ethylene glycol) (PEG), copoly(ether-esters) (e.g. poly(ethylene oxide-co-lactic acid) (PEO/PLA)), polyalkylene oxides such as poly(ethylene oxide), poly(propylene oxide), poly(ether ester), polyalkylene oxalates, phosphoryl choline containing polymer, choline, poly(aspirin), polymers and co-polymers of hydroxyl bearing monomers such as 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, PEG acrylate (PEGA), PEG methacrylate, methacrylate polymers containing 2-methacryloyloxyethyl-phosphorylcholine (MPC) and n-vinyl pyrrolidone (VP), carboxylic acid bearing monomers such as methacrylic acid (MA), acrylic acid (AA), alkoxymethacrylate, alkoxyacrylate, and 3-trimethylsilylpropyl methacrylate (TMSPMA), poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, polycaprolactone-PEG (PCL-PEG), PLA-PEG, poly(methyl methacrylate), MED610, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), poly(vinylidene fluoride)-PEG (PVDF-PEG), PLURONIC™ surfactants (polypropylene oxide-co-polyethylene glycol), poly(tetramethylene glycol), hydroxy functional poly(vinyl pyrrolidone), biomolecules such as collagen, chitosan, alginate, fibrin, fibrinogen, cellulose, starch, dextran, dextrin, hyaluronic acid, fragments and derivatives of hyaluronic acid, heparin, fragments and derivatives of heparin, glycosamino glycan (GAG), GAG derivatives, polysaccharide, elastin, elastin protein mimetics, or combinations thereof.
In some embodiments, polyethylene is used to construct at least a portion of the device. For example, polyethylene can be used in an orthopedic implant on a surface that is designed to contact another implant, as such in a joint or hip replacement. Polyethylene is very durable when it comes into contact with other materials. When a metal implant moves on a polyethylene surface, as it does in most joint replacements, the contact is very smooth and the amount of wear is minimal. Patients who are younger or more active may benefit from polyethylene with even more resistance to wear. This can be accomplished through a process called crosslinking, which creates stronger bonds between the elements that make up the polyethylene. The appropriate amount of crosslinking depends on the type of implant. For example, the surface of a hip implant may require a different degree of crosslinking than the surface of a knee implant.
Additional examples of polymeric materials can be found, for example, in U.S. Pat. No. 6,127,448 to Domb, entitled “Biocompatible Polymeric Coating Material;” US Pat. Pub. No. 2004/0148016 by Klein and Brazil, entitled “Biocompatible Medical Device Coatings;” US Pat. Pub. No. 2009/0169714 by Burghard et al., entitled “Biocompatible Coatings for Medical Devices;” U.S. Pat. No. 6,406,792 to Briquet et al., entitled “Biocompatible Coatings;” US Pat. Pub. No. 2008/0003256 by Martens et al., entitled “Biocompatible Coating of Medical Devices;” each of which is hereby incorporated by reference herein in its entirety.
In some embodiments, a portion of or the entire device is formed by one or more the aforementioned polymeric materials provided herein. In some embodiments, the polymeric material used to form the device further comprises an antimicrobial agent such that the antimicrobial agent is embedded as a part of the device itself. In some embodiments, a biomedical material such as titanium, silicone or apatite is used to modify the surface of the device such that the device is biocompatible and does not trigger adverse reactions in a patient (e.g., a recipient of an implant).
In some embodiments, a portion of or the entire device is made from a metal material. Exemplary metal materials include but are not limited to stainless steel, chromium, a cobalt-chromium alloy, Tantalum, titanium, a titanium alloy and combinations thereof.
Stainless steel is a very strong alloy, and is most often used in implants that are intended to help repair fractures, such as bone plates, bone screws, pins, and rods. Stainless steel is made mostly of iron, with other metals such as chromium or molybdenum added to make it more resistant to corrosion. There are many different types of stainless steel. The stainless steels used in orthopedic implants are designed to resist the normal chemicals found in the human body. Cobalt-chromium alloys are also strong, hard, biocompatible, and corrosion resistant. These alloys are used in a variety of joint replacement implants, as well as some fracture repair implants, that require a long service life. While cobalt-chromium alloys contain mostly cobalt and chromium, they also include other metals, such as molybdenum, to increase their strength. Titanium alloys are considered to be biocompatible. They are the most flexible of all orthopedic alloys. They are also lighter weight than most other orthopedic alloys. Consisting mostly of titanium, they also contain varying degrees of other metals, such as aluminum and vanadium. Pure titanium may also be used in some implants where high strength is not required. It is used, for example, to make fiber metal, which is a layer of metal fibers bonded to the surface of an implant to allow the bone to grow into the implant, or cement to flow into the implant, for a better grip. Tantalum is a pure metal with excellent physical and biological characteristics. It is flexible, corrosion resistant, and biocompatible.
It will be understood by one of skill in the art that the method and composition provided herein can be used to impart antimicrobial and/or any other advantageous property to any device that is used as a surgical implant. In some embodiments, devices provided herein include medical implants, scaffolds and/or surgical instruments. Exemplary medical implants include but are not limited to stents, balloons, valves, pins, rods, screws, discs, and plates. Exemplary medical implants include but are not limited to an artificial replacement of a body part such as a hip, a joint, etc.
In some embodiments, the devices include an implantable intervertebral device (e.g., a cervical fusion device).
In some embodiments, devices disclosed herein include those associated with dental surgeries, including but not limited to a disc, a bridge, a retainer clip, a screw, a housing, a bone graft, and/or a crown.
In some embodiments, devices disclosed herein include those associated with orthopedic surgeries, including, for example, intramedullary rods, temporary and permanent pins and implants, bone plates, bone screws and pins, and combinations thereof.
In some embodiments, a device provided herein further comprises a bioactive agent such as a graft, an osteoconductive or osteoinductive graft material, a bone morphogenetic protein, a growth factor and a buffer material. Exemplary osteoconductive or osteoinductive graft materials include but are not limited to hydroxyapatite BMP, growth factors (e.g., transforming growth factor (TGF) beta-1,2 and 3, BMP-2, BMP-3, BMP-7, insulin-like growth factor (IGF)-1, and possibly vascular endothelial growth factor (VEGF), neural EGFL like 1 (NELL-1), hydroxyapatite or calcium phosphate.
Additional information on implantable medical devices and osteoinductive materials can be found, for example, in United States Patent Publication No. 2009/0012620 by Youssef J., et al. and entitled “Implantable Cervical Fusion Device;” U.S. Pat. No. 5,348,026 to Davidson and entitled “Osteoinductive Bone Screw;” Barradas A. et al., 2011, “Osteoinductive Biomaterials: Current Knowledge of Properties, Experimental Models and Biological Mechanisms,” European Cells and Materials 21:407-429; U.S. Pat. No. 7,485,617 to Pohl J. et al. and entitled “Osteoinductive Materials,” United States Patent Publication No. 2011/0022180 by Melkent A., et al. and entitled “Implantable Medical Devices;” United States Patent Publication No. 2005/0010304 by Jamali, A. and entitled “Device and Method for Reconstruction of Osseous Skeletal Defects;” United States Patent Publication No. 2010/0036502 by Svrluga R. et al. and entitled “Medical Device for Bone Implant and Method for Producing Such Device;” U.S. Pat. No. 5,672,177 to E. Seldin and entitled “Implantable Bone Distraction Device;” and U.S. Pat. No. 4,611,597 to W. Kraus and entitled “Implantable Device for the Stimulation of Bone Growth;” each of which is hereby incorporated by reference in its entirety.
In some embodiments, the polymeric material forms a coating on the device before an antimicrobial agent is subsequently deposited.
In some embodiments, the antimicrobial agent is dispersed in the polymeric material before the mixture is deposited on the device to form a coating.
In some embodiments, the antimicrobial agent is dispersed in the polymeric material before the mixture is used to form a portion of the device or the entire device itself
In some embodiments, the antimicrobial agent constitutes about 0.1% or less by weight, about 0.2% or less by weight, about 0.3% or less by weight, about 0.4% or less by weight, about 0.5% or less by weight, about 0.6% or less by weight, about 0.7% or less by weight, about 0.8% or less by weight, about 0.9% or less by weight, about 1.0% or less by weight, about 1.1% or less by weight, about 1.2% or less by weight, about 1.3% or less by weight, about 1.4% or less by weight, about 1.5% or less by weight, about 1.6% or less by weight, about 1.7% or less by weight, about 1.8% or less by weight, about 1.9% or less by weight, about 2.0% or less by weight, about 2.1% or less by weight, about 2.2% or less by weight, about 2.3% or less by weight, about 2.4% or less by weight, about 2.5% or less by weight, about 2.6% or less by weight, about 2.7% or less by weight, about 2.8% or less by weight, about 2.9% or less by weight, about 3.0% or less by weight, about 3.2% or less by weight, about 3.5% or less by weight, about 3.8% or less by weight, about 4.0% or less by weight, about 4.5% or less by weight, about 5.0% or less by weight, about 7.0% or less by weight, about 10.0% or less by weight, about 15.0% or less by weight, about 20.0% or less by weight, about 30.0% or less by weight, about 40.0% or less by weight, about 50.0% or less by weight of the total weight of the mixture.
In some embodiments, the antimicrobial agent constitutes about 0.1% or less by weight, about 0.2% or less by weight, about 0.3% or less by weight, about 0.4% or less by weight, about 0.5% or less by weight, about 0.6% or less by weight, about 0.7% or less by weight, about 0.8% or less by weight, about 0.9% or less by weight, about 1.0% or less by weight, about 1.1% or less by weight, about 1.2% or less by weight, about 1.3% or less by weight, about 1.4% or less by weight, about 1.5% or less by weight, about 1.6% or less by weight, about 1.7% or less by weight, about 1.8% or less by weight, about 1.9% or less by weight, about 2.0% or less by weight, about 2.1% or less by weight, about 2.2% or less by weight, about 2.3% or less by weight, about 2.4% or less by weight, about 2.5% or less by weight, about 2.6% or less by weight, about 2.7% or less by weight, about 2.8% or less by weight, about 2.9% or less by weight, about 3.0% or less by weight, about 3.2% or less by weight, about 3.5% or less by weight, about 3.8% or less by weight, about 4.0% or less by weight, about 4.5% or less by weight, about 5.0% or less by weight, about 7.0% or less by weight, about 10.0% or less by weight, about 15.0% or less by weight, about 20.0% or less by weight, about 30.0% or less by weight, about 40.0% or less by weight, about 50.0% or less by weight of the total weight of the polymeric material.
In some embodiments, the device has more than one contact surfaces. It will be understood that the antimicrobial agent can be deposited on a portion of any one or all of these contact surfaces at any percentage as disclosed herein.
In some embodiments, an antimicrobial agent (e.g., alone or in combination with a polymeric material) is deposited upon a contact surface of the device, continuously or discontinuously. For example, an antimicrobial agent (e.g., alone or in combination with a polymeric material) can be deposited continuously over less than about 2%, less than about 5%, less than about 8%, less than about 10%, less than about 15%, less than about 20%, less than about 25%, less than about 30%, less than about 35%, less than about 40%, less than about 45%, less than about 50%, less than about 55%, less than about 60%, less than about 65%, less than about 70%, less than about 75%, less than about 80%, less than about 85%, less than about 90%, less than about 95%, less than about 98%, less than about 99% of a contact surface of the device.
In some embodiments, an antimicrobial agent (e.g., alone or in combination with a polymeric material) can be deposited discontinuously over a contact surface of the device; for example the antimicrobial agent can be deposited over the contact surface as discrete dots, circles, squares, triangles, ovals, or in any other suitable forms or pattern, rendering a total surface area being covered of less than about 2%, less than about 5%, less than about 8%, less than about 10%, less than about 15%, less than about 20%, less than about 25%, less than about 30%, less than about 35%, less than about 40%, less than about 45%, less than about 50%, less than about 55%, less than about 60%, less than about 65%, less than about 70%, less than about 75%, less than about 80%, less than about 85%, less than about 90%, less than about 95%, less than about 98%, less than about 99% of a contact surface of the device.
In some embodiments, one or more therapeutic agents are embedded or impregnated in a device provided herein. In some embodiments, one or more therapeutic agents are embedded or impregnated the polymeric material that forms the device itself or a coating on the surface of a device. In some embodiments, one or more therapeutic agents are added as an additional coating over silver nanoparticles or a coating comprising the silver nanoparticles. In some embodiments, the therapeutic agent can be mixed or dispersed in part of or throughout the polymer scaffold or implant.
It will be understood that any therapeutic agent can be used in combination with the silver nanoparticles provided herein. Exemplary therapeutic agents include but are not limited to one or more anti-microbial agents: aminoglycosides (such as amikacin, gentamicin, kanamycin, neomycin, netilmicin, tobramycin, and/or paromomycin); ansamycins (such as geldanamycin and/or herbimycin); carbacephem (such as loracarbef), carbapenems (such as ertapenem, doripenem, imipenem/cilastatin, and/or meropenem); cephalosporins (such as cefadroxil, cefazolin, cefalotin, cefalothin, cefalexin, cefaclor, cefamandole, cefoxitin, cefprozil, cefuroxime, cefixime, cefdinir, cefditoren, cefoperazone, cefotaxime, cefpodoxime, ceftazidime, ceftibuten, ceftizoxime, ceftriaxone, cefepime, ceftaroline fosamil and/or ceftobiprole); glycopeptides (such as teicoplanin, vancomycin and/or telavancin); lincosamides (such as clindamycin and/or lincomycin); lipopeptide such as daptomycin; macrolides (such as azithromycin, clarithromycin, dirithromycin, erythromycin, roxithromycin, troleandomycin, telithromycin, spectinomycin, spiramycin); monobactams (such as aztreonam, nitrofurans, furazolidone and/or nitrofurantoin), penicillins or penicillin combinations (such as amoxicillin, ampicillin, azlocillin, carbenicillin, cloxacillin, dicloxacillin, flucloxacillin, mezlocillin, methicillin, nafcillin, oxacillin, penicillin v, piperacillin, penicillin g, temocillin, ticarcillin, amoxicillin/clavulanate, ampicillin/sulbactam, piperacillin/tazobactam and/or ticarcillin/clavulanate); polypeptides (such as bacitracin, colistin, and/or polymyxin b); quinolones (such as ciprofloxacin, enoxacin, gatifloxacin, levofloxacin, lomefloxacin, moxifloxacin, nalidixic acid, norfloxacin, ofloxacin, trovafloxacin, grepafloxacin, sparfloxacin and/or temafloxacin); sulfonamides (such as mafenide, sulfonamidochrysoidine, sulfacetamide, sulfadiazine, silver sulfadiazine, sulfamethizole, sulfamethoxazole, sulfanilimide, sulfasalazine, sulfisoxazole and/or trimethoprim-sulfamethoxazole-co-trimoxazole); tetracyclines (such as demeclocycline, doxycycline, minocycline, oxytetracycline and/or tetracycline); drugs against mycobacteria such as clofazimine, dapsone, capreomycin, cycloserine, ethambutol, ethionamide, isoniazid, pyrazinamide, rifampicin, rifabutin, rifapentine, streptomycin); arsphenamine, chloramphenicol, fosfomycin, fusidic acid, linezolid, metronidazole, mupirocin, platensimycin, quinupristin/dalfopristin, rifaximin, thiamphenicol, tigecycline, tinidazole, trimethoprim, or combinations thereof.
Exemplary therapeutic agents also include but are not limited to one or more anti-inflammatory agents or any other agents that can be beneficial for the healing of the surgical site or promoting desired growth and development.
In some embodiments, one or more bioactive agents are embedded or impregnated in a device provided herein. In some embodiments, one or more bioactive agents are embedded or impregnated the polymeric material that forms the device itself or a coating on the surface of a device.
In some embodiments, one or more bioactive agents are associated with a device provided herein. In some embodiments, one or more bioactive agents are contained in a compartment of the device.
Exemplary bioactive agents include but are not limited to cells, a biocompatible buffer, growth media or extracellular matrices, growth factors, cytokines, includes metabolites, any small molecules or macromolecules.
In some embodiments, embryonic stem cells (e.g., blastocyst-derived) are cultured and produced within an implantable device as disclosed herein. In some embodiments, blastocyst-derived stem cells isolated from the inner cell mass of blastocysts can be used. In some embodiments, adult stem cells or somatic stem cells, which are found in various tissues (e.g., from bone marrow derived sources), can also be used. Additional adult stem cells include but are not limited to hematopoietic stem cells, mammary stem cells, intestinal stem cells, mesenchymal stem cells, endothelial stem cells, neural stem cells, olfactory adult stem cells, neural crest stem cells, and testicular cells.
In some embodiments, non-stem cells are used. Potentially, all of the 200 or so mammalian cell types within the body can be used in an implantable device as disclosed herein. Exemplary cells include but are not limited to, for example, cells found within a non-embryonic adult, such as insulin secreting cells (e.g., from adults or cadavers) or hepatocytes; islets of Langerhands; cells via somatic cell nuclear transfer (SCNT cells); cells via induced pluripotent stem cells (iPSs cells) either derived by genetic or chemical means; and cells from umbilical cord blood (UCB) cells.
In some embodiments, donor cells are used, including autologous (self) cells or non-autologous cells (e.g., allogenic or xenogenic cells from unrelated donors or other species).
In some embodiments, the cells or tissue used in the device can be suspended in a liquid trapped within a sub-compartment, adhered to the inner walls of the compartment or immobilized on an appropriate support structure provided within the compartment. For example, the cells can be embedded in a gel matrix (e.g., agar, alginate, chitosan, polyglycolic acid, polylactic acid, and the like). In some embodiments, a porous scaffold (e.g., an alignate scaffold) can be used to seed the content within a compartment or sub-compartments of an implantable device. In some embodiments, microcapsules or microbeads can be used to encapsulate or capture cells in the cellular compartment.
In some embodiments, a commercially available growth medium or matrix for mammalian cells is used. For example, Matrigel™ is the trade name for a gelatinous protein mixture secreted by Engelbreth-Holm-Swarm (EHS) mouse sarcoma cells and marketed by BD Biosciences and by Trevigen Inc. under the name Cultrex BME. This mixture resembles the complex extracellular environment found in many tissues and is used by cell biologists as a substrate for cell culture. Components of a standard growth medium or matrix for mammalian cells include but are not limited to extracellular matrix components, growth factors, various cytokines, and one or more pharmaceutical agents, as listed in Table 1.
Exemplary growth factors include but are not limited to adrenomedullin (AM), angiopoietin (Ang), autocrine motility factor, bone morphogenetic proteins (BMPs), brain-derived neurotrophic factor (BDNF), epidermal growth factor (EGF), erythropoietin (EPO), fibroblast growth factor (FGF) 1, 2, 3, glial cell line-derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), growth differentiation factor-9 (GDF9), hepatocyte growth factor (HGF), hepatoma-derived growth factor (HDGF), insulin-like growth factor (IGF), migration-stimulating factor, myostatin (GDF-8), nerve growth factor (NGF) and other neurotrophins, platelet-derived growth factor (PDGF), thrombopoietin (TPO), transforming growth factor alpha (TGF-α), transforming growth factor beta(TGF-β), tumor necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), placental growth factor (P1GF), fetal bovine somatotrophin (FBS), IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-17, and neural EGFL like 1 (NELL-1).
Exemplary small chemical molecules include any chemical compounds, including inorganic and organic compounds, for example, formaldehyde, acetylsalicylic acid, methanol, ibuprofen, and statins. Exemplary macromolecules include but are not limited to monoclonal and polyclonal antibodies, nucleic acid, lipid, fatty acid, and insulin.
In some embodiments, devices provided herein can be placed within any animal, including but not limited to a mammal (e.g., a human, a cow, a dog, a cat, a goat, a sheep, a monkey, a horse, a dolphin, a lion, a tiger, a rat, a mouse, an elephant, and etc.) via a surgical or otherwise invasive procedure.
In some further embodiments, particles of the second metal of the present invention of galvanic redox system can take any shape including spheres, cubic, wire, etc. In some embodiments, a metal composition that have a different electrode potential with the metal substrate, insulator or semiconductor polymers (or their mixtures) complex, can work as the electrodic sites (such as cathodic sites). The other part of the galvanic redox system is a metal substrate with different electrode potential, working as the other electrodic site (such as anodic site). The metal substrate also can be coated first with a specific metal (s first metal) in order to form the specific electrodic sites. The combinations between the cathodic and anodic sites are flexible to choose any kind of metals to form the galvanic redox system, so as to take advantages of the corresponding metal properties to prepare a biomedical device.
Some examples of the combination of the first metal and second metal for the galvanic redox system of invention are stainless/silver, zinc/silver, zirconium/silver, as the electrode potential of zinc is −0.76V, and that of zirconium is −1.45 V, both are significantly lower than that of silver (+0.799 V). Many dental implant alloys can be formed of metals with different electrode potentials, which can be made to have an increased osseointegration by making use of the galvanic redox system of invention. For examples, the Ti/Cr and Ti/Al were used in dental implants, the electrode potential of Al is −1.66V, Cr is −0.73, which is smaller than the potential of titanium (+0.06 V).
In another aspect of the present invention, it is provided a method of fabricating an implantable device, comprising forming a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed,
wherein forming the galvanic redox system comprises forming a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and
the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
The method of claim 13, wherein the non-zero surface potential is a positive surface potential.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, a stainless-steel alloy, a titanium alloy, a cobalt-chromium alloy, amalgam, or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole or in part with graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal comprises silver (Ag).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, fabrication of the galvanic redox system can include, but is not limited to, a technique such as electro-spray coating, electrospinning coating, simple dip coating, layer by layer coating, 3D coating, vapor deposition coating, anodizing coating, ion beam coating, plasma spraying, powder coating, extrusion coating, or sandblast coating, etc. These techniques are well known in the art. Detailed description of such techniques is of readily available public domain knowledge and is omitted for concise description of the invention.
In another aspect of the present invention, it is provided a method of treating or ameliorating a medical or cosmetic condition in a subject in need thereof, comprising applying an implantable device to the subject, the implantable device comprising a galvanic redox system formed on a body substrate of the implantable device, the implantable device having a non-zero surface potential when it is deployed,
wherein the galvanic redox system comprises a first metal site and a second metal site, the first metal site comprising a first metal having a first metal electrode potential (FMEP) and the second metal site comprising a second metal having a second metal electrode potential (SMEP), which FMEP being lower than SMEP and SMEP being substantially different such that the implantable device is galvanized when it is deployed, and
wherein:
the first metal site is a layout of the first metal formed on the body substrate or the body substrate itself comprising the first metal;
the second metal site comprises a plurality of particles comprising the second metal; and
the first metal and the second metal form a galvanic redox metal pair (“GRMP”).
The method of claim 13, wherein the non-zero surface potential is a positive surface potential.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the first metal is Fe, Al, Mg, Zn, Cu, Cr, Zr, a stainless-steel alloy, a titanium alloy, a cobalt-chromium alloy, amalgam, or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal is Ag, Ti, a silver oxide, a titanium oxide, Au, Pt, or a combination thereof. In some embodiments, the second metal can be replaced in whole or in part with graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device comprises an antimicrobial component having an optional antimicrobial agent, the antimicrobial component being included in the second metal side of the galvanic redox system or being an additional component deposited on top of the galvanic redox system.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprising the second metal is inlayed with or embedded within the body substrate of the implantable device or included in a coating formed from a polymer material.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the second metal comprises silver (Ag).
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the antimicrobial component comprises silver particles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the GRMP is selected from stainless-steel/silver, zinc/silver, zirconium/silver, chromium/titanium, aluminum/titanium, steel alloy/titanium, stainless steel/gold, stainless steel/graphite.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the plurality of particles comprises silver nanoparticles.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the polymer material comprises poly(lactide-co-glycolide) (PLGA), polylactide (PLA), poly glycolic acid (PGA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), et al., or a combination thereof.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the implantable device is a dental implant, an orthopedic implant, a stent or a cosmetic implant.
In some embodiments of the invention method, optionally in combination with any or all the various embodiments disclosed herein, the subject is a human being.
In some embodiments, the devices (e.g., a scaffold, a fixture, or an implant) can be used to mask other reagents that may possibly cause microbial infection. In some embodiments, a device can be used to introduce cells or tissues into a mammalian recipient; for example, a carrier of stem cell material. In some embodiments, the devices further include materials that will support or promote the growth and/or development of such cells or tissues.
Unlike the previous reported electrostimulation generated by external machines, our invention generated built-in electroforce on commercial implant surface to establish the internal electrostimulation of the implanted metal materials themselves, which precisely functions on the interface of the implants and body so as to improve osseointegration of the implantable device of invention.
Meanwhile, since the generation of the nanoscale galvanic redox system is technically high-translational, this technology can be used in deep bone tissue as well as the joints such as the knee, hip, and the shoulders where conventional external electrostimulation techniques are not applicable due to variation of the body shape causing difficulties of electrostimulation.
Additionally, the biological interface between an orthopedic implant and the surrounding host tissue has critical effects on clinical outcome. Implant loosening, fibrous encapsulation, corrosion, infection, and inflammation, as well as physical mismatch may have deleterious clinical effects. By employing the electrochemical theory of galvanic reduction-oxidation (redox), we generate a nanoscale galvanic redox system on the surface of metal materials to establish a surface potential that enhances the osseointegration of the metal materials (
The following outlines a general process in accordance with the present invention.
The fabrication of the galvanic redox system could be but not limited to electro-spray coating, electrospinning coating, simple dip coating, layer by layer coating, 3D coating, vapor deposition coating, anodizing coating, ion beam coating, plasma spraying, powder coating, extrusion coating, sandblast coating, etc. The metal couples to form the galvanic redox system could be any two metals having different electrode potentials.
Beside the stainless/silver, they also could be zinc/silver, zirconium/silver, because the electrode potential of zinc is −0.76V, and zirconium is −1.45 V, both are significantly lower than that of silver (+0.799 V). Many dental implant alloys have metals with different electrode potentials, which could be used to Osseointegration by this galvanic redox theory. For examples, the Ti/Cr and Ti/Al were used in dental implants, the electrode potential of Al is −1.66V, Cr is −0.73, which is smaller than the potential of titanium (+0.06 V).
Synthesis of the nanosilver particle-PLGA coating: Nanosilver particles between 20 nm and 40 nm silver particles (QSI-Nano® Silver) were obtained from QuantumSphere, Inc. (Santa Ana, Calif.). The nanosilver-PLGA coating is manufactured using a solvent casting technique known in the art. Briefly, the desired amount of nanosilver will be mixed with 17.5% (w/v) PLGA [85:15 poly(lactic-co-glycolic acid, inherent viscosity: 0.64 dl/g in chloroform; Durect Co., Pelham, Ala.]-chloroform solution. The concentration of silver refers to the weight ratio of nanosilver mixed with PLGA.
Coating nanosilver PLGA onto titanium implants: The nanosilver/PLGA solution will be layered only onto titanium K-wire implants by immersion with a 5 minute interval between applications of each nanosilver PLGA layer. A 3-layer nanosilver/PLGA coating construct can be initially tested. The coated K-wires will be dried at 37° C. for at least 12 hours before use as we previously described6. We have successfully coated the nanosilver PLGA on K-wires (
In vitro antimicrobial activity: In vitro antimicrobial activity of nanosilver particle-PLGA coatings will be determined using a standardized microplate proliferation assay as known in the art. Briefly, the nanosilver/PLGA coatings will be incubated with different logarithmic concentration of S. aureus in 200 μl of BHIB in 96-well plates at 37° C. for 1 h to allow adherence of the S. aureus to the coated K-wires. After incubation, coated K-wires will be rinsed with PBS to remove loosely attached bacteria, and then re-cultured in broth for 18 h at 37° C. in another 96-well microplate. During this second incubation step, the viable bacteria attached to the surface of the implants will start to multiply, releasing CFU into the wells. After removal of the implants, 100 μl of released bacteria will be transferred into another 96-well plate and then amplified by adding 100 μl of fresh broth for another 40 h at 37° C. Proliferation of the released cells will be measured at a wavelength of 595 nm using a microplate reader (Tecan, Durham, N.C.) to generate a time-proliferation curve. The coatings with the most potent antimicrobial activity will be evaluated in vivo.
In vivo efficacy of nanosilver/-PLGA coatings. Different characterization techniques can be used to determine the most efficacious nanosilver/PLGA coating. For example, a mouse model of orthopedic implant infection with the endpoints i-iii: (i) In vivo bioluminescence imaging to measure bacterial burden; (ii) Biofilm formation and adherent bacteria; and (iii) Infection-induced inflammation. Nanosilver/PLGA coatings will be evaluated against an intermediate S. aureus inoculum (e.g. 1×103 CFU) that consistently produces an infection and biofilm formation on the implant and is detectable for 6 post-operative weeks. The nanosilver/-PLGA coatings can be compared to each other, the vehicle coating alone and to the current standard of care i.v. vancomycin prophylaxis used for MRSA by evaluating the following 4 groups: (1) Nanosilver/PLGA coating 1.0%; (2) Nanosilver/PLGA 2.0%; (3) PLGA vehicle coating alone (no Nanosilver); and (4) PLGA vehicle coating alone+i.v. vancomycin (100 mg/kg) at 2 h pre- and 6 h post-operatively. Overall, these data show that nanosilver selectively inhibits fibroblast proliferation over osteoblast proliferation (e.g.,
Having described the invention in detail, it will be apparent that modifications, variations, and equivalent embodiments are possible without departing the scope of the invention defined in the appended claims. Furthermore, it should be appreciated that all examples in the present disclosure are provided as non-limiting examples.
The following non-limiting examples are provided to further illustrate embodiments of the invention disclosed herein. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent approaches that have been found to function well in the practice of the invention, and thus can be considered to constitute examples of modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
Studies on Using an Engineered Galvanic Redox System to Generate Positive Surface Potentials that Promote Osteogenic Functions
Successful osseointegration of orthopaedic and orthodontic implants is dependent on a competition between osteogenesis and bacterial contamination on the implant-tissue interface. Previously, by taking advantage of the highly interactive capabilities of silver nanoparticles (AgNPs), we effectively introduced an antimicrobial effect to metal implant materials using a AgNP/poly(DL-lactic-co-glycolic acid) (PLGA) coating. Although electrical forces have been shown to promote osteogenesis, creating practical materials and devices capable of harnessing these forces to induce bone regeneration remains challenging. Here, we applied galvanic reduction-oxidation (redox) principles to engineer a nanoscale galvanic redox system between AgNPs and 316L stainless steel alloy (316L-SA). Characterized by SEM, EDS, AFM, KPFM, and contact angle measurement, the surface properties of the yield AgNP/PLGA-coated 316L-SA (SNPSA) material presented a significantly increased positive surface potential, hydrophilicity, surface fractional polarity, and surface electron accepting/donating index. Importantly, in addition to its bactericidal property, SNPSA's surface demonstrated a novel osteogenic bioactivity by promoting peri-implant bone growth. This is the first report describing the conversion of a normally deleterious galvanic redox reaction into a biologically beneficial function on a biomedical metal material. Overall, this study details an innovative strategy to design multifunctional biomaterials using a controlled galvanic redox reaction, which has broad applications in material development and clinical practice.
Despite progressive advancements in bone repair devices and techniques, approximately 5.8% of metal implant failures transpire due to insufficient bone growth and osseointegration.1 The osseointegration quality of an implant relies on its ability to promote the differentiation and incorporation of host tissue cells while inhibiting the adhesion and proliferation of bacterial cells.2 Therefore, it is imperative to design orthopaedic and orthodontic implants that promote the osteogenesis of host tissue cells, but that also concurrently reduce microbial infections.3-4
To achieve this goal, processes that modify osteoinductive/osteoconductive material surface physiochemical properties, including the topography,5 surface chemical property,6 and electrical property,7-8 have been investigated. For instance, electrical stimulation can promote bone regeneration.9 Although the mechanism is not completely understood, collagen's piezoelectric property can generate a built-in electric field in the bone organic matrix,10 which may activate the membrane receptors on osteoprogenitor cells to subsequently induce osteogenesis.11 Beyond this inherent property, faradic products generated around cathodic sites during electrical stimulation also appear to contribute to bone regeneration.12 The cations, such as Ca2+, have the ability to rapidly deposit around the cathode, and anions, such as PO43−, HPO42− and OH−, subsequently aggregate around the cations.13 These depositions result in the formation of hydroxyapatite at the cathode, which promotes bone formation.13 Attempts to induce osteogenesis with electric forces have used various methods, including direct electrical current,6 capacitive coupling,14 and inductive coupling.8 However, the requirement of external devices to generate an electrical potential, invasive procedural methods, and high infection rates have considerably halted the application of electric stimulation in clinical settings.15
It is well known that galvanic reduction-oxidation (redox) reactions occur on the surface of carbon steel in moist environments.16-18 In this system, iron (Fe) acts as an anode, and the numerous interstitial doped surface carbon (C) atoms act as nanoscale cathodic sites. The electron flow from the anode (Fe) to the cathode (C) leads to an increased electron density and a higher negative electric potential on the anode than on the cathodic sites.16-18 To harness this phenomenon, we sought to delicately engineer a similar nanoscale galvanic redox system that generates a positive surface potential (SP) on a biomedical metal material, and as a result, promotes bone growth and osseointegration of a metal implant.
Due to the large surface-to-mass ratio, silver nanoparticles (AgNPs) offer a greater active surface, higher solubility, and more chemical reactivity than non-nanoscale silver preparations. In comparison with non-nanoscale silver preparations, AgNPs have a greater release of oxidative Ag+ and/or more partially oxidized AgNPs with chemisorbed (surface-bound) Ag(I).19 Importantly, the electrode potential of the Ag particles significantly increases with a decrease in particle size, especially when their size is reduced to nano-scale.20 In addition, the immense active surface of the spherical AgNPs is critical for their antibacterial properties. Accumulating evidence demonstrates that AgNPs are effective, broad-spectrum antimicrobial agents that can be used in a wide range of doses with a diversity of materials to prevent and manage contamination and biofilm formation without toxicity.21-24 Thus, AgNPs are desirable candidates for building a galvanic redox system with antimicrobial properties. Meanwhile, our previous studies have shown that poly(DL-lactic-co-glycolic acid) (PLGA) is an osteoconductive material capable of supporting a homogeneous distribution of AgNPs. PLGA is used widely with other components of conducting polymers that permit electric current to pass.25 Therefore, in this study, we coated AgNPs/PLGA on a biomedical metal, 316L stainless steel alloy (316L-SA), to empower a built-in electrical force on the surface of a metal implant. The central theme of this study is: AgNPs can function similarly to doped carbon atoms in carbon steel and initiate an electron flow from the substrate metal, 316L-SA, to the cathodic AgNPs in the coated surface, as the electron transfer is driven by the difference in electrode potential between the AgNPs and 316L-SA. As a result, we expected that the controlled galvanic redox reaction of the AgNP/PLGA-coated 316L-SA (SNPSA) would create a unique surface electrical property that could be regulated by AgNP concentration to effectively stimulate local osteogenesis and osseointegration.
Although 316L-SA contains a 16-18.5% of chromium (by weight), and can form a passivation layer of chromium (III) oxide (Cr2O3) when exposed to oxygen, it is still more active than Ag, as shown in galvanic series charts delineating the relationships between different metals and their relative propensity to undergo redox reactions.26-27 Thus, the different electrode potentials between 316L-SA and AgNPs make the galvanic redox reactions possible. In comparison, when titanium is exposed to oxygen, it immediately forms a stable, protective titanium oxide passivation layer on its surface that imparts a noble property. In this case, the electrode potential of the titanium substrate is close to that of Ag in the galvanic series,26-27 and we inferred that there would be no such galvanic redox reaction between the AgNPs and titanium substrate. To test our theory, titanium was used as a minimally reactive substrate to fabricate AgNP/PLGA-coated titanium (SNPT).
Spherical AgNPs (20-40 nm, QSI-Nano Silver) were purchased from QuantumSphere, Inc. (Santa Ana, Calif., United States). PLGA (lactic:glycolic=85:15, inherent viscosity: 0.64 dl/g in chloroform) was purchased from Durect Co. (Pelham, Ala., United States). Kirschner (K)-wires of 316L-SA and titanium (length: 70 mm, diameter: 0.8 mm) were purchased from Synthes, Inc. (Monument, Colo., United States), while 316L-SA and titanium discs (diameter: 7 mm) were sliced from metal rods purchased at Stainless Supply (Monroe, N.C., United States) using an electrical discharging machine at the University of California, Los Angeles (UCLA). All the other used chemicals were purchased from Sigma-Aldrich (St. Louis, Mo., United States).
We employed an electro-spraying method to prepare the AgNP-coated metal materials. Spherical AgNPs were dispersed into PLGA/1,4-dioxane solution and then sprayed onto the metal materials. PLGA was used because it is both biodegradable and biocompatible, and was approved by the U.S. Food and Drug Administration for clinical application. Briefly, metal K-wires and discs were fixed on a lathe mandrel and rotated at a speed of 3,450 rpm. A total of 0.25 mL AgNP/PLGA/1,4-dioxane solution was electro-sprayed onto each K-wire surface over the course of 5 min. For each disc, a total of 0.05 mL AgNP/PLGA/1,4-dioxane solution was electro-sprayed onto the surface over the course of 1 min. The coated samples were placed into an oven at a temperature of 40° C. overnight and then transferred to a fume hood for 2 days of air-drying. After drying completely, the AgNP/PLGA-coated metal materials were hermetically sealed and stored at −20° C. until their use. Electro-spraying resulted in higher AgNP proportions in the AgNP/PLGA-layer without particle aggregation. The densities of the AgNP/PLGA layer were 0.263, 0.278, and 0.293 g/cm3 at proportions of 0%, 10%, and 20% AgNP, respectively, and the densities of AgNPs in the coating surface were 0, 6.95, and 14.65 μg/cm2 for 0%, 10%, and 20% AgNP/PLGA-coated metal materials, correspondingly.
SEM (Nova NanoSEM 230-D9064, FEI Company, Hillsboro, Oreg., United States) was used to evaluate the morphology of AgNP/PLGA-coated metal materials, while EDS was documented simultaneously.21,28 The surface atomic composition of silver (SACs) was analyzed based on the EDS measurement. The testing parameters were set to WD: 15 mm, primary electron energy: 10 keV, and process time: 5 s. For the EDS measurements, five samples were scanned for each group. Three different 80×40 μm areas were selected from each sample. Each area was scanned in quintuplicate.
The surface roughness (Ra; the arithmetic average of the absolute roughness profile values) of AgNP/PLGA-coated metal materials was assessed by topographic AFM imaging using the Bruker Dimension Icon Scanning Probe Microscope (Bruker Nano, Inc., Santa Barbara, Calif., United States) in ambient conditions. Tapping (AM-AFM) mode imaging employed silicon cantilever probes (RTESP, Bruker Nano, Inc.) with nominal tip radii of 8 nm, spring constants of approximately 30 N/m, and resonant frequencies of 260-325 kHz. Height and phase images (2×2 μm) were acquired simultaneously using a 1 Hz scan rate. An automatic algorithm was used to flatten the images. Ra was quantified using the NanoScope Analysis V1.40 software package (Bruker Nano, Inc.).
Localized SPs of SNPSA and SNPT were characterized by KPFM. KPFM imaging was conducted in the dual-pass amplitude modulated lift mode using Pt-Ir coated silicon probes (SCM-PIT, Bruker Nano, Inc.) with nominal tip radii of 20 nm, spring constants of approximately 3 N/m, and resonant frequencies of 60-80 kHz. Co-localized topographic and SP images were acquired over 25×25 μm regions at a lift height of 100 nm. Reported values refer to the contact potential difference between the Pt—Ir tip and surface. To minimize measurement variability, a single KPFM probe was used in the comparisons between SNPSA and SNPT, and five different locations on each sample surface from five samples in each group were analyzed.
Wettability and surface free energy values were obtained from contact angle (θ) measurements.28-31 Advancing contact angles of multiple standard liquids (water-miscible dipolar liquids: formamide and ethylene glycol; water-immiscible non-polar liquid: diiodomethane) on the tested AgNP/PLGA-coated metal materials were measured using a contact angle analyzer (FPA125; First Ten Angstroms, Portsmouth, Va., United States). The surface tension properties of these standard liquids were listed in Table 7.
The surface tension components of these liquids were analyzed based on the measured contact angles. Based on the Derjaguin, Landau, Vervey, and Overbeek (DLVO) model, the solid surface free energy (γS) can be divided into a non-polar Lifshiz-van der Waals component (γSLW) and a polar Lewis acid-base component (γSAB), which is expressed as the geometric mean of the Lewis acid component electron acceptor) and Lewis base component (γS−, electron donor).30 For a solid surface, the process can be described by Eq. 1. For solid/liquid interfacial interaction, γS, γSLW, γSAB, γS+, and γS− can be calculated according to Eq. 2.30-31 In addition, the surface fractional polarity (SFP) was determined by γSAB/γS, and the surface electron accepting/donating index (SEADI) was defined as the ratio of the electron-accepting parameter [(γS+)1/2] and electron-donating parameter [(γS−)1/2]. Five samples were tested for each group.
γS=γSLW+γSAB=γSLW+2·(γS+·γS−)1/2 (Eq. 1)
γL·(1+cos θ)=2·(γSLW·γLLW)1/2+2·(γS+·γL+)1/2+2·(γS−·γL−)1/2 (Eq. 2)
where γL, γLLW, γL+ and γL−, represent surface tension, non-polar Lifshiz-van der Waals component, Lewis acid component, and Lewis base component of standard liquids, respectively.
Due to the dynamic and irreversible changes that surface properties of a material undergo during a successive osteogenesis process,32 we used a COM treatment to mimic the physiology in which the biological and non-biological components meet and interact on the implant surface. Transwell® inserts were used to separate the cells and the coating surface during incubation (
MC3T3-E1 cells were seeded on SNPSA and SNPT metal discs at a density of 2×103 cells per disc and cultivated in the osteogenic medium in 24-well cell culture plates at 37° C. Cell proliferation on the AgNP/PLGA-coated metal discs was evaluated by the Vybrand® MTT Cell Proliferation Assay Kit (Thermal Fisher Scientific, Canoga Park, Calif., United States) after 9 days of cultivation. Alkaline phosphatase (ALP) activity, assessed by the 1-Step™ NBT/BCIP Substrate Solution (Thermal Fisher Scientific) at day 9, and the degree of mineralization, assessed by Alizarin Complexone staining (Thermal Fisher Scientific) at day 21, were used to quantify cellular differentiation. Images were taken by a fluorescence microscope (Olympus BX51, Tokyo). The mineralized area was defined as [(staining area/total disc area)×100] (%) using Image J software.
After 6 days of cultivation, total RNA or total protein was isolated by the RNeasy Mini Kit with DNase treatment (Qiagen, Valencia, Calif., United States) or RIPA Buffer (Pierce Biotechnology, Rockford, Ill., United States). One μg total RNA was used for reverse transcription with the iScript™ Reverse Transcription Supermix for quantitative real-time PCR (qRT-PCR) (Bio-Rad Laboratories, Hercules, Calif., United States). qRT-PCR was performed with TaqMan® Gene Expression Assays (Life Technologies) and SsoFast™ Probes Supermix with ROX (Bio-Rad Laboratories) on a 7300 Real-Time PCR system (Applied Biosystems Inc, Foster City, Calif., United States). Osteogenic growth factors, such as transforming growth factor (Tgf)β1, bone morphogenetic protein (Bmp)2, and Bmp4, were analyzed for osteogenesis. Concomitant glyceraldehyde 3-phosphate dehydrogenase (Gapdh) was used as a housekeeping standard. Data analysis was achieved using the ΔΔCT method. Western blot analysis was performed to quantify the corresponding protein amounts. Anti-BMP2 (Abcam, Cambridge, Mass., United States), anti-BMP4 (Abcam), anti-TGFβ1 (Santa Cruz Biotechnology, Santa Cruz, Calif., United States), and GAPDH (Santa Cruz Biotechnology) primary antibodies were used at a dilution of 1:1,000. All the experiments were repeated in triplicate.
All surgical procedures were approved by the UCLA Office of Animal Research Oversight (protocol #2012-120). A femoral intramedullary rod (FIR) model was used to assess the osteogenic ability of the metal materials that were utilized as intramedullary fixation devices in vivo.33 12-week old male Sprague-Dawley rats were randomly assigned to groups with different types of K-wire implants, with 5 rats in each treatment group. Briefly, the rats were anesthetized by isoflurane inhalation, the left femur was aseptically prepared, and an approach to the distal femur was made via a lateral knee arthrotomy. A 20-gauge needle was used to create an entry port into the proximal aspect of the femur medullary canal in order to ream the canal in preparation for placement of the intramedullary rod. A coated K-wire (2.7 cm in length) was inserted with the narrow portion first entering into the medullary canal, and then seated into the cortical bone in the distal aspect of the femur. The overlying muscle and fascia were closed with a 4-0 Vicryl absorbable suture. Following surgery, the animals were housed in separate cages and allowed to eat and drink ad libitum. Weight-bearing began immediately postoperatively, and the animals were monitored daily. Buprenorphine was administered for 2 days as an analgesic, but no antibiotics were administered post-surgery. The rats were euthanized by CO2 treatment at 8 weeks post-implantation. No animals were excluded from the analysis.
Animals were euthanized at 8 weeks post-implantation. FIR model femurs were harvested and fixed in 4% paraformaldehyde for 48 hours. The samples were scanned using high-resolution μCT (SkyScan 1176, Bruker micro-CT N.V., Kontich, Belgium) at an image resolution of 18.0 μm (90 kV and 278 μA radiation sources with a 0.1 mm aluminum filter). 3D high-resolution images were generated by the CTAn software, following instructions provided by the manufacturer, and improved by Blender software. The ratio of bone volume (BV) to total volume (TV) was used to quantify bone tissue generation in vivo.
After μCT scanning, specimens were dehydrated with a graded solution of ethanol and cleared with xylenes. Specimens were then embedded in a fresh solution of methyl methacrylate, dibutyl phthalate, and Perkadox-16, and subsequently underwent polymerization. Specimens were cut as consecutive slides using Donath's technique and the EXAKT Cutting and Grinding System (EXAKT Technologies, Oklahoma City, Okla., United States), and stained with Sanderson's Rapid Bone Stain. Van Gieson-Picrofuschsin was used as a counterstain. Specimens were imaged using an Olympus BX51 microscope. The area of mineralized bone was further quantified by Image J software.
All statistical analyses were conducted in consultation with the UCLA Statistical Biomathematical Consulting Clinic. Statistical analyses were computed by OriginPro 8 (Origin Lab Corp., Northampton, Mass., United States). Data are generally presented as mean±the standard deviation and compared by one-way ANOVA and two-sample t-tests Mann-Whitney and Kruskal-Wallis ANOVA tests were used for non-parametric data. A Pearson's correlation coefficient was used for correlation tests. The p-values less than 0.05 were considered statistically significant.
The SNPSA and SNPT materials were fabricated by the same electro-spraying method, and their graphical structures were illustrated in
To test our hypothesis that the positive SP depends on the AgNP proportion in the PLGA layer, AgNP/PLGA matrices with different proportions of AgNPs were electro-sprayed onto the 316L-SA and titanium materials. EDS analysis identified Ag as an elemental component on the material surfaces (Table 2), which provides direct evidence that AgNPs were incorporated into the surfaces of the AgNP/PLGA-coated metal materials. SEM and AFM analyses revealed an even and smooth AgNP/PLGA layer on the 316L-SA and titanium without any distinct morphological differences (
The surface hydrophobic/hydrophilic properties of SNPSA and SNPT were compared by a contact angle measurement. The results showed that the surface contact angles of water-miscible dipolar liquids, formamide and ethylene glycol, were significantly decreased on both SNPSA and SNPT with increasing AgNP proportions in the AgNP/PLGA matrix, while the contact angles of water-immiscible non-polar diiodomethane were slightly increased (Table 3). These findings indicate that AgNP incorporation contributed to the hydrophilicity of the AgNP/PLGA-coated metal material surfaces. More importantly, the surface contact angles of water-miscible dipolar liquids on SNPSA were much smaller than the angles on SNPT when the same AgNP proportion was present in both of the respective surfaces (Table 3).
* Data are shown as the mean ± standard deviation (n = 6).
The calculated γS, γSLW, γSAB, and γS− of AgNP/PLGA-coated metal materials are summarized in Table 4. As expected, 0%-SNPSA and 0%-SNPT surfaces presented similar surface free energy values; however, the incorporation of AgNPs significantly increased γSAB, which resulted in a higher SFP and SEADI in the AgNP/PLGA-coated metal materials, especially for the SNPSA (Table 4). These findings indicate that AgNPs play an important role in the proposed galvanic system. The SEADI of SNPSA was much higher than that of SNPT, which suggests that the SNPSA surface undergoes active electron transfer attributed to the electrochemical redox reaction. Moreover, the SEADI and SFP of SNPSA materials became significantly larger with increasing AgNP proportion, but the corresponding SNPT materials only experienced a limited increase in SEADI and SFP with increasing AgNP proportions (Table 4). These data strongly support our hypothesis that the nanoscale galvanic redox system is established on SNPSA, but not the surface of SNPT, as shown in
After COM treatment, the sample surface was characterized by SEM, EDS, AFM, and contact angle measurement. Although SNPSA and SNPT presented similarly smooth surface morphologies pre-COM treatment (
* Data are shown as the mean ± standard deviation (n = 6).
To determine whether the surface potential generated on SNPSA surface can promote osteogenic differentiation in vitro, pre-osteoblastic MC3T3-E1 cells were cultured on SNPSA and SNPT discs. Previously, electric fields have been reported to induce the expression of osteogenic growth factors, including TGFβ1, BMP2, and BMP4, in osteoblastic cells.34-35 In this study, after 6 days of cell cultivation, Tgfβ1, Bmp2, and Bmp4 transcription levels of MC3T3-E1 cells grown on SNPSA were significantly increased in an AgNP-proportion-dependent manner, but there were no significant differences among MC3T3-E1 cells grown on SNPT (
To confirm whether the surface potential generated on SNPSA could promote bone formation in vivo, SNPSA and SNPT implants were inserted into the femurs of rats to create a FIR model.33 3D μCT demonstrated that, after 8 weeks of implantation in the rat distal femoral cavity, more bone formed around 20%-SNPSA implants than around non-Ag coated metal materials and 20%-SNPT implants (
Histological analysis of 0%-SNPSA and 0%, 20%-SNPT showed a gap (a region of no staining) between the new bone and the implants due to the residual AgNP/PLGA layer, but almost no gap was observed in the 20%-SNPSA implants (
In this study, we documented a novel bioengineering strategy that generates built-in electrical forces on metal materials, which can facilitate the osteogenesis and osseointegration in vitro and in vivo. In this strategy, nano-sized silver particles were embedded into a PLGA matrix and coated onto the metal surface. Due to the different electrode potentials between the substrate metal and AgNPs, the coating matrix modified the surface electron density and surface potential, and by doing so, altered the electrochemical property of the implant surface. This is the first report that describes the employment of a galvanic redox mechanism and nanotechnology to modify a metal surface, which introduces a novel bioactivity to a metal implant typically used for structural support.
Of the elements in the engineered redox pair on the surface of SNPSA implants, Fe, the major element (>62%) of 316L-SA, can be oxidized to Fe2+ and release electrons that are transferred to the AgNP cathodes on the coating surface (
Fe−2e−→Fe2+ (Eq. 3)
Ag++e−→Ag (Eq. 4)
2H++2e−H2 (Eq. 5)
The high SPs found on the SNPSA surfaces by KPFM (
The hydrophilicity of the SNPSA surface was significantly increased compared to that of SNPT (Table 2, 3), which can be attributed to the electro-wetting effect.36-37 The relationship of the wettability and the SP can be described qualitatively by the following equation (Eq. 6):
Here, V is the electrode potential in relation to the potential of the uncharged interface, θ(V) is the contact angle of the coating surface under the external electric field (after coating in this preparation), θ(0) is the contact angle without the external electric field (before coating in this preparation), δ is the thickness of the coating, ε is dielectric constant of the coating, and γLV is the interfacial tension between liquid/vapor phases. Therefore, the higher SP of SNPSA enhanced its surface hydrophilicity.
The cathodic reaction during the COM treatment is different from the cathodic reaction in a moist environment due to the high amount of water, the high ionic strength, and the physiological pH value (7.2-7.4). The predominant cathodic reactions during the COM treatment are described in the equations below (Eq. 7, 8):
2H2O+2e−→H2+20H− (Eq. 7)
O2+4H++4e−2H2O (Eq. 8)
The generated OH− promoted the degradation of PLGA, which led to a rough surface observed by SEM and AFM (
Traditionally, galvanic reactions between dissimilar metals in direct contact have negative impacts on the surrounding tissue because the continuous electron flow generates elevated oxidation and corrosion of the implants.39 This usually leads to poor implant performance and rejection.39 However, by engineering a controlled galvanic redox reaction on the surface of the 316L-SA, we introduced a novel biological activity—osteogenesis—to a metal material by surface modification alone. Considering that stainless steel alloys comprise the majority of metals used for biomedical bone fixation, are stronger and less expensive than titanium, and account for more than half of the total biomedical metal market,40 the newly fabricated SNPSA materials that hold bactericidal and osteogenic dual activities may exhibit particular benefits for orthopaedic and orthodontic applications.28 These enhanced bioactive orthopaedic and orthodontic implants could be particularly applicable in scenarios that require elevated osseointegration and/or built-in electrostimulation. Therefore, this study describes an innovative and highly translational strategy to create osteogenic materials for bone regeneration and opens the possibility of developing materials with significantly improved biological functions.
In agreement with our hypothesis, the AgNP/PLGA coating on different metal substrates, which lead to different electrochemical properties, osteoinductivity, and consequent osseointegration, may also distinguish applications for the metal substrates in vivo. For example, SNPSA materials may be more suitable for permanent intramedullary fixation, especially in scenarios where a large volume of bone tissue is lost and osteoinductivity of the implants is required. Additionally, cases of permanent orthopedic and dental implantation in which osseointegration is crucial, such as joint replacement, prosthetic limbs, and teeth, may find SNPSA particularly useful because of its osteoinductive and antimicrobial properties. On the other hand, although titanium materials usually exhibit good biocompatibility and osseointegration due to the stable oxide layer on its surface,41 our results demonstrate that introducing a thin AgNP/PLGA coating significantly improves the osseointegration capacity of the less expensive 316L-SA compared to a titanium substrate. The titanium alloy may impart titanium dioxide nanoparticles, which have been reported to alter the viability and behavior of multiple bone related cell types, increase bone resorption, and lead to clinical incidents of osteolysis, implant loosening, and joint pain.42 Thus, for fractures without major tissue deficiencies, SNPT materials may be a more desirable choice for external fixation.
By characterizing the surfaces of the coated metal materials using SEM, EDS, AFM, KPFM, and contact angle measurement, we successfully demonstrated that delicately establishing a nanoscale galvanic redox system to alter the SP of a traditional biomaterial can induce novel bioactivities. For instance, by engineering a nanoscale galvanic redox system between AgNPs and 316L-SA, the AgNP/PLGA coating endowed bactericidal activities to the 316-SA and also introduced novel osteogenic stimulation properties into the system. This markedly advances the orthopaedic and orthodontic applications of SNPSA materials. Importantly, the novel osteoinductivity was only present in the composite materials that could interact in a galvanic redox system, but was not found in the individual components of the composite materials. From the example presented in this study, the AgNP/PLGA coating converted a normally deleterious galvanic redox reaction (e.g., rusting,17-18 poor implant performance, and rejection39) on metal surfaces into a biological benefit that promoted pen-implant bone growth (data not shown). The universal galvanic redox reaction can also be applied to other metallic materials, such as copper or zinc, and used in orthopaedic, dental, and cardiovascular devices. From these findings, this study enables insight into both the generated electrical forces and potential applications of galvanic redox reactions in biomaterial engineering. We foresee that this study will offer a strong foundation for developing a new class of galvanic redox biomaterials that endow novel biological functions for use in regenerative medicine.
20-40 nm-diameter spherical silver nanoparticles (QSI-Nano® Silver, QuantumSphere, Inc., Santa Ana, Calif.) were thoroughly mixed with 17.5% (w/v) PLGA (lactic: glycolic=85:15, inherent viscosity: 0.64 dl/g in chloroform; Durect Co., Pelham, Ala.) solution. The proportion of silver nanoparticles refers to the weight ratio of silver nanoparticles to PLGA. 316L stainless steel alloy Kirschner (K)-wire (length: 1 cm, diameter: 0.6 mm; Synthes. Monument, Colo.) and discs (thickness: 1.59 mm, diameter: 6.35 mm; Applied Porous Technologies, Inc., Tariffville, Conn.) were soaked in the silver nanoparticle/PLGA-chloroform solution for 30 s and air-dried completely. The soak-dry process was repeated three times for each SNPSA implant. After incubating for 12 h at 37° C. to ensure a uniform coating, SNPSAs were stored at −20° C. until use. Morphology of the SNPSA was evaluated by scanning electron microscopy (SEM; NovaNano SEM 230-D9064, FEI Company, Hillsboro, Oreg.) (
Surface free energy of SNPSAs was obtained from contact angle measurements. Contact angles of multiple standard liquids on the tested SNPSAs were measured using a contact angle analyzer (FTA125; First Ten Angestroms, Portsmouth, Va.). In order to obtain an accurate description of the wetting behavior of various SNPSAs, the surface free energy of the solid (γS),was considered to be the sum of separate dispersion (γsd) and non-dispersion (γsnd) contributions. From this two-component model, the following relationship was derived from the dispersion γd and non-dispersion (also known as ‘polar’) γnd interactions between liquids and solids.
γL×(cos θ+1)=2×(γLd×γshu d)1/2+(γLnd×γsnd)1/2 (1)
Eq. (1), known as the geometric mean model, allows the calculation of the solid surface free energy using the contact angle (θ) and the surface tension components of the standard liquids, where γL, γLd, and γLnd represent the surface tension and its dispersion and non-dispersion components of the standard liquids, respectively. The surface tension components of the standard liquids are listed in Table 8.
The Gram-positive vancomycin-intermediate S. aureus (VISA/MRSA) strain Mu50 (ATCC 700699) was cultured in brain heart infusion broth (BHIB; BD, Sparks, Md.) at 37° C.; while biofilm-forming, Gram-negative opportunistic pathogen P. aeruginosa PAO-1 (ATCC 15692) was cultured in Luria Bertani broth (LB; Fisher Scientific, Hampton, N.H.) at 30° C. 103, 104, and 105 colony forming units (CFU) of bacteria were suspended in 1 ml culture broth and incubated with the SNPSA K-wires at 225 rpm on a shaker for 1, 2, 6, and 24 hours.
At the end of the incubation, Mu50 and PAO-1 bacteria attached to the surface were collected by 0.9% saline solution and plated onto 10-cm BHIB or LB culture medium plates overnight, respectively.
After 18 h incubation, the number of colonies on each plate was counted and the total viable CFU load was determined.
Femurs isolated from 12-week old male 129/sv mice were used to assay SNPSA antimicrobial activity ex vivo. Briefly, after locating the femoral intercondylar notch, an intramedullary canal was manually reamed into the distal femur with a 25-gauge needle. A SNPSA K-wire was then placed into the intramedullary canal with 2 μl Mu50 or PAO-1 bacteria suspended in phosphate buffered saline (PBS, pH 7.2; Invitrogen, Carlsbad, Calif.).
Femurs with implants were then placed on 100-μm cell strainers (BD) inside 6-well culture plates containing 2 ml α-minimal essential medium (α-MEM; Invitrogen) supplemented with 1% HT supplement (Invitrogen) and fetal bovine serum (FBS; Invitrogen).
In order to avoid direct contact between SNPSAs and cell culture medium, the distal femur with a protruding SNPSA was angled superiorly, and the proximal femur was soaked in culture medium (
After 18 h of incubation at 37° C., 5% CO2, and 95% humidity, SNPSAs were removed from the intramedullary canal and incubated in 1 ml nutrient PBS (1×PBS with 0.25% glucose, 0.2% ammonium sulfate, and 1% sterile bacterial growth broth) for 18 h. 100 μl of released bacteria was transferred into a 96-well microplate and amplified by adding 100 μl fresh bacterial culture broth for another 40 h.
Proliferation of the released daughter cells was monitored at a wavelength of 595 nm using an Infinite f200 microplate reader (Tecan, Durham, N.C.) to generate a time-proliferation curve for each well of the microplate, as previously described.
In this assay, lagging or absent bacterial growth was diagnostic of partial or complete inhibition by the SNPSA, such that only a few or no daughter cells were able to colonize the substrate.
SNPSA discs were incubated at 37° C. for 20 h with 500 μl α-MEM containing 10% FBS and either 0.1 mg/ml bovine serum albumin (BSA; Fisher Scientific) or 0.1 mg/ml BMP-2 (Medtronic, Minneapolis, Minn.). To harvest all adsorbed proteins, SNPSAs were then incubated in 10 mM TRIS (Fisher Scientific) and 1 mM EDTA (Fisher Scientific) for 6 h at 4° C. Protein concentration was measured using the Bio-Rad® Protein Assay (Bio-Rad, Hercules, Calif.) with the Tecan Infinite f200 microplate reader.
2×103 pre-osteoblastic MC3T3-E1 murine cells (passage 18, subclone 4, ATCC CRL-2593) were seeded on SNPSA discs with 500 μl osteogenic medium (a-MEM supplied with 10% FBS, 1% HT supplement, 100 unit/ml penicillin, 100 μg/ml streptomycin, 50 μg/ml ascorbic acid and 100 mM β-glycerophosphate) in 24-well plates at 37° C., 5% CO2, and 95% humidity. All media for cell culture were purchased from Invitrogen. Cell proliferation was estimated using the Vybrand® MTT Cell Proliferation Assay Kit (Invitrogen). ALP activity and degree of mineralization (assessed by Alizarin Red staining) were used to quantify the effect of silver nanoparticle/PLGA-coated stainless steel alloy on osteoblastic differentiation.
Rat Fc Model p All surgical procedures were approved by the UCLA Office of Animal Research Oversight (protocol #2008-073). Using aseptic technique, a 25-30 mm longitudinal incision was made over the anterolateral aspect of the left femur of 12-week old male Sprague-Dawley (SD) rats. The femoral shaft was then exposed by separating the vastus lateralis and biceps femoris muscles. Using a micro-driver (Stryker, Kalamazoo, Mich.), four canals were drilled on each femur with 2-mm interface. SNPSA K-wires were implanted into each predrilled canal. For bacterial inoculation, 103 CFU S. aureus Mu50 or P. aeruginosa PAO-1 in 10 μl PBS (105CFU/ml) was pipetted into the canal before implantation. After inoculation, the overlying muscle and fascia were closed with 4-0 Vicryl absorbable suture to secure the implant in place. Following surgery, the animals were housed in separate cages and allowed to eat and drink ad libitum. Weight bearing was started immediately postoperatively, and the animals were monitored daily. Buprenorphine was administered for 2 days as an analgesic, but no antibiotic was administered.
At 2, 4, 6, and 8 weeks post-surgery, high-resolution lateral radiographs were obtained while the animals were under isoflurane anesthesia. The animals were euthanized at 8 weeks post-implantation. Operated femurs were dissected, harvested, and fixed in 10% buffered formalin (Fisher Scientific). Following 48 h fixation, samples were scanned using high-resolution micro-computed tomography (microCT; Skyscan 1172, Skyscan, Belgium) at an image resolution of 20.0 μm (55 kVp and 181 μA radiation source with 0.5 mm aluminum filter). 2D and 3D high-resolution reconstruction images were acquired using the software provided by the manufacturer.
After 3D microCT scanning, the specimen was decalcified using 10% EDTA solution (pH 7.4, Fisher Scientific, Hampton, N.H.) for 21 days, washed with running tap water for 3-4 h, transferred to a 75% ethanol solution, and embedded in paraffin. 5-μm sagittal sections of each specimen were collected. Hematoxylin and eosin (H&E) staining and Masson's Trichrome staining were used to assess morphology. Taylor-modified Brown and Brenn Gram staining and Giemsa staining were used to assess bacterial contamination and inflammation, respectively. In addition, IHC staining for osteocalcin (OCN, Santa Cruz Biotechnology, Santa Cruz, Calif.) was applied to evaluate new bone generation.
All results are presented as mean ±standard error of mean (s.e.m.). Statistical significance was computed using one-way ANOVA and independent-samples t-test (Origin 8; OriginLab Corp., Northampton, Mass.). P<0.05 was considered statistically significant. All statistical analyses in this manuscript were conducted per consultation with the UCLA Statistical Biomathematical Consulting Clinic (SBCC).
SNPSA was produced by repeated incubations of 316L steel alloy in silver nanoparticle/PLGA-chloroform solution. A uniform layer of silver nanoparticle/PLGA composite was observed on the surface of the stainless steel alloy (
SEM revealed that the thickness of silver nanoparticle/PLGA layer coated on K-wires was 43.36±0.08 μm (
The contact angles on the SNPSAs obtained before and after incubation in osteogenic medium are summarized in Table 9. Notably, the values of contact angle for the liquids applied on 0%-SNPSA differed only slightly before and after incubation in osteogenic medium. In contrast, the values of contact angle for the liquids applied on 1%- and 2%-SNPSAs dramatically changed after the incubation (Table 9).
*Data were shown as mean ± SEM (N = 6)
# SNPSAs were incubated in osteogenic medium for 9 days.
Using the contact angle values and Eq. (1), surface free energy and its dispersion and non-dispersion components of SNPSAs were calculated (
Interestingly, the dispersion component yd decreased with increasing silver proportion (
As a result, the polarity of SNPSAs, defined as
increased with silver proportion (
Analysis of bacterial colonization showed that, when compared to 0%-SNPSA, 1%- and 2%-SNPSAs inhibited the initial adherence of S. aureus Mu50 (
This result suggested that S. aureus Mu50 proliferated extensively on 0%-SNPSA surface after adherence. 1% silver nanoparticles slightly reduced initial adherence of 103 CFU S. aureus Mu50 but significantly inhibited its proliferation on the coated alloy (
When the initial inocula of both species were increased to 104 and 105 CFU, about 2×103 bacteria initially adhered to the 0%-SNPSA and proliferated during the incubation (
Ex vivo Antimicrobial Activity of SNPSAs
In order to further evaluate the effect of silver nanoparticle/PLGA coating on preventing bacterial adherence and biofilm formation on the surface of implants, an ex vivo contamination model (
Control 0%-SNPSA did not inhibit ex vivo bacterial adherence or proliferation, while silver-proportion-dependent antimicrobial activity was observed in 1%- and 2%-SNPSAs (
Protein adsorption was detected on SNPSAs (
The MTT assay was used to compare mouse MT3T3-E1 pre-osteoblastic cell proliferation on different SNPSAs (
Interestingly, along with the culture time, SNPSAs with higher silver proportions promoted cell proliferation more potently (
Furthermore, SNPSAs also significantly promoted ongrowth terminal differentiation of osteoblasts, as indicated by mineralization, during the 21-day culture period (
No obvious radiographic signs of bone formation were observed in rat FCs implanted with either uncontaminated (
Microscopic examination revealed bacterial persistence (
Newly formed bone around SNPSA implants was further evaluated by H&E staining, Trichrome staining, and IHC staining with an antibody against OCN, a marker of mature differentiated osteoblasts, at 8 weeks after implantation with 103 CFU initial bacterial inoculum. Only minimal bone formation around the 0%-SNPSA groups was observed (
Since the first applications of surgically-implanted materials in humans, bacterial infections have represented a common and challenging problem. Bacterial adherence to the foreign implanted materials and subsequent biofilm formation are hallmarks of implant-associated infections. As a result, prevention of bacterial colonization and biofilm formation on implants by administration of prophylactic antibiotics has been extensively studied. Interestingly, most of these studies are focused on preventing S. aureus contamination, as this species is the leading cause of implant-associated infections due to its high affinity to bone, rapid induction of osteonecrosis, and resorption of bone matrix. However, other bacterial species, including P. aeruginosa, S epidermidis, Klebsiella ozaenae, and Escherichia coli, are also commonly involved in implant-associated infections in orthopedic surgery, and some studies have even reported P. aeruginosa as a major isolated organism. Because pathogens involved in implant-associated infections are diverse, and bacteria in biofilms are protected from the host immune responses and antibiotics, the restricted activity of antibiotics against implant infections limits their clinical effectiveness. This is especially the case in infections involving antibiotic-resistant bacterial strains (e.g. MRSA strains), which are increasing in both healthcare and community settings and are becoming a major threat to public health.
Because of its antimicrobial properties, silver has been extensively used in water recycling and sanitization and for treatment of wound infections. Currently, silver is gaining renewed attention as a medical antimicrobial agent due to its broad antibacterial spectrum and the difficulty of developing bacterial resistance to silver. For instance, silver is used to reduce bacterial colonization in a variety of pharmaceutical devices including vascular and urinary catheters, endotracheal tubes, and implantable prostheses. Mechanistically, silver prevents cell division and transcription by binding to and disrupting multiple components of bacterial structure and metabolism, including cellular transport, essential enzyme systems such as the respiratory cytochromes, and synthesis of cell wall components, DNA and RNA; nevertheless, the reservoir form of the active silver form may be diverse. Previously, ionic reservoir forms of silver such as silver nitrate (AgNO3) and silver sulfate (Ag2SO4) have been used to provide protection against bacterial infections. However, despite its effective short-term antibacterial activity, inadequate local retention and severe cytotoxic effects of ionic silver (Ag+) have made it undesirable for continually preventing bacterial colonization on the implants. Recent reports have shown that that 20-25 nm silver nanoparticles effectively inhibit microorganisms without causing significant cytotoxicity, and that 10-20 nm silver nanoparticles are nontoxic in mice and guinea pigs when administered by the oral, ocular and dermal routes. These findings suggest silver nanoparticles of the size evaluated in the present study are appropriate for therapeutic application from a safety standpoint.
In addition, the preparation and stabilization of silver nanoparticles remain challenging due to their tendency to aggregate. Several polymers have been used to stabilize silver nanoparticles, including polyethyleneimine, polyallylamine, poly(vinyl-pyrrolidone), and chitosan. The nucleophilic character of these polymers, albeit minor, is sufficient for them to bind to the metal particles by donating electrons.
The US Food and Drug Administration (FDA)-approved, biodegradable and biocompatible polymer PLGA has been chosen in this study because its hydrolysable ester bonds are subject to nucleophilic interactions with incorporated components such as silver particles. Another advantage of PLGA is that it could be applied onto implants using solvent casting techniques, which allow coating of alloys and even plastic surfaces with polished, irregular or porous materials.
For instance, up to 2% silver nanoparticles were coated onto 316L stainless steel alloy within PLGA without aggregation (
In this study, the results from in vitro and ex vivo assays demonstrated that 2%-silver nanoparticle/PLGA coating effectively prevented bacterial adherence and biofilm formation on the stainless steel alloy implants (
Notably, surface free energy of SNPSA, especially its non-dispersion component, increases with silver proportion after incubation in osteogenic medium (
As a result, the non-dispersion component of surface free energy, the total surface free energy, and the polarity are all increased after incubation in osteogenic medium in a silver-proportion-dependent manner (
In summary, we demonstrated that SNPSA successfully inhibited bacterial adherence and biofilm formation in a silver-proportion-dependent manner. Unexpectedly, we also found that SNPSA materials promoted MC3T3-E1 pre-osteoblast proliferation and maturation in vitro. Finally, we used a rat FC model to show that 2%-SNPSA implants have significantly induced bone generation despite bacterial contamination, even at a bacterial inoculum that could cause invasive tissue infection.
From a materials and device development perspective, SNPSA exhibited strong bactericidal and osteoinductive properties that make it a promising pharmaceutical material in orthopedic surgery. The results also indicated that silver nanoparticle/PLGA coating is a practical process that is non-toxic, easy to operate, and free of silver nanoparticle aggregation. In addition, our results revealed that the antibacterial and osteoinductive activities of SNPSA are silver-proportion-dependent, raising the interest in increasing the silver proportion of the coating in future investigations. Further improvement of interfacial adhesion of silver nanoparticle/PLGA coating to different metal surfaces, such as stainless steel alloys, titanium and titanium-based alloys, and cobalt alloys, should be made for clinical application of silver nanoparticle/PLGA-coated implants in orthopedic surgery, especially when permanent implants such as pins for the fixation of bone fracture are indicated.
Formation of an antimicrobial coating or layer is described in PCT/US2012/061217, the teaching of which, including references cited therein, is incorporated herein in its entirety. For the reason of concise description, the reference listing for Example 2 is omitted, and such references can be found in PCT/US2012/061217.
The various methods and techniques described above provide a number of ways to carry out the invention. Of course, it is to be understood that not necessarily all objectives or advantages described may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that the methods can be performed in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objectives or advantages as may be taught or suggested herein. A variety of advantageous and disadvantageous alternatives are mentioned herein. It is to be understood that some preferred embodiments specifically include one, another, or several advantageous features, while others specifically exclude one, another, or several disadvantageous features, while still others specifically mitigate a present disadvantageous feature by inclusion of one, another, or several advantageous features.
Furthermore, the skilled artisan will recognize the applicability of various features from different embodiments. Similarly, the various elements, features and steps discussed above, as well as other known equivalents for each such element, feature or step, can be mixed and matched by one of ordinary skill in this art to perform methods in accordance with principles described herein. Among the various elements, features, and steps some will be specifically included and others specifically excluded in diverse embodiments.
Although the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the embodiments of the invention extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and modifications and equivalents thereof.
Many variations and alternative elements have been disclosed in embodiments of the present invention. Still further variations and alternate elements will be apparent to one of skill in the art. Among these variations, without limitation, are the specific number of antigens in a screening panel or targeted by a therapeutic product, the type of antigen, the type of cancer, and the particular antigen(s) specified. Various embodiments of the invention can specifically include or exclude any of these variations or elements.
In some embodiments, the numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
In some embodiments, the terms “a” and “an” and “the” and similar references used in the context of describing a particular embodiment of the invention (especially in the context of certain of the following claims) can be construed to cover both the singular and the plural. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations on those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. It is contemplated that skilled artisans can employ such variations as appropriate, and the invention can be practiced otherwise than specifically described herein. Accordingly, many embodiments of this invention include all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Furthermore, numerous references have been made to patents and printed publications throughout this specification. Each of the above cited references and printed publications are herein individually incorporated by reference in their entirety.
It is to be understood that the embodiments of the invention disclosed herein are illustrative of the principles of the present invention. Other modifications that can be employed can be within the scope of the invention. Thus, by way of example, but not of limitation, alternative configurations of the present invention can be utilized in accordance with the teachings herein. Accordingly, embodiments of the present invention are not limited to that precisely as shown and described.
This application is a continuation of International application No. PCT/US19/27933, filed Apr. 17, 2019, which claims the benefit of U.S. Provisional Patent Application No. US 62/659,093, filed on Apr. 17, 2018. The teaching of these applications is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62659093 | Apr 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2019/027933 | Apr 2019 | US |
| Child | 17073945 | US |
