Patent Application
20050177245
This invention is in the field of orthopedic implants, in particular, implants which are made at least in part of absorbable material.
The patent literature describes a variety of tissue implant materials and devices having two regions of differing composition and/or microstructure.
U.S. Pat. Nos. 6,149,688 and 6,607,557, to Brosnahan et al., describe an artificial bone graft implant having two basic portions, each composed of a biocompatible microporous material. The core of the implant is formed of a highly porous composition and the shell of a low porosity dense composition. An implant formed of a unitary structure having a gradient of pore sizes is also described. Specific implant materials mentioned include biocompatible metallics, ceramics, polymers, and composite materials consisting of phosphate(s), bioactive glass(es) and bioresorbable polymer(s).
U.S. Pat. No. 5,769,897, to Härle, describes an artificial bone material which has a strength sustaining first component and a biointegration promoting second component. The first and second materials can be selected from a group including bioceramic materials, carbon ceramics, aluminum oxide ceramics, glass ceramics, tricalcium phosphate ceramics, tetracalciumphosphate ceramics, hydroxylapatite, polyvinylmethacrylate, titanium, implantation alloys, and biocompatible fiber materials.
U.S. Pat. No. 5,152,791, to Hakamatsuka et al., describes a prosthetic artificial bone having a double-layered structure obtained by molding a porous portion having a porosity from 40 to 90% and a dense portion having a porosity not more than 50% into an integral body. The implant material is a ceramic or glass containing calcium and phosphorus.
U.S. Pat. No. 5,607,474, to Athanasiou et al., describes a multi-phase bioerodible polymeric implant/carrier. U.S. Pat. No. 6,264,701 to Brekke describes bioresorbable polymer devices having a first region with an internal three-dimensional architecture to approximate the histologic pattern of a first tissue; and a second region having an internal three-dimensional architecture to approximate the histologic pattern of a second tissue. U.S. Pat. No. 6,365,149, to Vyakarnam et al., describes gradients in composition and/or microstructure in porous resorbable polymer forms. U.S. Pat. No. 6,454,811, to Sherwood et al., describes use of gradients in materials and/or macroarchitecture and/or microstructure and/or mechanical properties in synthetic polymeric materials.
U.S. Pat. No. 4,863,472, to Törmälä et al, describes a bone graft implant having bone graft powder located inside and/or below a supporting structure. The supporting structure is manufactured at least partially of a resorbable polymer, copolymer or polymer blend. The supporting structure also includes porosity which allows the surrounding tissues to grow through the supporting structure but which prevents the migration of the bone graft powder through the pores outside the supporting structure.
Further, the patent literature describes implants which contain cavities or spaces which can be filled with material to induce bone growth.
U.S. Pat. No. 6,548,002, to Gresser et al., describes a spinal wedge incorporating peripheral and/or central voids which can be filled with grafting material for facilitating bony development and/or spinal fusion. The wedge can be made of a biodegradable, biocompatible polymer which may include a buffer.
U.S. Pat. No. 6,652,073 and U.S. Published Patent Application No. 2003/1095632, both to Foley et al., describe implants having a cavity in which bone growth material is placed. U.S. Pat. No. 6,652,073 describes an implant body of bone. U.S. Published Application 2003/1095632 lists titanium, composite materials, including carbon composites, and surgical stainless steel as examples of suitable implant body materials. For spinal implants, a variety of methods have been described for securing the implant. U.S. Pat. No. 6,576,017, to Foley et al., U.S. Pat. No. 6,562,073, to Foley, U.S. Pat. No. 6,461,359, to Tribus et al, and U.S. Pat. No. 5,645,599, to Samani et al., describe devices with an intervertebral body and flange-like structures. The flange-like structures can be attached to vertebrae. U.S. Pat. No. 5,306,309 to Wagner et al. describes a spinal disk implant in which the intervertebral body has an engagement region which has one or more three-dimensional features extending above the general level of the transverse faces. The engagement features are intended to sink into the cancellous bone as load is applied.
The invention provides absorbable orthopedic implants. The implants of the invention are useful for applications including, but not limited to, osteotemies, spinal interbody fusion, long bone lengthening, and trauma reconstruction.
In an embodiment, the invention provides an implant comprising a ring of biocompatible material. The ring may be made of an absorbable biocompatible material. The ring may be used in combination with a second, more porous, absorbable material. This second material may be a continuous body or composed of multiple pieces (e.g. granules or chunks). The ring may be connected to one or more plates which allow attachment of the ring to neighboring bone. For example, in a spinal implant, anterior plates allow attachment of the implant to neighboring vertebrae.
In another embodiment, the invention provides an implant comprising a first material, not in the form of a ring, in combination with a full or partial wedge of a second, more porous, absorbable material. The first material may be connected to one or more plates which allow attachment of the implant to neighboring bone.
Suitable materials for the implants of the invention include, but are not limited to, absorbable polymer composites. One suitable absorbable material is a fully dense composite of an absorbable material with ceramic or mineral particles. Another suitable absorbable material is a porous composite of an absorbable polymer, ceramic or mineral particles, fibers, and a surfactant. Inclusion of ceramic or mineral particles can provide a buffering affect, increase osteoconductivity, and increase the mechanical strength of the composite.
The invention provides orthopedic implants comprising absorbable material. The implants of the invention comprise a tissue spacer which comprises absorbable material and, optionally, one or more plates for attachment to tissue. The tissue spacer may be wholly absorbable or may contain some nonabsorbable components. Nonabsorbable components of the tissue spacer can include, but are not limited to, load-bearing portions of the tissue spacer or reinforcement materials such as fibers. The anterior plates may be absorbable or nonabsorbable. The terms “biodegradable” and “absorbable” are used interchangeably to mean capable of breaking down over time, either inside a patient's body, or when used with cells to grow tissue outside the body. When placed inside a patient's body, the absorbable portions of the implants of the invention will degrade over time and be removed by the body's natural processes.
In an embodiment, the invention provides an orthopedic implant comprising
As used herein, a full wedge is the shape formed by two inclined planes that merge to form an edge. Partial wedge shapes suitable for use with the invention exclude at least the edge or tip of a full wedge shape, and may exclude a larger portion of the tip end of a full wedge. The angle of a wedge or partial wedge is the angle of inclination between the planes forming the superior and inferior surfaces of the wedge or partial wedge. The angle of inclination, θ1 can be between about 5 degrees and about 20 degrees. In different embodiments, the angle θ1 is 7.5 degrees, 10 degrees, 12.5 degrees, or 15 degrees.
As used herein, a ring may be in the form of a circle, an oval, a rectangle, or another shape forming a closed curve. In the embodiment shown in
In general, the planes forming the superior and inferior surfaces of the first material need not be parallel and can have an angle of inclination θ2 between them. Typically, as shown in
A tissue spacer comprising a first region connected to a full or partial porous wedge can also be connected to one or more anterior plates (60) as shown in
In addition, as shown in
The implant comprising a tissue spacer comprising a first region connected to a porous full or partial wedge can be useful in spinal applications as well as for osteotomies, long bone lengthening, and trauma reconstruction. An osteotomy is a surgical procedure necessary to correct a patient's bone alignment. In an osteotomy, the bone is transected or cut to realign the bone ends.
The first region preferably has an initial Young's Modulus between about 1.0 GPa and about 30 GPa and a compressive strength between about 10 MPa and about 500 MPa. In an embodiment the initial Young's Modulus is between about 10 GPa and about 30 GPa. At between six to nine months after implantation, the first region preferably retains between about 70% to 90% of its initial strength. In an embodiment, the first region preferably retains about 80% of its initial strength. The full or partial wedge preferably has an initial Young's Modulus between about 0.5 Gpa and about 5 GPa. In an embodiment, the initial Young's Modulus is between about 1 GPa and about 5 GPa and a compressive strength between zero MPa and about 30 MPa. In an embodiment, the first region and/or full or partial wedge has mechanical properties matching those of bone tissue into which it is to be inserted. These mechanical properties include a Young's modulus of about 15 GPa for cortical bone and a Young's modulus of about 500 MPa for cancellous bone.
In different embodiments, the porosity of the first region is between zero and about 30%, or between zero and about 15%. In an embodiment, the first region is substantially nonporous, having porosity less than about 5%.
In an embodiment, the first region of the tissue spacer is formed of a substantially nonporous (fully dense) absorbable material comprising absorbable polymer, an optional ceramic or mineral component such as beta-tricalcium phosphate and an optional buffering component such as calcium carbonate. The absorbable polymer selected is soluble or at least swellable in a solvent and is able to degrade in-vivo without producing toxic side products. Typical polymers are selected from the family of poly-lactide, poly-glycolide, poly-caprolactone, poly-dioxanone, poly-trimethylene carbonate, and their co-polymers; however any absorbable polymer can be used. Polymers known to the art for producing biodegradable implant materials include polyglycolide (PGA), copolymers of glycolide such as glycolide/L-lactide copolymers (PGA/PLLA), glycolide/trimethylene carbonate copolymers (PGA/TMC); polylactides (PLA), stereocopolymers of PLA such as poly-L-lactide (PLLA), Poly-DL-lactide (PDLLA), L-lactide/DL-lactide copolymers; copolymers of PLA such as lactide/tetramethylglycolide copolymers, lactide/trimethylene carbonate copolymers, lactide/.delta.-valerolactone copolymers, lactide.epsilon.-caprolactone copolymers, polydepsipeptides, PLA/polyethylene oxide copolymers, unsymmetrically 3,6-substituted poly-1,4-dioxane-2,5-diones; polyhydroxyalkanate polymers including poly-beta-hydroxybutyrate (PHBA), PHBA/beta-hydroxyvalerate copolymers (PHBA/HVA), and poly-beta-hydroxypropionate (PHPA), poly-p-dioxanone (PDS), poly-delta-valerolatone, poly-epsilon-caprolactone, methylmethacrylate-N-vinyl pyrrolidone copolymers, polyesteramides, polyesters of oxalic acid, polydihydropyrans, polyalkyl-2-cyanoacrylates, polyurethanes (PU), polyvinyl alcohol (PVA), polypeptides, poly-beta-maleic acid (PMLA), and poly-beta-alkanoic acids. The polymer can be chosen, as is known to the art, to have a selected degradation period. For intervertebral spacers the degradation period is preferably up to about 4 years, or between about 6 weeks and about 2 years, or between about 12 weeks and about 1 year. For osteotomy wedges, the degradation period is preferably up to about 2 years, or between about 3 weeks and about 1 year, or between about 6 weeks and about 9 months.
The ceramic or mineral component of the material adds both mechanical reinforcement and biological activity to the material. The ceramic (or mineral) component is chosen from calcium sulfate (hemi- or di-hydrate form), salts of calcium phosphate such as tricalcium phosphate or hydroxyGPatite, various compositions of Bioglass®, and blends or combinations of these materials. In an embodiment, more than one mineral component is included in the composite. Particles can range in size from sub-micron to up to 1 mm, depending on the desired role of the component chosen. The volume fraction of ceramic particles can range from about 1% to about 40%, from about 5% to about 30%, or from about 10% to about 20%.
Incorporation of calcium-containing minerals can help buffer the degradation of biodegradable polymers. Other useful buffering compounds include compounds as disclosed in U.S. Pat. No. 5,741,321 to Agrawal et al., hereby incorporated by reference. Volume fractions of the buffering compound are from about 1% to about 40%, from about 5% to about 30%, or from about 10% to about 20%. Particle sizes for the buffering compound are less than about 2 mm or less than about 1 mm.
Either absorbable or nonabsorbable fibers can also be added to the material to provide additional reinforcement as is known to those skilled in the art. The fibers may be aligned or have a random orientation.
Fully dense portions of the tissue spacer can be fabricated by injection molding, machining, or other methods as known in the art.
The first region may also be made of nonabsorbable biocompatible material such as a metal, a plastic, or a ceramic. Nonabsorbable materials suitable for use in implants are known to those skilled in the art.
In an embodiment, the porosity of the full or partial wedge is between about 50% and about 90%. In different embodiments, the porosity of the full or partial wedge is greater than about 50% or greater than about 70%. Preferably, the full or partial wedge is sufficiently porous to allow for bony ingrowth. In an embodiment, the average pore size of the full or partial wedge between about 10 microns and about 2000 microns, between about 50 microns and about 900 microns and about 100 microns to about 600 microns. The more porous portion of the tissue spacer can be capable of soaking up fluids such as blood or bone marrow and therefore can be loaded with bioactive agents, drugs or pharmaceuticals. Both autologous and bioactive agents can be used with the tissue spacer of the invention. Autologous bioactive agents include, but are not limited to, concentrated blood, such as Platelet-Rich Plasma (PRP) and Autologous Growth Factor (AGF), and the patient's own bone marrow. Synthetic bioactive agents, include, but are not limited to, bone morphogenic proteins (e.g. BMP-2 growth factors (VEGF, FGF, TGF-b, PDGF, IGF) or synthetic or analogous versions of these peptides).
The implant may also be seeded with cells of the type whose ingrowth is desired. Osteoblasts and osteocytes are bone-forming cells which could be adsorbed onto the porous portion of the device. Mesenchymal stem cells, bone marrow cells, or other precursor cells which have the potential to differentiate into bone-forming cells may also be used.
The implant material of this invention can also be preseeded with autologous or allogenic tissue. The autologous or allogenic tissue may be minced or particulated. In an embodiment, the tissue is dermal tissue, cartilage, ligament, tendon, or bone. These allogenic tissues can be processed to preserve their biological structures and compositions, but to remove cells which may cause an immune response. Similarly, autologous tissues can be utilized and processed as described for allografts.
In an embodiment, the porous full or partial wedge comprises up to four main components: 1) an absorbable polymer, 2) a ceramic, 3) fibers, and 4) a surfactant. The device can be prepared with only the first two components; however additional performance properties can be achieved with addition of the third and fourth components. Porous materials made with these components provide a porous polymeric scaffold, incorporate a high level of biologically active or biologically compatible ceramic or mineral, and provide a high level of toughness and strength. When the material includes surfactant, the porous material becomes more wettable, overcoming some of the limitations of the intrinsically hydrophobic material. Table 1 lists typical percentages of each of these four components. Table 2 lists typical physical properties of the formulations in Table 1.
The absorbable polymer forms the core component of the porous portion of the tissue spacer and is needed for formation of the porous structure of the implant material. The polymer selected is soluble or at least swellable in a solvent and is able to degrade in-vivo without producing toxic side products. Typical polymers are selected from the family of poly-lactide, poly-glycolide, poly-caprolactone, poly-dioxanone, poly-trimethylene carbonate, and their co-polymers; however any absorbable polymer or combinations of absorbable polymers can be used. The polymer has a molecular weight sufficient to form a viscous solution when dissolved in a volatile solvent, and ideally precipitates to form a soft gel upon addition of a non-solvent. The polymer can be selected as is known to the art to have a desired degradation period. For a full or partial wedge, the degradation period is preferably up to about 2 years, or between about 3 weeks and about 1 year, or between about 6 weeks and about 9 months.
The ceramic component of the material adds both mechanical reinforcement and biological activity to the material. The ceramic (or mineral) component is chosen from calcium sulfate (hemi- or di-hydrate form), salts of calcium phosphate such as tricalcium phosphate or hydroxyapatite, various compositions of Bioglass®, and blends or combinations of these materials. Particles can range in size from sub-micron to up to 1 mm, depending on the desired role of the component chosen. For example, a highly-reinforced composite material can be prepared by incorporating nano-particles of hydroxyapatite. Alternatively, large particles of calcium sulfate (>100 μm) can be incorporated which will dissolve in 4 to 6 weeks, increasing the overall porosity of the material and stimulating bone formation. Incorporation of calcium containing minerals can also help buffer the degradation of biodegradable polymers to avoid acidic breakdown products. The ceramic component can also take the shape of elongated particles or fibers to provide enhanced mechanical properties.
Addition of fibers to the composite can increase both the toughness and strength of the material, as is well known to the art. Fibers suitable for use with the invention include both absorbable and nonabsorbable fibers. Preferential alignment of fibers in a porous material can produce anisotropic behavior as described in U.S. Pat. No. 6,511,511, where the strength is increased when the load is applied parallel to the primary orientation of the fibers. In the present invention, up to 30% by mass of the material can be comprised of fibers. Preferred polymeric fiber materials can be selected from the family of poly-lactide, poly-glycolide, poly-caprolactone, poly-dioxanone, poly-trimethylene carbonate, and their co-polymers; however any absorbable polymer could be used. Polysaccharide-based fibers can be chosen from cellulose, chitosan, dextran, and others, either functionalized or not. Non-polymeric fibers can be selected from spun glass fibers (e.g. Bioglass®, calcium phosphate glass, soda glass) or other ceramic materials, carbon fibers, and metal fibers.
The optional addition of a bio-compatible surfactant can improve the surface wettability of the porous construct. This can improve the ability of blood, body fluids, and cells to penetrate large distances into the center of an implant by increasing the capillary action. Examples of bio-compatible surfactants are poly-ethylene oxides (PEO's), poly-propylene oxides (PPO's), block copolymers of PEO and PPO (such as Pluronic surfactants by BASF), polyalkoxanoates, saccharide esters such as sorbitan monooleate, polysaccharide esters, free fatty acids, and fatty acid esters and salts. Other surfactants known to those skilled in the art may also be used.
Any porous portions of the tissue spacer can be fabricated through polymer precipitation and vacuum expansion. Methods for the preparation of precipitated polymers are well-known to the art. In general, the process comprises mixing a dried polymer mix with a solvent, e.g. acetone, precipitating the polymer mass from solution with a non-solvent, e.g. ethanol, methanol, ether or water, extracting solvent and precipitating agent from the mass until it is a coherent mass which can be pressed into a mold or extruded into a mold, and curing the composition to the desired shape and stiffness. The optional surfactant is incorporated into the matrix of the material at the time of manufacture. Methods for incorporating reinforcement materials such as fibers and ceramics are known to the art. Methods for incorporating fiber reinforcements, for example, are described in U.S. Pat. No. 6,511,511, hereby incorporated by reference. Kneading and rolling may be performed as described in U.S. Pat. Nos. 6,511,511 and 6,203,573, hereby incorporated by reference. Curing and foaming the polymer in the mold to form a porous implant may then be done.
The material for the anterior plate may be an absorbable polymer optionally combined with a ceramic component and/or a buffering component. The anterior plate may also be made of a nonabsorbable material such as a polymer, a metal, or a ceramic. The anterior plate may be joined to the first region by making the first region and anterior plate as a single piece. Alternately, the anterior plate may be mechanically attached to the first region by screws, rivets, or snaps or other means as known in the art. The anterior plate may also be chemically bonded to the first region. The location of the connection between the plate and the load bearing portion may depend on the type of connection.
In another embodiment, the invention provides an orthopedic implant comprising
The embodiment shown in
The primary function of the outer ring is to withstand high compressive loads. In an embodiment, the load-bearing outer ring is fully dense. In an embodiment, the load-bearing outer ring is formed of a substantially nonporous (fully dense) absorbable material comprising absorbable polymer, an optional ceramic component such as beta-tricalcium phosphate and an optional buffer such as calcium carbonate. This material was previously discussed as a suitable material for the first region of a different embodiment. Other nonabsorbable materials such as polymers, metals, or ceramics may be suitable for the outer ring. In other embodiments, the outer ring is not fully dense and has porosity less than about 40%, preferably less than about 35%. Absorbable polymers can be chosen, as is known to the art, to have a selected degradation period. For intervertebral spacers the degradation period is preferably up to about 4 years, or between about 6 weeks and about 2 years, or between about 12 weeks and about 1 year.
In an embodiment, the porosity of the inner core is between about 50% and about 90%. In different embodiments, the porosity of the full or partial wedge is greater than about 50% or greater than about 70%. Preferably, the inner core is sufficiently porous to allow for bony ingrowth. In an embodiment, the average pore size of the full or partial wedge between about 10 microns and about 2000 microns, between about 50 microns and about 900 microns and about 100 microns to about 600 microns. The more porous portion of the tissue spacer can be capable of soaking up fluids such as blood or bone marrow and therefore can be loaded with bioactive agents, drugs or pharmaceuticals. The inner core may be made of the same materials that are suitable for use in the full or partial wedge previously discussed. For the inner core, the degradation period is preferably up to about 2 years, or between about 3 weeks and about 1 year, or between about 6 weeks and about 9 months.
The embodiment shown in
If an anterior plate is attached to the outer ring, the material for the anterior plate may be an absorbable polymer optionally combined with a ceramic component and/or a buffering component. The anterior plate may also be made of a nonabsorbable material such as a polymer, a metal, or a ceramic. The anterior plate may be joined to the plate by making the ring and anterior plate as a single piece. Alternately, the anterior plate may be mechanically attached to the ring by screws, rivets, or snaps or other means as known in the art. The anterior plate may also be chemically bonded to the ring.
In another embodiment, the invention provides an absorbable orthopedic implant comprising
As illustrated in
The embodiment shown in
The ring preferably has an initial Young's Modulus between about 1.0 GPa and about 30 GPa and a compressive strength between about 10 MPa and about 500 MPa. In an embodiment, the initial Young's Modulus is between about 10 GPa and about 30 GPa.
In an embodiment, the ring is formed of a substantially nonporous (fully dense) absorbable material comprising absorbable polymer, an optional ceramic component such as beta-tricalcium phosphate and an optional buffer such as calcium carbonate. This material was previously discussed as a suitable material for the first region of a different embodiment. Nonabsorbable polymers, metals or ceramics may also be used for the ring. Absorbable polymers can be chosen, as is known to the art, to have a selected degradation period. For intervertebral spacers, the degradation period is preferably up to about 4 years, or between about 6 weeks and about 2 years, or between about 12 weeks and about 1 year.
The material for the anterior plate may be an absorbable polymer optionally combined with a ceramic component and/or a buffering component. The anterior plate may also be made of a nonabsorbable material such as a polymer, a metal, or a ceramic. The anterior plate may be joined to the ring by making the ring and anterior plate as a single piece. Alternately, the anterior plate may be mechanically attached to the ring by screws, rivets, or snaps or other means as known in the art. The anterior plate may also be chemically bonded to the ring.
All references cited herein are hereby incorporated by reference to the extent that there is no inconsistency with the disclosure of this specification.
As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term “comprising”, particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.
Whenever a range is given in the specification, for example, a time range or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges are intended to be included in the disclosure.
Although the description herein contains many specificities, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of the invention. Thus, additional embodiments are within the scope of the invention and within the following claims. The following examples are provided for illustrative purposes, and are not intended to limit the scope of the invention. Any variations in the materials, methods and devices herein which would occur to the skilled artisan from the inventive teachings herein are within the scope and spirit of the present invention.
The implant shown in
The implant shown in
The material is formed into a 75% porous construct, average pore size 200 μm, with an initial compressive strength of 2.4 MPa and compressive stiffness of >100 MPa. The calcium sulfate fraction dissolves in about 4-6 weeks and the polymer fraction dissolves in about 8 months. The material can be fabricated into plugs, blocks, cubes, and granules to fill a wide variety of defects.
The material is formed into a 70% porous construct with an initial compressive strength of 16 MPa and compressive stiffness of >200 MPa. The hydroxyapatite fraction absorbs slowly by osteoclastic activity, and the polymer fraction dissolves in about 18-36 months.
Nonporous absorbable materials may comprise polylactic acid, beta phase tricalcium phosphate and calcium carbonate. Exemplary compositions are summarized in Table 3. The nonporous materials can be made by dry blending the polymer resin with the ceramic components prior to injection molding. The particle size can range from about 10 to about 70 microns. In an embodiment, the particle size is about 20 to about 40 microns.
Several compositions of nonporous absorbable composites were tested to determine their mechanical properties. 3.5 mm diameter rods (length=70 mm) were used for flexural testing and 5.5 mm rods (cut to ˜5.5 mm in length) were used for compression testing. For comparison, at approximately room temperature unreinforced poly(L-lactide) has a compressive strength of 125.5 MPa and a compressive modulus of 5.1 GPa (Verheyen, C C et. al. “Evaluation of hydroxlapatite/poly(L-lactide) composites: Mechanical behavior” J of Biomed Mat Res, Vol 26, 1277-1296 (1992)). Unreinforced poly(D,L) lactide has a bending strength of 101.6 MPa and a bending modulus of 2.25 GPa (Heidemann, W et. al. “Degradation of poly(D,L)lactide implants with or without addition of calciumphosphates in vivo” Biomaterials, Vol 22, 2371-2381 (2001)).
The accelerated degradation study used a buffered simulated body fluid (pH=7.4) at 47° C. At the appropriate evaluation time points, the samples were removed from the 47° C. incubator and were preconditioned at 37° C. for at least one hour prior to testing. Flexural samples were tested in wet conditions at 37° C. in 3-point bend per ASTM D-790. Samples tested in compression were removed from the buffered solution and placed in vials. These samples were sent overnight to a contract testing lab. Prior to testing, compression samples were preconditioned in deionized water for at least two (2) hours. The test temperature was 37° C. Compression testing was conducted on Composite 2 and Composite 3 using a loading rate of 6 mm/min. The testing was stopped after the initial yield stress was visualized.
Tables 4 and 5 summarize the mechanical properties of three composites that were degraded at 47° C.
A real-time degradation study used a buffered simulated body fluid (pH=7.4) at 37° C. to determine change in compressive properties of a 70/30 PLDLA composite. The results are shown in Table 6.
This application claims the benefit of U.S. Provisional Application 60/542,640, filed Feb. 5, 2004, which is hereby incorporated by reference to the extent not inconsistent with the disclosure herein.
| Number | Date | Country | |
|---|---|---|---|
| 60542640 | Feb 2004 | US |
