Patent Application
20220152271
The present invention refers to compositions and to 3D methods to produce a Poly(e-caprolactone)—PLC—and Graphene Oxide (GO) scaffold with bactericidal properties against bacteria that cause infections in patients implanted with medical devices. As such, the present invention relates to the technical field of polymers, particularly to PLC/GO composites, to medical biotechnology, and specifically to medical devices with concurrent bactericidal properties.
One of the main challenges associated to implantable devices is to find efficient strategies to face bacterial adhesion and consequent infection [1]. Device colonization by bacteria can lead to its malfunction, as it may result in biofilm formation at the implantation site [2]. This represents a serious health problem, worsened by growing antibiotic resistance, and causing the loss of the implanted device or even sepsis [3]. This has been subject of extensive research, but the desirable successful prevention or effective solution are yet to be achieved. Common organisms associated to polymeric meshes infection are Staphylococcus spp. [4,5], with Staphylococcus epidermidis on the leading positions [6], but also Gram-negative Enterobacteriacea, such as the rod-shaped Escherichia coli. These are both biofilm-forming bacteria which produce extracellular polysaccharides when proliferating on a surface [7], enhancing their survival efficiency. S. epidermidis has a naturally high resistance to antimicrobials, which generates great concerns. E. coli also resists to antibiotics such as penicillin, since the outer membrane surrounding the cell wall provides an additional barrier. Bacterial adhesion to device's surface is not a one-time phenomenon, but rather an evolving process. Initially, there is a rapid attachment to the surface, mediated either by nonspecific factors (such as surface tension, hydrophobicity, and electrostatic forces) or by specific adhesins [8], followed by an accumulation phase, during which bacteria adhere to each other and form the biofilm [9]. Alternatives to antibiotics are being thoroughly explored, and carbon-derived materials are receiving growing attention [10]. Since graphene's (G) first isolation in 2004 [11], its derivatives have been developed and investigated, commonly conjugated with polymers to produce composites or used to modify their surface [12-14]. In 2010, the antibacterial properties of graphene-based materials (GBMs) were explored for the first time [15], leading to a growing number of reports that describe some GBMs as antimicrobial nanomaterials [16-21]. The interaction between GBMs and biological systems has also been studied [22-25], giving some insights regarding their effect on different types of organisms. Nevertheless, these interactions need to be explored in more detail regarding GBMs immobilized in polymeric matrices, since their characteristics may vary. Antimicrobial properties, for instance, are known to be different when comparing GBMs in suspension with GBMs immobilized on a surface [21, 26-28]. Moreover, direct physical contact of bacteria with GBMs at a surface (either with sharp edges or basal planes) is a requirement for GBMs-containing biomaterials to have an antibacterial action, with no effect being observed when no direct contact is established [28,29]. Smaller and more oxidized forms of GBMs have been associated with higher biocompatibility towards mammalian cells [30]. Furthermore, stronger bactericidal properties have been described in oxidized forms of graphite (GO) and graphene nanoplatelets (GNPs) [18, 21, 31]. It is described that the orientation and exposure of GO sheets on the fibers' surface are important parameters, being essential factors for antibacterial properties [28]. To create 3D-structured scaffolds in tissue engineering, combination of additive manufacturing (AM) with wet-spinning has been described [32-34]. Poly(e-caprolactone) (PCL) is currently among the most popular synthetic polymers used [35]. PCL fibers assembled into random or organized 3D structures have been broadly studied in the scope of tissue engineering approaches [36-39]. PCL is highly appealing due to its physical-chemical and mechanical characteristics [40,41], and non-toxic degradation products. It received Food and Drug Administration (FDA) approval and European Conformity (CE) marking for a number of drug delivery and medical device applications [40]. Besides, this polymer presents additional advantages, namely availability, relatively low cost, suitability for modification [42], and a relatively long biodegradation time, which makes it widely used also in long-term implants [43]. Improvements in PCL performance have been attempted through its modification, namely by adding new components like GO [39]. Although few studies are available [44], GO incorporation in PCL matrices has led to improvements in terms of hydrophilicity, mechanical and thermal properties, and biocompatibility [45-47].
However, the ability of these methods to produce PCL/GO matrices with antibacterial properties cannot be extrapolated and the methods chosen for fiber-based composite antimicrobial scaffolds production must be such that to enhance GO exposure.
This is because GO antibacterial effects have been associated with either induced oxidative stress or bacteria physical disruption, thus requiring GO exposure in the fiber surface, to contact with bacteria.
On one hand, fibers need to be wide enough to incorporate GO sheets presenting diameters ranging from 2 to 10 μm. This excludes nanometric fibers production techniques, such as electrospinning [46, 48-50].
On the other hand, GO exposure in composites produced by melt-dependent techniques is known to be difficult to obtain [28], since GO sheets are usually covered or encapsulated by the polymer in the obtained fibers [51].
Thus, the methods known in the art for incorporation of GO in PCL matrices do not solve the problem of controlling the orientation and exposure of GO sheets on the fibers surface so as to achieve antibacterial properties.
These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.
The present invention discloses the parameters of a composition of Poly(e-caprolactone)—PLC—and Graphene Oxide (GO) for use in killing bacteria that cause infections in patients implanted with medical devices, for example Staphylococcus epidermidis and Escherichia coli. This composition can be employed in a method for 3D printing of PLC/GO fibers and fibrous scaffolds by additive manufacturing and wet spinning. In the above-mentioned compositions and method the PLC/GO concentrations and the fiber diameter are such that GO sheets are incorporated but at the same time exposed at the polymer surface, coffering bactericidal properties to the material, while keeping biocompatibility. Thus, one embodiment of the present inventions refers to a composition of Poly(e-caprolactone) and Graphene Oxide for use in killing bacteria that cause infections in patients implanted with medical devices comprising: a solvent consisting of Tetrahydrofuran (THF); Graphene Oxide (GO) at final concentration between 5% and 7.5% (w/w), most preferably 5% (w/w); Poly(e-caprolactone)—PCL—at final concentration between 7.5% and 15% (w/v), most preferably 7.5% (w/v); A coagulation non-solvent consisting of ethanol, as described in claim 1.
In another embodiment, the said bacteria that causes infections in patients implanted with medical devices comprises for example Staphylococcus epidermidis and Escherichia coli, as described in claim 2.
In another embodiment, the said Poly(e-caprolactone) and Graphene Oxide polymer is constructed into a scaffold, as described in claim 3.
In another embodiment, the said Poly(e-caprolactone) and Graphene Oxide polymer is constructed into a fibrous scaffold, as described in claim 4.
Another embodiment of the present invention refers to a fibrous scaffold of Poly(e-caprolactone) and Graphene Oxide for killing bacteria that cause infections in patients implanted with medical devices comprising: a solvent consisting of Tetrahydrofuran (THF); Graphene Oxide (GO) at final concentration between 5% and 7.5% (w/w), most preferably 5% (w/w); Poly(e-caprolactone)—PCL—at final concentration between 7.5% and 15% (w/v), most preferably 7.5%; a coagulation non-solvent consisting of ethanol, as described in claim 5.
In another embodiment, the fibers have a diameter from 50 to 100 μm, most preferably of 100 μm, as described in claim 6.
In another embodiment, the said bacteria that causes infections in patients implanted with medical devices comprises for example Staphylococcus epidermidis and Escherichia coli, as described in claim 7.
In another embodiment, the said composition or scaffold is comprised in a medical device. implanted in an animal or the human body, as described in claim 8.
In another embodiment, the said medical device is selected from the list consisting of surgical sutures, 3D scaffolds for tissue engineered implants as well as other non-limiting examples of implantable medical devices such as a stent, a vascular implant, a dental implant, and a bone implant, as described in claim 9. Another embodiment of the present invention refers to a method for constructing a fibrous scaffold of Poly(e-caprolactone) and Graphene Oxide by additive manufacturing and wet-spinning of comprising the steps of:
as described in claim 10.
In another embodiment of the present invention's method, the said extrusion of THF/PCL/GO mixture is performed layer-by-layer in a 3D plotting machine or a 3D printer, as described in claim 11.
The present invention describes the parameters of a composition of Poly(e-caprolactone)—PLC—and Graphene Oxide (GO) for use in killing bacteria that cause infections in patients implanted with medical devices, for example Staphylococcus epidermidis and Escherichia coli. This composition can be employed in a method for 3D printing of PLC/GO fibers and fibrous scaffolds by additive manufacturing and wet spinning. In the above-mentioned compositions and method the PLC/GO concentrations and the fiber diameter are such that GO sheets are incorporated but at the same time exposed at the polymer surface, coffering bactericidal properties to the material, while keeping biocompatibility.
The GO is prepared according to the Modified Hummer's Method (MHM) [52] adjusting reagents volume/mass for larger scale production (2000 mL flasks). Briefly, 320 mL of H2SO4 (VWR, Germany) are mixed with 80 mL of H3PO4 (Chem-Lab, Belgium) in a 4:1 ratio, and stirred at room temperature (RT) for an improved oxidation. 8 g of graphite (carbon graphite micropowder, American Elements, purity above 99%, diameter between 7 and 11 μm) are added to this solution and then cooled down to 0° C. using an ice bath before gradual addition of 48 g of KMnO4 (JMGS, Portugal). The solution is heated up to 35° C. and stirred for 2 hours. After lowering the temperature to 0° C., 1200 mL of distilled water are slowly added. This is followed by careful addition of H2O2 35% (WWR, Germany) until oxygen release stops. After overnight resting, the solution is decanted to separate the solid deposit from the acidic supernatant. The remaining product is washed with dH2O and this aqueous solution is centrifuged at 4000 rpm for 20 minutes at RT. This step is repeated until the washing water pH is equal to dH2O pH. By the end of this process, sonication is performed for 6 h to exfoliate the oxidized material into graphene oxide.
To prepare PCL (obtained from Sigma-Aldrich, average Mn 80000 g mol) incorporating GO, an appropriate solvent needs to be used. Thus, the first parameter for the present invention's composition was the selection of an effective PCL solvent that efficiently disperses GO. The dispersion homogeneity and stability of GO was evaluated in different organic solvents, commonly considered potential solvents for PCL, namely: chloroform (VWR, Germany), acetone (JMGS, Portugal) and tetrahydrofuran (THF, VWR, Germany). GO aqueous dispersion is centrifuged for 1 h at RT and 15000 rpm and the supernatant water is decanted. GO was resuspended in each of the solvents and PCL dissolution tests were carried out by using a polymer concentration of 15% w/v with permanent magnetic stirring (300 rpm) at RT. GO dispersion in chloroform was not achieved, revealing large GO aggregates and an absence of GO affinity to this solvent. On the contrary, acetone and THF exhibited a similar behavior, producing dispersions with perfectly dispersed GO, stable even after 10 days. All solvents tested were able to dissolve PCL, although this dissolution was only partial when acetone was used.
THF was therefore demonstrated to be able to perfectly disperse GO while efficiently dissolving PCL, and thus THF is the optimal solvent (Table 1).
A THF/polymer mixture was then used to evaluate the optimal solvent/non-solvent combination. PCL non-solvents, namely isopropanol (VWR, Germany) and ethanol (VWR, Germany), were tested, to assess the best coagulation bath to obtain the polymer filaments.
Ethanol showed compatibility with good design definition and relatively fast polymer fiber precipitation during solvent/nonsolvent exchange. Moreover, ethanol excess is easy to eliminate from the scaffolds through evaporation. Isopropanol was also tested as a coagulation bath and although a similar performance was observed when compared to ethanol, a slightly worse fiber definition was achieved. As such, ethanol was selected as the optimal composition component for the coagulation bath (Table 2).
Different PCL and GO concentrations were tested, ranging from 7.5% to 15% w/v (weight of PCL per volume of solvent) and from 0% to 10% w/w (weight of GO per weight of PCL), respectively. Results of the assessment of the optimal PLC/GO combination is shown in Table 3.
For the 7.5% (w/v) PCL concentration, GO concentrations between 0% and 10% (w/w) were tested, although the highest GO concentration hindered the solution extrusion process, causing frequent needle clogging.
Regarding the 15% (w/v) PCL solution, GO concentration could not be increased above 5% (w/w), since higher concentrations affected the printing process due to constant clogging observed. Moreover, major effects in fiber morphology were observed.
A PCL concentration of 7.5% (w/v) and a range of GO concentrations from 5% to 7.5% (w/w) provided therefore the optimal conditions, allowing the production of porous fibers with different amounts of GO loading.
Thus, in the preferred embodiment of the present invention's composition GO is dispersed in a solvent consisting of THF at final concentrations between 5% (w/w) and 7.5% (w/w). PCL is then dissolved overnight at RT in these dispersions to a final polymer concentration of 7.5% (w/v). Polymer filaments are obtained in a non-solvent coagulation bath consisting of ethanol.
Given their suitable viscosity, the above-mentioned compositions allow the development of a method for fiber-based production of composite scaffolds employing a combination of additive manufacturing and wet-spinning in which a dispensing tip is fed with a polymeric composition solution and submerged in a non-solvent of the polymer that causes its precipitation and filament formation.
In one embodiment, compositions are loaded into a glass syringe with a needle with internal diameter of 184 μm (28 G) that is used for scaffold plotting and the THF/GO/PLC solution is extruded into an ethanol coagulation bath using a syringe pump.
When printed, PCL and PCL/GO scaffolds are rinsed 3-5 times with ethanol, dried in a fume hood and cut using a 4 mm diameter stainless steel biopsy puncher (Integra). Scaffolds are sterilized with ethylene oxide following the established protocol for medical material sterilization (Millex).
Thus, another embodiment of the present invention refers to a method for constructing PLC/GO fibers by additive manufacturing and wet spinning of comprising the steps of:
In another embodiment of the present invention's method, the layer-by-layer fabrication of the scaffolds can also be performed using a 3D plotting machine (such as a xyz plotter), adapting the setup previously described by Neves et al. [53]. Printing parameters such as flow rate (F) of the syringe pump and deposition speed (Vdep) of the xyz plotter (defined as relative percentage to the plotter firmware parameters), can be adjusted, ranging from 0.5 mL/h to 1.0 mL/h and from 50% to 120%, respectively
In one embodiment the printing parameters are defined as F=0.5 mL/h and Vdep=80%, which showed to be the optimal option, given the ideal compromise between good fiber definition and time consumption.
The 3D design can be varied and optimized in terms of xyz inter-fiber distances and staggering. The best fit for well-defined, precisely spaced structures is achieved by xy distances ranging from 200 μm to 400 μm, z-steps from 20 μm to 80 μm, and staggering between layers from 50 μm to 200 μm. A final 3D design of the scaffolds is displayed in
Scanning electron microscopy (SEM) observation of the scaffolds corroborates the precise plotting of filaments, showing the staggering between layers, visible in both top view and cross-section images (
Fibers' average diameter can be measured along different fibers, 0% GO scaffolds presenting average diameters of 107±11 μm, 5% GO scaffolds of 102±9 μm and 7.5% GO scaffolds of 103±13 μm. From the SEM analysis, it is also possible to confirm GO incorporation in the fibers and its exposure. Top views of the fibers surface show GO exposure for both 5% and 7.5% GO concentrations (
Focusing on the cross-sections, it is possible to observe that the inner porosity of the fibers changes with the presence of GO within the PCL matrix. The size and the irregularity of the combs increase in a direct proportion to the amount of incorporated GO. SEM analysis allows to demonstrate that GO/PCL scaffolds with a 3D network of macropores is successfully fabricated and GO exposure at the fibers surface is achieved in 5% and 7.5% GO scaffolds.
Thus, employing the above-mentioned compositions and method of additive manufacturing with wet-spinning it is possible to obtain PLC/GO fiber production with a 50-150 μm diameter range (
Regarding the antimicrobial potential of the developed structures, namely antibacterial activity towards Staphylococcus epidermidis, the effect of GO presence is noticed after a relatively short period (2 h), apparently being bactericidal (
PCL/GO scaffolds antibacterial effect assessed after 2 h and 24 h incubation with S. epidermidis shows that in the 2 h incubation assay, higher amounts of dead bacteria are found in 5% GO (1.10±0.93 bacteria/104 μm2) and 7.5% GO (1.94±1.10 bacteria/104 μm2) comparing to 0% GO scaffolds (0.07±0.10 bacteria/104 μm2) (p=0.0014 and p<0.0001, respectively) (
The incorporation of GO promotes bacterial death, with the percentages of dead bacteria increasing from only 2.9% in 0% GO to 41.8% in 5% GO and 53.8% in 7.5% GO (
In a 24 h incubation assay presented in the bactericidal effect of GO-containing scaffolds is confirmed and the death rates are higher comparing to the ones obtained after 2 h incubation, being 13.7% in 0% GO, and reaching 71.9% in 5% GO and 77.8% in 7.5% GO scaffolds (
Moreover, the number of live bacteria that adhered to the scaffolds was significantly lower in GO-containing scaffolds (p=0.0001), with only around 1.7 bacteria/104 μm2), comparing to around 5.3 bacteria/104 μm2 in PCL with 0% GO scaffolds. These interesting results also demonstrate that while the number of live bacteria increases in PCL with 0% GO scaffolds from 2 h to 24 h, this does not occur in GO-containing scaffolds. In 5% and 7.5% GO, the number of live bacteria is maintained over the 24 h, revealing the bactericidal effect of these scaffolds over time.
GO appeared to act as a killing agent, rather than contributing for the formation of an antifouling surface. Data revealed that a GO concentration of 5% seems to be enough to produce the desired bactericidal effects in all the performed assays, since no statistically significant differences were found between this concentration and the highest one (7.5% GO).
Thus, an antibacterial effect is unraveled, possibly towards different bacteria, including but not limited to S. epidermidis, one of the most commonly found microorganism in implant-associated infections.
Regarding the in vitro biocompatibility, HFF-1 human fibroblast cell line spread morphology after 7 days of culture in all conditions indicates that scaffolds are noncytotoxic (
Since bacterial infection represents a constant threat when implantable medical devices are used, our data suggests promising performance of PCL/GO scaffolds in several biomedical applications, namely as surgical sutures or 3D scaffolds for tissue engineering, in which PCL alone is currently used.
Thus, another embodiment of the present invention refers to the medical devices comprising the above-mentioned compositions, fibers and fibrous scaffolds that are implanted in an animal or the human body such as surgical sutures, 3D scaffolds for tissue engineered implants as well as other non-limiting examples of implantable medical devices such as a stent, a vascular implant, a dental implant, and a bone implant.
In conclusion, wet spinning combined with additive manufacturing allowed the production of well-defined PCL/GO fibrous scaffolds with average fiber diameters of 100 μm. A concentration of 5% GO was enough to expose GO sheets at the surface of the composite fibers. Antimicrobial properties of composite PCL/GO 3D-organized fibrous scaffolds were assessed for the first time, revealing GO time-dependent bactericidal effect and an increase in death rate from about 14% in neat PCL scaffolds to nearly 80% in composite scaffolds with 7.5% GO, after 24 h of contact. In vitro biocompatibility evaluation showed that PCL and composite PCL/GO scaffolds allowed human fibroblasts adhesion and spreading along the fibers during 7 days of culture. As such, GO-containing fibrous scaffolds developed in this invention promoted bacterial death, while allowing human cells adhesion. These features demonstrate the parameters of GO incorporation in polymer fibrous scaffolds for antimicrobial properties on implanted device-associated infections.
The above described embodiments are combinable.
Top view (where dx and dy are displayed) and cross-section view (where dz is shown and the staggering between layers is visible)
The lower lane represents zoomed regions of the upper lane images. Scale bar: top—5 mm; bottom (zoom)—500 μm.
PCL and composite PCL/GO fibrous scaffolds with approximately 1.2 cm×1.2 cm were printed, according to the 3D model previously disclosed in
Scale bar (from the top to the bottom row): top view—400 μm, 50 μm, 2 μm; bottom—200 μm, 50 μm.
S. epidermidis adhesion to PCL scaffolds with 0%, 5% and 7.5% GO, after 2 h and 24 h incubation in 10% v/v plasma supplemented TSB. Bacteria were stained with the LIVE/DEAD Backlight kit (ThermoFisher) and counted by confocal microscopy. Stacked bars graph with live and dead bacteria counting per 104 μm2 of fiber is displayed. Statistically significant differences on the number of live and dead (*) bacteria compared to 0% GO scaffolds are indicated on top of the stacked bars (p=0.05; non-parametric Kruskal-Wallis test).
Representative confocal microscopy images of HFF-1 human fibroblasts interaction with PCL scaffolds with 0%, 5% and 7.5% GO, after 1 day and 7 days of culture. Cells are identified by staining the nuclei with DAPI (DNA) and cytoskeleton (F-actin staining). The scaffold fibres can be identified by the faint-clear dashed lines. Images represent single plane projections of a 150 μm height z-stack. Scale bar: 100 μm.
The following references should be considered herewith incorporated in their entirety.
The following claims further set out embodiments of the invention.
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Biomaterials 2005; 26:5500-8.
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Inhibition of Bacterial Biofilm Formation due to Specific Surface-Interface Interactions. ACS Omega 2017; 2:3070-82. doi:10.1021/acsomega.7b00371.
| Number | Date | Country | Kind |
|---|---|---|---|
| 115361 | Mar 2019 | PT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/PT2020/050010 | 3/12/2020 | WO | 00 |
