Process for coating a biomedical implant with a biocompatible polymer and a biomedical implant therefrom

Abstract

The present invention disclosed a process to coat the surface of flexible polymeric implant with biocompatible polymer such that the coating does not crack when the implant is subjected to mechanical forces such as tension, torsion or bending while retaining the inherent properties of the coated polymer.

Claims

1. A process for obtaining an implant with a biocompatible polymer coating, said process consisting of: (a) dipping an implant in a solution comprising a first biocompatible polymer to obtain an implant with a wet dip coating comprising the first biocompatible polymer; and (b) electrospinning a second biocompatible polymer onto the implant with the wet dip coating of step (a) to obtain an implant with a biocompatible polymer coating comprising the first biocompatible polymer and electrospun fibers of the second biocompatible polymer; wherein a portion of the fibers of the second biocompatible polymer are embedded into the dip coating and another portion of the fibers of the second biocompatible polymer are not embedded into the dip coating, and the biocompatible polymer coating remains intact, without the formation of cracks or tears after application of a mechanical force selected from the group consisting of bending, tensile stress, compression and torsion.

2. The process as claimed in claim 1, wherein the first biocompatible polymer and the second biocompatible polymer are selected from the group consisting of silk fibroin, polylactic acid (PLA), poly ε-caprolactone (PCL), and collagen.

3. The process as claimed in claim 2, wherein at least one of the first biocompatible polymer and the second biocompatible polymer is silk fibroin.

4. The process as claimed in claim 1, wherein said implant is made up of a material selected from the group consisting of metals, polymers, ceramics, and composites thereof.

5. The process as claimed in claim 4, wherein said implant is made of a metal.

6. The process as claimed in claim 5, wherein the metal is titanium.

7. The process as claimed in claim 4, wherein said implant is made of a polymer.

8. The process as claimed in claim 7, wherein the polymer is polydimethylsiloxane (PDMS) or polyethylene.

9. The process as claimed in claim 4, wherein said implant is made of a ceramic.

10. The process as claimed in claim 9, wherein the ceramic is hydroxyapatite.

11. The process as claimed in claim 1, wherein said implant is selected from the group consisting of a breast implant, an ocular implant, a cardiovascular stent, and a catheter tube.

12. The process as claimed in claim 1, wherein said implant is in a form selected from the group consisting of a tube, a sheet, a film, and a 3D shape.

13. The process as claimed in claim 1, wherein the thickness of said biocompatible polymer coating is in the range of 100 nm to 5 μm.

14. The process as claimed in claim 1, wherein the fiber diameter of the electrospun fibers is in the range of 100 nm to 1000 nm.

15. The process as claimed in claim 1, wherein said biocompatible polymer coating includes at least one of a functional molecule, a drug, a biomolecule, a growth factor and a protein.

16. A process for coating the surface of a polydimethylsiloxane (PDMS) implant with a silk fibroin layer, said process consisting of: a) dipping a polydimethylsiloxane (PDMS) implant in a solution comprising regenerated silk fibroin to obtain a wet PDMS implant with a regenerated silk fibroin coating; b) placing the wet PDMS implant with the regenerated silk fibroin coating of step (a) on a collector of an electro-spinning system; c) dissolving lyophilized silk fibroin (SF), and optionally an antibiotic, in Hexafluroisopropanol (HFIP) to obtain a SF-HFIP solution; d) using the SF-HFIP solution of step (c) for electrospinning silk fibroin fibers onto the wet PDMS implant with the regenerated silk fibroin coating of step (b) and; e) randomizing deposition of the electrospun silk fibroin fibers by aid of syringe translation and/or collector translation and/or rotation to obtain the PDMS implant with a silk fibroin layer comprising the regenerated silk fibroin coating and the silk fibroin fibers; wherein a portion of the silk fibroin fibers are embedded into the regenerated silk fibroin coating and another portion of the silk fibroin fibers are not embedded into the silk fibroin coating, and the silk fibroin layer remains intact, without the formation of cracks or tears after application of a mechanical force selected from the group consisting of bending, tensile stress, compression and torsion.

17. The process of claim 16, wherein the lyophilized SF and the antibiotic are dissolved in HFIP to obtain the SF-HFIP solution step (c).

18. The process as claimed in claim 16, wherein said coating includes at least one of a functional molecule, a drug, a biomolecule, a growth factor and a protein.

19. The process of claim 1, wherein the first biocompatible polymer and the second biocompatible polymer are compositionally the same.

20. The process as claimed in claim 1, wherein the first biocompatible polymer is silk fibroin.

Description

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

(1) FIG. 1: Schematic representation of the procedure for making self reinforced SF coatings. a—PDMS disc; b—Polymer solution; c—Polymer powder; d—solution of polymer; f—syringe pump; g—syringe; h—needle; i—voltage unit; j—wet PDMS disc stuck onto the collector; k—collector; l—PDMS disc with dip and electrospun fibers obtained, 1—Process of dip coating the PDMS disc in polymer solution; 2—Dip coated PDMS disc transferred to the collector; 4—Polymer powder obtained by a process like lyophilization; 5—Dissolution of polymer powder at particular concentration in suitable solvent; 6—Process of electrospinning

(2) FIG. 2: Schematic representation of bending stability test.

(3) FIG. 3: Scanning electron micrograph Dip coated sample before bending.

(4) FIG. 4: Scanning electron micrograph Dip coated sample after bending.

(5) FIG. 5: Scanning electron micrograph Dip coated+electrospun (self-reinforced) sample before bending.

(6) FIG. 6: Scanning electron micrograph Dip coated+electrospun (self-reinforced) sample after bending.

(7) FIG. 7: Release of Cephalexin into DI water at 25° C. over a time period of 15 h.

(8) FIG. 8: Optical microscopy image after bending stability test on sample prepared as per protocol described in Example 7.

DETAILED DESCRIPTION OF THE INVENTION

(9) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(10) In the view of above, the present invention provides a novel process to coat the surface of flexible polymeric implant with biocompatible polymer such that the coating does not crack when the implant is subjected to mechanical forces such as tension, torsion or bending while retaining the inherent properties of the coated polymer.

(11) Accordingly the present invention provides a process for obtaining an implant with a biocompatible polymer coating, said process comprising: (a) dipping the implant in a solution of biocompatible polymer to obtain an implant with a dip coating; and (b) immediately electrospinning the same polymer onto the implant with dip coating of step (a) to obtain an implant with a biocompatible polymer coating; wherein, fibres of the biocompatible polymer are partially embedded into the dip coating, and said coating remains intact/independent of cracks/tears even after application of mechanical forces selected from the group consisting of bending, tensile stress, compression, and torsion.

(12) In one embodiment of the present invention, the electrospinning is directly done onto a dip coated wet substrate. As a result of which some fibers are embedded into the dip coated layer, while others on the surface are not embedded. The combination of this partial embedment and lower thickness of coating helps in preventing cracking. In another embodiment, the present inventors also prepared a coated implant where the fibers are completely embedded in a coating of silk fibroin as suggested from prior art, it is observed that the coating does not meet the cracking resistance requirements and results are as shown in example 1.

(13) In another embodiment of the present invention, the biocompatible polymer is selected from the group consisting of silk fibroin, polylactic acid (PLA), poly ε-caprolactone (PCL), and collagen.

(14) In yet another embodiment of the present invention, the biocompatible polymer is silk fibroin.

(15) In still another embodiment of the present invention, the implant is made up of a material selected from the group consisting of metal, polymer, ceramic, and composites thereof.

(16) In another embodiment of the present invention the metal is titanium.

(17) In yet another embodiment of the present invention the polymer is polydimethylsiloxane (PDMS) or polyethylene.

(18) In still another embodiment of the present invention the ceramic is hydroxyapatite.

(19) In another embodiment of the present invention, the implant is selected from the group consisting of breast implant, ocular implant, cardiovascular stent, and catheter tube.

(20) In yet another embodiment of the present invention, the implant is in a form selected from the group consisting of tube, sheet, film, and 3D shape.

(21) In still another embodiment of the present invention the thickness of said biocompatible polymer coating is in the range of 100 nm to 5 μm. In yet another embodiment of the present invention the fiber diameter of said biocompatible polymer coating after electrospinning in the range of 100 nm to 1000 nm. The implant undergoes deformation when subjected to tensile strength, compression, torsion or bending forces during handling and/or use.

(22) In another embodiment of the present invention the biocompatible polymer coating is modified with functional molecules, drugs, biomolecules, growth factors, proteins to enhance the effectiveness of the biocompatible polymer coating in biomedical applications.

(23) Another embodiment of the present invention provides the process for coating the surface of polydimethylsiloxane (PDMS) implant with silk fibroin layer, wherein said process comprises the steps of: a) dipping polydimethylsiloxane (PDMS) implant in a solution of regenerated silk fibroin to obtain wet PDMS implant with regenerated silk fibroin coating; b) immediately placing the wet PDMS implant with regenerated silk fibroin coating of step (a) on collector of electro-spinning system; c) dissolving lyophilized silk fibroin (SF) in Hexafluroisopropanol (HFIP) to obtain a SF-HFIP solution; d) using the SF-HFIP solution of step (c) for electrospinning onto the wet PDMS implant with regenerated silk fibroin coating of step (b); e) randomizing deposition of electrospun fibers by aid of syringe translation and/or collector translation and/or rotation to obtain polydimethylsiloxane (PDMS) implant with silk fibroin layer.

(24) The SEM analysis of the dip coating showed a thickness of ˜400 nm. The coatings are found to be uniform and continuous. However, it is observed that the coating on these discs cracked after bending. The bending protocol followed is as per that given in the literature.

(25) Still another embodiment of the present invention provides an implant with a biocompatible polymer coating prepared by the aforementioned process.

(26) Silk fibroin is electrospun onto the dip-coated samples in wet condition. This process ensured embedding of silk fibroin nano-fibers into the RSF matrix, which led to achieve a classical self-reinforced fiber composite system.

(27) From FIG. 3 it is observed that regenerated silk fibroin forms a continuous coat onto PDMS discs after dip coating and drying. The coat shows no macro or micro cracks and/or any deformities when observed under the scanning electron microscope.

(28) From FIG. 4 it is observed that when the silk fibroin dip coated PDMS discs were subjected to bending, the coating near the central region showed cracking in the direction perpendicular to bending. The cracks are indicated by arrows in the Figure.

(29) From FIG. 5 it is observed that on the PDMS discs that were subjected to sequential dip coating and electrospinning, there was a continuous silk fibroin coat throughout. The electrospun fibers were partially embedded into the coat, providing a classical self-reinforced composite.

(30) From FIG. 6 it is observed that through scanning electron microscopy that PDMS samples with self-reinforced silk fibroin coating showed a continuous coat even after being subjected to bending. Also, it was observed that the fibers showed thinning at certain places along the length, which indicates that the fibers took up the load. The arrows indicate regions of deformation observed in the fibers supporting the fact that the fibers bear the load during bending.

(31) In UV spectroscopy, the signature peak of 262 nm for cephalexin is monitored and as shown in FIG. 7, the coating enabled continuous release of this molecule over a period of 15 h.

(32) The FIG. 8 shows that when the fibers are completely embedded in a coating of silk fibroin as suggested from prior art, the coating does not meet the cracking resistance requirements and it shows cracks.

(33) The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

EXAMPLES

Example 1: Preparation of Regenerated Silk Fibroin (RSF) Solution

(34) Bombyx mori silk cocoons were procured from Central Sericultural Research and Training Institute, Srirampura, Manandavadi Road, Mysore-570008, India. They were cut and degummed (sericin removal) by boiling in 0.5% w/v solution of sodium bi-carbonate (NaHCO.sub.3) (Thomas Baker). The silk fibroin obtained was dried for 48 h under vacuum at 60° C., −720 mmHg. The dried silk fibroin was cut and dissolved in 9.3 M aq. solution of Lithium Bromide (Sigma) at 60° C. for 4 h. This solution was dialysed against deionised water for 48 h. The solution was centrifuged for 30 min at 10000 rpm, to remove any impurities or insoluble materials. The supernatant (RSF) was transfer into clean containers and was stored under 4° C. until further required (Maximum storage period is 8 days). The concentration of RSF solution was between 3% to 8% w/v. This solution was split into two parts. The concentration of one part was adjusted to 0.4% w/v by addition of deionised water. This was store under 4° C. and later used as the dipping solution. The second part was quenched in liquid nitrogen and was lyophilised at −55° C. for 8 h. The aerogel thus obtained was stored under −18° C. until further required.

Example 2: Preparation of Polydimethyl Siloxane (PDMS) Discs for Coating

(35) PDMS was obtained as a 2 part kit (Sylgard 184, Dow Corning). The resin and cross-linker were mixed in 10:1 ratio, by weight. The mixture was poured into polystyrene petriplates and kept in a vacuum oven, 40° C., −720 mmHg, for 24 h. The cured PDMS discs were peeled off and cut into 30 mm×10 mm rectangles using a scalpel. The cut specimens were cleaned in isopropyl alcohol (Merck) under continuous sonication for 20 min. The specimens were then kept in a vacuum oven at 60° C., −720 mmHg for 24 h. The dried discs were subjected to oxygen plasma at RF power 50 W, for 1 min. The plasma treated discs were stored under deionised water until further required.

Example 3: Dip Coating PDMS Using RSF

(36) Plasma treated PDMS discs (Example 2) were taken out from the deionised water and then dipped into 0.4% w/v RSF solution (Example 1) for 10 min. The discs were then taken out and dried at 25° C. under ambient conditions.

Example 4: Sequential Dip Coating+Electrospinning onto PDMS

(37) Lyophilised RSF (Example 1) was dissolved into hexafluroisopropanol (HFIP) (Gujrat Flurachemical Pvt. Ltd.), under continuous stirring, to obtain a 3% w/v solution. This solution was poured into a 5 ml disposable syringe (Dispovan), whose needle was blunted.

(38) Plasma treated PDMS (Example 2) discs were taken out from the deionised water and then dipped into 0.4% w/v RSF solution for 10 min. The discs were taken out and placed on an aluminium foil in the wet condition. This foil was attached to the plate collector of the electrospinning setup, ensuring good contact between the foil and the collector. Ground terminal of the electrospinning setup was attached to the collector.

(39) The syringe with SF-HFIP solution was placed on the syringe pump of the electrospinning setup and the live terminal was attached to its needle. Electrospinning was done onto the discs in the wet condition with the following parameters: Distance between the collector plate and the needle tip: 10.5 cm Needle gauge: 24 Pump speed: 1.5 ml/h Voltage: 25 kV Syringe translation: 0.98 m/s Plate translation: Syringe translation linked

(40) After 3.5 h of electrospinning, the discs were carefully removed and place in a methanol (Merck) bath for 10 min. After this methanol treatment, the discs were kept in a vacuum oven, 60° C., −720 mmHg, for 24 h, to remove the methanol.

Example 5: Bending Stability of the Coating

(41) Samples from Example 3 and Example 4 were divided into two sets each. One set was kept as it was while the other set was subjected to bending deformation. This was done by holding the two ends of the specimen, along the 30 mm axis, between the thumb and the index finger; and bending the samples along the axis till the two ends met. This was repeated three times on each sample of the set. The protocol followed is as described by Borkner et al. A 10 mm×10 mm square was observed under a scanning electron micrograph to study the coating surface. As seen in FIG. 6, the fibers exhibit areas of stress whitening, indicating that the fibers take up the load applied during bending. However, the coating remains intact and the substrate surface is not exposed. The arrows indicate regions of deformation observed in the fibers supporting the fact that the fibers bear the load during bending.

Example 6: Sequential Dip Coating+Electrospinning onto PDMS Using Drug Molecule

(42) Lyophilized RSF (Example 1) (30 mg) and Cephalexin (30 mg) (a standard antibiotic) was dissolved into 1 ml of hexafluroisopropanol (HFIP) (Gujarat Fluorochemicals Pvt. Ltd.) with mild stirring for 10 minutes. 2 ml of this solution was then used for electrospinning onto RSF dip coated PDMS discs (15 mm diameter) using the same electrospinning conditions as described in Example 4. After 3 h of electrospinning, the PDMS discs were carefully removed and annealed in water vapor at 95° C. for 2 h. One annealed PDMS disc was then dipped in 1 ml DI water at 25° C. for 15 h and the release of cephalexin in DI water was measured. In UV spectroscopy, the signature peak of 262 nm for cephalexin was monitored and as shown in FIG. 7, the coating enabled continuous release of this molecule over a period of 15 h.

Example 7: Sequential Dip Coating+Electrospinning+Dip onto PDMS as Suggested from WO2017093181

(43) The samples obtained in Example 4 were further dipped in a 0.4 w/v % solution for 10 minutes and air-dried at room temperature. The coating thickness obtained using this method was found to be in the range of 5-10 microns. This sample was then subjected to the bending stability test as described in Example 5. As can be seen in FIG. 8, the coating completely cracks at several locations and is not stable under bending loads. A thin coating (100-1000 nm) with only partially embedded polymeric fibers in the dip coat will produce a stable coating resistant to mechanical forces such as bending.

ADVANTAGES OF THE INVENTION

(44) The present invention provides a novel, cost effective, efficient process to coat the surface of implant with biocompatible polymers such that the coating does not crack when subjected to mechanical forces such as bending, compression, tensile or torsion while retaining the inherent properties of the biocompatible polymer.