NERVE GUIDANCE CONDUITS, METHODS OF PRODUCTION AND USES THEREOF

Abstract

The present disclosure relates to a silk fibroin tubular conduit, a new methodology for obtaining said silk fibroin tubular conduit, and respective uses. The tubular conduit of the present disclosure can be used in treatment of diseases that involve the repair and/or regeneration of tissues, nerves or bone. In particular, the tubular conduit can be used for peripheral nerve regeneration.

Claims

1. A tubular conduit comprising an enzymatically cross-linked silk fibroin hydrogel, wherein said tubular conduit is predominantly -sheet conformation and comprises a porosity up to 70% and a pore size up to 30 m.

2. The tubular conduit of claim 1, wherein the pore size up to 10 m.

3. The tubular conduit of claim 2, wherein the pore size is between 1-7 m.

4. The tubular conduit of claim 1, wherein the tubular conduit has a wall with a thickness of 0.2 mm-2 mm.

5. The tubular conduit of claim 1, further comprising a conductive agent selected from the group consisting of: gold, silver, polypirrole, and mixtures thereof.

6. The tubular conduit of claim 1, wherein the cross-linked silk fibroin hydrogel is enzymatically cross-linked with horseradish peroxidase and hydrogen peroxide.

7. The tubular conduit of claim 1, wherein said hydrogel comprises between 5-25% (wt %) of silk fibroin.

8. The tubular conduit of claim 1, wherein said hydrogel comprises between 12-18% (wt %) of silk fibroin.

9. The tubular conduit of claim 1, wherein the porosity is 1-50%.

10. (canceled)

11. The tubular conduit of claim 1, wherein the tubular conduit has an internal diameter of 1 mm-10 mm.

12. The tubular conduit of claim 1, wherein the tubular conduit has a length of 5 mm-100 mm.

13. The tubular conduit of claim 1, wherein the tubular conduit further comprises hyaluronic acid, alginate, casein, polyethylene oxide, polyethylene glycol, collagen, fibronectin, keratin, polyaspartic acid, polylysine, chitosan, pectin, polylactic acid, polycaprolactone, polyglycolic acid, polyhydroxyalkanoate, polyanhydride, and mixtures thereof.

14. The tubular conduit of claim 1, wherein the tubular conduit further comprises a biological active agent, a therapeutic agent, an additive, a pharmaceutically acceptable excipient, a pharmaceutically acceptable carrier, and mixtures thereof.

15. The tubular conduit of claim 14, wherein the biologically active agent is selected from the following list: a peptide, a protein, a nucleic acid, an antibody, an aptamer, an anticoagulant agent, a growth factor, a cytokine, an antibiotic, an immunosuppressor, a steroid, non-steroidal anti-inflammatory drug, and mixtures thereof.

16. The tubular conduit of claim 1, wherein the tubular conduit comprises dorsal root ganglia, Schwann cells and/or stem cells.

17. A composition comprising a silk fibroin hydrogel enzymatically cross-linked with horseradish peroxidase and hydrogen peroxide, for use in medicine or in veterinary, wherein said composition is administrated in a tubular conduit, and wherein said tubular conduit comprises a -sheet conformation obtainable from the enzymatically cross-linking of the silk fibroin hydrogel, porosity up to 70%, and a pore size up to 30 m.

18. The composition of claim 17, wherein the composition is a treatment for diseases that involve the repair and/or regeneration of tissues, nerves or bone.

19. (canceled)

20. (canceled)

21. (canceled)

22. The composition of claim 17, wherein the tubular conduit further comprises dorsal root ganglia and/or Schwann cells.

23. (canceled)

24. A method for producing the tubular conduit of claim 1, comprising: preparing an aqueous silk fibroin solution with a concentration of 5-25% (wt %), adding horseradish peroxidase and hydrogen peroxide to the aqueous silk fibroin solution to form an enzymatically cross-linked silk fibroin hydrogel; injecting said silk fibroin hydrogel into a mould with desired dimensions, wherein said mould comprises an outer wall and an inter wall; incubating the mould at 37 C. for 0.5-5 hours, for the complete formation of the hydrogel; placing the silk fibroin hydrogel in liquid nitrogen for at least 30 seconds, until temporary development of -sheet; removing the outer wall of the mould; and inducing a -sheet conformation by placing in the silk fibroin hydrogel in an ethanol solution for at least 30 minutes or by freezing the silk fibroin hydrogel.

25. The method of claim 24, further comprising drying the silk fibroin hydrogel by freeze drying for obtaining a pore size of 0.5 m-2 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of disclosure.

[0077] FIG. 1. Schematic representation of the preparation of a tubular conduit/nerve guidance conduit of silk fibroin.

[0078] FIG. 2. Schematic representation of embodiment of a tubular conduit/nerve guidance conduit of silk fibroin after production.

[0079] FIG. 3. Schematic representation of possible methods for obtain the tubular conduit described in the present disclosure.

[0080] FIG. 4. Schematic representation of kinking resistance ability of thick wall conduits.

[0081] FIG. 5. Schematic representation of SEM micrographs revealing the increased porosity achieved by reducing silk concentration from 16% to 8%. The cross-section is specially affected, with high interconnectivity from the inner to the outer walls of the conduit.

[0082] FIGS. 6A-6B. Schematic representation of: Stereomicroscope pictures of the different silk conduits obtained with different drying methods (FIG. 6A); SEM micrographs of the different silk conduits obtained with different drying methods that lead to different micro-structure and porosity (FIG. 6B).

[0083] FIGS. 7A-7C. Schematic representation of: 3D micro-ct reconstruction of thick and thin wall conduits obtained used different sized moulds (FIG. 7A); SEM micrographs of the mentioned conduits, where wall thickness varies (FIG. 7B); Stereomicroscope images of thick and thin wall conduits, in hydrated and dry state (FIG. 7C).

[0084] FIGS. 8A-8C. Schematic representation of silk conduits containing gradients of bioactive molecules. FIG. 8A: Scheme of desired prototypes containing three different and increasing concentrations, from proximal to distal sites. FIG. 8B: Fabrication of a silk conduit (hydrogel step) with three different zones, that correspond to different growth factor concentrations. FIG. 8C: Different concentrations interface of obtained silk conduit.

[0085] FIG. 9. Schematic representation of a simple hydrated silk conduit (white) when compared to a conductive silk-polypirrole conduit (black).

[0086] FIG. 10. Schematic representation of a silk conduit when incorporating just 1% of hair keratin in the silk polymeric solution, cellular adhesion increased, which is proved qualitatively by Live/dead assay as well as quantitatively, by Alamar blue assay; (1% FD Keratin=freeze-dried conduit containing 1% keratin).

[0087] FIGS. 11A-11B. Schematic representation of the degradation profiles of several silk conduits formulations in the presence of 0.2 U/ml of protease for 30 days (FIG. 11A). By varying only the method of drying, weight loss in vivo and in vitro will be modified (FIG. 11B); (FD=freeze-dried; AD=air dried at 50 C.; Eth=Directly from ethanol; FDMP=Freeze-dried more porous).

[0088] FIG. 12. SEM micrographs and respective EDS spectra of the silk conduits after 30 days in Simulated Body Fluid. The Air Dried formulation was the only one that presented bioactivity, corresponding to the detection of calcium phosphates by EDS and visualization of cauliflower crystals in SEM micrographs.

[0089] FIG. 13. Schematic representation of mechanical properties of some embodiment of the silk conduits: Tensile stress and Tensile modulus; ((FD=freeze-dried; AD=air dried at 50 C.; Eth=Directly from ethanol; FDMP=Freeze-dried more porous)

[0090] FIG. 14. Differences in the silk conduits permeability of a 4 kDa molecule due to the method of drying and due to the thickness of the conduit's wall.

[0091] FIGS. 15A-15B. Schematic representation of: Results of Alamar Blue cellular density quantification and Live/dead qualitative assay after Schwann cells were seeded in all formulations of thick wall tubes after 7 days (FIG. 15A); Results of Alamar Blue cellular density quantification and Live/dead qualitative assay after BJ skin fibroblasts were seeded in all formulations of thick wall tubes after 7 days (FIG. 15B); (FDMP=Freeze-dried more porous).

[0092] FIGS. 16A-16B. Schematic representation of: Results of Alamar Blue cellular density quantification and Live/dead qualitative assay after Schwann cells were seeded in all formulations of thick wall tubes after 7 days (FIG. 16A); Results of Alamar Blue cellular density quantification and Live/dead qualitative assay after BJ skin fibroblasts were seeded in all formulations of thick wall tubes after 7 days (FIG. 16B).

[0093] FIG. 17. Schematic representation of: Longitudinal view of thick and thin wall conduits after 4 weeks in vivo subcutaneous implantation in mice.

DETAILED DESCRIPTION

[0094] The present disclosure relates to a silk fibroin tubular conduit, a new methodology for obtaining said silk fibroin tubular conduit, and respective uses. In particular, the use for peripheral nerve regeneration.

[0095] In an embodiment, by changing the method of solvent extraction, diverse conduits can be obtained, that will implicate changes in all features of the conduits (see FIG. 6).

[0096] In an embodiment, the mold used to inject the silk polymeric solution has a crucial impact on the size specifications of the final conduit, which in other hand, it has an impact on the conduits characteristics. Several different wall thicknesses may be obtained, as seen in FIG. 7.

[0097] In an embodiment, tubular/nerve conduit of the present disclosure may have different drugs/bioactive/conductive molecules and/or a random drug distribution in the tube sections. In particular (see FIG. 8): [0098] (I) Growth factors gradient: Growth factors relevant to regeneration, such as GDNF, NGF, BDNF, FGF of VEGF can be incorporated. Since the lack of vascularization and nutrients supply in the distal site of injuries is a major complication leading to cell dead and there is the need to guide proximal growing axons to the distal site, one of the objective is to have higher amounts of growth factors in this distal area. Since in a middle step of forming the NGC we will be handling a viscous silk hydrogel, it is possible to make gradients of several molecules, increasing its concentration from proximal to the distal site, where it is most needed [0099] (II) Conductive conduits: An important aspect of synthetic nerve grafts is their ability to conduct electricity. Studies have showed that electrical stimulation can significantly promote the regeneration of peripheral nerve injuries. [0100] (III) Incorporation of proteins, in particular: as a method to increase biological properties, the inclusion of human hair keratin is very feasible and already proved to be effective, increasing cellular viability in the conduits containing only 1% of keratin in the polymeric solution.

[0101] In an embodiment, simple conduits are composed only of silk. However, since the main purpose of these biomaterials is for peripheral nerve regeneration applications, many different molecules can be added to the conduits, for varying purposes.

[0102] In an embodiment, different drying methods or simply not drying the silk conduits after the fabrication method affects all properties of the conduits. Degradation is one of these parameters that is largely affected. The conduits that are not dried, or used directly from ethanol, degrade much faster than the others (after 21 days) and tend to disaggregate in blocks in both thin and thick wall tubes (see FIG. 11B). The freeze-dried formulations have an intermediate degradation, while the air dried formulations lasts for longer periods of time (only degrades 5% after 30 days). With these results is possible to verify that using the exact same methodology and concentration, and changing only the method of drying, we can tune the degradation from total degradation to almost not degrading after 30 days, according to needs.

[0103] In an embodiment, the drying of the conduits in different manners has implications in the physico-chemical characteristics of silk conduits. After 30 days in Simulated Body Fluid (SBF), the only formulation that presented bioactivity capabilities or that allowed the formation of calcified crystals, was the air dried formulation. That was proved by EDS technique, which detected a high concentration of calcium phosphates (ions phosphor and calcium) and by SEM, which detected these crystals in the surface of the conduit. For peripheral nerve regeneration purposes, calcification is not desired. However, this feature can be of high importance in hard tissue regeneration applications, such as bone regeneration.

[0104] In an embodiment, nerve conduits must not collapse and retain mechanical stability to withstand the traction of moving joints. Peripheral nerves are under tensile loads in situ and experience .sup.11% strain in resting position. Concerning this strain, thick tubes tolerate a higher tensile stress when compared to thinner tubes. Among the thick, FDMP and AD present higher tensile stress for the same % of strain. Regarding the tensile modulus, corroborating the previous results, thick tubes present higher modulus. Again, the FDMP and air dried revealed higher stiffness when compared to others. Corroborating the previous results, the air dried formulation, due to bioactivity and stiffness could easily find application in hard tissue regeneration applications.

[0105] In an embodiment, depending on the application of silk conduits, more or less permeability is an important feature to consider. In the case of peripheral nerve regeneration, it is important to keep permeability to oxygen and nutrients for the regenerating nerve, however maintaining a close and protective environment. Therefore, permeability assays are of outmost importance. By simply changing the method of drying or the thickness of the conduit walls, different permeability is obtained. In a 48 h assay, a fluorescent molecule (fitc-dextran with 4 kDa of weight) was injected in the lumen of the conduits and the ends were sealed. The release of this molecule through the conduit walls was evaluated. In thick wall conduits, only ethanol formulation allows 80% passage of molecule. On the other hand, all thin wall tubes allow the 4 kDa molecule to cross through the walls, regardless of the formulation, reaching 100% of release after 48H. The microscopic images of the conduits after the assay suggest some molecules are entrapped in the thick wall conduits.

[0106] In an embodiment, the wall conduits varied from 700 m in thick wall conduits to 300 m in thin wall conduits, which made a significant difference in terms of permeability. For instance, in the air dried formulation, the release went from 20% to 100%, due to the wall thickness alone.

[0107] In an embodiment, the cytocompatibility and in vitro biological performance was carried out by means of using different cell types relevant for peripheral nerve regeneration, namely Human Schwann cells and human skin fibroblasts (BJ). All formulations of conduits were tested. Quantitative results of cellular density after 7 days in culture are shown (Alamar Blue assay) and corroborated by qualitative images (Live/dead assay).

[0108] In an embodiment, the silk conduits formulations of the present disclosure were implanted in male CD1 mice, in four subcutaneous pockets on the animals' backs. Animals were sacrificed 4 weeks after implantation, and conduits were explanted with the surrounding connective tissue for analysis. Sections were prepared and stained with hematoxylin and eosin (H&E). It is possible to see the expected formation of a fibrous capsule around the conduits. However that tissue does not show a high concentration of inflammatory cells, indicating that the host response to the silk conduit was negligible and in agreement with prior findings on the host response to silk fibroin biomaterials. It is also possible to see that there is no infiltration or migration of cells through the conduits walls, proving the conduits impermeability to undesired cells such as fibroblasts and consequent formation of scar tissue.

TABLE-US-00001 TABLE 1 Commercially available nerve guides and wraps. Apart from Avance, Qigel and RevolNerve, all other listed nerve devices are FDA approved. Commercial name Company Material Neuragen/Neurawrap Integra Type I collagen Neurolac Polyganics PDLLA/CL Neurotube Synovis PGA Neuromatrix/Neuroflex Collagen Type I collagen conduits and NeuroMend wrap matrix Inc. Salubridge/Salutunnel Salumedica Polyvinyl alcohol hydrogel Surgisis/Axoguard AxoGenInc Porcine small intestine submucosa Avance AxoGenInc Decellularized nerve QiGel, Re-Axon Medovent Chitosan RevolNerve Orthomed Collagen type I and III from porcine skin

[0109] In an embodiment, silk fibroin from the silk worm Bombyx mori, has often been used as a textile material, yet, more and more attention has been given to silk lately due to its appropriate processing, biodegradability and the presence of easy accessible chemical groups for functional modifications. Studies suggest that silk is not only biodegradable but also bioresorbable, characteristics for tissue engineering and regenerative medicine. The major advantage of silk compared to other natural biopolymers is its excellent mechanical property. Other important advantages include good biocompatibility, water based processing, biodegradability and the presence of easy accessible chemical groups for functional modifications. Studies suggest that silk is not only biodegradable but also bioresorbable.

[0110] In an embodiment, regarding the application of this biomaterial in peripheral nerve regeneration, it is known that silk fibroin supports the viability of dorsal root ganglia and Schwann cells without affecting their normal phenotype or functionality.

[0111] The present disclosure refers to the development of a nerve guidance conduit derived from silk fibroin, using a different methodology than the ones referred to in the literature, intended for bridging nerve defects, for peripheral nerve regeneration.

[0112] In an embodiment, the porosity of the tube wall may be defined by the drying method. For peripheral nerve regeneration, it is necessary to have some porosity that allows the exchange of oxygen and nutrients from the outside to the region of the lesion. However, such porosity must block the infiltration of cells, such as fibroblasts that will induce fibrosis and scar tissue formation. In addition, tubes frozen with liquid nitrogen presented cracks and are more brittle, for which they were excluded.

[0113] In an embodiment, the tubes that were not dried and were used directly after being soaked in ethanol cannot be observed by SEM.

[0114] In an embodiment, the kink resistance ability was determined by bending the conduits 180 on a flexible wire. The thick wall formulations that were produced by inducing -sheet conformation with ethanol present kink resistance ability, with no occlusion of the lumen whatsoever. This feature is important, since nerves are close to articulations and might be subjected to forces. The device used must be capable of bending during patient movement without kinking and compression.

[0115] In an embodiment, the tubular conduit can be obtainable by the following steps: [0116] preparing an aqueous silk fibroin (SF) solutionconcentration to be defined according to final intended features; [0117] adding of horseradish peroxidase (100 L/ml of silk solution) and hydrogen peroxide (65 L/ml of silk solution)quantity to be defined according to final intended features; [0118] injecting the enzymatically cross-linked SF hydrogel into the mould (with the preferred dimensions); [0119] incubating the whole system at 37 C. for 2 hours for the complete formation of the hydrogel; [0120] placing the whole system in liquid nitrogen (190 C.) for 30-45 seconds, until temporary development of -sheet (with low temperature); [0121] the induction of -sheet conformation by freezing at 80 C. and freeze-drying may be performed to avoid the use of organic solvents; [0122] For the methodology involving the -sheet conformation using organic solvents such as ethanol, after placing the whole system in liquid nitrogen (190 C.) for 30-45 seconds [0123] removing outer mould; [0124] placing in ethanol absolute for 1 hour for induction of -sheet conformation; [0125] removing the inner mould; [0126] placing in water (FIG. 2); [0127] proceed with most suitable method of drying according to the final requirements.

[0128] Aqueous solutions of silk fibroin with different concentrations work as precursors for the formation of the hydrogel. The silk fibroin solutions are capable of forming hydrogels in the presence of horseradish peroxidase and hydrogen peroxide (oxidizer) at mild temperatures and within physiological pH range. During the gelation procedure, it is allowed the combination of bioactive reagents, detecting reagents and any combination thereof. At this stage and in order to tackle peripheral nerve regeneration difficulties such as excessive fibrosis and scar tissue formation or to stimulate vascularization, we can include anti-fibrotic substances, angiogenic growth factors such as VEGF or even neurotrophic growth factors such as NGF and GDNF. The blending of silk with other polymers to enhance mechanical properties or cell adhesion such as keratin is also feasible. Later on this process, and its innovation, resides in the rest of the process and the additional steps necessary until the obtainment of the final nerve guidance conduit. We also envision the incorporation of conductive and drug-delivery nanoparticles, as gold nanoparticles. These have the capability of delivering agents of interest in the case of peripheral nerve regeneration and guide electrical impulses, since electrical stimulation is a proved method to improve regeneration, so by this approach we can have two advantages in the addition of one component.

[0129] The physicochemical and biological performances of the silk nerve guidance conduit (e.g., compressive modulus, storage modulus, stiffness, swelling behaviour, durability, degradation profile, porosity, permeability, suture ability) can be tuned for specific uses, by means of using different drying methods, different sized moulds and concentrations of silk fibroin in the same process. Furthermore, the inner diameter, thickness of the wall and length of the nerve guidance conduit can be tuned according to the final needs of the user and depends solely on the moulds used. According to the final objectives (animal model and size of nerve defect), different sizes are needed and can easily be obtained.

[0130] In an embodiment, with this methodology, it is possible to fine-tune the permeability of the nerve guidance conduit, in particular, by controlling the porosity of the tube wall.

TABLE-US-00002 TABLE II Pore size/Drying method Pore size (m) Dried at 50 C. (passage in ethanol) 0 3 m Frozen at 80 C. and freeze dried 1.5 0.5 m (passage in ethanol) Frozen with liquid N.sub.2 and freeze dried 0.9 0.3 m (passage in ethanol) Frozen at 80 C. and freeze dried 2 0.5 m (no passage in ethanol)

[0131] The simplicity of a regular mold casting or dipping technique does not allow for fine control over conduits wall thickness, uniformity and pore size or distribution. We were able to refine this mold casting method by introducing an extra step in the process: the formation of a hydrogel. This additional cross-linking step leads to a stronger and more stable three-dimensional network, thus conferring the scaffold higher mechanical properties, more elasticity and a lower degradation rate, when compared to tubes that did not undergo this step before turning in -sheet conformation.

[0132] The term comprising whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0133] It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of steps described is illustrative only and can be varied without departing from the disclosure. Thus, unless otherwise stated the steps described are so unordered meaning that, when possible, the steps can be performed in any convenient or desirable order.

[0134] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0135] The above-described embodiments are combinable.

[0136] The following claims further set out particular embodiments of the disclosure.

[0137] The following references, should be considered herewith incorporated in their entirety: [0138] 1. Oh S H, Kim J H, Song K S, Jeon B H, Yoon J H, Seo T B, et al. Peripheral nerve regeneration within an asymmetrically porous PLGA/Pluronic F127 nerve guide conduit. Biomaterials. 2008 April; 29(11):1601-9. PubMed PMID: 18155135. [0139] 2. Belkas J S, Shoichet M S, Midha R. Peripheral nerve regeneration through guidance tubes. Neurological research. 2004 March; 26(2):151-60. PubMed PMID: 15072634 [0140] 3. Ichihara S, Inada Y, Nakamura T. Artificial nerve tubes and their application for repair of peripheral nerve injury: an update of current concepts. Injury. 2008 October; 39 Suppl 4:29-39. PubMed PMID: 18804584. [0141] 4. Johnson E O, Soucacos P N. Nerve repair: experimental and clinical evaluation of biodegradable artificial nerve guides. Injury. 2008 September; 39 Suppl 3:S30-6. PubMed PMID: 18722612. [0142] 5. Yang Y, Chen X, Ding F, Zhang P, Liu J, Gu X. Biocompatibility evaluation of silk fibroin with peripheral nerve tissues and cells in vitro. Biomaterials. 2007 March; 28(9):1643-52. PubMed PMID: 17188747.