Biological performance of a degradable poly(lactic acid-epsilon-caprolactone) nerve guide: influence of tube dimensions

Development of fibrous biodegradable polymer conduits for guided nerve regeneration

The technique of microbraiding with modification was employed as a novel method for the fabrication of fibrous tubular scaffolds for nerve tissue engineering purposes. The biodegradable polymers used in this study were poly(L-lactide-co-glycolide) (10:90) and chitosan. The polymeric fibers were microbraided around a Teflon mandrel to make it as a tubular construct. The conduits were then studied for their surface morphology, swelling behaviour and biocompatibility. The surface morphology was analysed by scanning electron microscope, swelling behaviour by weight increase due to water uptake and biocompatibility by in vitro cytotoxicity assessment in terms of cell morphology and cell viability by the MTT assay of polymer extract treated cells. These conduits may also be used for regeneration of tissues, which require tubular scaffolds such as blood vessel, spinal cord, intestine etc.

Preparation and physicochemical characterization of biodegradable nerve guides containing the nerve growth agent sabeluzole

The objective of this study was to develop and characterize a biodegradable drug-loaded nerve guide for peripheral nerve regeneration. Sabeluzole, a nerve growth agent, was selected as model compound. Four biodegradable polymers were selected for this study: a copolymer of polylactic acid and polycaprolactone (PCL); a copolymer of polyglycolic acid and polycaprolactone PCL; a copolymer of PCL/polydioxanone (PDO) and PDO. Placebo and drug loaded nerve guides were obtained by melt compression and melt extrusion. It was observed that melt compression and melt extrusion are feasible techniques to prepare the nerve guides. Based on the physicochemical characterization, all samples show absence of crystalline sabeluzole, indicating the formation of an amorphous dispersion. The in vitro release measurements show that the release of sabeluzole is complete, reproducible and can be controlled by the proper selection of the polymer. The release mechanism for all samples follows Fickian release behaviour.

Peripheral nerve regeneration by microbraided poly(L-lactide-co-glycolide) biodegradable polymer fibers

Tiny tubes with fiber architecture were developed by a novel method of fabrication upon introducing some modification to the microbraiding technique, to function as nerve guide conduit and the feasibility of in vivo nerve regeneration was investigated through several of these conduits. Poly(L-lactide-co-glycolide) (10:90) polymer fibers being biocompatible and biodegradable were used for the fabrication of the conduits. The microbraided nerve guide conduits (MNGCs) were characterized using scanning electron microscopy to study the surface morphology and fiber arrangement. Degradation tests were performed and the micrographs of the conduit showed that the degradation of the conduit is by fiber breakage indicating bulk hydrolysis of the polymer. Biological performances of the conduits were examined in the rat sciatic nerve model with a 12-mm gap. After implantation of the MNGC to the right sciatic nerve of the rat, there was no inflammatory response. One week after implantation, a thin tissue capsule was formed on the outer surface of the conduit, indicating good biological response of the conduit. Fibrin matrix cable formation was seen inside the MNGC after 1 week implantation. One month after implantation, 9 of 10 rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The MNGCs were flexible, permeable, and showed no swelling apart from its other advantages. Thus, these new poly(L-lactide-co-glycolide) microbraided conduits can be effective aids for nerve regeneration and repair and may lead to clinical applications.

In vitro degradation and biocompatibility of poly(DL-lactide-epsilon-caprolactone) nerve guides

Bridging nerve gaps by means of autologous nerve grafts involves donor nerve graft harvesting. Recent studies have focused on the use of alternative methods, and one of these is the use of biodegradable nerve guides. After serving their function, nerve guides should degrade to avoid a chronic foreign body reaction. The in vitro degradation, in vitro cytotoxicity, hemocompatibility, and short-term in vivo foreign body reaction of poly((65)/(35) ((85)/(15) (L)/(D)) lactide-epsilon-caprolactone) nerve guides was studied. The in vitro degradation characteristics of poly(DLLA-epsilon-CL) nerve guides were monitored at 2-week time intervals during a period of 22 weeks. Weight loss, degree of swelling of the tube wall, mechanical strength, thermal properties, and the intrinsic viscosity of the nerve guides were determined. Cytotoxicity was studied by measuring the cell proliferation inhibition index (CPII) on mouse fibroblasts in vitro. Cell growth was evaluated by cell counting, while morphology was assessed by light microscopy. Hemocompatibility was evaluated using a thrombin generation assay and a complement convertase assay. The foreign body reaction against poly(DLLA-epsilon-CL) nerve guides was investigated by examining toluidine blue stained sections. The in vitro degradation data showed that poly(DLLA-epsilon-CL) nerve guides do not swell, maintain their mechanical strength and flexibility for a period of about 8-10 weeks, and start to lose mass after about 10 weeks. Poly(DLLA-epsilon-CL) nerve guides were classified as noncytotoxic, as cytotoxicity tests demonstrated that cell morphology was not affected (CPII 0%). The thrombin generation assay and complement convertase assay indicated that the material is highly hemocompatible. The foreign body reaction against the biomaterial was mild with a light priming of the immunesystem. The results presented in this study demonstrate that poly((65)/(35) ((85)/(15) (L)/(D)) lactide-epsilon-caprolactone) nerve guides are biocompatible, and show good in vitro degradation characteristics, making these biodegradable nerve guides promising candidates for bridging peripheral nerve defects up to several centimeters.

Prefabrication of Vascularized Bone Graft Using Guided Bone Regeneration

This article describes the prefabrication of a vascularized bone graft composed of autologous particulate cancellous bone and marrow (PCBM), a vessel bundle, and a biodegradable membrane. The PCBM was placed around the saphenous vessel bundle of rats and rolled with a biodegradable membrane of L-lactide-epsilon-caprolactone copolymer to prepare the prefabricated vascularized bone graft (group A). As controls, combinations of PCBM and membrane (group B), vessel bundle and membrane (group C), and PCBM and vessel bundle (group D) were prepared. A radiographic study revealed radio-opacity in the implantation site of group A 1 week later, in contrast to the other groups. Newly formed bone in the membrane roll was histologically confirmed, and neomicrovasculature circulating from the vessel bundle through the newly formed bone tissue was observed. The increase in alkaline phosphatase activity and osteocalcin content was significant for the group A preparation compared with the other groups. We concluded that the combination of autologous PCBM, a vessel bundle, and a biodegradable membrane was promising in the prefabrication of vascularized bone with good blood circulation.

Multilayered peptide incorporated collagen tubules for peripheral nerve repair

Successful nerve regeneration process was achieved with improved mechanical strength by crosslinking tubular nerve guides made up of collagen. The multilayered collagen sheets were prepared from laminar evaporation of collagen solution. Scanning electron micrograph of the collagen tubes crosslinked with glutaraldehyde (GTA), microwave irradiation showed porous, fibrillar structures of collagen filaments in these matrices. The mechanical property of the crosslinked collagen tubes was carried out by tensile strength measurements. Fourier transform infrared spectra of the collagen films show that the native triple helicity was unaltered during multilayered preparation. It was observed that the structural integrity is unaltered during the multilayer preparation. Microscopic analysis indicates that the tubule surface acts as a surface of adherence and proliferation for the sprouting axons from the cut proximal nerve stumps. Solute diffusion studies on these tubes indicate that they are highly porous to wide range of molecular sizes during regeneration. Among the two types of crosslinking, the microwave irradiated collagen conduits results in ample myelinated axons compared with GTA group, where we observed more unmyelinated axons.

Multi-channeled biodegradable polymer/CultiSpher composite nerve guides

Innovative methods to fabricate porous, biodegradable conduits were developed to produce nerve guides with multiple longitudinally aligned channels. The geometry of the nerve guide's channels was designed to be appropriate for harboring neurite extension. Both the coated mandrel and mandrel adhesion techniques permit flexibility in the number of channels, channel organization, and channel diameters. In this study, the composite nerve guides were comprised of poly(caprolactone) (PCL) and porous collagen-based beads (CultiSphers). The incorporation of the collagenous beads results in enhanced cortical neuron adhesion, viability, and neurite extension as compared to PCL alone. Additionally, Schwann cell studies indicated that the PCL/CultiSpher composite is a suitable substrate for cell adhesion. Mechanical properties of the PCL/CultiSpher material and in vitro degradation rates indicate the potential usefulness of this novel composite for use in the fabrication of nerve guides.

Peripheral nerve regeneration in RGD peptide incorporated collagen tubes

This paper describes the regeneration of lesioned sciatic nerve with collagen tubes incorporated with RGD cell-adhesive peptide. Collagen implants of 14 mm were grafted to bridge a gap length of 10 mm nerve defect in a rat model. The regenerated tissues were analyzed histomorphologically. The number of myelinated axons in the regenerated mid-graft of the RGD peptide incorporated groups was statistically significant (p<0.05) than control collagen tube and autograft control after 30 days postoperatively. After 90 days of implantation, the mean counts were still statistically significant in the case of RGD peptide group than control collagen and autograft groups. Immunofluorescence studies demonstrated the staining of S100 proteins in the peripherally located cells indicating the proliferation of Schwann cells in the early days of regeneration. The staining pattern of integrin-alphaV was observed mostly in the perineurial regions in close proximity to the RGD peptide incorporated collagen tubes. Other studies like sciatic functional index, conduction velocity at 90 days postoperatively suggest complete regeneration of lesioned nerves with RGD incorporated collagen implants.

Functional assessment of sciatic nerve recovery: biodegradable poly (DLLA-epsilon-CL) nerve guide filled with fresh skeletal muscle

The aim of this study was to compare functional peripheral nerve recovery in the rat sciatic nerve model after reconstruction of a 10-mm gap with a biodegradable poly (DLLA-epsilon-CL) nerve guide, as filled with either fresh skeletal muscle or phosphate-buffered saline (PBS). During 24 weeks of recovery, motor and sensory functional evaluation was tested by extensor postural thrust (EPT) and withdrawal reflex latency (WRL), respectively. At the end of the experiment, anesthetized animals were prepared for motor nerve conduction velocity (MNCV) studies, followed by gastrocnemius and soleus muscle weight measurement. Motor functional recovery was greater in the muscle-grafted group, and reached a significant difference from weeks 8-12 (P < 0.05). The results of this investigation suggest that filling a nerve guide with fresh skeletal muscle induces faster maturation of regenerated nerve fibers in comparison with traditional tubular repair.

Photoconstructs of nerve guidance prosthesis using photoreactive gelatin as a scaffold

We devised a novel nerve prosthesis composed of an elastomeric gelatinous tube and multifilament gelatinous fibers, both of which were prepared from styrene-derivatized gelatin, which allows in situ formation of a bioactive substance-incorporated gel. An in vitro study showed that the axonal regeneration potential of a photocured gelatin layer impregnated with laminin, fibronectin, and NGF was almost comparable with that of coated Matrigel. A nerve conduit and fibers prepared from photoreactive gelatin was subjected to visible-light irradiation with rotation in the presence of camphorquinone as a photoinitiator using a custom-designed apparatus. A sample of transparent gelatinous conduit with an inner diameter of 1.2 mm and a wall thickness of 0.6 mm and gelatin fibers ranging from 10 to 100 pm in diameter were produced. The photocured elastomeric gelatinous tube was flexible and had structural integrity that allowed mechanical handling without breaking. A novel nerve guidance prosthesis composed of tubes packed with fibers was assembled. This photofabrication technology may enable the design of a tailor-made shape and rapid morphogenesis and functional recovery of damaged nerve tissue.

Controlled release of nerve growth factor enhances sciatic nerve regeneration

Based on previous studies demonstrating the potential of growth factors to enhance peripheral nerve regeneration, we developed a novel growth factor delivery system to provide sustained delivery of nerve growth factor (NGF). This delivery system uses heparin to immobilize NGF and slow its diffusion from a fibrin matrix. This system has been previously shown to enhance neurite outgrowth in vitro, and in this study, we evaluated the ability of this delivery system to enhance nerve regeneration through conduits. We tested the effect of controlled NGF delivery on peripheral nerve regeneration in a 13-mm rat sciatic nerve defect. The heparin-containing delivery system was studied in combination with three doses of NGF (5, 20, or 50 ng/mL) and the results were compared with positive controls (isografts) and negative controls (fibrin alone, NGF alone, and empty conduits). Nerves were harvested at 6 weeks postoperatively for histomorphometric analysis. Axonal regeneration in the delivery system groups revealed a marked dose-dependent effect. The total number of nerve fibers at both the mid-conduit level and in the distal nerve showed no statistical difference for NGF doses at 20 and 50 ng/mL from the isograft (positive control). The results of this study demonstrate that the incorporation of a novel delivery system providing controlled release of growth factors enhances peripheral nerve regeneration and represents a significant contribution toward enhancing nerve regeneration across short nerve gaps.

Acceleration effect of basic fibroblast growth factor on the regeneration of peripheral nerve through a 15-mm gap

In this study, nerve guides composed of poly(D,L-lactide) (PDLLA) were fabricated and used in the repair of transected sciatic nerves (15-mm gaps) of rats. Nerve guides with a two-ply structure (inner layer dense, outer layer microporous) were prepared by controlling the solvent evaporation rate. Then basic fibroblast growth factor (bFGF) was embedded in the inner layer of the nerve guides. Thus the inner dense layer not only could prevent the ingrowth of fibroblast and avoid the outgrowing nerve cable, but it also could retain the released bFGF in the guide lumen. The outer porous layer allowed vascular ingrowth and the diffusion of essential nutrients into the guide lumen. The data show that by using this nerve guide, the transected 15-mm sciatic nerve was regenerated successfully within 4 months. The recovery of function of the regenerated nerves was significantly accelerated by bFGF, as indicated by an electrostimulation test and histologic assays. In addition, the bFGF retained its bioactivity during embedding and continuously was released from the matrix, as confirmed by the results of both the dorsal root ganglia (DRG) and the Schwann cell culture in the presence of PDLLA matrix containing bFGF. The released bFGF enhanced the ability of the nerve fibers to sprout from dorsal root ganglia, and it accelerated the proliferation of Schwann cells.

Rat costochondral cell characteristics on poly (L-lactide-co-epsilon-caprolactone) scaffolds

This study was designed to examine the adhesion, proliferation, and morphology of chondrocytes on new scaffolds; and to examine these cells histologically for the ability of the chondrocytes to maintain chondrogenic properties after subcutaneous implantation into nude mice. Both 75:25 poly (L-lactide-co-epsilon-caprolactone) (75PLC) and 50:50 poly (L-lactide-co-epsilon-capro-lactone) scaffold (50PLC) were tested as a scaffold for rat costochondral resting zone chondrocytes in comparison with a type I collagen sponge scaffold (collagen scaffold). Both of the poly (L-lactide-co-epsilon-caprolactone) scaffolds (75PLC and 50PLC) were coated with type I collagen solution and the effects of the collagen coat (hybrid-PLC) were also examined. The hybrid-75PLC bound the same number of cells as the collagen scaffold, whereas the 75PLC and the 50PLC bound 60% and 50% fewer cells than the collagen scaffold, respectively. The cell growth on the scaffolds progressed with culture time in all scaffolds. Cell morphology was assessed by scanning electron microscopy for differences in the structure of cellular interaction. Chondrocytes on every scaffold maintained a spherical shape. The hybrid-PLCs were superior to the PLCs with respect to the number of cells attached. The PLCs had an advantageous degradation characteristic in that they retained their original shape better than the collagen scaffold. Additionally, in the PLCs seeded, the cells retained their integrity 4 weeks after implantation, although the volume of collagen scaffold decreased by 50%.

Biocompatibility of implantable synthetic polymeric drug carriers: focus on brain biocompatibility

Numerous polymeric biomaterials are implanted each year in human bodies. Among them, drug delivery devices are potent novel powerful therapeutics for diseases which lack efficient treatments. Controlled release systems are in direct and sustained contact with the tissues, and some of them degrade in situ. Thus, both the material itself and its degradation products must be devoid of toxicity. The knowledge and understanding of the criteria and mechanisms determining the biocompatibility of biomaterials are therefore of great importance. The classical tissue response to a foreign material leads to the encapsulation of the implant, which may impair the drug diffusion in the surrounding tissue and/or cause implant failure. This tissue response depends on different factors, especially on the implantation site. Indeed, several organs possess a particular immunological status, which may reduce the inflammatory and immune reactions. Among them, the central nervous system is of particular interest, since many pathologies still need curative treatments. This review describes the classical foreign body reaction and exposes the particularities of the central nervous system response. The recent in vivo biocompatibility studies of implanted synthetic polymeric drug carriers are summarized in order to illustrate the behavior of different classes of polymers and the methodologies used to evaluate their tolerance.

Bio-compatibility of type I/III collagen matrix for peripheral nerve reconstruction

Nerve gaps are usually bridged by autografts. With improving technical methods biocompatible conduits may become an alternative graft to reconstruct nerves. Non-neural conduits fail to support regeneration over larger gaps due to lacking viable Schwann cells. Thus, tissue engineering of nerves is focusing on implantation of viable Schwann cells into suitable scaffolds. In this study, we tested collagen type I/III tubes as a potential nerve guiding matrix. Revascularization, foreign body reaction, biodegradation and Schwann cell settlement were evaluated by immunocytochemistry, light, fluorescence and scanning electron microscopy, after different implantation times. The conduits were completely revascularized between day 5 and 7 post-operatively and well integrated into the host tissue. Host response was characterized by a moderate invasion of ED1/ED2-positive macrophages. Biodegradation of the tubes was slowly enough to maintain a stable support structure for extended regeneration processes. Implanted Schwann cells adhered, survived and proliferated on the inner surface of the conduits and were able to form nerve guiding columns of Büngner. From this results, we conclude that collagen-type I/III can serve as template to design "living" nerve conduits, which may be able to ensure nerve regeneration through extended nerve gaps.

Rat Schwann cells in bioresorbable nerve guides to promote and accelerate axonal regeneration

A micro-structured, biodegradable, semipermeable hollow nerve guide implant was developed to bridge nerve lesions. Quantitative comparison of cell migration and axonal growth using time lapse video recording in vitro revealed that axons grow eight times faster than neuritotrophic Schwann cells migrate. To accelerate regeneration, purified Schwann cells are best injected into nerve guides before implantation. Nerve guides made from resorbable poly-lactide-co-glycolide support Schwann cell attachment, cell survival, and axonal outgrowth in vitro. The therapeutic concept aims at the development of an 'intelligent neuroprosthesis' that first mediates regeneration and then disappears.

Adhesion and growth of human Schwann cells on trimethylene carbonate (co)polymers

Seeding of artificial nerve grafts with Schwann cells is a promising strategy for bridging large nerve defects. The aim of the present study was to evaluate the adhesion and growth of human Schwann cells (HSCs) on 1,3-trimethylene carbonate (TMC) and epsilon-caprolactone copolymers, with the final goal of using these materials in the development of an artificial nerve graft. The adhesion, proliferation, and morphology of HSCs on copolymers containing 10 and 82 mol % of TMC and on the parent homopolymers were investigated. HSCs adhered faster and in greater numbers on the copolymer with 82 mol % of TMC and on the TMC homopolymer compared with the other (co)polymers. On all polymer films, cell adhesion was lower than on gelatin (positive control). Despite differences in cell adhesion, cells displayed exponential growth on all tested surfaces, with similar growth rates. Cell numbers doubled approximately every 3 days on all substrates. When the polymer films were coated with fibronectin, no significant differences in cell adhesion and proliferation were observed between coated polymer surfaces and gelatin. The results indicate that all tested materials support the adhesion and proliferation of HSCs and can in principle be used for the preparation of flexible and slowly degrading nerve guides.

The effect of transforming growth factor-beta1, released from a bioabsorbable self-reinforced polylactide pin, on a bone defect

Transforming growth factor-beta 1 (TGF-beta1)is a polypeptide growth factor which has been shown to increase bone formation in experimental studies. In this study it was combined to a bioabsorbable self-reinforced poly-LD-lactic acid fracture fixation pin. To assess the effect of TGF-beta1 on the healing of a bone defect, the pins were implanted in the rat distal femur next to a bone defect filled with a viscose cellulose sponge. The pins used in the study group (13 rats) contained 50 microg of TGF-beta1, whereas in the control group of nine rats an identical pin without the growth factor was used. In the histologic examination at 1, 3 and 6 weeks no difference was detected in the amount of bone inside the viscose cellulose sponge between the rats treated with TGF-beta1 and those with no added growth factor. At 3 weeks there was more fibroblast-rich mesenchymal tissue inside the viscose cellulose sponge in the rats treated with TGF-beta1. In the radiographic examination at 3 weeks there was an increase in the amount of new periosteal bone on the bone defect in the TGF-beta1-treated rats.

Copolymers of trimethylene carbonate and epsilon-caprolactone for porous nerve guides: synthesis and properties

Copolymers of trimethylene carbonate and epsilon-caprolactone were synthesized and characterized with the aim of assessing their potential in the development of a flexible and slowly degrading artificial nerve guide for the bridging of large nerve defects. The effect of the monomer ratio on the physical properties of the polymers and its influence on the processability of the materials was investigated. Under the applied polymerization conditions (130 degrees C, 3 days using stannous octoate as a catalyst) high molecular weight polymers (Mn above 93 000) were obtained. All copolymers had glass transition temperatures below room temperature. At trimethylene carbonate contents higher than 25 mol% no crystallinity was detected. A decrease in crystallinity resulted in the loss of strength and decrease in toughness, as well as in an increased polymer wettability. Amorphous poly(trimethylene carbonate), however, showed excellent ultimate mechanical properties due to strain-induced crystallization (Tm = 36 degrees C). Low crystallinity copolymers could be processed into dimensionally stable porous structures by means of immersion precipitation and by combination of this technique with the use of porosifying agents. Porous membranes of poly(trimethylene carbonate) could be prepared when blended with small amounts of high molecular weight poly(ethylene oxide). Poly(trimethylene carbonate) and poly(trimethylene carbonate-co-epsilon-caprolactone) copolymers with high epsilon-caprolactone content possess good physical properties and are processable into porous structures. These materials are most suitable for the preparation of porous artificial nerve guides.

Study of a (trimethylenecarbonate-co-epsilon-caprolactone) polymer--part 2: in vitro cytocompatibility analysis and in vivo ED1 cell response of a new nerve guide

Future surgical strategies to restore neurological function in peripheral nerve loss may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. Random copolymers of trimethylene carbonate and epsilon caprolactone (P(epsilonCL-TMC), 50: 50) have been synthesized by ring opening polymerization using rare earth alkoxides as initiator. Their potential use as nerve guide repairs has been assessed through indirect and direct in vitro biocompatibility tests and in vivo soft tissue response to EDI subclass macrophages. In vitro, we exposed monolayers of human skin fibroblasts and an established continuous cell line (Hela) to liquid extracts (either pure or diluted in the culture medium) of epsilonCL-TMC copolymer including positive (phenol) and negative controls. Then, colorimetric assays (Neutral red and MTT) were performed. The extracts of epsilonCL-TMC induced no significant cytotoxic effect. We also exposed in vitro Schwann cells to pieces of P(epsilonCL-TMC) and P(LA-GA) copolymers. We evaluated cell attachment at 1 and 3 h by measuring the activity of the lysosomal enzyme (N-acetyl-beta-hexosaminidase) and cell proliferation at 1, 3, 6 and 9 days by measuring the cell metabolic activity (MTT assay). Values for attachment slightly decreased between 1 and 3 h but were significantly higher than on agars (negative control). Cells plated on epsilonCL-TMC showed a rate of proliferation comparable with that of normalized controls and higher than on PGA-PLA at day 9. Finally, we evaluated in vivo the soft tissue response after implantation of cylindrical tubes of P(epsilonCL-TMC) and P(LA-GA) copolymers with an immunohistochemistry staining procedure for the newly recruited ED1 macrophages. An image analysis system automatically measured the optical density of labelled positive ED1 cells at 9, 21 and 60 days after implantation. epsilonCL-TMC copolymer showed a mild soft tissue reaction with no adverse chronic inflammatory reaction. These data allowed us to consider this conduit as a potential effective substitute in nerve repair. El sevier Science Ltd. All rights reserved.

A new nerve guide conduit material composed of a biodegradable poly(phosphoester)

There is a resurgence of interest in the development of degradable and biocompatible polymers for fabrication of nerve guide conduits (NGCs) in recent years. Poly(phosphoester) (PPE) polymers are among the attractive candidates in this context, in view of their high biocompatibility, adjustable biodegradability, flexibility in coupling fragile biomolecules under physiological conditions and a wide variety of physicochemical properties. The feasibility of using a biodegradable PPE, P(BHET-EOP/TC), as a novel NGC material was investigated. Two types of conduits were fabricated by using two batches of P(BHET-EOP/TC) with different weight-average molecular weights (Mw) and polydispersity indexes (PI). The polymers as well as conduits were non-toxic to all six types of cells tested, including primary neurones and neuronally differentiated PC12 cells. After in situ implantation in the sciatic nerve of the rat, two types of conduits triggered a similar tissue response, inducing the formation of a thin tissue capsule composed of approximately eight layers of fibroblasts surrounding the conduits at 3 months. Biological performances of the conduits were examined in the rat sciatic nerve model with a 10 mm gap. Although tube fragmentation, even tube breakage, was observed within less than 5 days post-implantation, successful regeneration through the gap occurred in both types of conduits, with four out of 10 in the Type I conduits (Mw 14,900 and PI 2.57) and 11 out of 12 in the Type II conduits (Mw 18,900 and PI 1.72). The degradation of conduits was further evidenced by increased roughness on the tube surface in vivo under scanning electron microscope and a mass decrease in a time-dependent manner in vitro. The Mw of the polymers dropped 33 and 24% in the Type I and II conduits, respectively, in vitro within 3 months. Among their advantages over other biodegradable NGCs, the PPE conduits showed negligible swelling and no crystallisation after implantation. Thus, these PPE conduits can be effective aids for nerve regeneration with potential to be further developed into more sophisticated NGCs that have better control of the conduit micro-environment for improved nerve regeneration.

A Schwann cell-seeded intrinsic framework and its satisfactory biocompatibility for a bioartificial nerve graft

To optimize the internal environment of a collagen nerve tube, we designed a Schwann cell-seeded intrinsic framework and its biocompatibility was investigated. We fixed 6-0 polyglactin woven filaments (Vicryl) or polydioxanone monofilaments (PDS) on a silicone ring in a net fashion. It was coated with matrigel and then incubated with cultured newborn or adult Schwann cells. Furthermore, we implanted 1.5-cm-long filament-filled collagen tubes in a rat model. Using a live/dead fluorescent assay and electron microscopy, we found that adherent Schwann cells onto filaments remained viable and oriented longitudinally along filaments. The preliminary in vivo study indicated that a mild inflammatory reaction was present around the tube wall. However, nerve regeneration occurred around and between filaments. We concluded that the arrangement of Schwann cell columns onto filaments was achieved, mimicking Bünger bands. It was shown that the biomaterials did not impede nerve regeneration.

Electronmicroscopical evaluation of short-term nerve regeneration through a thin-walled biodegradable poly(DLLA-ɛ-CL) nerve guide filled with modified denatured muscle tissue

The aim of this study was to evaluate short-term peripheral nerve regeneration across a 15-mm gap in the sciatic nerve of the rat, using a thin-walled biodegradable poly(DL-lactide-epsilon-caprolactone) nerve guide filled with modified denatured muscle tissue (MDMT). The evaluation was performed using transmission electron microscopy and morphometric analysis. Evaluation times ranged from 3 to 12 weeks after reconstruction. Already, 3 weeks after reconstruction, myelinated nerve fibers could be observed in the distal nerve stump. Twelve weeks after reconstruction, the number of (non)myelinated nerve fibers had significantly increased in the distal nerve stump. From this study, we can conclude that a thin-walled biodegradable poly(DL-lactide-epsilon-caprolactone) nerve guides filled with MDMT can be successfully applied in the reconstruction of severed nerves in the rat model. Furthermore, we showed fast nerve regeneration across the 15-mm nerve gap and found that the use of MDMT functioned as a mechanical support preventing a collapse of this thin-walled nerve guide.

Peripheral nerve regeneration using bioresorbable macroporous polylactide scaffolds

The ability of DRG-derived neurons to survive and attach onto macroporous polylactide (PLA) foams was assessed in vitro. The foams were fabricated using a thermally induced polymer-solvent phase separation. Two types of pore structures, namely oriented or interconnected pores, can be produced, depending on the mechanism of phase separation, which in turn can be predicted by the thermodynamics of the polymer-solvent pair. Coating of the porous foams with polyvinylalcohol (PVA) considerably improved the wettability of the foams and allowed for cell culture. The in vitro biocompatibility of the PVA-coated supports was demonstrated by measuring cell viability and neuritogenesis. Microscopic observations of the cells seeded onto the polymer foams showed that the interconnected pore networks were more favorable to cell attachment than the anisotropic ones. The capacity of highly oriented foams to support in vivo peripheral nerve regeneration was studied in rats. A sciatic nerve gap of 5-mm length was bridged with a polymer implant showing macrotubes of 100 microm diameter. At 4 weeks postoperatively, the polymer implant was still present. It was well integrated and had restored an anatomic continuity. An abundant cell migration was observed at the outer surface of the polymer implant, but not within the macrotubes. This dense cellular microenvironment was found to be favorable for axogenesis.

Studies on nerve cell affinity of chitosan-derived materials

Reparation of the central nervous system (CNS) is important because when it is impaired its recovery is difficult and concomitant malfunction of other parts of body occurs. In our previous studies, chitosan was found to be a good material supporting nerve repair. The purpose of this article was to study the ability of chitosan and some chitosan-derived materials to facilitate the growth of nerve cells. Those materials were chitosan, glutaraldehyde-crosslinked chitosan, glutaraldehyde-crosslinked chitosan-gelatin conjugate, a chitosan-gelatin mixture, chitosan coated with polylysine (CAP), and a chitosan-polylysine mixture (CPL). Gelatin and polylysine were used as controls. After nerve cells (gliosarcoma cells and normal cerebral cells) were grown on those materials, their attachment, spread, and growth were observed. The adsorption of some extracellular matrix molecules such as laminin and fibronectin on the materials and the role the molecules play in nerve cell attachment and spreading were also studied by enzyme-linked immunosorbent assay and MTT method. We found that both CAP and CPL have excellent nerve cell affinity, defined as the ability to promote nerve cell to grow and function normally. Those two materials may be promising for the repair of the nervous system. Materials precoated with laminin, fibronectin, and serum were analyzed for their nerve cell affinity. Results suggest that after being precoated with laminin and fibronectin solution or serum, all material have better nerve cell affinity.

In vivo and in vitro degradation of poly[(50)/(50) ((85)/(15)(L)/(D))LA/epsilon-CL], and the implications for the use in nerve reconstruction

Nerve guides can be used for the reconstruction of peripheral nerve defects. After serving their function, nerve guides should degrade. p[(50)/(50) ((85)/(15)(L)/(D))LA/epsilon-CL] degrades completely within 1 year without the formation of a slow degrading crystalline fraction. Although the tensile strength (TS) of a p[(50)/(50) ((85)/(15)(L)/(D))LA/epsilon-CL] nerve guide is negligible after 2 months, nerve regeneration across a 1-cm gap in the sciatic nerve of the rat is faster and qualitatively better than after reconstruction using autologous nerve grafts. During degradation p[(50)/(50) ((85)/(15)(L)/(D))LA/epsilon-CL] swells, especially during the first 3 months. This can have a negative influence on the regenerating nerve. p[(50)/(50) ((85)/(15)(L)/(D))LA/epsilon-CL] nerve guides could only be used in the clinical situation in case of short nerve gaps (several mm) in small nerves (for instance digital nerves). Refinements will be needed to successfully reconstruct longer nerve gaps (several cm).

Facial nerve repair accomplished by the interposition of a collagen nerve guide

OBJECT

Facial nerve paralysis due to a surgical procedure or trauma is a frequently observed complication. The authors evaluated facial nerve repair achieved by the interposition of a collagen nerve guide.

METHODS

Ten cats were divided into three groups. Group 1 consisted of six animals in which a 5-mm facial nerve segment on one side was resected and replaced by a collagen tube that was sutured to bridge both nerve stumps. On the opposite side a 5-mm segment of facial nerve was resected, reversed 180 degrees, and sutured to the stumps as an autograft nerve. Group 2 consisted of two cats in which the collagen nerve guide was interposed on one side and the nerve on the other side was left intact. Group 3 consisted of two cats in which a reversed autograft nerve was placed on one side and the nerve on the other side was left intact. Histological, electrophysiological, and horseradish peroxidase labeling examinations were performed starting 3 weeks after surgery. Light and electron microscopic examinations of collagen tube-implanted specimens revealed a well-vascularized regenerated nerve. The electrophysiological study confirmed the recovery of electrical activity in regenerated axons. Horseradish peroxidase labeling also confirmed restoration of the whole facial nerve tract.

CONCLUSIONS

The collagen nerve guide shows great promise as a nerve conduit.

Poly(DL-lactide-epsilon-caprolactone) nerve guides perform better than autologous nerve grafts

The aim of this study was to compare the speed and quality of nerve regeneration after reconstruction using a biodegradable nerve guide or an autologous nerve graft. We evaluated nerve regeneration using light microscopy, transmission electron microscopy and morphometric analysis. Nerve regeneration across a short nerve gap, after reconstruction using a biodegradable nerve guide, is faster and qualitatively better, when compared with nerve reconstruction using an autologous nerve graft. Therefore, we conclude that in the case of a short nerve gap (1 cm), reconstruction should be carried out using a biodegradable nerve guide constructed of a copolymer of DL-lactide and epsilon-caprolactone.

Evaluation of functional nerve recovery after reconstruction with a poly (DL-lactide-epsilon-caprolactone) nerve guide, filled with modified denatured muscle tissue

The aim of this study was to compare the speed of functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide, as filled with either modified denatured muscle tissue (MDMT) or phosphate-buffered saline (PBS). To evaluate both motor and sensory nerve recovery, walking-track analysis and electrostimulation tests were carried out after implantation periods, ranging from 3-15 weeks. Functional nerve recovery after reconstruction of a 15-mm nerve gap, with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with modified denatured muscle tissue, was slightly faster, compared with nerve reconstruction of a 10-mm gap with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with PBS. We conclude that our experiments have demonstrated that the use of MDMT increases the speed of recovery after reconstruction of a nerve gap with a p(DLLA-epsilon-CL) biodegradable nerve guide. Furthermore, the use of MDMT might open perspectives for repair of longer nerve gaps.

Influence of glial growth factor and Schwann cells in a bioresorbable guidance channel on peripheral nerve regeneration

Using an established rat peripheral nerve regeneration model, we investigated the role of glial growth factor (GGF) in nerve regeneration in combination with a novel bioresorbable poly(lactic-co-glycolic) acid (PLGA) guide in vivo. Schwann cells, established from a 1-cm segment of excised rat sciatic nerve, were isolated and seeded onto nerve guides with or without GGF (n = 24/group). Living nerve guides were re-established in these animals, and nerve regeneration was assessed over a period of 12 weeks. Histological studies revealed a reduction in the total axon count and the number of myelinated axons in the presence of exogenously added Schwann cells compared to saline controls. In contrast, the addition of GGF alone enhanced the total number of axons and significantly increased the number of blood vessels. Although combining GGF with Schwann cells negated the enhanced numbers of axons and blood vessels seen with GGF alone, this combination resulted in the highest myelination index and the fastest conduction velocities recorded. The PLGA guide material did not trigger any histologically detectable host response and was permissive for nerve regeneration in this animal model. The results from this study demonstrate the potential utility of this guide in vivo and establish a promotional role for GGF in nerve regeneration.

Biohybride nerve guide for regeneration: degradable polylactide fibers coated with rat Schwann cells

The restricted capacity of the nervous system to regenerate calls for novel therapeutic concepts. We have tested biocompatible polylactide fibers as potential nerve guides that could bridge proximal nerve stumps and synaptic target regions after nerve lesion. Polylactides have the great advantage that they degrade and resorb after completion of regeneration. Material surface properties were optimized three-fold by oxygen plasma treatment, polyanion coating and the seeding of Schwann cells from rat sciatic nerve. Immunocytochemistry and scanning electron microscopy revealed that in vitro axonal outgrowth of dorsal root ganglia on two specifically synthesized lactide polymers can be greatly improved by these surface treatments. The approach aims to develop an 'intelligent neuroprosthesis' that in vivo facilitates directed axonal regrowth in the first place and disappears thereafter.

Functional assessment of sciatic nerve reconstruction: biodegradable poly (DLLA-epsilon-CL) nerve guides versus autologous nerve grafts

The aim of this study was to compare functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with modified denatured muscle tissue (MDMT), or an autologous nerve graft. We evaluated nerve recovery using walking track analysis (measurement of the sciatic function index [SFI]) and electrostimulation tests. Functional nerve recovery after reconstruction with a biodegradable p(DLLA-epsilon-CL) nerve guide filled with MDMT was faster when compared with nerve reconstruction using an autologous nerve graft. We conclude that in case of a short nerve gap in the rat, reconstruction can best be carried out using a p(DLLA-epsilon-CL) biodegradable nerve guide filled with MDMT.

Long-term evaluation of functional nerve recovery after reconstruction with a thin-walled biodegradable poly (DL-lactide-epsilon-caprolactone) nerve guide, using walking track analysis and electrostimulation tests

This study was performed to evaluate the long-term functional nerve recovery after reconstruction of a 10-mm gap in the sciatic nerve of the rat, with a thin-walled nerve guide, composed of a biodegradable copolymer of DL-lactide and epsilon-caprolactone [p(DLLA-epsilon-CL)]. To evaluate both motor and sensory nerve recovery, walking track analysis and electrostimulation tests were carried out after implantation periods ranging from 3 to 52 weeks postoperatively. The first signs of both motor and sensory nerve recovery could be observed after 5 weeks. After 15 weeks, 70% of the sciatic function and 90% of the sensory nerve function had been recovered. After this period, the sciatic function index (SFI) did not improve further, whereas the sensory nerve function appeared to return to normal. When the results of the SFI measurements, minus those obtained from rats with severe automutilation, are extrapolated, further improvement of the SFI might be expected after 52 weeks. The fact that 100% sensory nerve recovery was obtained, as measured by the electrostimulation test, could be explained by sensory reinnervation from surrounding areas. The SFI was not fully reestablished because automutilation had a great impact on the use of walking track assessment.

Biocompatibility of a biodegradable in situ forming implant system in rhesus monkeys

Formulations of a polymeric delivery system containing a 75/25 poly(DL-lactide-co-caprolactone dissolved in either N-methyl-2-pyrrolidone or dimethyl sulfoxide were injected both subcutaneously (SC) and intramuscularly (IM) into rhesus monkeys. Each monkey received an SC and IM injection of each of the two formulations, for a total injection volume of 4 mL. The monkeys were observed daily for overt signs of toxicity, and after 4 weeks biopsies of each implant site were fixed, stained, and evaluated histologically for tissue reaction to the polymer system. Tissue response was graded upon the presence and level of fibrous connective tissue and inflammatory cell infiltrate. The polymer formulations appeared to be safe, as the animals remained healthy and active throughout the study with no changes in food or water consumption, weight loss, or abnormal behavior observed. Tissue response to both formulations was considered mild and similar to that for other biodegradable polymers, in that the reaction was limited to tissue immediately adjacent to the residual polymer fragments and consisted of a mild fibroplasia with the presence of a few lymphocytes and macrophages. There were no differences between the two formulations in tissue response, and both formulations were considered acceptable for use as injectable implant systems.

Facial nerve repair using a collagen conduit in cats

We evaluated facial nerve regeneration using a collagen tube as a nerve conduit in five cats. In three 5 mm of the facial nerve were resected, a collagen tube was implanted, and a 5 mm segment of the opposite facial nerve was resected, reversed 180 degrees, and sutured back as an autologous nerve graft. In one a collagen tube was implanted on one side, and in the remaining one a 5 mm nerve segment was reversed. Histological, electrophysiological, and horseradish peroxidase labelling examinations were carried out 4-24 weeks postoperatively. Histological study showed that the nerve was well vascularised and regenerated. Electrophysiological examination confirmed the recovery of evoked electromyograms through to the regenerated axons. Horseradish peroxidase examination also confirmed restoration of the whole facial nerve. The collagen tube is an efficient nerve conduit.

Poly(alpha-hydroxyacids) for application in the spinal cord: resorbability and biocompatibility with adult rat Schwann cells and spinal cord

Future surgical strategies to restore neurological function in the damaged human spinal cord may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. We have studied the in vitro and in vivo degradability of various aliphatic polyesters as well as their effects on rat Schwann cells in vitro and on spinal cord tissue in vivo. In vitro, cylinders made of poly(D,L-lactic-co-glycolic acid) 50:50 (PLA25GA50) started to degrade at 7 days, compared with 28 days for cylinders made of poly(D,L-lactic acid) (PLA50). This faster degradation of PLA25GA50 was reflected by a much higher absorption of water. In vivo, after implantation of PLA25GA50 or PLA50 cylinders between the stumps of a completely transected adult rat spinal cord, the decrease in molecular weight of both polymers was similar to that found in vitro. In vitro degradation of poly(L-lactic acid) (PLA100) mixed with increasing amounts of PLA100 oligomers also was determined. The degradation rate of PLA100 mixed with 30% oligomers was found to be similar to that of PLA50. In vitro, PLA25GA50 and the breakdown products had no adverse effect on the morphology, survival, and proliferation of cultured rat Schwann cells. In vivo, PLA25GA50 cylinders were integrated into the spinal tissue 2 weeks after implantation, unlike PLA50 cylinders. At all time points after surgery, the glial and inflammatory response near the lesion site was largely similar in both experimental and control animals. At time points later than 1 week, neurofilament-positive fibers were found within PLA25GA50 cylinders or the remains thereof. Growth-associated protein 43, which is indicative of regenerating axons, was observed in fibers in the vicinity of the injury site and in the remains of PLA25GA50 cylinders. The results suggest that poly(alpha-hydroxyacids) are likely candidates for application in spinal cord regeneration paradigms involving Schwann cells.

Biodegradation and tumorigenicity of implanted plates made from a copolymer of epsilon-caprolactone and L-lactide in rat

Flat plates made from a copolymer of epsilon-caprolactone and L-lactide (P-CL-LA) [50:50 (w/w), molecular weight 1.62 x 10(5); 20 x 10 x 1 mm size] were subcutaneously implanted into 50 young, male Wistar rats (P-CL-LA group). After 24 months the plates had become a mass of small pieces, which were concentrated in an area of 3 x 2 x 1 mm. For comparison, 50 rats were implanted with medical-grade polyethylene plates (PE group) while another set of 50 rats was subjected to the same operation but without an implant (Sham Op group). Tumors arose in 25 rats from the P-CL-LA group: 24 were malignant mesenchymal tumors at the implant sites. In the PE group, tumors appeared in 16 rats (14 at the implant sites and two ectopically). The average tumor latency was 578+/-84 days in the P-CL-LA group and 452+/-102 days in the PE group. There was no difference in tumor incidence between the P-CL-LA and PE groups (p < 0.05). In the Sham Op group, two malignant tumors appeared over 2 years. Pathologically, these induced tumors arose from the inflammatory cells surrounding the degrading fragments of P-CL-LA within the tissue capsule. This indicates that relatively slowly degrading material can induce malignant tumors at a similarly high rate to nonabsorbable medical grade PE, at least in this animal model.

Measuring the progression of foreign-body reaction to silicone implants using in vivo MR microscopy

We used in vivo magnetic resonance (MR) microscopy to follow the growth of fibrous capsule as a foreign body reaction to silicone implants in rats. Anesthetized rats were imaged 1, 7, 14, and 28 days after silicone-coated MR imaging coils were sutured to their neck muscles. On the twenty-eighth day, rats were sacrificed and coils and adjacent tissues were removed en bloc and fixed in formalin, reimaged with MR, and sectioned for conventional histology. Three-dimensional (3-D) spin-echo [3DFT] acquisition gave in-plane resolution of 32 x 32 microns in vivo and 16 x 16 microns ex vivo. All MR images showed a diffuse band of elevated signal intensity between the silicone of the coil and adjacent tissue. The border of the hyperintense band was thin and not well defined at seven days post-implantation. From 7-28 days, the band showed relatively homogeneous signal intensity and its thickness increased 44% on the rectus muscle side and 78% on the subcutaneous side. The capsule thickness determined either by MR in vivo and ex vivo microscopy or conventional histology was not significantly different, and there was a significant correlation between thickness measurements among those methods. MR in vivo microscopy provides sufficient resolution and spatial information to serially evaluate the growth of the foreign body fibrous capsule over time, thus achieving greater accuracy and consistency in measurements.

In vitro nerve repair--in vivo. The reconstruction of peripheral nerves by entubulation with biodegradeable glass tubes--a preliminary report

Biodegradeable "controlled release" inorganic polymer glass tubes can be manufactured to fit the dimensions of any nerve and their rate of solubility can be adjusted to encompass the time taken for nerve regeneration. They have been used in a number of biological applications. The facial nerve was repaired in a group of five sheep by entubulation with biodegradeable glass tubes. The sheep were assessed 10 months after repair and compared with a similar sized group of normal sheep. It was found that while there was a reduction in the peak velocity of conduction in the repaired nerves and in the range of conduction velocities, the minimum conduction velocity was within normal limits. There was a diminution in all of the measured variables of nerve morphometry but in no case did this reach statistical significance. These findings are consistent with the view that regeneration of the nerves had taken place to a degree at least as effective as that seen in nerves of a similar size repaired by conventional means.

Long-term evaluation of degradation and foreign-body reaction of subcutaneously implanted poly(DL-lactide-epsilon-caprolactone)

The aim of this study was to evaluate the degradation and foreign-body reaction of poly(DL-lactide-epsilon-caprolactone) (PLA85CL50) bars. This specific biomaterial is used for the construction of nerve guides, which can be used in the reconstruction of short nerve gaps. Subcutaneously implanted PLA85CL50 bars were harvested after implantation periods ranging from 3 to 12 months and evaluated for the rate of degradation and the degree of foreign-body reaction. It was observed that this copolymer degraded completely within 12 months and that no lactide or epsilon-caprolactone crystals were formed. Furthermore, we conclude that the foreign-body reaction of PLA85CL50 is very mild. These properties make the amorphous copolymer of DL-lactide and epsilon-caprolactone (50:50) suitable for the construction of nerve guides.

Light-microscopic and electron-microscopic evaluation of short-term nerve regeneration using a biodegradable poly(DL-lactide-epsilon-caprolacton) nerve guide

The aim of this study was to evaluate short-term peripheral nerve regeneration across a 10-mm. gap, using a biodegradable poly(DL-lactide-epsilon-caprolacton) nerve guide, with an internal diameter of 1.5 mm and a wall thickness of 0.30 mm. To do so, we evaluated regenerating nerves using light microscopy, transmission electron microscopy and morphometric analysis after implantation of 12-mm nerve guides in the sciatic nerve of the rat. Evaluation times ranged from 3-10 weeks. Three weeks after reconstruction, myelinated nerve fibers could be observed in the distal nerve stump. Ten weeks after reconstruction, the regenerating nerves already resembled normal nerves. In conclusion, we show that poly(DL-lactide-epsilon-caprolacton) nerve guides can be successfully applied in the reconstruction of severed nerves in the rat model. Furthermore, we have observed the fastest nerve regeneration described thus far, after reconstruction using a biodegradable nerve guide.