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Final Report Summary - NERVEREGENERATION (Nerve guidance channels based on synthetic polymer – polysaccharide biomaterials)

Current strategies to repair damaged axonal pathways in peripheral nervous system (PNS), besides autologous nerve grafts that is a gold standard procedure, have concerned the application of bridging techniques that guide axonal regeneration across the lesion site. ‘NerveRegeneration’ IRG project of Marie Curie actions within 7th Framework Programme is focused on the development and evaluation of a series of novel guide channels based on biocompatible and biodegradable polymers for PNS regeneration. The goal of the ‘NerveRegeneration’ project was to develop novel polymeric materials of natural and synthetic origin to be constituents of nerve guidance channels, and analyse those biomaterials and the manufactured tubes through physical-chemical evaluation as well as in vitro biocompatibility. Optionally in vivo studies were considered. Main objectives of the project were as follows: 1. Develop novel synthetic polymer and polysaccharide derivative based biomaterials; 2. Investigate influence of irradiation on those biomaterials – radiation is used as a fabrication technology and as a sterilization tool; 3. Develop fabrication method of guidance channels with improved biocompatibility and optimal biodegradability for efficient peripheral nerve reconstruction. Materials chosen for development of nerve guidance channels included SP (synthetic polymer) and polysaccharides and its derivatives (PSC). Several PS, their blends and copolymers underwent extensive examination with respect to the proposed application, and their suitability to radiation sterilization. Selected PSC, such as hyaluronic acid, derivatives of cellulose and chitosan were investigated as potential candidates for admixture to SP or as an internal scaffold of the conduits. SP materials of synthesized in-house poly(trimethylene carbonate) (PTMC), poly(L-lactic acid) (PLLA) and methyl cellulose (MC) were utilized for production of the conduits. Alternatively SP tube was filled with hydrogel formed in situ through crosslinking of CMCS chains during radiation sterilization. These two approaches are presented in the schemes below. In either case the tubes combine sufficient strength, mainly due to presence of PLLA constituent, and high flexibility because of PTMC rubbery-like polymer.

Two methods of manufacturing of nerve guidance channels were proposed and consequently developed. METHOD1 was based on cyclic phase separation/precipitation of polymer or polymer blend from its solution deposited on a stainless steel bar in a non-solvent. METHOD1 allows for production of the tubes without utilisation of sophisticated equipment, yet resulting tubes combine considerable mechanical strength and high flexibility. Inclusion of PSC was possible in situ during production. METHOD2 is based on spraying of PS solution (addition of PSC is possible) onto rotating stainless steel bar that controls inner diameter of the resulting conduit. METHOD2 is efficient and obtained tubes have very reproducible properties. Utilization of both methods resulted in production of channels of tailored porosity and mechanical performance. Extraction of integrated water-soluble PSC allow for controlling porosity and shows potential for releasing bioactive molecules such as NGF, which can be incorporated in the tube walls, directly in the vicinity of regenerating nerve. Internal filling/scaffold may be a carrier of nerve growth factors as well. In this case, manufacturing and sterilisation of the conduits can be followed by inclusion of NGF. It is anticipated that axons can grow inside the hydrogel, which provides 3D support, and if the gel contains NGF, the regeneration of injured nerve will proceed more effectively.

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