Nerve Guidance Conduit Application Of Magnesium Alloys

Abstract

Surgery is insufficient for peripheral nerve injuries larger than 5 mm. Function loss and scar formation occur as a result of slow healing rate and inflammation cells filling the damaged gap. Therefore, isolation of damaged area from surrounding tissue is crucial for treatment. For this purpose, NGCs have increasingly gained interest both in literature and clinic. Biocompatibility, slow biodegradation and semi-permeable structure that allow oxygen/nutrition/waste transfer and prohibits inflammation cells are the main requirements for NGCs. Therefore, biodegradation rate and degradation product toxicity of the material and a fabrication method that provides porosity control are crucial. In the literature, fabrication of NGCs with low cost and easy to use methods by using polymers is widely studied. On the other hand, even though metals can provide higher mechanical strength and electrical conductivity, they are not preferred for NGCs since it is not possible to obtain micro-scale porosity by conventional methods. In this thesis, development of a magnesium alloy-like compound with a similar composition of a magnesium alloy widely studied in the literature for stent applications and obtained FDA approval, for the use of NGC applications was studied. Magnesium is an abundant element found in human body, with high nutritional value, low density, high specific strength, high electrical conductivity and low toxicity. Therefore, it was planned to achieve enhanced physical, chemical and biological performance by using magnesium based alloy-like compound for NGC. For the fabrication of the compound, instead of conventional approaches, electrospinning were selected due to its ease of use and porosity control capability, and the spinning was conducted with the nitrates of alloy components and polyvinylpyrrolidone or polyvinylalcohol used as raw materials of the solution. Solution parameters such as concentration, temperature and viscosity, and electrospinning parameters such as voltage, distance and feeding rate were optimized with naked-eye observations and SEM. Electrospun samples were then underwent a gas flow-temperature-time controlled calcination under argon atmosphere in order to crystallize the components into alloy-like compound and remove non-alloy components. The calcination profile containing multiple temperature and duration steps was designed according to the thermal analyses applied to electrospun samples where all possible endothermic and exothermic phase transformations such as glass transition temperature, melting temperature and crystallization temperature were measured and analyzed with mathematical reaction kinetics. The crystallographic structure, elemental composition and morphological properties of the calcinated samples as well as removal of non-alloy components were determined with XRD, EDX, SEM and XPS. Additionally, physical and chemical properties such as absorption/swelling capacity, wettability, permeability and degradation rate were obtained as a part of characterization studies. In the final stage of the thesis, the cell-material interaction of the developed NGC candidate material was examined with MTT assay, haemocytometric counting and several staining/imaging techniques in terms of cell viability, attachment, proliferation and growth using fibroblast cell line. The physical, chemical and biocompatibility data obtained in this thesis showed that the fibrous magnesium based alloy-like compound fabricated with electrospinning could be a potential candidate for NGC applications.