Manipulating biofunctionalized electrospun scaffolds with designed architectural features for the regeneration of the central nervous system

Abstract

With the increasing applications of electrospun scaffolds in neural tissue engineering, this thesis focused on the architectural designs and biofunctionalization of electrospun scaffolds for neural tissue engineering applications. The aim of this thesis is to develop an understanding of the cellular responses to scaffolds for the treatment of trauma and neurodegeneration within the central nervous system. In the first part of this thesis, 3D non-woven polystyrene nanofibres were produced by the electrospinning process in order to provide a non-biodegradable and robust platform to investigate the relationship between fibre alignment and neurite extension. The process of electrospinning was optimized to manipulate ultrafine polystyrene nanofibres. The introduction of a cationic surfactant, DTAB, eliminated beads-on-string structure yielding uniform diameter PS nanofibres. Fibre diameter was affected by polymer concentration. An ascending linear relationship was established between PS concentration and electrospun PS diameters. Different aligned PS scaffolds were readily collected via adjusting the rotating speed of the collecting mandrel PS fibre alignment influenced the direction of neurite outgrowth. Both parallel and perpendicular contact guidance were observed on highly and partially aligned PS nanofibres; however, the primary neurites exhibited no preferred extension on randomly oriented PS nanofibres with little processes. Laminin was adsorbed on the PS nanofibres in order to supply the combined biological and architectural cues. The administration of laminin changed the mechanism from perpendicular to parallel contact guidance. These findings suggest the possibility of controlling neurite extension by modifying the alignment of PS nanofibres. The second part of the thesis examined the effect of electrospun PCL on pathology and healing processes via implanting the scaffolds in the CPu of adult rats. The ultrafine PCl nanofibrous scaffolds were manipulated using electrospinning with various alignments. Typical inflammatory responses were observed surrounding the implantation of these electrospun PCl scaffolds, with an increasing thickness of accumulated reactive astrocytes surrounding the implanted scaffolds. There was no axonal outgrowth within the scaffolds. The nanofibre topography research illustrates that aligned electrpsun PCL nanofibres might slow down the activation of astrocytes. However, the alignment had limited effects on cell proliferation or apoptosis. Thesis findings suggest that the reactive astrocytes might playa key role in prohibiting neurite penetration probably via physical and biochemical cues. However altering and optimizing the morphology of electrospun nanofibres may provide a controllable platform to regulate the levels of inflammatory responses. In the last part of this thesis, neurotropic factors (BDNF/GDNF) and an ECM protein (laminin) were covalently immobilized on the PCL scaffolds in order to facilitate reinnervation as well as suppress inflammatory responses via the co-operation of physical and biological cues. The administration of these proteins indeed reduced the inflammatory responses compared to that of the unmodified scaffolds in part 2. Significant astrocytic responses were suppressed with the administration of BDNF/GDNF/laminin, with a narrower glial scar observed. All these proteins facilitated cell proliferation. However, no evidence of neurite infiltration was observed in our experiments probably due to the physical barriers that hurdle the interactions between neurons and scaffolds or the excessive amount of BDNF/GDNF/laminin that switched off neurite regeneration and sprouting. These results indicate that the immobilization of these proteins could be beneficial to modulate the endogenous immune response to scaffold implantation.