Chemical and Biomolecular Engineering - Theses
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ItemNovel biocompatible and biodegradable poly(ethylene glycol)- based scaffolds for soft tissue engineering( 2013)The development of new three-dimensional (3D) biocompatible constructs with improved properties for tissue regeneration is central to advances in the field of tissue engineering. Materials of natural and synthetic origin have been widely investigated for the production of tissue engineering scaffolds via various fabrication methods. Continuing research aims to fabricate scaffolds that possess the important properties of biodegradability, biocompatibility, mechanical integrity, and minimal immunogenicity. Achieving this objective is generally quite difficult since these properties are often dependant on each other and tailoring one property often compromises the other. In this research, we have employed novel synthetic approaches utilising epoxy/amine and acid chloride/alcohol chemistries to prepare poly(ethylene glycol) (PEG)-based scaffolds that are biocompatible and biodegradable, and possess excellent mechanical integrities, making them suitable for various soft-tissue engineering applications. Initially ultrathin Chitosan-PEG hydrogel films (CPHFs) were prepared using epoxy-amine chemistry via diepoxy functionalised PEG, chitosan amines and the co-cross-linker cystamine. The resultant films were very robust and possessed desirable biocompatible and biodegradable properties while supporting the attachment and proliferation of corneal endothelial cells (CECs). To eliminate the issues associated with the use of naturally sourced polymers, we were able to subsequently develop fully synthetic 50 μm thin PEG hydrogel films (PHFs). Acid chloride/alcohol chemistry, together with a facile fabrication method was utilised to produce the PHFs. PHFs were found to possess excellent tensile properties and promoted the in vitro attachment and proliferation of corneal endothelial cells with natural morphologies. In vitro degradation and cytotoxicity studies demonstrated the biodegradable and non-toxic characteristics. In an in vivo ovine model, the hydrogel films adhered naturally onto the interior corneal surface while displaying neither toxicity nor immunogenicity. The PHFs did not hinder the function of the native corneal endothelium, demonstrating their suitability for implantation. To further exploit acid chloride/alcohol chemistry, 3D porous PEG sponges and scaffolds were produced via novel gas foaming, and salt-templating techniques respectively. The rapid exothermic reaction and the HCl gas production results in the formation of highly porous polyester PEG sponges (PPSs), while a salt template was utilised to control pore sizes to produce the hydrogel scaffolds (SPHs). Both PPSs and SPHs possessed excellent mechanical integrities and demonstrated biodegradability and minimal toxicity in vitro. In vivo studies revealed complete infiltration of PPSs and SPHs with vascular tissue within 8 weeks. The porous scaffolds have minimal immunogenicity, and non-toxicity as demonstrated by an in vivo rat model, and can undergo complete degradation to non-toxic products by 16 weeks. The novel PEG hydrogel films and porous scaffolds demonstrate highly desirable physico-chemical properties with excellent biocompatible responses in vivo. Encompassing all the desirable properties of biocompatibility, biodegradability, mechanical integrity and complete tissue integration in vivo, the fabricated scaffolds are excellent candidates for advanced soft-tissue engineering applications.