The design, construction and properties of hybrid inorganic/organic biomaterials

• Main Author: Akkarachaneeyakorn, Khrongkhwan
• Published: University of Bristol 2015
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686249

The central themes of this thesis are focused on the design, construction and properties of hybrid inorganic/organic soft composites. The aim of the first experimental chapter was to synthesize plate-like hydroxyapatite (HA) in the presence of amino acids. The morphological effects of alanine, arginine, proline, lysine and glycine on calcium phosphate crystallization at neutral pH was studied. While the platelet morphologies of the produced colloids were influenced by the octacalcium phosphate transformation effect at the synthesis pH of 7, the amino acids were found to influence the highly positive surface charge and the size of nanoparticles, i.e. increasing the size of the side chain generally produced a progressive decrease in size of HA. As-prepared HA/alanine nanoparticles were then used to fabricate composite electrospun mats in two polymeric systems, i.e. chitosan and gelatine. Whereas HA nanoparticles were dominantly found at the surface of the chitosan fibres, they were embedded within the gelatine fibres. This was resulted from the repulsion of positively charged nanoparticles and positively charged chitosan fibres. The second experimental chapter detailed studies on a polymer/surfactant miniemulsion system as a synthetic medium for amorphous calcium phosphate particles for controlling the structure and morphology ofthe inorganic phase. The calcium phosphate nanofilaments were initially obtained inside the droplets before being redissolved to form spherical amorphous calcium phosphate. The growth process of the materials also continued from the centre to form filamentous structure outside the droplets and lengthened with time up to 300 nm. Subsequently, P123/DEHP/calcium phosphate organogel was produced by slow evaporation of the organic solvent from the reaction system. The range of gel was also prepared by varying the amount of mineral contents. As increasing the amount of calcium and phosphate salts, the structure of gel was disrupted and became phase separated due to crystallization of inorganic material. The produced hybrid gel was then successfully used in proof-of-concept studies demonstrating it could be used for the in vitro occlusion of exposed dentine tubules in a bovine model of tooth hypersensitivity. The final chapter investigated the use of Pickering emulsions (colloidosome) to prepare microreactors in water with the ability to catalyse the in situ formation of a supramolecular hydrogel matrix. Alkaline phosphatase encapsulated silica colloidosomes were transferred to FMOC-tyrosine phosphate containing solution. Counter diffusion of the FMOC-tyrosine phosphate across the nanostructured silica membrane resulted in reaction with the entrapped enzymes inside the colloidosomes and the formation of a Fmoc-tyrosine based hydrogel. Subsequently, the hydrogel was transferred into the extra-protocellular environment via a dissolution-reprecipitation process (Ostwald ripening). The reversible disassembly/reassembly properties of the hydrogel were also investigated by heating and cooling. The hydrogel structure interestingly changed by forming bundle of hydrogel packed inside the microcompartments while the external long filaments disappeared due to the polymerisation of saturated Fmoc-TyrOH monomer after diffusion into the microcompartments