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This dissertation, Selective laser sintering of poly(L-Lactide)/carbonated hydroxyapatite porous scaffolds for bone tissue engineering by Wenyou, Zhou, 周文友, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis titled Selective Laser Sintering of Poly(L-Lactide)/Carbonated Hydroxyapatite Porous Scaffolds for Bone Tissue Engineering Submitted by ZHOU Wenyou for the degree of Doctor of Philosophy at The University of Hong Kong in August 2007 The aim of this project was to investigate the feasibility of utilizing the selective laser sintering (SLS) technology to build 3D porous bone tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA) microspheres and poly(L- lactide)/carbonated hydroxyapatite (PLLA/CHAp) nanocomposite microspheres. Two major issues were addressed in this study: (1) preparation and characterization of PLLA and PLLA/CHAp nanocomposite microspheres to satisfy the SLS processing requirements; and (2) design and production of 3D porous scaffolds using a modified Sinterstation 2000 SLS machine to meet the mechanical, in vitro degradation and biological requirements for bone tissue engineering applications. Firstly, the nanoemulsion method was applied to synthesize carbonated hydroxyapatite nanospheres as the osteoconductive filler for building the nanocomposite tissue engineering scaffolds. The as-synthesized CHAp nanospheres were basically in an amorphous state, about 20 nm in size and tending to form tiny agglomerates. PLLA microspheres and PLLA/CHAp nanocomposite microspheres were prepared by the oil-in-water and solid-in-oil-in-water emulsion solvent evaporation procedures respectively. The resultant microspheres had a size range of 5 to 30 m, suitable for the SLS process. Microstructural analyses revealed that the CHAp nanosphere agglomerates were more or less evenly embedded throughout the PLLA microspheres, forming a nanocomposite structure. The effects of CHAp on the isothermal and non-isothermal crystallization behavior of PLLA were investigated. iv The CHAp nanoparticles acted as an efficient nucleating agent, thereby increasing the isothermal crystallization rate and decreasing the fold surface energy of PLLA. The effective activation energies for non-isothermal crystallization of PLLA and PLLA/CHAp as a function of the relative crystallinity and average crystallization temperature were obtained by the Friedman differential isoconversion method. Secondly, the custom-made miniature sintering platform allowed small quantities of the biomaterial powders to be processed in the modified SLS machine. With this platform, prototypes of bone tissue engineering scaffolds with porous structure were successfully built from the PLLA microspheres and PLLA/CHAp nanocomposite microspheres. The effects of laser power, scan spacing and part bed temperature on the scaffold structure were studied and eventually a set of recommended sintering parameters was obtained. SEM showed that the actual pore size was smaller than the design value due to the phenomenon of growth, which cannot be avoided entirely and should therefore be taken into account during the design stage. The PLLA/CHAp scaffolds exhibited a lower compressive yield strength and modulus than the PLLA counterparts sintered under similar conditions. This phenomenon was caused by the poorer fusion behavior of the nanocomposite powder due to its higher viscosity and molar heat capacity. The compression properties of both the PLLA and PLLA/CHAp scaffolds only matched those of human cancellous bone and could the

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