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Title: Fabrication and characterization of polymer-hydroxyapatite nanocomposites for bone tissue engineering
Other Titles: Gu zu zhi gong cheng ju he wu-qian ji lin hui shi na mi fu he cai liao de zhi bei yu biao zheng
Authors: Li, Kai ( 李凱)
Department: Department of Physics and Materials Science
Degree: Doctor of Philosophy
Issue Date: 2010
Publisher: City University of Hong Kong
Subjects: Hydroxyapatite.
Biomedical materials.
Polymeric composites.
Nanocomposites (Materials)
Tissue engineering.
Bone regeneration.
Notes: CityU Call Number: R857.M3 .L5 2010
xv, 183 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2010.
Includes bibliographical references.
Type: thesis
Abstract: Hydroxyapatite (HA) with a chemical structure of Ca10(PO4)6(OH)2 is a major component and an essential ingredient of normal bone and teeth. Synthetic HA is commonly used as a filler material for conventional polymer composites due to its excellent biocompatibility and bioactivity. Polyethylene-HA composite (HAPEXTM) filled with 40vol% HA microparticles has been used for orbital floor prosthesis, middle ear implant and maxillofacial surgery. HAPEXTM is restricted to such orthopedic applications due to its low mechanical strength. Accordingly, much effort has been devoted to the development of polymer composites with good biocompatibility and mechanical strength close to that of human cortical bones. Recent advances in nanotechnology offer unique opportunities to develop nanostructured materials for biomedical applications. Bone tissue is a natural composite consisting of HA nanocrystals embedded in the collagen fibrils. The incorporation of HA nanofillers into the polymer matrix can mimic closely the structure of human bones. In this study, HA nanomaterials (nano-HA) of different morphologies were synthesized using polymer assisted sol-gel and micelle-hydrothermal techniques. The structure and properties of synthesized products were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). XRD and FTIR results indicated that the synthesized products exhibit typical diffraction peaks and characteristic vibration bands of HA. Nano-HA synthesized from the sol-gel method displayed spherical morphology with diameters ranging from 50-70 nm. And nano-HA prepared via micelle template synthesis had a rod-like feature. Furthermore, simulated body fluid (SBF) immersion test revealed that both nano-HA materials exhibit good bioactivity due to the ease of apatite layer formation on their surfaces. Commercially available HA nanorods (nHA) with an average aspect ratio of 6 were selected as nanofillers for high density polyethylene (HDPE), polypropylene (PP), polyamide-6 (PA6) and polyetheretherketone (PEEK). The main objectives of this study were to investigate the structure, thermal and mechanical properties as well as bioactivity of polymer/nHA nanocomposites. Nanocomposites with polymer matrices based on HDPE, PP and PA6 were prepared by melt-compounding while the PEEK/nHA nanocomposites were fabricated using thermal sintering process. Tensile tests showed that the additions of low filler content improve the tensile modulus and yield strength at the expense of tensile ductility and impact strength. However, the tensile strength and stiffness of HDPE/nHA and PP/nHA nanocomposites are much lower than those of cortical bones. This is due to the low tensile strength of polyolefins. On the other hand, PA6 and PEEK based nanocomposites exhibit tensile strength close to that of cortical bones. The high tensile strength of PA/nHA nanocomposites derives from strong interfacial interactions between the polymer matrix and nHA. The main disadvantage of PA/nHA nanocomposites for orthopedic applications is the high moisture absorption of PA6. Thus only PEEK/nHA nanocomposites with high mechanical strength are promising load bearing materials to replace defective bones. In vitro SBF immersion and osteoblast cell culture tests were used to assess the bioactivity of polymer/nHA nanocomposites. In general, apatite mineral crystals and mouse osteblasts can be deposited, attached and proliferated on these nanocomposites, particularly for those with higher nanofiller content. These results imply excellent bioactivity of the polymer/nHA nanocomposites.
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