Author: Meng, Yanhua
Title: Development of calcium phosphate bioceramic composites for load-bearing application
Degree: Ph.D.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Hydroxyapatite -- Biocompatibility.
Bioactive compounds -- Biotechnology.
Department: Department of Industrial and Systems Engineering
Pages: xiii, 175 leaves : ill. ; 30 cm.
Language: English
Abstract: Hydroxyapatite (HA) ceramic has attracted much attention due to its superior biocompatibility and bioactivity as a substitute material in bone grafting. HA has a superior bioactivity such that chemical bonding can be generated on the interface between HA implants and natural bones. However, its clinical applications are limited to free of high load-bearing situations due to its poor mechanical strength. In this project, nano-HA ceramic composites with improved mechanical strength and comparatively high bioactivity were fabricated for different load-bearing applications in bone tissue engineering. Nano-sized HA particles were synthesized in the first step to mimic HA in natural bone. A new synthesis method of nano-size needle-like HA particles was developed. Ultrasonic vibration was introduced in the co-precipitation synthesizing process, which provided more nucleation energy for the HA crystals, improved the nucleation density and consequently refined the HA crystals. Surfactant cetyltrimethyl-ammonium bromide (CTAB) was introduced in the fabricating process to improve dispersing properties and control the growing direction of nano-size HA crystals. Nano-size needle-like HA particles were fabricated with the aid of ultrasonic vibration and surfactant. Multi-wall carbon nanotubes (MWNTs) were chosen as the reinforcing phase to enhance the strength of nano-HA ceramics due to their unique mechanical properties and superior biocompatibility. In this study, the surfaces of MWNTs were modified to improve the dispersion property. An improved dispersion of the surface modified MWNTs in the HA matrix was achieved. The flexural strength and toughness of the fabricated nano-HA-MWNT composites with 7vol% MWNTs reached 103MPa and 1.28 MPa·m1/2, which were improvement about 34% and 51% compared with those of unmodified HA ceramics. HA-ZrO2-MWNT composites were designed and fabricated to further improve the mechanical strength of HA ceramics. The flexural strength and the toughness of the HA-ZrO2-MWNT composites reached 183 MPa and 2.20 MPa·m1/2 which were close to those of cortical bone (flexural strength: 50-150MPa, toughness: 2-12MPa·m1/2), when the volume percentages of the reinforcing phases of ZrO2 and MWNTs were 27vol% and 7vol%, respectively. The in-vitro method was used to test the bioactivity of the composites. The surfaces of the HA-MWNT samples were covered by a new growth layer after immersion for 3 days. The EDX results showed that the covered layer was calcium phosphate material. The results indicated that both HA-MWNT and HA-ZrO2-MWNT composites had comparatively high bioactivity. The mechanical and biological properties of the HA composites can be designed according to certain application requirements. Finite element models were constructed to study the reinforcing effects of MWNTs. In addition, a load bearing case for a dental implantation was also studied using the finite element method to explore the applicability of the HA composites. To conclude, nano HA composites with improved mechanical strength that can be used in load-bearing conditions were fabricated. The achievements of the present project can improve the quality of implants for hard tissue surgery in load bearing conditions. The new reinforcing method with multi-phase and multi-shape reinforcing phases can also be used as a reference in the design process for other composites.
Rights: All rights reserved
Access: open access

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