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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Further application of hydroxyapatite reinforced high density polyethylene composite - skull reconstruction implants

Author: ZHANG, Yu

Year: 2005

Supervisor(s): Liz Tanner

The present study is to develop a further application of HA-HDPE composite - as a skull reconstruction implant. The impact properties of the composites were investigated using an instrumented falling weight impact machine. The impact resistance of the composites increased with decreasing HA filler volume fraction. The composites with higher molecular weight polyethylene matrix have higher impact resistance than those with lower molecular weight HDPE. The fracture resistance was markedly improved when sintered grade HA particles with smooth surfaces were used to replace the spray dried grade HA with rough surface. It has been found that HA-HDPE1 composites with 30% or lower HA volume fraction have comparable impact toughness with that of human skull.

In vitro biocompatibility of HA-HDPE composite was assessed using two types of osteoblast (HOB) cells, respectively from skull bone and femoral heads. The effect of HA morphology on the cellular response, such as cell proliferation, differentiation, and cell morphology was investigated. The results showed that HA-HDPE composite is a bioactive material and supports normal growth of osteoblasts for both types of HOB cells. Osteoblasts showed better response cultured on the composite with rough HA filler than smooth one. Generally, osteoblasts from skull showed a slightly lower proliferation rate and slower expression of alkaline phosphatase, with a more spindle-like morphology than femoral HOB cells.

The study showed that 30vol.%HA-HDPE composite is compatible in both mechanical and biological characteristics with human skull. This material therefore shows potential for success as a skull implant. Based on human skull database, the skull plate for implant has been designed and manufactured using purposely designed compression mould.