Overview

Bone, at the ultra-structural level, is a composite with mechanical properties that can be matched by man-made composites. It serves as the template for developing bone replacement materials. Research on biomaterials analogous to bone was started in the early 1980s by incorporating bioactive particles into biocompatible polymers in order to produce bone substitutes. Hydroxyapatite reinforced high-density polyethylene (HA/HDPE) is one of such materials and has been successfully used in human bodies. In this chapter, the structure and mechanical properties of bone are firstly reviewed. The production, structure, properties of HA/HDPE composites are then presented. Their biological performance is discussed subsequently, and examples of their clinical applications are given. Using the same or similar manufacturing processes, other bioactive composites have also been developed for tissue substitution or tissue regeneration.

8.1 Introduction

Numerous materials have been used for bone substitution ever since plaster of paris was tried for bone repair in the 19 ^th century. In modern-day orthopedic surgery, metals (such as stainless steel and titanium alloy) and ceramics (such as alumina and toughened zirconia) are common in a variety of implants and devices. However, these materials, having been developed originally for other purposes rather than medical applications, are considerably stiffer than human bone. The modulus mismatch between an implant material and the host tissue can cause bone to resorb at the bone-implant interface, which leads to implant instability...