Developing bio-stable and biodegradable composites for tissue replacement and tissue regeneration

Abstract

Bone is the substantial unit of human skeletal system, which supports the body and its movement. At the ultra-structure level, the bone matrix is a composite material consisting of bone mineral particles, which are mainly substituted, calcium-deficient hydroxyapatite, and collagen, which is a natural polymer. Bone 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 so as to produce bone substitutes. Over the last two decades, a variety of bioactive polymer matrix composites have been developed for tissue substitution and tissue regeneration. The bioactive phases in these composites are normally one of the calcium phosphates, especially synthetic hydroxyapatite (HA, Ca10(PO4)6(OH)2) which closely resembles bone apatite and exhibits osteoconductivity. If enhanced bioactivity is required, bioceramics having higher bioactivity such as Bioglass® and A-W glass-ceramic can be used as the bioactive phase in the composites. For tissue replacement, bio-stable polymers such as polyethylene (PE) and polysulfone (PSU) are used as the matrix polymer. For tissue regeneration, natural, biodegradable polymers such as polyhydroxybutyrate (PHB) and chitin are used as matrices. Furthermore, mechanical as well as biological performance of a particular composite can be controlled by varying the amount of the bioactive phase in the composite, thus meeting specific clinical requirements. For bioactive ceramic-polymer composites, major influencing factors such as shape, size and size distribution of bioactive particles, mechanical properties and volume percentage of the bioactive phase, properties of the matrix polymer, distribution of bioactive particles in the matrix and the particle-matrix interfacial state should be controlled in order to obtain materials of desirable properties. Various techniques are used to evaluate the composites.