Processing and properties of bone-analogue biodegradable and bioinert polymeric composites

This paper summarizes the processing and properties of bone-analogue composites aimed to be used in temporary or permanent orthopaedic applications. The studied matrices were two biodegradable starch based blends (with ethylene-vinyl alcohol copolymer or with cellulose acetate) and three high density polyethylene (HDPE) grades. Composites of these materials with hydroxyapatite (HA—the main inorganic constituent of the human bone) were produced by extrusion compounding and subsequently injection moulded. A non-conventional injection moulding technique known as shear controlled orientation in injection moulding (SCORIM) was used deliberately to induce a strong anisotropic character to the processed composites. For the case of HDPE based composites, an alternative reinforcement system based on carbon fibres (C fibres) was also studied. For that, a special moulding technique that combines, in a single equipment, a compounding with an injection unit was used. Composites featuring a sandwich like structure were also produced by mono-sandwich injection moulding. These composites combine a HDPE/HA outer layer and HDPE/C fibre reinforced core. The aim is to produce composites with a mechanical behaviour matching that of human cortical bone and simultaneously a strong bioactive (bone-bonding) character. For all the cases, the mechanical performance of the produced composites was assessed and the structure developed investigated and related to the processing conditions. It was possible to produce, both biodegradable and bioinert matrix composites, with properties that might allow for their application in the orthopaedic field.