Using Nonconventional Processing to Develop Anisotropic and Biodegradable Composites of Starch-Based Thermoplastics Reinforced with Bone-Like Ceramics

he development of polymer-matrix composites with sufficient mechanical properties may allow for an entirely new range of small-load-bearing biomedical applications for these systems. By combining polymers with bioactive ceramics, researchers hope to overcome the mismatch of mechanical properties that currently exists between bioceramics and natural loadbearing tissues. 1 The problem is that polymers by themselves are very ductile but not rigid enough, whereas ceramics are too stiff and brittle. The ideal material must evidence the best possible stiffness/ductility compromise, matching the modulus of bone but retaining some of the ductility of the composite matrix. A method of developing such a material should be based on trying to copy the structure (including anisotropy) and mechanical properties of bone, while at the same time ensuring that the material, once implanted, will exhibit a bioactive behavior. Composites of polyethylene reinforced with hydroxylapatite (HA) (initially developed by W. Bonfield et al.2,3) have recently become commercially available (HAPEX, Smith & Nephew ENT, Memphis, TN) and are already being used in the production of middle-ear implants and for orbital floor reconstruction.3 However, these systems do not yet exhibit properties that allow their use in load-bearing applications. Furthermore, the processing methods that have been assessed with the aim of increasing the materials’ mechanical performance—techniques such as hydrostatic extrusion—are not suitable for the production of materials with the thick cross sections and complex shapes typical of load-bearing implants. 4,5