ABSTRACT
One of the key issues identified in the failure of orthopedic implants has been the problem of insufficient tissue regeneration (i.e., lack of bioactivity) around the biomaterial immediately after implantation. This has motivated researchers to develop various bioactive composites with bone-mimicking properties for faster bone regeneration as well as to eliminate the problem of elastic modulus mismatch and stress shielding of the implant. The composite approach provides us the flexibility to manipulate such properties as strength, electrical conductivity, and modulus of the composites close to that of natural bone with the addition of second phases [1-3]. Hydroxyapatite (HAp) is the most well-known bioactive ceramic that has evolved in the most significant manner during the last few decades. Despite good bioactivity properties, the inherent brittleness of HAp has triggered widespread research activities to enhance fracture toughness by strengthening HAp with various reinforcements, like alumina and zirconia [4, 5]. Despite many years of research, the toughness of HAp composites could be enhanced to around 5 MPa⋅m0.5 only lately in HAp-Ti systems [6]. However, in many of these cases [1-5], the concern regarding the elastic modulus mismatch resulting in stress shielding was not addressed or solved.
