Biomedical materials for new millennium: perspective on the future

Abstract Millions of orthopaedic prostheses made of bioinert materials have been implanted with an excellent 15 year survivability of 75–85%. Improved metal alloys, special polymers, and medical grade ceramics are the basis for this success, which has enhanced the quality of life for millions of patients. However, an increasing percentage of our aging population require greater than 30 years survivability of the devices. It is proposed that to satisfy this growing need for very long term orthopaedic repair a paradigm shift is needed; a shift in emphasis from the replacement of tissues to the regeneration of tissues. Such a shift from a materials and mechanics approach to tissue repair requires an increase in the understanding and utilisation of biologically approaches. Two new biologically orientated alternatives in biomaterials for orthopaedics in the new millennium are discussed: tissue regeneration, where in situ repair is initiated in the host tissue, and tissue engineering, where repair is initiated in vitro on cellularly seeded scaffolds and then transplanted to the recipient. The concept of the use of class A bioactive materials to stimulate the regeneration of trabecular bone is described along with clinical applications. Eleven reaction stages lead to the enhanced proliferation and differentiation of osteoblasts and the recreation of trabecular bone architecture. Recent results showing the effects of microchemical gradients on the genetic activation of bone cells are related to the molecular design of hierarchical bioactive resorbable scaffolds for the tissue engineering of bone constructs.