Stimulation of Biological Function With Bioactive Glass

Abstract

An estimated 11 million people in the United States have at least one medical-device implant. Orthopedic implants account for 51.3% of all implants. They include fixation devices (usually fracture fixation) and artificial joints, used in 77% and 23% of the cases, respectively. Among the joint-replacement procedures, hip and knee surgeries represent 90% of the total and in 1988 were performed 310,000 times in this country. Currently more than half the joint-reconstruction devices are used with bone cement, which is a polymer grout that keeps the prosthesis components in place in the bone. The fixation in the other cases depends on the bone's ability to grow in contact with the device. This can be achieved by making the prosthesis surface porous such that bone grows into interstices or by making the surface chemically reactive with bone tissue such that a continuous, uninterrupted transition is formed from tissue to device. Bioactive glasses (BGs) and ceramics are the materials of choice to achieve this effect on bone-tissue bonding. Bone-growth stimulation is also sought in the treatment of difficult fractures. In the United States alone, there are 1.23 million fractures that require a bone plate. Of that total, approximately 1 million require between 10 cm3 and 100 cm3 of graft material to stimulate bone repair. At this time, autogenous bone graft represents the gold standard: This graft is typically bone tissue taken from the patient's own pelvic bone. Given the morbidity associated with this procedure and the frequently insufficient quantities available, extensive efforts for suitable alternatives are currently under way. Calcium phosphate ceramics and glasses, either by themselves or as carriers for bone (or “osteogenic”) cells or various bone-growth factors, are also prime candidates for these applications.