Bone repair in the twenty-first century: biology, chemistry or engineering?

Increases in reconstructive orthopaedic surgery, such as total hip replacement and spinal fusion, resulting from advances in surgical practice and the ageing population, have lead to a demand for bone graft that far exceeds supply. Consequently, a number of synthetic bone-graft substitutes (BGSs) have been developed with mixed success and surgical acceptance. Skeletal tissue regeneration requires the interaction of three basic elements: cells, growth factors (GFs) and a permissive scaffold. This can be achieved by pre-loading a synthetic scaffold with GFs or pre-expanded cells; however, a 'simpler' approach is to design intrinsic 'osteoinductivity' into your BGS, i.e. the capability to recruit and stimulate the patient's own GFs and stem cells. Through investigation of the mechanisms controlling bone repair in BGSs, linking interactions between the local chemical and physical environment, scientists are currently developing osteoinductive materials that can stimulate bone regeneration through control of the scaffold chemistry and structure. Moreover, this body of research is providing the foundations for future generations of BGSs and bone-repair therapies and may ultimately contribute towards improving the quality of life through maintenance of the skeleton and reversal of disease states, as opposed to the mending of broken bones that we currently practice. Will we be able to grow our own bones in a bioreactor for use as autologous graft materials in the future? Could surgery be limited to accidental trauma cases, with greater restoration of function through biochemical or gene therapies? The technology and research probes necessary to this task are currently being developed with the advent of nanotechnology, genomics and proteomics: are we about to embark on a chemical revolution in medicine? This paper aims to discuss some of the current thinking on the mechanisms behind bioactivity and biocompatibility in bone and how a fuller understanding of the interactions between cells and the materials used today could bring about completely new approaches for the treatment of bone fracture and disease tomorrow.