The objective of this research project is to create a novel, synthetic, biocompatible osteogenic bone substitute having mechanical properties similar to cortical bone. Every year in the U.S. alone, approximately 100,000 bone grafts are performed. Applications for bone substitutes include massive bone loss from neoplasia, comminuted fracture repair, spinal surgery, and fracture treatment in the elderly. The model bone substitute is 1) osteogenic (direct bone formation via transplanted live bone cells called osteoblasts), 2) osteoinductive (the ability to recruit bone forming cells), 3) osteoconductive (the scaffold supports bone in-growth), 4) mechanically stable (able to carry the load of the natural bone) and 5) readily available. Both the limited supply and diminished properties of autografts and allografts have led researchers on a quest for an optimum synthetic bone substitute. Because the mineral content of bone has a composition and crystal structure closely matching hydroxyapatite (HA), it is natural to first turn to bioceramics such as HA-based materials for bone implants. While dense bioceramics do not exhibit osteogenic or osteoinductive properties, HA is osteoconductive. When using HA, the surgeon is faced with a trade-off between the mechanical strength provided by dense ceramics, and the biological incorporation (bone in-growth) provided by porous ceramics. The lack of mechanical strength in combination with the ability to support bone in-growth has prevented HA, or any other bioceramic, from receiving wide spread acceptance as a cancellous or a cortical bone substitute. The research project uses Professor Crimp's background in ceramic processing to create a strong, yet porous HA-based bone substitute where osteogenic and osteoinductive properties are added by in vitro culture of these synthetic bone scaffolds with osteoblasts following protocols developed by the co-PI, Professor McCabe. HA whisker reinforced porous HA and biphasic calcium phosphate (BCP) ceramics will be fabricated using a modified foaming technique. BCP is a mixture of HA and beta-tri-calcium phosphate and is currently receiving attention as a potential bone substitute material. Of fundamental significance is the understanding of the linkages between bioceramic processing and the in vivo behavior by looking at osteoblast adhesion in vitro.
This research project will concentrate on tailoring the processing protocol for whisker reinforced ceramic materials for use as bone replacements to yield improvements in strength, at a fixed porosity level matching that of human cortical bone, while maintaining the inherent biocompatibility of the implant materials. These implants will be the only viable synthetic alternative (because of improved mechanical and osteogenic properties) to currently available graft materials for repair of damaged cortical bone tissue.
