Biomechanical optimization of a model particulate composite for orthopaedic applications.

Particulate composites are a potential solution to the need for an injectable, biocompatible, resorbable material that could be used to reinforce fractures and defects in bone and temporarily to stabilize porous ingrowth prostheses. We have developed a model system for producing and testing particulate composites to determine if mechanical properties suitable for orthopaedic applications can be achieved. The experiments used bovine cortical bone and various forms of hydroxyapatite for the particulate phase and a collagen and particulate reinforce gelatin-resorcinol-formaldehyde (G-R-F) adhesive for the matrix phase. Using unconfined compression testing, we measured the effects of variation in particulate type, size, shape, and volume fraction on the material properties of the particulate composites. We found that compressive strengths greater than 10 MPa and compressive moduli greater than 100 MPa could be achieved in this model system. Rough and irregular particulates exhibited higher compressive strengths and moduli than smooth and spherical particulates. Mechanical properties were largely independent of particulate size in the range of 125-850 microns diameter. This model system suggests that, with the development of new biocompatible matrix materials, particulate composites with mechanical properties suitable for orthopaedic applications can be achieved.