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There are many different materials currently available for cancellous bone grafting. There is however, very little information relating the morphology of these materials to cancellous bone. Work was undertaken to develop a quantitative method for comparing synthetic hydroxyapatite bone structures with cancellous bone. The bases for comparison were mean plate thickness, mean plate distance, mineral area fraction, mineral volume fraction and plate orientation coupled with mechanical tests. The aim of this work was to develop a protocol for assessing whether these critical parameters which influence the success of bone implants were achieved in the synthetic materials. The methodology is successful in providing quantitative information about the mineral area fraction, the mean plate distance or pore size and the intercept frequency as a function of angle. Combining these three provides a quantitative measure of how much mineral there is and how it is distributed and oriented. The mechanical tests yield strengths and moduli values based on apparent density. The results of the mechanical tests can also be plotted as functions of the more discrete structural features such as those quantified in the image analysis to allow for even more equitable and systematic comparisons of different porous materials.

There is increasing interest in the potential of composites of hydroxyapatite with phosphate- or silicate-based bioactive glasses, and certain of these glass additions have been found, in previous work, to aid densification and form a mechanically-reinforced, bioactive material; in particular, large improvements in flexural strength and fracture toughness were obtained through the addition of small amounts of phosphate glass. Less is known about the mechanical behavior of HA/bioglass composites, although in vivo studies by other workers have shown encouraging biological results. In this investigation, the sintering behavior, mechanical properties, and microstructure of composites of HA with up to 50 wt % glass, were analyzed. X-ray diffraction showed the phase composition of sintered composites with up to 5 wt % added bioglass to be non-stoichiometric HA with alpha-TCP or beta-TCP. Phase analysis of composites containing higher glass additions was impracticable due to peak broadening and overlap, although reaction products, at the highest glass additions and sintering temperatures, may include wollastonite-2M and beta-Na2Ca4(PO4)2SiO4. Sintered density, and mechanical properties other than fracture toughness, showed no significant improvement over HA.

A process for the replication of bovine cancellous bone in synthetic bioceramic materials for use as artificial bone graft substitutes is described. The process detailed here may be easily implemented to allow production of large numbers of blocks of material, even on a laboratory scale. The graft material has a pore morphology and interconnectivity identical with that of the original cancellous bone used as a starting material. Strength of the material is adequate, and at lower porosity levels it meets the FDA requirements for coralline materials for spinal applications. The synthetic graft is also shown to have excellent fluid-retention characteristics, making it a potential carrier for morphogenic agents such as solutions of bone morphogenic protein.