Evaluation of resistance to fragmentation of injectable calciumphosphate cement paste using X-ray microcomputed tomography

Property of resistance to fragmentation of injectable calcium-phosphate cement (CPC) pastes was evaluated. CPC pastes are widely used as bone fillers due to their biocompatibility and osteoconductivity. However, the potential for fractures due to the formation of voids and cracks in the CPC, called "fragmentation," reduces the biomechanical strength of CPCs. To develop new CPCs that do not exhibit fragmentation, a method for assessing the presence or absence of fragmentation is required. For in vitro evaluation of the fragmentation resistance, the internal structure of cement specimens allowed to stand in pure water or blood was observed using X-ray micro-computed tomography (X-ray μ-CT) method. In the case of cement specimens derived from commercially-available β-tricalcium phosphate powder ball milled and surface modified in 3,000 ppm inositol phosphate solution, no cracks or voids in the internal structure were observed in samples allowed to set in either pure water or blood. For in vivo verification of the fragmentation resistance, the same CPC pastes were implanted into pig thigh muscle and tibiae for 4 and 24 weeks, respectively. The implanted CPC specimens formed a lump without internal voids or cracks. These data showed that the CPC pastes with the fragmentation resistance both in vitro and in vivo and are thus unlikely to generate fractures. Furthermore, the evaluation method using X-ray μ-CT could enables rapid and simple verification of the fragmentation resistance of the injectable CPC pastes. To our knowledge, this is the first report of the use of this method to evaluate resistance to fragmentation of CPC pastes. Furthermore, because of its simplicity and ease of use, the X-ray μ-CT method shows promise as a gold standard.