Bone-bonding behavior of PMMA bone cement modified with alkoxysilane and calcium acetate

Polymethylmethacrylate (PMMA) bone cement is extensively subjected to clinical applications such as fixation of artificial hip joint in orthopedic fields. However it is unable to bond to living bone, hence the fixation is liable to be unstable after a long implantation period. Novel design of PMMA cement exhibiting bone-bonding ability, i.e. bioactivity is therefore desired. The essential prerequisite for an artificial material to bond to bone is formation of apatite layer on its surface after implanted in bony defect. This apatite layer can be formed even in a simulated body fluid (Kokubo solution) with similar ion concentrations to those of human extracellular fluid. It has been revealed that silanol (Si-OH) group and calcium ion (Ca2+) act as constituents for apatite nucleation in body environment. On the basis of these findings, we recently reported that the apatite formation can be observed on PMMA cement modified with 3-methacryloxypropyltrimethoxysilane (NIPS), which provides Si-OH groups, as well as with calcium acetate, which releases Ca2+, in Kokubo solution. In the present study, bone-bonding behavior of the modified cements was examined in vivo by implantation in rabbit tibiae. The cement modified with MPS and calcium acetate showed osteoconduction and direct contact with the bone, whereas reference specimen with similar composition to conventional PMMA bone cement did not. This type of chemical modification was found to be effective for providing PMMA bone cement with bioactivity.