Apatite formation on the PMMA bone cement modified with alkoxysilane and calcium salt in a simulated body fluid

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of orthopedic implants. However it does not show bone-bonding ability. So-called bioactive ceramics show direct bone-bonding to make tight fixation. Development of bioactive PMMA cement has therefore been long desired. The essential prerequisite for an artificial material to bond to bone is the formation of apatite layer on its surface when implanted in bony defect. This type of apatite layer can be formed on bioactive materials 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 effective constituents for apatite formation in body environment. On the basis of these findings, we modified the cement with alkoxysilane, which provides Si-OH group, as well as with calcium salts, which releases Ca2+. Ability of apatite formation on the cements was examined in Kokubo solution. The cement modified with alkoxysilane and calcium salts formed apatite within 7 d in Kokubo solution. The cements modified with Ca(CH3COO)(2) and Ca(OH)(2) kept compressive strength near the lower limit required by ISO5833, although the compressive strength decreased after exposure to Kokubo solution. Bioactive PMMA cement was successfully obtained via chemical modification with alkoxysilane and calcium salt.