DESIGN OF BONE-BONDING ORGANIC-INORGANIC HYBRIDS

抄録

Several kinds of ceramics such as Bioglass ®, glass-ceramic A-W and sintered hydroxyapatite exhibit specific biological affinity, i.e. direct bonding to surrounding bone, when implanted in bony defects. These bone-bonding ceramics are called bioactive ceramics and utilized as important bone substitutes. However, there is limitation on clinical applications, because of their inappropriate mechanical properties such as high Young's modulus and low fracture toughness. Novel materials exhibiting high machinability and flexibility as well as high bioactivity have been desired in medical fields. It is known that bioactive ceramics bond to bone through bone-like apatite layer which is formed on their surfaces by chemical reaction with body fluid. This apatite formation can be well reproduced even in an acellular simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. Previous researches have revealed that nucleation of the apatite is triggered by a catalytic effect of silanol (Si-OH) group formed on their surfaces and accelerated by the release of calcium ion (Ca²⁺) from the ceramics into the surrounding solution. These findings bring us an idea that bioactive organic-inorganic hybrids with high flexibility and machinability can be designed by chemical modification of Si-OH group and Ca²⁺ with organic polymers. In the present paper, we review several researches to obtain bioactive organic-inorganic hybrids by such an organic modification of Si-OH and Ca²⁺.