APATITE FORMATION ON ORGANIC POLYMERS BY BIOMIMETIC PROCESS USING NA2O-SIO2 GLASSES AS NUCLEATING-AGENT

The present authors previously reported that a dense and uniform bone-like apatite layer with a desired thickness can be formed on any kind and shape of solid substance by the following biomimetic method at normal temperature and pressure. First, a substrate is set in contact with particles of CaO-SiO2-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Second, the substrate is soaked in another solution highly supersaturated with respect to the apatite. In the present study, the CaO-SiO2-based glass as the nucleating agent was replaced by Na2O-SiO2 glasses, SiO2 glass and SiO2 gel. The induction periods for the apatite nucleation on poly-ethersulfone substrates were infinity, a little longer than 168, 96, 48, 1.5 and 0.5h for SiO2 glass, SiO2 gel, Na2O 10.SiO2 90, Na2O 20.SiO2 80, Na2O 30.SiO2 70 and Na2O 40.SiO2 60 mol% glasses, respectively, whereas 24h for MgO 4.6.CaO 44.7.SiO2 34.0.P2O5 16.2.CaF2 0.5 wt% glass G. The short induction period for the glasses with high Na2O contents is attributed to high dissolution rates of sodium and silicate ions from them. The adhesive strengths of the formed apatite layer to the poly(ethylene terephthalate), poly(methyl methacrylate), poly-ethersulfone and polyamide 6 were 5.37, 1.63, 6.80 and 2.91 MPa for Na2O 30.SiO2 70 mol% glass, whereas 3.48, 1.06, 4.40 and 0.63 MPa for glass G. It is considered that highly polar carboxyl or sulfinyl groups were formed on the polymer surfaces by the hydrolysis of their ester, amide or sulfonyl group in SBF with its pH considerably increased by the Na+ dissolution from the glass, and that these polar groups formed a fairly strong bond with the apatite. Thus formed apatite-organic polymer composites are expected to be useful as the bone-repairing as well as soft tissue-repairing materials.