Effect of the substitution of M2O3 (M = La, Y, In, Ga, Al) for CaO on the bioactivity of 2.5CaO x 2SiO2 glass.

Glasses were prepared whose compositions are defined by the following general formula: (2.5 - x)CaO x x/3M2O3 x 2SiO2 (0 < or = x < or = 0.6) (M = Ga, Al, In). Their bioactivity was studied "in vitro" by soaking the glasses in a simulated body fluid (SBF). The consequent formation of calcium phosphate layer was studied by means of electron microscopy (EM) equipped with an energy-dispersive system (EDS) for elemental analysis and Infrared (IR) spectroscopy. The results are compared to the literature relative to the substitution of La2O3 and Y2O3 for CaO. It is observed that, in general, the substitution of M2O3 for CaO in the binary CaO-SiO2 glass composition progressively reduces the ability to form a calcium phosphate layer on the surfaces exposed to simulated body fluid (SBF). The composition limit can be related to the ionic field strength of the substituting cation and to the CaO content of the base glass. According to the mechanism reported in the literature a silica gel-like surface layer initially forms on the surfaces exposed to SBF. The observed results can be attributed to the effect of the substitution of M2O3 for CaO on the acidic properties of the silanolic groups.