Effect of solution condition on hydroxyapatite formation in evaluating bioactivity of B2O3 containing 45S5 bioactive glasses

The effects of testing solutions and conditions on hydroxyapatite(HAp)formation as a means of in vitro bioactivity evaluation of B2O3 containing 45S5 bioactive glasses were systematically investigated.Four glass samples prepared by the traditional melt and quench process,where SiO2 in 45S5 was gradually replaced by B2O3(up to 30%),were studied.Two solutions:the simulated body fluid(SBF)and K2HPO4 solutions were used as the medium for evaluating in vitro bioactivity through the formation of HAp on glass surface as a function of time.It was found that addition of boron oxide delayed the HAp formation in both SBF and K2HPO4 solutions,while the reaction between glass and the K2HPO4 solution is much faster as compared to SBF.In addition to the composition and medium effects,we also studied whether the solution treatments(e.g.,adjusting to maintain a pH of 7.4,refreshing solution at certain time interval,and no disturbance during immersion)affect HAp formation.Fourier transform infrared spectrometer(FTIR)equipped with an attenuated total reflection(ATR)sampling technique and scanning electron microscopy(SEM)were conducted to identify HAp formation on glass powder surfaces and to observe HAp morphologies,respectively.The results show that refreshing solution every 24 h produced the fastest HAp formation for low boron-containing samples when SBF was used as testing solution,while no significant differences were observed when K2HPO4 solution was used.This study thus suggests the testing solutions and conditions play an important role on the in vitro bioactivity testing results and should be carefully considered when study materials with varying bioactivities.