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

Abstract

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.

Keywords: Bioactive glasses; Boron oxide; Hydroxyapatite; In vitro.

Graphical abstract

Fig. 1

Outline of the experimental details.

Fig. 2

XRD patterns of the prepared glass samples.

Fig. 3

Photos of the prepared glass samples.

Fig. 4

FTIR spectra of the commercial HAp powder and 0B after SBF immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 5

FTIR spectra of the commercial HAp powder and 5B after SBF immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 6

FTIR spectra of the commercial HAp powder and 9B after SBF immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 7

FTIR spectra of the commercial HAp powder and 14B after SBF immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 8

FTIR spectra of the commercial HAp powder and 0B after K₂HPO₄ solution immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 9

FTIR spectra of the commercial HAp powder and 5B after K₂HPO₄ solution immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 10

FTIR spectra of the commercial HAp powder and 9B after K₂HPO₄ solution immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 11

FTIR spectra of the commercial HAp powder and 14B after K₂HPO₄ solution immersion with three different solution treatments, where (a), (b) and (c) is still, adjusted and refreshed, respectively.

Fig. 12

SEM images of 0B after SBF immersion with three different solution treatments for 7 days, where (a), (b) and (c) is still, adjusted and refreshed, respectively.