Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions

Abstract

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37 degrees Celsius. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO(2) with B(2)O(3). Higher B(2)O(3) content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO(2) in a Na-depleted core. The concentration of Na(+) in the phosphate solution increased with reaction time whereas the PO(4) (3-) concentration decreased, both reaching final limiting values at a rate that increased with the B(2)O(3) content of the glass. However, the Ca(2+) concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K(2)HPO(4) and K(2)CO(3) produced a carbonate-substituted HA but the presence of the K(2)CO(3) had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.

Bioactive Glass 13-93 as a Subchondral Substrate for Tissue-engineered Osteochondral Constructs: A Pilot Study

“…This study provides evidence that increasing silicon released into the medium via BG 13-93 dissolution could modulate chondrocyte function. BG 13-93 is biodegradable, and when placed in an aqueous environment at 37°C, it converts to a calcium phosphate material analogous to hydroxyapatite [20,26]. As BG degrades, it also releases its ion content, which has the ability to stimulate osteoblast activity [3,4,40,42].…”

Structure and Characterization of Some High Chemically Resistance Silicate Glasses

“…The preparation of SBF solution was carried out according to Kokubo et al, [21]. The Tris-buffered SBF composition is (Na + 142.0, K + 5.0, Mg 2+ 1.5, Ca 2+ 2.5, Cl − 147.8, HCO 3-5.0, HPO 4 2-1.0 and SO 4 2-0.5 mol m -3 ). After soaking for 14 days the glass powders were removed from the SBF solusion using filter paper (1 μm), gently washed with acetone, and dried at room temperature.…”

“…Soluble silica is lost to the solution in the form of Si(OH) 4 , resulting from this breaking of Si-O-Si bonds and the continued formation of silanols at the glass-solution interface.…”

“…Silicate-based bioactive glasses are ordinarily used for biomedical applications. The limitation associated with Si-based bioactive glasses is the slow rate of degradation and conversion to apatite which further complicates the rate of implant resorption and simultaneous bone growth [4]. When the SiO 2 content exceeds 60 %, the bioactive glass is not able to induce the formation of apatite layer even after several weeks immersion in SBF solution and it failure to bond to either bone or soft tissue [5].…”

Sol–gel preparation of apatite-coated silica macrospheres from water glass and their adsorption of bovine serum albumin and lysozyme

“…The bottles were then kept in an oven at 80°C for 1 d. During the incubation, it is expected that the phosphate ions took out the calcium ions from the Ca-alginate chelate molecules in the SiO 2 macrospheres to yield apatite via the reactions similar to the glass-apatite conversion. 35)…”