Synthesis, testing and characterization of porous biocompatible porous bioactive glasses for clinical use

Abstract

The quest for the processing of glass scaffolds that remains amorphous upon sintering while maintaining a fast dissolution and conversion to hydroxyapatite rate is growing. Therefore; glasses within the borosilicate borophosphate and phosphate family were sintered into 3 dimensional (3D) porous scaffolds using 60 and 70 vol. % NH4(HCO3) as a foaming agent. In this work the sintering ability of (borosilicate S53B50), borophosphate (P40B10) and phosphate (Sr) bioactive glasses was investigated. The glass powders were crushed and sintered in air at a heating rate of 10°C/min for 2 hours at sintering temperatures between 480°C-600°C. The density of the samples was found to decrease when the temperature was increased up to 580°C. To process highly porous scaffolds with porosity required for scaffold applicable to tissue engineering, the powders were further mixed with 60 vol. % and 70 vol. % of NH4 (HCO3) foaming agent. Meanwhile, the density of the samples sintered with NH4 (HCO3) was found to decrease with an increase in NH4 (HCO3) content. This indicates an increase in porosity of the samples. The glass compositions reached an open porosity of more than 60% at the addition of 70 vol. % NH4 (HCO3). The in vitro properties of the scaffolds investigated in SBF showed that Upon immersion; the pH of the solution containing the borosilicate scaffolds increased due to the typical noncongruent dissolution of theses glass family leading to large Na+/H+ exchange and large alkaline and alkaline earth release. Borophosphate as well as phosphate scaffolds induced a decrease in pH upon dissolution attributed to the congruent dissolution of those materials and therefore; the large release of phosphorus within the media. The as prepared scaffolds showed a compressive strength of 1.29 ± 0.21, 1.56 ± 0.63, 3.63 ± 0.69 MPa for the samples borosilicate borophosphate and phosphate sintered with 60 vol. % NH4 (HCO3), respectively. From SEM/EDS, XRD and ICPOES analysis a clear precipitation of hydroxyapatite was reported on the borosilicate glass scaffolds. The borophosphate scaffold was found to be stable and to react at a slow rate. The crystallized phosphate glass; however was found to release very large amount of phosphate; compared to the amorphous glass; indicating preferential leaching of the phosphate rich crystal phase. Except for the borophosphate scaffolds; the mechanical properties dropped with increasing immersion time.