Interfacial reactions of glasses for biomedical application by scanning transmission electron microscopy and microanalysis

Dissolution behavior of high strength bioresorbable glass fibers manufactured by continuous fiber drawing

This article describes the dissolution behavior of three silica-based resorbable glasses manufactured by an industrial-type continuous fiber drawing process yielding fibers with tensile strength of 1800-2300MPa. The results of a long-term in vitro degradation testing of the manufactured high strength bioresorbable glass fibers are presented. The degradation was performed by exposing the glass fibers to SBF and TRIS for 26 weeks at physiological conditions at 37°C. All fibers showed continuous resorption throughout the study and two of the fibers revealed bioactivity by forming a calcium phosphate (CaP) layer in SBF.

Surface signatures of bioactivity: MD simulations of 45S and 65S silicate glasses

The surface of a bioactive (45S) and a bioinactive (65S) glass composition has been modeled using shell-model classical molecular dynamics simulations. Direct comparison of the two structures allowed us to identify the potential role of specific surface features in the processes leading to integration of a bioglass implant with the host tissues, focusing in particular on the initial dissolution of the glass network. The simulations highlight the critical role of network fragmentation and sodium enrichment of the surface in determining the rapid hydrolysis and release of silica fragments in solution, characteristic of highly bioactive compositions. On the other hand, no correlation has been found between the surface density of small (two- and three-membered) rings and bioactivity, thus suggesting that additional factors need to be taken into account to fully understand the role of these sites in the mechanism leading to calcium phosphate deposition on the glass surface.

In situ pH within particle beds of bioactive glasses

The in vitro behavior of three bioactive glasses with seven particle size distributions was studied by measuring the in situ pH inside the particle beds for 48h in simulated body fluid (SBF). After immersion, the surface of the particles was characterized with a field emission scanning electron microscope equipped with an energy-dispersive X-ray analyzer. In addition, the results were compared with the reactions of the same glasses formed as plates. A similar trend in pH as a function of immersion time was observed for all systems. However, the pH inside the particle beds was markedly higher than that in the bulk SBF of the plates. The pH decreased as power functions with increasing particle size, i.e. with decreasing surface area. The in vitro reactivity expressed as layer formation strongly depended on the particle size and glass composition. The average thickness of the total reaction layer decreased with the increase in sample surface area. Well-developed silica and calcium phosphate layers typically observed on glass plates could be detected only on some particles freely exposed to the solution. No distinct reaction layers were observed on the finest particles, possibly because the layers spread out on the large surface area. Differences in the properties of the bulk SBF and the solution inside the particle bed were negligible for particles larger than 800microm. The results enhance our understanding of the in vitro reactions of bioactive glasses in various product forms and sizes.