Influence of low amounts of zinc or magnesium substitution on ion release and apatite formation of Bioglass 45S5

R Wetzel,D S Brauer,O Bartzok

doi:10.1007/s10856-020-06426-1

Abstract

Magnesium and zinc ions play various key roles in the human body, being involved, among others, in skeletal development and wound healing. Zinc is also known to have antimicrobial properties. While low concentrations can stimulate cells in vitro, high concentrations of magnesium or zinc introduced into bioactive glasses significantly reduce glass degradation and ion release and inhibit apatite precipitation. On the other hand, magnesium and zinc ions improve the high temperature processing of bioactive glasses, even when present at low concentrations only. Results here show that by substituting small amounts of Mg or Zn for Ca, ion release remains high enough to allow for apatite precipitation. In addition, magnesium and zinc containing bioactive glasses are shown to be very susceptible to changes in particle size and relative surface area. For a given magnesium or zinc content in the glass, ion release and apatite formation can be enhanced dramatically by reducing the particle size, reaching comparable levels as Bioglass 45S5 of the same particle size range. Taken together, these findings suggest that when introducing these ions into bioactive glasses, ideally low Mg or Zn for Ca substitution as well as small particle sizes are used. This way, bioactive glasses combining good high temperature processing with fast ion release and apatite precipitation can be obtained, providing the potential additional benefit of releasing magnesium or zinc ions in therapeutic concentrations.

Highlights

Bioactive glasses are used to regenerate bone or re-mineralise dental tissue [1], and their capacity to release ions is an additional feature besides their degradation and apatite surface mineralisation [2]
We have reported that osteoblasts exposed to early doses of fluoride show increased markers for bone mineralisation in vitro [4] or that lithium ions released from bioactive glasses can upregulate the Wnt pathway in 17IA4 cells in vitro to potentially promote hard tissue repair [5]
Zinc for calcium substitution caused a dramatic drop in ion release at physiological pH, entirely inhibiting apatite precipitation owing to a lack of available calcium and phosphate ions

Summary

Introduction

Bioactive glasses are used to regenerate bone or re-mineralise dental tissue [1], and their capacity to release ions is an additional feature besides their degradation and apatite surface mineralisation [2]. As the lowest substitution in our previous study was 25% [14], this raises the question whether Mg or Zn could be incorporated at (lower) levels which do not negatively affect ion release or apatite precipitation, and provide the benefit of therapeutic Mg2+ or Zn2+ release combined with the formation of apatite surface layers. This is interesting as Mg and Zn ions have recently been shown to improve the sintering of bioactive glasses, even at low levels of Mg or Zn for Ca substitution [16]. The aim of the present study was to investigate the effect of low Zn or Mg for Ca substitution on the ion release and apatite precipitation behaviour of Bioglass 45S5 of two different particle size ranges

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Conclusion