Structural and physico-chemical analysis of calcium/strontium substituted, near-invert phosphate based glasses for biomedical applications.

U. Patel,A.C. Hannon,E.R. Barney,A.R. Kennedy,K.M.Z Hossain,R.M. Moss,I. Ahmed

doi:10.1016/j.actbio.2017.07.002

Abstract

Phosphate based glasses are extremely well suited for the delivery of therapeutic ions in biomedical applications, and in particular strontium plays an important role in the treatment of osteoporosis. We show firstly that the substitution of strontium for calcium in bioactive phosphate glasses can be used to control the dissolution rate of the glass, and hence the rate at which therapeutic ions are delivered. We then go on to examine in detail the influence of Sr/Ca substitution on the atomic sites in the glass, using advanced structural probes, especially neutron diffraction. The environments of most cations in the glass are unaffected by the substitution, with the exception of Mg, which becomes more disordered.

Highlights

Phosphate based glasses containing ions characteristically native to bone (Ca2+, Na2+, Mg2+, PO43-) have been widely investigated due to their fully resorbable properties, controlled dissolution rates, and biocompatible nature [1,2,3,4,5]
Our DSC results show that, when Sr substitutes for Ca, the general overall trend is for a small decrease in Tg, and a larger decrease in Tm. The reason for this behaviour is that Sr-O bonds are weaker than Ca-O bonds [19], and this effect is more significant than any change in the degree of cross-linking of the network
The 31P MAS NMR and Fourier transform infrared spectroscopy (FTIR) results show no evidence for changes in the phosphate part of the network as Sr substitutes for Ca, and this outcome is predicted to have negligible effects on the dissolution rate of these glasses

Summary

Introduction

Phosphate based glasses containing ions characteristically native to bone (Ca2+, Na2+, Mg2+, PO43-) have been widely investigated due to their fully resorbable properties, controlled dissolution rates, and biocompatible nature [1,2,3,4,5]. The ability to introduce new oxides to the basic sodium-calcium phosphate glass network is of great interest as it allows properties such as their dissolution rates to be tailored (see for example works studying the effect of MgO [10], TiO2 [11] and Fe2O3 [12]) and the addition of therapeutic ions for controlled release into the body [13]. One of the most common treatments for osteoporosis was administration of low doses (316–634 mg/kg per day Sr2+) of strontium ranelate or strontium chloride for 9-26 weeks This was shown to reduce bone resorption and stimulate bone formation via increased replication of preosteoblastic cells. By incorporating strontium into a fully degradable material, it should be possible to achieve a controlled release of strontium into the body over time

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