3D printing versus foaming of melt-derived bioactive glasses for bone regeneration

Abstract

Bioactive glasses have the ability to regenerate bone defects as they form a rapid bond with bone and their dissolution products can stimulate new bone growth. The original Bioglass® 45S5 composition (46.1 mol% SiO2, 26.9 mol% CaO, 24.4 mol% Na2O, and 2.6 mol% P2O5) is available as a clinical product in a particulate form, but surgeons require scaffolds that can act as temporary templates for bone repair. Bioglass 45S5 cannot be made into porous scaffolds while maintaining an amorphous glass structure, due to its susceptibility to crystallise during sintering. New melt-derived glass compositions have recently been developed which avoid crystallisation, enabling bioactive glasses to be made into porous constructs. The aim of this thesis was to investigate the relationship between glass composition and scaffold production techniques. Three glasses compositions were used, ICIE16 (49.46 SiO2, 36.27 CaO, 6.6 Na2O, 1.07 P2O5 and 6.6 K2O, in mol%), 13-93 (54.6 SiO2, 22.1 CaO, 6.0 Na2O, 1.7 P2O5, 7.9 K2O, 7.7 MgO, in mol%) and SBP-3 (44.5 SiO2, 17.8 CaO, 4.0 Na2O, 4.5 P2O5, 4.0 K2O, 7.5 MgO, 17.8 SrO, in mol%), each with an extended thermal processing window. These glasses were made into 3D scaffolds utilising two processing techniques: an adapted gel-cast foaming and, for the first time, robocasting. Here we present the adaption and optimisation of these techniques. The three glass compositions, ICIE16, 13-93 and SBP-3, all have different modified network connectivities (mean number of bridging Si-O-Si bonds per silicon atom, NC’) of 2.13, 2.84 and 3.01 respectively. In vitro and in vivo analysis were completed to understand how the different glass chemistry affected their bioactivity and dissolution characteristics. The composition of ICIE16 chemistry was the most similar to the original 45S5 composition was shown to promote and sustain better bone ingrowth than comparable scaffolds produced from SBP-3.