Research progress of bioactive glasses based bone repair materials

Bioactive glasses (BGs) are a kind of biomaterials with osteoconductive and osteoinductive properties and are able to create a strong bond with host bone and promote osteogenesis after implantation. According to their compositions, bioactive glasses can be classified as silicate BGs, phosphate BGs, and borate BGs. Nowadays, silicate BGs are still the most common, while phosphate BGs and borate BGs have higher dissolution and degradation rates. Melt-quenching and sol-gel process are two basic methods to produce melt-derived BGs and sol-gel BGs, respectively. The latter requires lower heat treatment temperature with higher specific surface area and biological activity. Bioactive glass-ceramics can be obtained by heat treatment, which improves the mechanical strength but slightly reduces the bioactivity. Nano-bioactive glasses with the higher specific surface area can be obtained by changing the structure size of the materials by other treatment methods. On this basis, 3D BGs scaffolds can be made, and hybrid BGs scaffolds as well by combining with other biomaterials to obtain the 3D interconnected pores with the hierarchical or bionic structures, to enhance the mechanical strength, osteogenic activity and provide mechanical support suitable for the host bone. However, the bioactivity of BGs depends on the degradation rate, to some extent, which is contradictory to the mechanical strength. An appropriate porosity or controllable degradation rate can be selected to meet the common needs of early support and osteogenesis. In basic studies, it was found that BGs could act on cells by releasing ions or through the macropinocytosis pathway, up-regulating the expression of related genes or promoting osteogenesis. The degradation rates of BGs are related to their structures and compositions, which enables the quantitative prediction of the change of mechanical strength during degradation. Progress has also been made in structural mechanics and testing methods.