Welcome to the Glass Age

48 “chronic”, as they are not responding to treatment by antibiotics alone. However, when the bioactive glass was implanted into the bone (along with the antibiotics), the infection subsided [4]. These findings are particularly important as many bacteria are becoming resistant to existing antibiotics. Glass particles alone can be difficult to handle, therefore many orthopaedic clinicians prefer to use bioactive glass in the form of a putty. So, putties have been developed consisting of polyethylene glycol (PEG) carriers packed with Bioglass that can be delivered using syringes (Figure 3.4). When bioactive glass particles are used to repair bone defects, they act as steppingstones, encouraging the bone to cross the gap before they biodegrade. For many bone defects, a more robust three-dimensional template (scaffold) is needed to act as a framework for bone growth. Importantly, the pores must be open to allow bone and blood vessel ingrowth. However, producing a porous scaffold from the original Bioglass is challenging, because the conventional strategy for making a porous architecture from a glass or ceramic would be to sinter particles together and heating Bioglass to the temperature required for sintering causes crystallisation [5]. There are two ways to prepare bioactive glass scaffolds that do not crystallise: altering the glass composition to one that does not crystallise or using the sol-gel process. Adding more components into the glass composition can increase the crystallisation temperature, thereby opening the processing window, and thus allow for sintering without crystallisation occurring. Figure 3.5 shows photographs of bioactive foam and 3D-printed bioactive scaffolds. The foam structure mimics the architecture of porous bone and can be created using vigorous agitation with surfactants, either by foaming glass particles in a water-based slurry prior to sintering, termed gel-cast foaming [6], or by introducing a foaming step into the sol-gel process [7]. The sol-gel process forms the silicate network through chemical synthesis, wherein nanoparticles form in solution Figure 3.5. Photographs of bioactive glass scaffolds: a sol-gel foam scaffold that mimics the pore architecture of porous bone (left) and a 3D-printed scaffold (right). Source: Julian R. Jones.