Bioactive glass

Overview
Bioactive glasses are a group of surface reactive glass-ceramics and include the original bioactive glass, Bioglass®. The biocompatibility of these glasses has led them to be investigated extensively for use as implant materials in the human body to repair and replace diseased or damaged bone.

History
Larry Hench and colleagues at the University of Florida first developed these materials in the late 1960s and have been further developed by his research team at the Imperial College London and other researchers worldwide.

Compositions
There have been many variations on the original composition which was Food and Drug Administration (FDA) approved and termed bioglass®. This composition is known as 45S5. Other compositions are in the list below.
 * 45S5: 46.1 mol% SiO2, 26.9 mol% CaO, 24.4 mol% Na2O and 2.5 mol% P2O5. Bioglass
 * 58S: 60 mol% SiO2, 36 mol% CaO and 4 mol% P2O5.
 * S70C30: 70 mol% SiO2, 30 mol% CaO.

Structure
Solid state NMR spectroscopy has been very useful in elucidating the structure of amorphous solids. Bioactive glasses have been studied by 29Si and 31P solid state MAS NMR spectroscopy. The chemical shift from MAS NMR is indicative of the type of chemical species present in the glass. The 29Si MAS NMR spectrscopy showed that Bioglass 45S5 was a Q2 type-structure with a small amount of Q3; i.e., silicate chains with a few crosslinks. The 31P MAS NMR indicated a Q0 species; i.e., PO44- with predominately sodium cations. (Lockyer et al. 1995)

Medical Applications
Bioactive glasses have many applications but these are primarily in the areas of bone repair and bone regeneration via tissue engineering.
 * Synthetic bone graft materials for general orthopaedic, craniofacial (bones of the skull and face), maxillofacial and periodontal (the bone structure that supports teeth) repair. These are available to surgeons in a particulate form.
 * Cochlear implants.
 * Bone tissue engineering scaffolds. These are being investigated in many forms, in particular as porous (contains pores into which cells can grow and fluids can travel) 3-dimensional scaffolds.

References Lockyer, M. W. G., Holland, D. & Dupree, R., NMR investigation of the structure of some bioactive and related glasses. J. Non-Crys. Sol., 1995, 188, 207-219.