In vitro bioactivity of 45S5 bioactive glass as a function of indentation load

Many fabrication routes used to process biomaterials result in residual stresses. The presence of residual stress can cause failure or even change the dissolution rates of many materials, in particular biomaterials that are designed to be resorbed. Stored strain energy can add extra thermodynamic driving force for dissolution and result in varied dissolution rates depending on the sign of the stress. This work describes in vitro testing in phosphate buffer solution after micro-indenting the surface of bioactive glass 45S5 discs with varying loads. Indentation and fracture characteristics of the bioactive glass are discussed. Local dissolution and morphology of mineral deposits at the surface were analyzed by scanning electron microscopy to determine the effects of local residual stresses on bioactivity. It was found that the compressive stress field surrounding indents (above a threshold indentation load) slowed the dissolution of the bioactive glass significantly.