Bioglass, which has a composition of sodium carbonate, calcium carbonate, phosphorous pentoxide and silica, has been shown to bond to living bone. This ability is dependent on controlled surface reactions. Investigators with 45S5 bioglass have demonstrated that the formation of a SiO2-rich layer and a calcium phosphate film on its surface in an aqueous environment is associated with the film bonding the bioglass to bone. The objects of this research were: 1. To study SiO2 dependence on the formation of a silica-rich layer and calcium phosphate films on a bioglass surface in a simulated physiological solution, and 2. To establish a correlation between in vitro surface reactions and in vivo bonding ability. It was discovered that three types of reactions occur in a simulated physiological solution depending on bioglass composition: 1. A calcium phosphate film and SiO2-rich layer form simultaneously and the reaction rate is fast for bioglasses which have a lower content of SiO2 (approximately 46 mol% SiO2). 2. A SiO2-rich layer forms first and a calcium phosphate film develops later between the aqueous environment and the SiO2-rich layer for bioglasses whose SiO2 content is between 46--55 mol %. 3. A calcium phosphate film does not form for glasses whose SiO2 content is more than 60 mol %.

Migration of sodium in thin films of soda-silica glass deposited on a stainless steel substrate has been studied. The amounts of charge trapping and local heating were a strong function of beam parameters for thin films. For example, the time required for the sodium Auger signal to decay to 50% of its initial value increased as the beam energy was increased or as the current density was decreased. The rearrangement of sodium due to charge trapping was calculated and compared to experimental data. The calculated and experimental data agree well and indicate that fields of -lo5 V cm-' exist during analysis. The depth distribution of sodium indicates that either electrons or ion bombardment can cause sodium migration during analysis. The cross-section for electroninduced desorption was measured to be 3 X lo-'' cm2 for sodium in this glass, therefore it is only important at very high current densities.