Evaluation of the reaction kinetics of CORTOSSTM, a thermoset cortical bone void filler

The primary objective of this research is to evaluate the reaction kinetics of CORTOSSTM, a thermoset, Bis-GMA (2,2-bis[4-(2-hydroxymethacryloxypropyl) phenyl]propane) composite system as a function of time, material storage temperature and the temperature of the surrounding environment (site temperature). This study utilizes probability theory to predict the percentage of bifunctional monomers with 0,1 and 2 functional groups that have been reacted. This is a strong indicator of the potential for leaching unreacted components. A differential scanning calorimeter (DSC) was used to measure the isothermal enthalpy at varying site temperatures. After isothermal monitoring, the samples were dynamically heated from the respective isothermal temperature to 175°C at 15°C/min to measure the residual enthalpy from the unreacted functional groups. The experimental results indicate that the degree of conversion for this bifunctional system ranged from 76% to 86%. Applying probability theory it has been determined that 95% of the bifunctional monomers are present with at least one double bond reacted and up to 5% of monomers remain unreacted. This is consistent with theoretical values postulated for various diffusion controlled thermoset systems (Macromolecules 32 (1999) 3913). Overall, curing under physiological conditions yielded a faster reaction rate and a significantly higher degree of conversion as compared to the lower site temperature conditions.