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 CORTOSS(TM), 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 degrees C at 15 degrees 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 approximately 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.