ISOTHERMAL AND NONISOTHERMAL POLYMERIZATION OF A NEW BONE-CEMENT

A new bone cement based on poly(ethylmethacrylate) (PEMA), hydroxyapat ite powder (HA) and n-butylmethacrylate monomer (n-BMA) has been studi ed using isothermal and nonisothermal polymerization. Methacrylate mon omers are highly reactive and release a considerable amount of heat du ring polymerization. A quantitative understanding of the methacrylate polymerization is necessary because the thermal history of the polymer ization has considerable influence on the final properties of a bone c ement. In the first part, polymerization kinetics are analysed by mean s of differential scanning calorimetry (DSC). DSC data are used to eva luate a phenomenological model describing the cu re kinetics of this n ew bone cement. In the second part, a kinetic model coupled with the e nergy balance is used to obtain temperature and degree of conversion p rofiles in the bone-cement-prosthesis system, under non-isothermal con ditions, as function of initial temperature and thickness of the cemen t. Material properties, boundary and initial conditions and the kineti c behaviour are the input data for the numerically solved heat-transfe r model. The temperature at the bone/cement interface, can be consider ed as a weak point, often responsible for total joint replacement fail ure. For this particular bone cement exhibiting a low exotherm and low glass transition temperature, the interfacial temperature is lower th an the threshold level for thermal tissue damage (50 degrees C). The c onversion occurs almost completely, avoiding problems with unreacted m onomers that can be released by the cement, giving rise to tissue dama ge.