POLYMERIZATION KINETICS OF ACRYLIC BONE CEMENTS BY DIFFERENTIAL SCANNING CALORIMETRY

Bone cements are widely used for the fixation of metallic prostheses i n orthopaedics and to form replacements for skull defects in neurosurg ery. Acrylic bone cements are based on a mixture of methyl methacrylat e (MMA) and a fine powder of polymethyl methacrylate (PMMA). The polym erization of the bone cement occurs in contact with the bone and the p rosthesis which act as the boundaries of a bulk polymerization reactor . The kinetic behaviour of the bone cement plays a fundamental role fo r the final performance of the implant. In this paper, the isothermal and non-isothermal polymerization behaviour of a commercial bone cemen t is described. A simple phenomenological model, accounting for the au toacceleration effect, for a diffusion controlled termination mechanis m and for the reaction between inhibitor and initiator, is proposed. T he reaction kinetics is analysed by DSC. DSC data are used for the det ermination of the rates of polymerization under isothermal and non-iso thermal conditions. The experimental data are processed to calculate t he parameters of the proposed phenomenological kinetic model. The anal ytical and numerical details related to the integration of the model a re discussed.