IN-SITU POLYMERIZATION BEHAVIOR OF BONE CEMENTS

The polymerization behaviour of bone cements during total hip replacem ents is characterized by a fast and highly non-isothermal bulk reactio n. In the first part of this paper the reaction kinetics are analysed by calorimetric analysis in order to determine the rates of polymeriza tion in isothermal and non-isothermal conditions. A phenomenological k inetic model, accounting for:the effects of autoacceleration and vitri fication, is presented. This model, integrated with an energy balance, is capable of predicting the temperature across the prosthesis, the c ement and the bone and the degree of reaction in the cement, during in situ polymerization. The temperature and the degree of reaction profi les are calculated, as a function of the setting time, taking into acc ount the system geometry, the thermal diffusivity of bone, prosthesis and cement, and the heat rate generated by the reaction according to t he kinetic model. Material properties, boundary and initial conditions are the input data of the heat transfer model. Kinetic and heat trans fer models are coupled and a numerical solution method is used. The mo del is applied in order to study the effects of different application procedures on temperature and degree of reaction profiles across the b one-cement-prosthesis system.