Thermal characterization of PMMA-based bone cement curing

In thermal characterization tests of polymethylmethacrylate bone cement performed according to the ASTM Standard Specification for Acrylic Bone Cement, time-temperature profiles of bone cement were observed to be sensitive to the thickness of the cement patty and the mold material. Due to the heat transfer from cement to the surrounding mold, such tests might underestimate the exothermic temperature of bone cement. Developing test methods to better characterize cement thermal behavior is necessary for accurate cement curing simulations. In this paper, the effects of the mold material and geometry on experimental measurements of bone cement setting temperature and setting time were evaluated by conducting the polymerization in different test molds. Finite element (FE) numerical simulations were also performed to provide a further understanding of these effects. It was found that the mold material and geometry significantly influence the values of the parameters measured using the ASTM standard. Results showed that the setting temperature measured was about 50 degrees C lower in a polytetrafluoroethylene (PTFE) mold than in a polyurethane (PU) foam mold for the 6 mm thickness cement. The measured peak temperature using PTFE molds varied about 75 degrees C for different mold heights (6mm vs. 40 mm), but only by 28 degrees C with PU molds. The measured setting time with PTFE molds varied by about 740 s for different mold heights (6 mm vs. 40 mm), while only by about 130 s for PU molds. Using PU foam materials for the test mold decreases cement heat transfer effects due to the poor heat conductivity of PU foam and provides more consistent measured results. FE parametric studies also support these observations. Poor conductivity materials, like PU foam, make better molds for the characterization of bone cement thermal behavior.