Complexity in non-isothermal polymerization of PMMA based bone cement: Thermal, chemical, and mechanical effects on polymerization fronts

Poly (methyl methacrylate) (PMMA) bone cements have been successfully used as a space-filler between the bony structure and the metal prosthesis through the last half century, however, the material does have several drawbacks. The main one is that aseptic loosening is still the major reason for revision in clinical life. The etiology of cement loosening remains unclear. This is, in part, the result of limited understanding of what factors affect long-term performance of cement in vivo . In this study, it is hypothesized that the structural and mechanical properties across the cement mantle are heterogeneously distributed due to the process of MMA polymerization, under in vivo non-isothermal conditions (i.e., bone (37°C) [arrow right] prosthesis (RT)). The goals of this study are to investigate the effects of complexities of the chemical, thermal, and diffusional-dependent polymerization interactions on the structural and mechanical properties and to develop empirical test techniques that allow one to monitor and predict the complexities of the in vivo non-isothermal polymerization of the PMMA bone cement. A new empirical polymerization model, based on a new overall rate constant analysis technique, was developed using isothermal differential scanning calorimetry (Iso-DSC) to precisely predict the local polymerization behavior. This complex polymerization behavior, under non-isothermal conditions, formed the spatio-temporal polymerization front that progressed from the warmest side to the coolest side. During the polymerization front progression, higher porosity at the coolest side and higher residual stresses at the warmest side were developed depending on the thermal gradient. The heterogeneous micromechanical property distribution across the cement mantle correlates with the structural property distributions. Under the in vivo non-isothermal condition, the structural and mechanical heterogeneities in the 20-35°C case led to the higher crack formations under the compression test. Polymerization fronts are a possible reason why aseptic failure of the PMMA bone cements still remains at a high rate. The non-isothermal condition leads to the asymmetric heterogeneities in the structural and mechanical properties across the cement mantle