Noninvasive in vivo EPR monitoring of the methyl methacrylate polymerization during the bone cement formation

The curing of poly(methyl methacrylate) (PMMA) bone cement is done by a free radical polymerization. As the amount of free radicals present is a marker of the amount of unpolymerized chains present in the polymer, it is assumed that this could be related to the mechanical properties such as strength or density. In this study, the direct observation of the free radicals produced during the PMMA bone cement formation was obtained for the first time in vivo using low-frequency EPR spectrometers (1.2 GHz). Low frequency permits measurements in live animals due to the increased microwave penetration. The amount of polymerization radicals was carried out noninvasively over days on the same animals. The decay rates obtained in vitro and in vivo were compared: the decay rates were significantly lower when the curing process occurred in vivo compared to the situation in vitro. As the kinetics are rather different in vitro and in vivo, this emphasizes the value of the present method that permits the noninvasive monitoring of the curing process directly in vivo.