Rheological properties of acrylic bone cement during curing and the role of the size of the powder particles.

Abstract

A dynamic compressive rheometric technique was used to determine the true or complex viscosity (eta*) of three poly (methyl methacrylate), PMMA-based bone cement formulations (one commercially available and two experimental), as a function of the time that elapsed from commencement of hand mixing of the cement constituents (t). For each cement, two rheological parameters [namely, the time of onset of cure (t(ons)) and the critical cure rate (CCR), which is herein defined as the complex viscosity rate computed at t(ons)] were determined from the eta*-t data. For each cement, particle analysis was used to obtain the powder particle size distribution, from which the following parameters were obtained: (a) the overall mean particle diameter D(m), and (b) the relative amounts of small-sized PMMA beads (mean diameter d between 0 and 40 mum) (alpha) and large-sized PMMA beads (d > 75 mum) (beta). It is seen that the key particle parameter is not D(m) per se but alpha and beta. Thus, the highest values of t(ons) and CCR were obtained from a cement with the highest values of alpha and beta. An explanation for these trends is given, and two areas for further research work in this field are outlined.