Effects of environment on the creep properties of a poly(ethylmethacrylate) based bone cement

The effect of test environment on the creep behavior of a poly(ethylmethacr ylate) bone cement was investigated. The aim of the study was to assess the influence of environment on the inherent material behavior, and so it was convenient to perform tests in tension on well-prepared samples. In additio n to control tests in air, the liquid environments studied were water, Ring er's solution and Intralipid. Creep tests were performed in each of these e nvironments with a range of aging times, test temperatures and applied stre sses. In order to compare the effects of the environments, the creep curves were fitted to a generalized form, from which a creep rate was determined. The ratio of these creep rates between different environments at each test ing condition was then used as a basis for a comparison of the detailed eff ects of environment. It was found that in all cases the water-based environments (water and Ring er's) had similar effects and gave the largest creep rates. Intralipid was then intermediate and air gave the lowest creep rates. These effects are ma inly due to plasticization by water, although with Intralipid, some increas ed monomer leaching occurred, which served to reduce the creep rates. The i nfluence of environment on the effects of aging time, temperature and stres s were complex, although in general any conditions which increased water pl asticization (longer aging, higher temperature and to a lesser extent, high er stress) gave an increase in creep rate. The major exception to this was at temperatures of 40 degreesC and above, where the effects of water plasti cization were diminished, due to the inherent increase in molecular mobilit y of the material. (C) 2001 Kluwer Academic Publishers.