In vitro testing of ten bone cements after different time intervals from polymerization

Biological response of cells to implanted bone cement is a fundamental but often neglected issue in successful cemented implants. In this study, ten a crylic bone cements for orthopedics were assayed using two different in vit ro testing methods on L929 cells. The cements were mixed as prescribed, cur ed for either 1 h or 7 days and then extracted in minimum essential medium (MEM) according to the ISO standard for the preparation of samples. For the evaluation of cytotoxicity, the neutral red uptake assay (NRU) and the inc orporation of propidium iodide (PI) were used to detect the viability/death of cells. The two methods were shown to be well correlated (p < 0.0001) in the case of both the 1-h and the 7-day extracts. Two cements, i.e. CERIM LT and CMW2, were found to be toxic after 1-h curin g through both the spectrophotometric NRU assay and the cytofluorometric as say with PI. After 7-day curing, these two cements, as well as the Zimmer-l ow viscosity cement, were toxic according to the NRU assay, The toxic effec t of all the cements disappeared after dilution of extracts 1 : 2 with MEM, except in the case of CERIM LT, In the search for the component inducing t he toxic effect, the possible contribution of the residual monomer was disc arded on the basis of literature data and the influence of various other fa ctors was analyzed, including the contrast medium (barium sulphate or zirco nium dioxide) and the concentrations of N,N-dimethyl-paratoluidine and of b enzoyl peroxide (< 1% or greater than or equal to 1%). Unlike zirconium dio xide, barium sulphate was found to damage the cells at the 1-h endpoint. Be nzoyl peroxide at concentration greater than or equal to 1% was found to af fect cells at the same endpoint, whereas dimethyl-paratoluidine had no effe ct regardless of the proportion.