Effect of N-acetylcysteine Addition on Monomer Elution of PMMA Cement

Objective: In the previous study (2010 IADR #3032), addition of N-acetylcysteine (NAC) to PMMA (polymethylmethacrylate) cement could reduce the polymerization of PMMA cements. The release of unreacted monomer from PMMA bone cement may cause cytotoxicity. This study aimed to evaluate the effect of NAC addition to PMMA on the release of monomer from PMMA bone cement. Methods: All specimens were prepared by mixing pre-polymerized PMMA powder which containing various concentrations of NAC (0, 0.25, 0.50, 0.75 or 1.00 wt%) and MMA liquid manually at a ratio of 2:1 in room temperature. For HPLC analysis, disk type (12mmx2.0mm) specimens (n=5) were polymerized for 40min, then immersed in 2mL of HPLC grade water. The aliquots of 20μL were analyzed on HPLC (Waters Instruments, USA) with a reverse-phase C18 column (4x250mm, Inertsil ODS-4, Japan) after 2hrs, 24hrs and 7 days immersion. The mobile phase was 67% methanol with 33% water in isocratic conditions at the flow rate of 0.8mL/min. Detection was performed at 205nm. The amounts of released monomer were determined by referring to the calibration graphs of standard MMA solutions. All liquids used were HPLC grade (Merck, Germany). Result: The MMA released from the PMMA bone cement without NAC ranged from 0.06±0.02 wt% for 2 hrs, 0.10±0.01 wt% for 24hrs to 0.14±0.03 wt% up to 7days. As for PMMA with 0.5 wt% NAC, the amount of MMA released were 0.10±0.03 wt%, 0.16±0.01 wt% and 0.24±0.02 wt%, resptectively. While for PMMA with 1.0 wt% NAC, residues ranged from 0.28±0.21 wt%, 0.71±0.28 wt% to 0.79±0.04 wt%, respectively. The amount of the residual monomers released was higher in the NAC-supplemented PMMA bone cements than that in the PMMA without NAC. Conclusion: Addition of NAC to PMMA bone cement may disturb polymerization, then increase the released of monomer from PMMA bone cement.