The effects of PMMA particle number on MG-63 osteoblast cell function

Implants used for joint replacement are often cemented into place to increase stability. As the person ambulates, the implanted materials slide against each other producing small wear debris particles. There is increasing evidence that wear debris particles that are present in periprosthetic tissues have direct effects on osteoblasts. Particles resulting from polymethylmethacrylate (PMMA) cements used for fixation may also be involved directly in aseptic loosening of implants. However, it is not known if these particles have a direct or indirect effect on bone formation. The objective of this study was to determine the effect of PMMA particle number on osteoblast cells. MG-63 osteoblast-like cells were challenged with 200 microg/mL, 20 microg/mL and 2 microg/mL PMMA diluted in culture medium. Cells were incubated with the particles for 24, 48, and 72 hours. MG-63 cellular proliferation was unaffected at 24 and 48 hours regardless of the concentration. However, at 72 hours, the low and high dose treatments resulted in a 50% reduction in cell numbers. Interestingly, at 72 hours cellular protein levels were increased in all treated groups by at least 50%. Cellular damage was evident as early as 24 hours in all experimental groups and continued for the duration of the study. Morphological observations showed significant vacuole formation in all experimental groups. Also, there was an overall increase in cell size that coincided with increasing levels of PMMA with noted micronucleoli at the highest dosage. The increase in micronucleoli may be reflective of increased cellular damage. Overall, a PMMA particle challenge resulted in significant membrane perturbations, and that phenomenon was found to be dose and time dependent.