The biological response of macrophages to PMMA particles with different morphology and size

We used polymethylmethacrylate (PMMA) particles to investigate the relationship between particle properties and biological responses of macrophages. In a previous study, we reported that biological response of these immune cells was activated by a specific PMMA particle size. In this study, biological responses of macrophages to particle parameters other than and in conjunction with size were evaluated. However, particle size as a biologically active factor of the biological response has not been characterized in detail. Here, macrophage viability and proinflammatory cytokine production were investigated to elucidate the relationship between particle size, added volume, and added surface area, and the biological response of macrophages. Decrease of cell viability was observed when relatively large particles were tested (5.6-19.3 μm). Production of proinflammatory cytokines was elicited by 5.6- and 9.6-μm particles. Cell death occurred when the added volume exceeded 1×105 μm3 per cell. Proinflammatory cytokines were produced upon stimulation with added volume between 1×105 and 4.5×105 μm3 per cell. Cell death was elicited when the added surface area per cell exceeded 1×105 μm2 and proinflammatory cytokines were produced with the added surface area per cell between 1×105 and 3×105 μm2. These results suggested that biologically active factors exert their effect through added volume and added surface area rather than through particle size. This work will contribute to biological responses after total joint replacement since particles generated in the joint as a result of load bearing lead to tissue reaction and joint loosening.