Effect of silica particles on membrane damage. Cellular membrane damage in HaCaT cells after incubation with nSP70 (circles), nSP300 (squares) and mSP1000 (diamonds) for 24 h was evaluated by the LDH release assay. The percentage cellular membrane damage was calculated relative to the negative (medium) controls. Data are presented as means ± SD (n = 3).*P < 0.01 vs same dose of nSP300 and mSP1000.