Fig. 4

a Cytotoxicity of Cu NDs on L929 and chondrocyte. b Cytotoxicity of Cu NDs on activated RAW264.7 and inactivated RAW264.7. c Cell viability of L929 and chondrocyte with different treatments. d Cell viability of activated RAW264.7 and inactivated RAW264.7 with different treatments. e Fluorescence images of Calcein-AM/PI staining of chondrocyte after incubation with different concentrations of PRP in HPP@Cu gel. Scale bars = 100 μm. f Cell viabilities of chondrocyte under different treatment conditions. Data represent means ± SD, n = 5. **p < 0.01, ##p < 0.01, and &&p < 0.01. NS means not significant. g Quantification of the ratio of apoptotic and living cells by flow cytometry analysis according (h). h Flow cytometry analysis of apoptotic and necrotic cells under different treatment conditions. In a–d, data represent means ± SD, n = 5