Abstract: Objective To compare physicochemical properties and biocompatibility of cobalt-chromium (Co-Cr) alloy in 3D printing technology and conventional alloy casting technique. Methods The experimental group and the control group each contained 10 Co-Cr alloy specimens fabricated by selective laser melting (SLM) and traditional casting technology respectively. The Rockwell hardness tester HR-150A and the metallurgical microscope were used to compare two groups respectively, and then polarization curve was measured on metal specimens under self-corrosion potential. Leaching solution of the test piece was prepared in a sterile environment, and was divided into negative control group, 3D printing Co-Cr alloy group and cast Co-Cr alloy group (5 per group). Using CCK-8 reagent, the cytotoxicity of the extract to mouse fibroblast L-929 was determined, and the apoptosis was detected by AnnexinⅤ-FITC/PI fluorescence staining; the apoptosis rate of different groups was calculated by flow cytometry. Results The Rockwell hardness of the 3D printing group and the casting group were 70.6±0.1 and 68.5±0.2, respectively. The 3D printing group was stronger than the casting group, and the difference between two groups was statistically significant (P<0.005). The 3D printed Co-Cr alloy structure didn’t have a second phase; the cast structure was dendritic, and the second phase was strengthened. The current densities of the 3D printing and casting groups of Co-Cr alloys under self-corrosion potential were 4.338 1×10^-9 A/cm² and 3.378 5×10^-8 A/cm², respectively. The current density of the casting group was higher than that of the 3D printing group. At 24, 48 and 72 h, the average OD of the negative control group was approximately 0.44, 1.14, 1.50, the 3D group was 0.39, 0.95, 1.09, the casting group was 0.35, 0.76, 1.01. The differences in cytotoxicity between groups were statistically significant (P<0.05). The casting group had the strongest cytotoxicity, and the cytotoxicity of each group gradually increased with time. Flow cytometry suggested primarily normal cells existed in three groups, and the apoptotic rates were (2.497±0.121)%, (3.513±0.055)%, (5.407±0.401)%, and there was statistical significance among each group (P<0.01). Conclusion Compared with traditional casting technology, the cobalt-chromium alloy using 3D printing technology has better mechanical properties and biocompatibility, and has better prospect for clinical application.

Key words: 3D printing, conventional casting, cobalt-chromium alloy, cell apoptosis