[Effect of osteon-like concentric microgroove structures of different sizes on the osteoclastic differentiation of macrophages].

Objective: To investigate the effect of the sizes of osteon-like concentric microgroove structures on the osteoclastic differentiation of macrophages on titanium surfaces, and to provide reference for the surface modification of implants. Methods: The silicon wafers sputtered with titanium were selected as the control group (smooth surface specimens) and four concentric groups (concentric circles with the maximum diameter of 200 μm, the minimum diameter of 20 μ m, the spacing of concentric circles of 10 or 30 μm, the width of microgrooves of 10 or 30 μm, and the depth of microgrooves of 5 or 10 μm) specimens (the total sample size in each group was 27). The width of microgrooves of C10-5 and C10-10 groups was 10 μm, the depth was 5 and 10 μm, and the width of microgrooves of C30-5 and C30-10 groups was 30 μ m, the depth was 5 and 10 μ m, respectively. The physicochemical properties of the material surfaces were characterized using scanning electron microscopy and contact-angle measurement. The proliferation, adhesion of macrophage-like cell line RAW264.7 and the formation of osteoclast actin-rings on the specimen surfaces were observed by cell counting kit-8 (CCK-8), immunofluorescence staining and laser confocal microscopy. Tartrate resistant acid phosphatase (TRAP) quantitative detection, real-time fluorescence quantitative PCR (RT-qPCR) and Western blotting were used to investigate the regulation of osteon-like concentric microgroove structures on the specimen surfaces on the osteoclastic differentiation of macrophages. Results: Macrophages aggregated and grew disorderly on the surface of the smooth group, and arranged in concentric circles along the microgroove structures on the surfaces of the concentric groups. After 5 days of culture, the cell proliferation of C30 groups (the A values of C30-5 group and C30-10 group were 1.335±0.018 and 1.340±0.033, respectively) was significantly higher than that of C10 groups (the A values of C10-5 group and C10-10 group were 0.967±0.015 and 1.182±0.020, respectively)(all P<0.05). The cell proliferation of the four concentric groups was significantly higher than that of the control group (the A value was 0.796±0.012), with statistical significance (all P<0.05). After osteoclastic induction for 5 days the osteoclasts induced in the C10-5 and C10-10 groups exhibited smaller actin rings and fewer numbers. The TRAP activity in each concentric group was significantly lower than that in the control group (P<0.05). The expression levels of osteoclast differentiation-related genes TRAP (0.610±0.022) in the C10-10 group was lowest, and CtsK (0.489±0.136, 0.445±0.037) in the C10-5 and C10-10 groups were lower compared to the smooth group and other concentric groups, with statistical significance (all P<0.05), the expression levels of osteoclast differentiation-related proteins TRAP (0.648±0.041), MMP-9 (0.688±0.026) in the C10-10 group were lowest, and CtsK (0.491±0.016, 0.453±0.010) in the C10-10 and C30-10 groups were also lower compared to the smooth group and other concentric groups, with statistical significance (all P<0.05). Conclusions: The osteon-like concentric microgroove structures inhibit the osteoclastic differentiation of macrophage-like cell line RAW264.7, with the microgrooves 10 μm wide and 10 μm deep showing the most significant inhibitory effect on the osteoclastic differentiation.