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In Vitro and in Vivo Studies of Selective Laser Melting-Mediated Surface Concave Microwell Treatment to Enhance Osteogenesis and Osseointegration of Nanohydroxyapatite/Polyamide 66 Implants

The structural and functional combination of an implant and living bone is greatly influenced by the surface characteristics of the implant. To enhance the implant-bone interface regarding the osteointegration of nanohydroxyapatite/polyamide66 (nHA/PA66) material, concave microwells that were 100 μm, 200 μm and 400 μm in size (denoted by P100, P200, and P400, respectively) were prepared on the nHA/PA66 substrate surface by selective laser melting (SLM) technology. The surface characteristics of these samples were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), 3D scanning laser microscopy and static water contact angle measurements. We examined the effects of different concave microwell sizes on the adhesion, proliferation and osteogenesis of C3H10T1/2 cells in vitro by cell counting kit-8 (CCK-8), SEM, alkaline phosphatase assay, alizarin red staining, and western blot, and continued our evaluating through micro-CT, histological analysis and push-out tests to verify the osseointegration ability in vivo. P100, P200 and P400 surface modification led to significant increases in concave microwell diameter, depth and surface roughness, and the contact angle measurements showed that only the hydrophilicity of P100 microwells was improved. In vitro testing revealed that P100 microwells could effectively promote the adhesion, proliferation and osteogenic differentiation of C3H10T1/2 cells; in vivo studies further confirmed that P100 microwells significantly increased new bone volume, enhanced bone remodeling, and improved material-bone interface bonding force and instigated rapid osteointegration of nHA/PA66 with host bone. However, these phenomena were not observed for P200 and P400 microwells. Overall, P100 was associated with improved cell adhesion, proliferation and osteogenic differentiation in vitro and greater implant fixation in vivo. These results suggest that surface concave microwell treatment of nHA/PA66 material through SLM technology provides a fast, simple and effective method for clinical applications involving bone tissue regeneration.