In addition to customizing shapes of metal bone substitutes for patients, the 3D printing technique can reduce the modulus of the substitutes through the design and manufacture of interconnected porous structures, achieving the modulus match between substitute and surrounding bone to improve implant longevity. However, the porous bone substitutes take more risks of postoperative infection due to its much larger surface area compared with the traditional casting solid bone substitute. Here, we prepared of gentamicin-loaded silk fibroin coatings on 3D-printed porous cobalt-chromium-molybdenum (CoCrMo) bone substitutes via electrophoretic deposition technique. Through optimization, relatively intact, continuous, homogeneous, and conformal coatings with a thickness of 2.30 ± 0.58 μm were deposited around the struts with few pore blocked. The porous metal structures exhibited no loss in mechanical properties after the anode galvanic corrosion in EPD process. The initial osteoblastic response on coatings was better than that on metal surface, including cell spreading, proliferation and cytotoxicity. Antibacterial efficacy experiments showed that the coatings had an antibacterial effect on both adherent and planktonic bacteria within 1 week. These results suggested that the beneficial properties of anode electrophoretic deposited silk fibroin coatings could be exploited to improve the biological functionality of porous structures made of medical metals.
The difficulties associated with metal implants and soft tissue integration have significantly affected the applications of metal implants in soft-tissue-related areas. Prompted by the close association between soft tissue integration and the immune response, an immunomodulation-based strategy is proposed to manipulate the immune microenvironment and improve metal implantsoft tissue integration. Considering their vital roles in soft tissue responses to metal implants, macrophages are used and the cytokines fingerprints of M1 and M2 macrophage immune microenvironments are evaluated for their potential modulatory effects on metal implant-soft tissue integration. The modulatory effects of different immune microenvironments on model soft tissue cells (human gingival epithelium cells) cultured on model metal implants (titanium alloy disks) are then described, with the underlying possible mechanism FAK-AKT-mTOR signaling unveiled. As further proof of concept, IL-4/PDA (polydopamine)-coated titanium alloy implants, aiming at modulating M2 macrophage polarization, are prepared and found to improve the in vivo metal implant-soft tissue integration. It is the authors' ambition that this immunomodulation-based strategy will change the negative perception and encourage the active development of metal materials with favorable soft tissue integration properties, thus improving the success rates of perforating metal implants and broadening their application in soft-tissue-related areas.
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