A multifunctional osteogenic system of ultrasonically spray deposited bone-active coatings on plasma-activated magnesium

Biomimetic bone-active coatings composed of inorganic nano-hydroxyapatite (i.e., nHA) and organic silk fibroin (i.e., SF) are layer-by-layer deposited on Mg-Zn-Ca alloy by a controllable ultrasonic spray method. Meanwhile, plasma activation is developed as a promising strategy to pretreat magnesium surfaces, which facilitates the direct adhesion of coatings with enhanced bonding interfaces. In this work, we engineer the nHA/SF composite coatings with excellent mechanical properties and adhesion force. The optimized parameters of ultrasonic spray bring significant influence on the surface morphologies of coatings. Assisted by hybrid plasma of oxygen and nitrogen (i.e., O2/N2 plasma), the activated Mg-Zn-Ca surfaces are uniformly covered by a robust and compact nHA/SF composite coating, establishing a multifunctional system with superior corrosion resistance and biological performance. Interestingly, secondary oxygen plasma treatment of nHA/SF coatings (A-nHA/SF) promotes the hydrophilicity, leading to a rapid self-repair effect from surface damage. The improvement of anti-corrosion and self-repair provides a dependable platform for better cell adhesion, proliferation, spreading and differentiation. These favorable factors contribute to the preferable in vivo biocompatibility and the promotion of newly formed bones for the A-nHA/SF-coated Mg implants. This study lays important foundations for coating strategy on biomedical magnesium alloy as multifunctional osteogenic system in bioactive implantable applications.