Constructing Multilayer Silk Protein/Nanosilver Biofunctionalized Hierarchically Structured 3D Printed Ti6Al4 V Scaffold for Repair of Infective Bone Defects

Abstract

Biomaterials-enabled regenerative medicine in orthopedics is challenged with infective bone defects that do not heal normally. Three-dimensional (3D) scaffold biomaterials simultaneously emulating skeletal hierarchy and eliciting sustainable osteogenetic and antibacterial functionalities represent a potent solution holding increasing fascination. Here we describe a simple combinatorial strategy for constructing such scaffolds. Fully porous titanium was first tailor-made by metallic powder 3D printing and subjected to in situ hydrothermal growth of a micro/nanostructured titanate layer, to which nanosilver encapsulated, physically cross-linked silk fibrin multilayer films were anchored through polydopamine-assisted, silk-on-silk self-assembly. The hydrophilicity, protein adsorption, and surface bioactivity of the scaffolds were investigated. Employing clinically relevant pathogenic Staphylococcus aureus bacteria, we tested that the silver immobilized scaffolds not only reduced adherence of bacteria on the surface, they also actively killed those planktonic, and these performances were largely maintained over an extended period of 6 weeks. Additionally, our engineered scaffolds were amenable to 14 days' continuous, intense bacterial attacks showing little sign of biofilm colonization, and they were interestingly capable of eradicating bacteria in already formed biofilms. High cargo loading, durable topical Ag⁺ release, and overwhelming oxidative stress were shown to contribute to this sustainable antibacterial system. Irrespective of certain degree of cellular stress at early stages, our scaffolds elicited generally enhanced cell proliferation, alkaline phosphatase enzyme production, and matrix calcification of osteoblastic MC3T3-E1. These multifunctionalities, coupled with the design freedom, shape flexibility, and cost-effectiveness offered by 3D printing, make our scaffold biomaterials a promising option for customized restoration of complicated infective bone defects.

Keywords: additive manufacturing; antibacterial; biomimetic; osteogenic; porous titanium; silk fibrin; silver nanoparticles (AgNPs).