Bioinspired Polydopamine Functionalization Of Titanium Surface For Silver Nanoparticles Immobilization With Antibacterial Property

Titanium is extensively used as load-bearing implants due to its excellent biocompatibility and high mechanical strength. However, the titanium surfaces of implants are suitable for microbial colonization and biofilm formation, which may lead to a high potential for chronic osteomyelitis or limb loss, even death. Besides, the host tissue response to titanium implant is not always favorable due to its bioinert nature with a native oxide layer. There is clearly a pressing need to develop a method for preventing the bacterial infection and improving osteogenic activity of titanium implants. In this study, an antibacterial composite layer was fabricated on titanium surface via chemical oxidation to produce nanostructures, grafting to generate polydopamine (PDA) layer and subsequent in situ reduction process to embed Ag nanoparticles (AgNPs) onto Ti-PDA surface. The main results and progress of this work are listed as following:To further enhance the biological properties of microrough titanium surfaces, titania nanotextured thin films were produced by simple chemical oxidation, without significantly altering the existing acid-etched microtopograpy. The nanotextured layers on titanium surfaces can be controllably varied by tuning the oxidation parameter such as the composition of oxidant etchant, duration time and temperature. Results showed that the oxidation treatment significantly reduced water contact angles and increased the surface energy compared to the surfaces prior to oxidation. The murine bone marrow stromal cells (BMSCs) were used to evaluate the bioactivity. In comparison, oxidative nanopatterning of microrough titanium surfaces led to improved attachment and proliferation of BMSCs. The rate of osteoblastic differentiation was also represented by the increased levels of alkaline phosphatase activity and mineral deposition.Further, a bioinspired PDA layer was deposited on nanotextured titanium surface by simply dipping the substrate into an alkaline dopamine solution. The in vitro bioactivity of the polydopamine coated titanium was assessed by incubation in simulated body fluids (SBF). The results showed that surface-anchored catecholamine moieties in polydopamine enriched the interface with calcium ions, facilitating the deposition of hydroxyapatite. The results of protein adsorption showed that Ti-PDA surfaces adsorbed greater amount of bovine serum albumin (BSA) than other titanium surfaces. The adhesion and proliferation of osteoblast cells were also enhanced on Ti-PDA surfaces.The reductive property of the PDA coating was utilized to facilely introduce AgNPs onto titanium surfaces by immersing the Ti-PDA in silver nitrate solution. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) revealed that the content of AgNPs on titanium surface increased with the reaction time (1h,2h and4h). Less than20%silver release as Ag+has been found after5days when all the modified surfaces were exposed to deionized water. The Ti-P-Agl and Ti-P-Ag2samples inhibited the growth of staphylococcus aureus and preserved good cytocompatibility, while the Ti-P-Ag4sample showing low surface toxicity to the osteoblast cells. Our results showed that the content of the AgNPs were important in the control of the cytotoxicity and this study opens a new window for the design of antibacterial titanium surfaces on which the biological actions of the AgNPs can be accurately tailored.