Electrophoretic Deposition Of Biofunctional Macromoleculars On Titanium Implant Surface

Background and Objective:Titanium and titanium alloys are employed extensively in biomedical devices and components since the pioneering work of Branemark. Despite their great success in clinic, there are many challenges to overcome for extensive applications, because the implant failure may occur when the implants are positioned in bones with poor bone quality, insufficient bone quantity and poor postoperative healing that result from trauma, infection, osteoporosis and diabetes mellitus. In order to achieve greater application in compromised tissue conditions, a series of techniques have been explored to modify the titanium implant including alteration of surface physicochemical, morphological, biochemical properties of titanium implant. Another strategy is to cover titanium implant with the hydrogel coating.In the first portion, EPD was attempted to prepare pure chitosan and chitosan/gelatin coatings on titanium substrates. Gelatin was involved because it has been frequently blended with chitosan to improve mechanical and biological properties of the materials.Gelatin is a natural polymer that is derived from collagen. It has a number of properties which make it a suitable biomaterial, such as good biocompatibility, biodegradability, low immunogenicity and low cost. As gelatin can form a polyelectrolyte complex with chitosan at suitable pH values, it could be assembled onto titanium substrates by the vehicle of chitosan. Therefore, we hypothesized that chitosan and gelatin could be co-deposited on the titanium via EPD and the addition of gelatin would improve the mechanical and biological properties of the coating. The temperature of solution plays a key role in preserving the protein activity and cell viability during the EPD procedure. We tried to fabricate chitosan/gelatin coatings on titanium substrates by EPD processes at the temperature around four degree Celsius. However, the gel formation of gelatin in this temperature blocked the migration of the chitosan/gelatin particles under the influence of electric field. Therefore, silk fibroin, a fibrous protein extracted from natural silk, was used to form polyelectrolyte complex with oppositely charged chitosan in the mixed solution. Then, chitosan and silk fibroin could be co-deposited onto cathodic titanium substrate at low temperature (about 4℃).Mateirals:Pure chitosan and chitosan/gelatin (CS/G) blend solutions were prepared and deposited on titanium substrates via EPD. After EPD, the physiochemical property of coatings of different groups was described by Acridine Orange staining (AO), Scanning Electron Microscope (SEM), Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray powder Diffraction Pattern (XRD) and shear strength test. The cell behaviors on coatings of different groups were evaluated by Cell Counting Kit-8 (CCK-8), SEM and Rhodamine Phalloidin staining. Chitosan/silk fibroin composite coatings were deposited onto titanium substrates via EPD at about four degree Celsius which was recommended for protein stability and cell viability. The prepared coatings were characterized by fluorescence microscopy, scanning electron microscopy (SEM), element alalysis, thermo gravimetric analysis Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and shear strength test.Results:It was found that all chitosan/gelatin coatings had similar macro porous structure. The gelatin content and bonding strength of the coatings gradually increased with the increase of the gelatin in the blend solution. In vitro test demonstrated that human osteoblast-like cells (MG63) achieved better affinity on the coatings with higher gelatin content. The obtained gelatinous chitosan/silk fibroin coatings had a similar macroporous structure with pore size range from 100 to 300μm. The silk fibroin content in the coatings increased proportionally with the increase of the silk fibroin in the electrophoretic solutions. The shear and tensile bond strength of the coatings to titanium substrates increased with the increasing silk fibroin content. In vitro biological tests indicated that chitosan/silk fibroin composite coatings had better cellular affinity than pure chitosan coatings.Conclusion:Therefore, it was concluded that EPD was an effective and efficient technique to prepare chitosan-based coatings on the titanium surface, and that CS/G coatings with higher gelatin contents were promising candidates for further loading of functional molecules. The low temperature EPD is an advanced technique for preparing functional coating on titanium surface and chitosan/silk fibroin composite coatings were promising candidates for loading of bioactive protein and appropriate cells.