Preparation, Characterization And Evaluation Of Drug-Loadable Biopolymer/Calcium Phosphate Composite Coatings With Porous Structure

Biomedical titanium implants can meet the application for bear-loading bone repair, because titanium has good properties such as low density, excellent corrosion resistance, no sensitization response and good biocompatibility. A key issue for implants is to accelerate osteointegration and improve its quality. In this thesis, an approach was adopted by controlling the surface composition and structure for facilitating the attachment and proliferation of cells, as well as to loading and sustained release of antibiotics against for providing a desired environment for bone growth.Titanium substrate was firstly treated with alkali-heat treatment to form titanium dioxide on th surface. Then, porous chitosan/calcium phosphate (CPC) coating was deposited on the substrate by electrochemical method. Collagen/Chitosan/Calcium phosphate (CC) coating was prepared by electrochemical co-deposition. The composition and surface topography, biological behaviors and drug release behaviors of the coatings were studied. The main results are summarized as:(1) For electrochemical deposition of porous CPC coating by calcium phosphate and chitosan in the electrolyte, the results showed:The coating with porous structure could be achieved by adjusting deposition potential, the concentration of chitosan and calcium phosphate in the electrolyte. The scratch strength between substrate and the CPC coating was obviously increased with the addition of chitosan. The mechanism of porous CPC coating formation was proposed as hydrogen gas bubble modeling based on the thermodynamics of calcium phosphate systems and the pore formation behavior. When the pH in electrolyte was ranged from4.3to5.5, the deposition potential was crucial for controlling the formation rate of hydrogen gas bubbles, and the average pore size from5um to500nm could be formed if the potential was fixed from1.5V to1.1V. And the outer interconnecting pore size was bigger than the inner ones.(2) For electrochemical deposition of CC composite coating by calcium phosphate, chitosan and collagen in the electrolyte, the result showed that when the deposition parameters were set as pH=4.9, U=1.3V, T=37℃, CCs=3.4mg/mL, CCol=0.16mg/mL, CCa=40mM, Cp=13.3mM, the collagen could be self-organized to form collagen fibril and mineralized to form a layer, and the mineralized layer existed as the out layer of the coating. During the deposition, the mineralization of collagen was easy to mineralize because the collagen could induce the formation of calcium phosphate, and the mineralization degree could be controlled by the collagen concentration in the electrolyte; the microstructure of the mineralized collagen layer also depended on the pH, electrolyte and the deposition potential.(3) For evaluation of bioactivity and cell behavior in vitro, soaking in stimulated body fluid (SBF) showed that the porous CPC coating and CC coating both had good bioactivity, and the CC coating was better; The laser scanning confocal microscope (LSCM) and SEM observations of the MG63cell cultured on the coatings indicated that the CC coatings were more favorable for cell spreading at the starting stage (4h) than CPC coatings; the MTT results showed the CC coating> the CPC coating> Ti for cell attachment; these could be attributed to that collagen played a significant role in enhancing mineralization and cell attachment. The MC3T3-el cell culture result indicated that the pore size of the coatings influenced the cell behaviors, and the microstructure of mineralized collagen layer in CC coating and the crystalline phases of calcium phosphate in CPC coating also had impacts on cell behavior.(4) For the drug loading and release behavior evaluation for the coatings, the release of antibiotic was faster in the coating with larger pores. The drug release rate in CC coating was slower than that in CPC coating. The drug sustained release behavior could be enhanced with coverage of CS membranes. A better approach was suggested to incorporate drug loaded CS nano-particles into the porous coating, and the present porous coatings with larger pore size could provide a platform to accommodate the nano-particles.Our work demonstrated that the chitosan/calcium phosphate coatings and collagen/chitosan/calcium phosphate coatings on alkali treated titanium substrates had good cytocompatibility and reasonably good drug loading-release behavior, these coatings could be used to enhanced ossteointegration and make significances in bear-loading bone substitution.