Electrochemical Preparation And Characterization Of The HAp/Ag Composite Coating

As the increase of life quality,further improvements of bioactivity and safety of the biomaterials are very much demanded.Hydroxyapatite(HAp) coated titanium is an ideal biomaterial commonly used for prosthesis and implants in surgery and orthopaedics.Hydroxyapatite,the main inorganic compound of natural bone,is osteoconductive and able to accelerate bone ingrowth.In addition,it is also selected as an attachment to the surface of implants during the early stages after implantation. Metallic titanium possesses high mechanical strength,excellent corrosion resistance, and good compatibility with bone,however,the bioactive environment on HAp may be also a soil for bacteria to propagate.Infection remains a leading cause of morbidity of injured patients.About 90%of all biomaterials still have bacteria after sterilization. Metallic silver and silver salt own high antibacterial activity.Therefore,the antibacterial hydroxyapatite(HAp)-silver(Ag) composite coating on titanium has been attractive and valuable for clinical application.In this paper,the electrochemical deposition was employed to deposit a HAp/Ag composite coating on titanium.The experiments were carried out to study the conditions of preparation and properties(especially the antibacterial property) of the composite coating.The main results and progress of this work are listed as following:1.The 5-30μm silver granules were pre-deposited on titanium in the electrolyte containing KI and AgNO₃.After that,the electrocodeposition was carried out to form a DCPD/Ag coating on the titanium plate with silver granules in the solution containing CaCl₂,NaH₂PO₄,AgNO₃ and KI.The DCPD/Ag composite coating was then transformed to HAp/Ag by the treatment in 2.5 M NaOH at 75℃for 3 h.The maximum adhesion strength of the composite coating to titanium substrate reached 31.04±4 MPa,which was much stronger than that of the pure HAp coated titanium (14.65±2MPa).It is indicated,from the results of the antibacterial tests,that the composite coating has total inhibition to E.coli and it is nontoxic compared to the pure hydroxyapatite coating.The SEM images reveal that the osteoblasts attach and proliferate well on the HAp/Ag coating by cell culture experiments.2.The 5-20 nm silver nanoparticles were prepared by sodium citrate reduction of AgNO₃.The silver sol was diluted to solutions with different Ag concentration by ethanol as the deposit solution.Then the silver nanoparticles were electrophoretic deposited on the top of titanium substrate.Subsequently,hydroxyapatite was electrochemically deposited on the top of silver particles.According to the SEM images and antibacterial tests,it is demonstrated that when the concentration of the electrophoretic solution is higher,more silver particles would be deposited on the surface,and it shows a better antibacterial property.However,the particles may aggregate on titanium greatly when the concentration of silver particles exceeds a critical point,and the antibacterial activity declines.Accordingly,the technique was optimized to prepare the composite biomaterial with high antibacterial property.It is found that the aggregation of the silver nanoparticles may lead to low ability of Ag⁰ release,which is the key factor of antibacterial activity.Furthermore,we synthesized silver nanopaticles with different shapes including tetrahedron/cube and hexagon and compared their antibacterial activity with each other.It is indicated that antibacterial property can be influenced by not only the surface area and size but also the shape of particles.