Preparation and Research of pH-Responsive Antibacterial Coatings Based on Polyphenol-silver Complexes
Titanium and titanium alloys have a wide range of clinical applications in dental implants,bone screws,and artificial hip joints.However,due to their biological inertia and lack of antibacterial properties,excellent osseointegration cannot be achieved after surgery,they are prone to bacterial infection,inflammation,and implant failure.Surface modification can effectively endow it with biological functions such as promoting bone growth,antibacterial and anti-inflammatory.In view of the bacterial infection of the implant,according to the low pH value of the surrounding environment of the infected tissue,the construction of pH-responsive antibacterial function on the surface of the implant has become a research hotspot.In this study,metal-polyphenol network(MPN)was used to graft silver ions in TiO2(titanium dioxide)nanotubes,and the responsive release of silver ions was achieved by the pH responsiveness of MPN.In order to endow the surface of medical titanium with pH-responsive antibacterial function,TiO2 nanotubes(TNTs)were prepared on the surface of pure titanium by anodic oxidation,followed by ultrasonic deposition of a polydopamine layer(PDA)and then the complex of gallic acid and silver ion was loaded into the nanotubes by chemical grafting.Silver ions had good antibacterial ability.Gallic acid,as a polyphenol compound,had anti-inflammatory,anti-oxidation and other biological functions.It could cooperate with metal ions to enhance antibacterial activity.The complexation of gallic acid and silver ions could form pH-responsive MPN.The preparation of silver-loaded titanium dioxide nanotubes on the surface of pure titanium was realized.The morphology and composition of the coating were analyzed by SEM,XRD,FTIR and XPS,and the release behavior of silver ions and antibacterial ability of coatings at different pH were evaluated.SEM and XRD results showed that the prepared TNTs were mainly anatase titanium dioxide.The TNTs-PDA-Ag sample had a porous surface,the diameter of the tube was reduced to 60 nm,and the effective loading of silver ions was realized.FTIR and XPS results showed that the crosslinking of PDA and GA occurred on the surface of TNTs-PDA-Ag,and silver ions were successfully loaded by phenolic hydroxyl groups.The atomic percentage of Ag on the surface was about 2.9％,and the percentage of C(69.13％)was significantly increased compared with that of TNTs-PDA(37.09％).After in vitro mineralization,HA(hydroxyapatite)was formed on the surface of TNTs-PDA-Ag.The Ag+release rate of the coating was heterogeneous in different pH phosphate buffer solution.When the coating was immersed in pH 4.5 environment for 7 days,the silver ion release rate and release ratio(97.65％)of silver ions were significantly higher than those under neutral conditions.In the antibacterial experiment,the release concentration of Ag+was between 5.56-13 μmol/L,which had obvious antibacterial effect on Escherichia coli.The prepared silver-loaded titanium dioxide nanotube coating can effectively improve the bone biocompatibility of the material,and has pH-responsive antibacterial function,which has great application potential on the surface of medical titanium.
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