Construction And Biological Properties Of Ag Loaded Polydopamine Films On NiTi Alloy

NiTi alloys have been widely applied in the bio-medical field owing to their unique shape memory effect,superelasticity,and good biocompatibility,however,the lack of antibacterial properties and the Ni release might induce possible post-surgical infections,carcinogenic,and teratogenic response.In this paper,the Ag loaded polydopamine films were constructed on the surface of NiTi alloy to impart antibacterial properties to the alloy while improving corrosion resistance,inhibiting Ni ion release,and improving biocompatibility.XPS,FT-IR,FE-SEM,TEM,AFM,electrochemical-based analytical test,ion release test,and in vitro antibacterial test were used to systematically investigate the structure,corrosion resistance,Ag ion release behaviors,and antibacterial properties of the Ag loaded polydopamine films.The NiTi alloy was immersed in dopamine solution to prepare polydopamine（PDA）film.With increase of immersion time,dopamine continuously self-polymerized and deposited on the surface of NiTi alloy,which increased the thickness of the PDA film,improved the corrosion resistance,and inhibited Ni ion release;The increase of surface roughness of PDA film,the enhancement of hydrophilicity and the reactive groups on the surface of the film were favorable to the cell adhesion and proliferation.Using in situ reduction of Ag ions on the surface of PDA film,the Ag loaded polydopamine film（PDA/Ag film）was constructed by preparing PDA film on the surface of NiTi alloy and then immersed in AgNO₃ solution.The Ag nanoparticles distributed on the surface of the PDA film lead to the fast Ag ions release of PDA/Ag film during the initial stage after immersing in PBS solution,good short-term antibacterial performance.After immersing in PBS solution for 14 days,the Ag release tends to stop.During the forming of the PDA/Ag film,the oxidation of Ag ions increases the crosslinking degree of the PDA film,therefore,reducing the self corrosion current density and significantly enhances the corrosion resistance.PDA/Ag/PDA films were constructed by preparing PDA/Ag films on the surface of NiTi alloy and then immersed in dopamine solution to prepare a surface PDA film.The surface PDA film covered on Ag nanoparticles delayed the dissolution rate of Ag ions in PBS solution,which reduced the short-term antibacterial effect but improved the antibacterial persistence.The release rate of Ag ions in PBS solution of PDA/Ag/PDA film increased and then decreased,and the rate reached the maximum at the 7th-12th hours.The release of Ag ions did not stop after 28days.In addition,the self-corrosion current density of the PDA/Ag/PDA film decreased,and the corrosion resistance was enhanced compared to that of the PDA/Ag film.The NiTi alloy was immersed in a mixture of dopamine and AgNO₃ to construct an Ag loaded polydopamine film（PDA@Ag film）in one step,and PDA wrapped the Ag nanoparticles in the film.The Ag content increased and then decreased from the free surface of the PDA@Ag film to the NiTi surface.The results showed that low AgNO₃ concentration,high dopamine concentration,and long immersion time could increase the PDA content in the PDA@Ag film,reduce the self-corrosion current density,Ag content,and Ag ion release rate,which were beneficial to improve the corrosion resistance and antibacterial persistence.In contrast,high AgNO₃ concentration,low dopamine concentration,and short immersion time could reduce the PDA content in PDA@Ag film and increase the self-corrosion current density,Ag content,and Ag ion release rate,which were beneficial to improve the short-term antibacterial effect.When the NiTi alloy was immersed in a mixture of2mg/m L dopamine and 40 m M AgNO₃ for 12 h,the prepared PDA@Ag film had good corrosion resistance,fast Ag ion release rate and long duration in the PBS solution,and excellent antibacterial performance,with the antibacterial rate of more than 99%against S.aureus and E.coli at 24 h.