Long-Term In Vitro Corrosion Behavior Of Degradable Absorbable Zinc Metals In Various Simulated Body Fluids

Zinc-based biodegradable materials have gained significant attention in recent years due to their biodegradability,biocompatibility,intrinsic physiological relevance and proregeneration properties.More importantly,the thermodynamic stability of zinc is between the widely studied degradable magnesium and iron,indicating zinc possesses a moderate degradation rate in vivo.Therefore,zinc-based metals are considered as the most likely breakthroughs in biodegradable metallic materials.However,as a newcomer in degradable metals,the research of zinc-based biodegradable materials has just been at its early stage.There are still many problems to explore,especially the deeper understanding of its the degradation behavior of zinc in the service of the implant site.It is an effective way to predict the long-term corrosion behavior of zinc in vivo with simulating the physiological environment in vitro.It provides a basis for data accumulation and guidance for further surface modification work,as well as guidance for the selection of simulated body fluids for zinc research in vitro.However,most of the studies focused on its short-term corrosion degradation,lack offering systematic studies on its long-term corrosion degradation in terms of electrochemical corrosion,evolution of corrosion products,corrosion modes and corrosion mechanisms.The corrosion evolution of zinc in phosphate buffered saline(PBS),Ringer's solution(RS),simulated body fluid(SBF)and DME/F-12 cell culture medium(F12)was studied by long-term immersion(56 days),including the evolution of electrochemical corrosion,surface corrosion products and corrosion modes after removal of corrosion products.According to the transient(pre-immersion)and in-situ dynamic electrochemical(open circuit potential,potentiodynamic polarization and electrochemical impedance spectroscopy)corrosion behavior results at different time points,it shows that the samples in F12 exhibit the greatest electrochemical impedance and the lowest corrosion degradation rate;the samples in PBS exhibit the smallest electrochemical impedance and the highest corrosion degradation rate;the electrochemical impedances and corrosion rates of samples in RS and SBF are similar and lie between that of samples in F12 and PBS.The morphology and structure of corrosion products were analyzed by optical microscopy and scanning electron microscopy.The composition of corrosion products was determined by X-ray diffraction,infrared spectroscopy and X-ray photoelectron spectroscopy.The results showed that the surface of sample immersed in PBS was mainly composed of zinc phosphate,the thickest porous white corrosion product layer;the surface of sample immersed in RS was covered by a relatively thick and dense rod-like corrosion product layer composed of calcium carbonate and zinc carbonate;the surface of sample immersed in SBF was covered by a loose white spherical granular corrosion product layer composed of amorphous calcium phosphate and zinc phosphate;the surface of sample immersed in F12 was covered by a very thin and dense corrosion product layer composed of phosphate,calcium phosphate,carbonate and organic compounds.The corrosion pattern evolution of zinc in simulated body fluids with different composition was analyzed after removing corrosion products.The results show that the samples in PBS,RS and SBF exhibit severe localized corrosion.Corrosion pits(holes)or corrosion grooves appear.The porous or incomplete corrosion product layer results in the formation of self-catalytic effect and galvanic corrosion model in pit areas.Further,the longitudinal corrosion of zinc substrates is promoted.Moreover,there are relatively uniform corrosion pits on the surface of F12 sample,which are similar to uniform corrosion mode.The results showed that the composition of solution was important for evaluating the degradation behavior of zinc in vitro.In the carbonate solution system,the formed corrosion products were mainly composed of carbonate.Besides,phosphate corrosion products were formed on the surface of zinc in other solutions.The formation of insoluble salts and the presence of organics on the surface in F12 delayed the degradation of zinc.In this study,the corrosive models of different solution compositions were established to investigate the mechanism of the effects of different components on the long-term degradation behavior of pure zinc in vitro.The research provides data accumulation and research basis for the selection of simulated body fluids for zinc in vitro evaluation,late surface modification and potential biomedical applications.