| Bone is an important part of human body and has vital functions including protecting organs and supporting movement.Orthopedic implants,such as bone nails and plates,are often used for internal fixation of fracture treatment.Metals have become the most important raw materials for implant devices due to their excellent mechanical properties,fatigue resistance,and ease of processing.However,traditional metal implants have to be removed through secondary surgery after the injured tissue has healed,which increases the medical burden of patients.Biodegradable metals can not only provide sufficient mechanical support at the initial stage of fracture repair,but also be degraded and absorbed after healing,avoiding the need for secondary surgery.Therefore,they are expected to replace traditional metals and become the preferred materials for orthopedic implants.In recent years,magnesium(Mg)alloy and zinc(Zn)alloy have gained popularity as promising candidates for biodegradable implant materials.Among them,Mg alloy has excellent biocompatibility and density close to human bone.However,the degradation rate of Mg alloy in physiological medium is too fast to meet the required mechanical strength during the formation of new tissue.Zn alloy also has good biocompatibility,but contrary to Mg alloy,the degradation rate of Zn alloy in physiological medium is too slow,and it will still exist in human body for a long time after tissue repair,which is not conducive to show the advantages of biodegradable implants.In addition,implant-associated infections during and after implantation increase the risk of implantation failure.Polymer surface modification provides one feasible strategy for simultaneously regulating the degradation rate of degradable metals and reducing the probability of microbial infection.In this paper,according to the characteristics of Mg alloy and Zn alloy,a targeted polymer coating modification scheme is designed.The specific research contents are divided into the following two parts:(1)Based on the electropolymerization characteristics of pyrrole,gallic aciddoped polypyrrole(PPy/GA)coating was prepared on Mg alloy surface by electrochemical deposition method.The effects of deposition conditions on the corrosion protection abilities of the PPy/GA coatings were investigated.And the effects of the PPy/GA coatings on the adhesion strength,biocompatibility,and antibacterial properties of Mg alloy substrate were investigated.The results showed that when the deposition voltage was 0.95 V,the deposition time was 5 min,and the molar ratio of gallic acid to pyrrole monomer in the deposition solution was 0.2,the PPy/GA-coated Mg alloy showed good performance on corrosion resistance.Compared with pure polypyrrole coating,gallic acid doping improved the adhesion strength between polypyrrole coating and Mg alloy substrate from grade 1 to grade 0.In vitro cytocompatibility tests showed that the PPy/GA coating exhibited acceptable cell compatibility.In vitro antibacterial tests revealed that the PPy/GA-coated Mg alloy showed remarkable antibacterial rates of 99.77 ± 3.59 % and 99.61 ± 1.56 % against Escherichia coli and Staphylococcus aureus,respectively,indicating that PPy/GA coating endowed Mg alloy excellent antibacterial property.(2)Natural polymer γ-polyglutamic acid(γ-PGA)was modified with dopamine(DA)to obtain γ-PGA-g-DA.Subsequently,based on the electrostatic interaction and chelation between γ-PGA-g-DA and copper ion(Cu),γ-PGA-g-DA/Cu colloidal particles were prepared by self-assembly method.The effect of assembly conditions on the stability of colloidal particles was investigated.Then,the γ-PGA-g-DA/Cu composite coatings were prepared on Zn alloy surface by electrophoretic deposition technology.The effects of the coating on the degradation behavior,biocompatibility,and antibacterial properties of Zn alloy were studied.The results showed that the γ-PGA-g-DA/Cu colloidal particles could exist stably in the mixed solution of dimethyl sulfoxide and absolute ethanol,and their surface charge values were about-25 m V.When the deposition voltage was 150 V,and the deposition time was 5 min,the γ-PGAg-DA/Cu coatings were dense and uniform.In vitro degradation rate of bare Zn alloy was 0.0246 ± 0.0037 mm/year.The γ-PGA-g-DA/Cu coatings accelerated the degradation of Zn alloy substrate to 0.0456 ± 0.0028 mm/year.In vitro cytocompatibility tests revealed that the release of copper could reduce the cytotoxicity caused by zinc ions and improve the living environment of cells.With the increase of copper content in the γ-PGA-g-DA/Cu coatings,the antibacterial properties of the coating samples were gradually enhanced.The highest antibacterial rate of the coatedZn alloy against Escherichia coli and Staphylococcus aureus was achieved with 99.72± 1.36 % and 98.68 ± 1.37 %,respectively,showing significant antibacterial ability. |
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