Preparation And Properties Of Antibacterial Active Coatings On 3D Printed Porous Titanium Scaffolds

Medical titanium and titanium alloys have a series of advantages such as low density,excellent mechanical properties and corrosion resistance,good biocompatibility and low elastic modulus,and are widely used in medical fields such as dentistry and orthopedics.3D printing technology has the advantages of rapid prototyping and high precision.Using 3D printing technology to fabricate personalized titanium implants can adjust the 3D porous/mesh structure parameters,make the mechanical properties of metal scaffolds more in line with the requirements of defect repair,and realize the precise matching of bone defect sites.Therefore,3D printed metal implants have received extensive attention.However,the lack of biological activity on the surface of 3D printed titanium implants prevents direct bonding with bone tissue.In addition,titanium implants have the insufficient antibacterial ability,and bacteria tend to adhere to the implant surface and proliferate,forming dense biofilm,which will lead to the failure of implant surgery.Therefore,it is of great significance to modify the surface of 3D printed titanium implants to improve their biological activity and endow them with antibacterial ability.In this paper,the mesoporous bioactive glass（MBG）was prepared by a self-assembled template method,and the mesoporous bioactive glass coating was bonded to the 3D printed titanium implant by the dip method to improve its bioactivity.Introduce antibacterial elements zinc,copper,and silver into the active coating to give the coating antibacterial properties,and explore the optimal doping amount of antibacterial elements zinc,copper,and silver,that is,while imparting antibacterial properties to 3D printed titanium implants,without causing cytotoxicity.In this paper,the physicochemical properties,in vitro mineralization properties,antibacterial properties and cytocompatibility of mesoporous bioglass-coated porous scaffolds with different elements contents were investigated.Firstly,MBG coatings doped with 1 mol%,3 mol%and 5 mol%Zn were prepared on the surface of 3D printed titanium scaffolds by dipping method.The thickness of the coating was about4-5μm,and the coating bonded well with the substrate.It was found that zinc existed in the MBG coating in the form of amorphous Zn O and Zn²⁺.The doping of Zn significantly reduced the specific surface area of the MBG coating.With the increase of Zn content from 1 mol%to 5 mol%,the specific surface area of the MBG coating decreased from 377.6 m²/g to 174.5 m²/g,resulting in the decrease of apatite induced formation ability.The bactericidal effect of Zn on E.coli and S.aureus was significant and dose-dependent.The results of in vitro mouse osteoblast（MC3T3-E1）experiment showed that the MBG coated scaffold mixed with 1 mol%Zn promoted the proliferation and adhesion of the cells.The relative growth rate of the scaffolds doped with 1 mol%Zn was 100%,showing good cytocompatibility.Secondly,MBG coatings doped with 1 mol%,4 mol%and 7 mol%Cu were prepared on the surface of 3D printed titanium scaffolds.Copper existed in the glass structure in the form of crystalline Cu O,Cu²⁺,and Cu⁺.The doping of Cu also significantly reduced the specific surface area of the MBG coating（the specific surface area of the MBG coating doped with 7 mol%Cu was only 40.28 m²/g）and hindered in vitro mineralization.The bactericidal effect of Cu on E.coli and S.aureus was very significant.When doped with 4 mol%Cu,the bacteria were almost completely killed.The results of in vitro mouse osteoblasts showed that the addition of 1 mol%Cu could promote cell proliferation and adhesion.The relative growth rate of the scaffolds doped with 1mol%Cu was 94%after co-culture for 7 days,while the cytocompatibility of MBG scaffolds with 4 mol%and 7 mol%Cu was poor.Again,MBG coatings doped with 0.5 mol%,1 mol%and 1.5 mol%Ag were prepared on the surface of 3D printed titanium scaffolds.The study found that silver existed in the form of elemental Ag.Different from the results of doping Zn and Cu,the doping of Ag has no significant effect on the specific surface area of the mesoporous bioglass.In the in vitro mineralization experiment,no matter which dose of Ag was doped,it showed good mineralization ability.Ag had a very significant bactericidal effect on E.coli and S.aureus.When doped with 0.5 mol%Ag,the bacteria were completely killed,and the antibacterial rate was 100%.The results of in vitro mouse osteoblast experiment showed that the addition of 1 mol%Ag had the best effect on promoting cell proliferation and adhesion.After co-culture for 7 days,the relative growth rate of the scaffolds doped with 1 mol%Ag was 111%,showing the best effect on promoting the proliferation and adhesion of osteoblast.The relative growth rates of the scaffolds doped with 0.5 mol%Ag and 1.5mol%Ag were 104%and 99%,respectively,which were higher than those of pure titanium scaffolds,indicating that MBG coated scaffolds with 0.5～1.5 mol%Ag had good cytocompatibility.Finally,the effects of Zn,Cu and Ag on the performance of MBG were compared,and it was found that the doping of Zn and Cu significantly reduced the specific surface area of MBG,while the doping of Ag had no significant effect on the specific surface area of MBG,but the specific surface area decreased with the increase of doping amount（Zn,Cu,Ag）.In addition,in vitro mineralization experiments showed that both Zn and Cu doping would hinder the mineralization of MBG,and the inhibition effect was positively correlated with the doping amount,while Ag had almost no effect on the mineralization.The antibacterial experiments showed that the antibacterial effect of the MBG coating scaffolds doped with Ag was the best,and the antibacterial effect of the MBG coating scaffolds doped with Cu was better than that doped with Zn,and the antibacterial rate showed a dose-dependence.The cytocompatibility experiments showed that the MBG coated scaffolds doped with Ag showed a good effect on promoting cell proliferation and adhesion after co-culture for 7 days.Zn and Cu showed a good effect on promoting cell proliferation and adhesion at 1 mol%,while they showed poor cytocompatibility at other doping levels.Finally,the optimal doping amount of Zn,Cu and Ag is determined to be 1 mol%,1 mol%and 1 mol%respectively.