Study On Bone Tissue Engineering Scaffold Modified By Zinc-based Ligand Coordinated-black Phosphorus And Its Photothermal Antibacterial And Osteogenic Properties

To solve the problem of postoperative infection of orthopedic implant surgery,a multifunctional bone tissue engineering scaffold is prepared in this study,of which the antibacterial and osteogenic behavior can be regulated by near-infrared irradiation.In brief,the hydroxyapatite scaffold is prepared by 3D printing,and then modified with the zinc-based ligand coordinated black phosphorus for the endowment of near-infrared responsiveness.Under near-infrared irradiation with higher power density,the high-temperature?46-50°C?generated by the zinc-based ligand coordinated black phosphorus?ZnL₂-BPs?on scaffold can effectively kill the adherent bacteria,and under near-infrared irradiation with lower power density,the local mild heat?40-42°C?generated by ZnL₂-BPs is slightly higher than that of the human body,thereby promoting the formation of new bone surrounding the scaffold.In this study,ZnL₂-BPs was prepared by the reaction between zinc p-toluenesulfonate?ZnL₂?and black phosphorus nanosheets?BPs?.The obtained ZnL₂-BPs are systematically characterized by zeta potential measurement,X-ray photoelectron spectroscopy?XPS?,ultraviolet-visible light absorption spectrum as well as macro turbidity observation.The results show that the zeta potential increased from-30 mV of BPs to+28 mV of ZnL₂-BPs,the oxidation of ZnL₂-BPs in air is much slower than that of bare BPs,and the stability of ZnL₂-BPs in water is significantly improved.Subsequently,the hydroxyapatite scaffold?HA?with three-dimensional structure is immersed in a polylactic acid-glycolic acid copolymer?PLGA?solution containing ZnL₂-BPs,and then taken out to dry to obtain a photothermal responsive and biodegradable bone tissue engineering scaffold?ZnL₂-BPs@HA-PLGA?.The as-prepared ZnL₂-BPs@HA-PLGA can maintain the photothermal performance even after 6 weeks of degradation.What is more important,its degradation products are calcium ions,zinc ions,phosphate ions,lactic acid and glycolic acid,which show no toxicity and side effects to the human bodies.In a next step,the photothermal antibacterial performance and the photothermal osteogenetic performance of ZnL₂-BPs@HA-PLGA are systematically investigated.The results of in vitro antibacterial test show that the antibacterial efficiency of ZnL₂-BPs@HA-PLGA against Staphylococcus aureus?S.aureus?and Escherichia coli?E.coli?can reach more than 99%under near-infrared irradiation.According to results of live/dead staining,scanning electron microscope observation,reactive oxygen species?ROS?levels,membrane potentials,internal adenosine triphosphate?ATP?levels,and protein leakage,it is clear that ZnL₂-BPs and the hyperthermia generated by photothermal therapy?PTT?can kill bacteria synergistically.In particular,the presence of ZnL₂-BPs can reduce the membrane potential of bacteria and upregulate the intracellular ROS level,making bacteria more vulnerable to the hyperthermia of PTT and hence being efficiently inactivated.In the following cell experiments in vitro,ZnL₂-BPs@HA-PLGA has been well demonstrated for the good biocompatibility and osteogenic performances.Especially,when the temperature of ZnL₂-BPs@HA-PLGA is increased to 40.5±0.5°C under near-infrared irradiation,both the proliferation and osteogenic differentiation of human bone mesenchymal stem cells can be significantly improved.Based on the outstanding in vitro antibacteria and osteogenesis of ZnL₂-BPs@HA-PLGA mediated by near-infrared irradiation,the in vivo performances are assessed by using a rat tibia defect model with bacterial infection.In particular,ZnL₂-BPs@HA-PLGA contaminated with S.aureus is implanted into the tibia defect of rat,and the implantation site is subjected to near-infrared irradiation at a power density of 1.5 W/cm² to regulate the antibacterial performance.Afterwards,the implantation site is periodically subjected to near-infrared irradiation at a power density of 1.0 W/cm² for the regulation of osteogenesis.Our results show that the ZnL₂-BPs@HA-PLGA+Light group can not only eradicate the bacterial infection after implantation,but also benefit the peri-implant bone regeneration.To our knowledge,this is the first study about photothermally tuning the antibacterial and osteogenic behavior of bone-related implants by using the zinc-based ligand coordinated black phosphorus.In addition to the antibacterial and osteogenic effects mediated by near-infrared irradiation,the ZnL₂-BPs@HA-PLGA fabricated in this study is satisfactory for the non-toxicity of degradation products,thereby having a wide prospect in clinical application.