Construction Of Multifunctional Titanium Surface By Promoted Click Reaction And Study On Its Bioadaptability

With the development of society and aging population,the number of bone defect patients increases year by year.Because of the satisfied physical and chemical performance,titaniumbased implants are one of the most widely used orthopedic implants and the global dependence on those implants is increasing.In this context,the drawbacks of titanium-based implants become increasingly prominent,especially bacterial infection and aseptic loosening caused by their biologically inert surfaces,which have become two important reasons for the failure of implantation.The ideal titanium-based implants should have excellent antibacterial activity and osteointegration ability,which are contradictory and hard to satisfy on the surfaces.Based on the urgent clinical need for multifunctional titanium implants,this thesis developed a promoted click reaction(CuAAC-Bor)for surface functionalization of titanium implants.We have prepared multifunctional titanium surfaces with excellent antibacterial activity,angiogenic and osteogenic ability through the CuAAC-Bor and new designed fusion peptide.The main research content is as follows:(1)At present,the commonly used click reaction system containing copper sulfate/sodium ascorbate(CuAAC-Asc)sometimes has inadequate efficiency for surface functionalization,and it is difficult to achieve excellent biological activity.To address this problem,a promoted click reaction system with copper nanoclusters(Cu NCs)formed in situ was developed.Compared with CuAAC-Asc,CuAAC-Bor has a higher efficiency of peptide grafting for surface functionalization.The titanium surfaces prepared by CuAAC-Bor would show stronger bioactive activity than those by CuAAC-Asc.Meanwhile,combined with molecular dynamics simulation and machine learning,we had studied the influence factors of CuAAC,such as peptide conformation,peptide's radius of gyration,group reactivity,charged situation and revealed the positive correlation between peptide size and reaction efficiency.CUAAC-Bor is expected to expand the application scope of click reaction in surface functionalization.(2)Based on the HHC36 and QK peptide,a novel fusion peptide(FP)with antibacterial activity and osteointegration ability was designed and synthesized.The FP peptide was covalently grafted on titanium surface(Ti-FP)through Cua Ac-Bor.The Ti-FP surface exhibited excellent antibacterial activity against four common clinical bacteria(S.aureus,MRSA,E.coli and P.aeruginosa)by by disruption of bacterial membranes.Meanwhile,Ti-FP surface could also inhibit biofilm formation.Here,we further explained the reason why Ti-FP surface showed better antibacterial activity than Ti-MP surface grafted with the same equivalent density of HHC36.Combined with molecular dynamics simulation,it revealed that a larger bacterial accessible surface area of HHC36 on Ti-FP than that on Ti-MP,caused the stronger antibacterial activity of Ti-FP.(3)In this thesis,we investigated the cytological properties of multifunctional titanium(Ti-125FP)surface in vitro.Compared with Ti surface,Ti-125 FP surface not only exhibited excellent antibacterial activity,but also promoted the adhesion and proliferation of human umbilical vein endothelial cells(HUVECs)and human marrow mesenchymal stem cells(h BMSCs).The biocompatibility of HUVECs and h BMSCs was increased 1.37-folds and 1.30-folds after 36 hours and 5 days of culture respectively,compared with Ti.At the same time,Ti-125 FP also promoted the expression of angiogenesis-related genes and proteins of HUVECs.In addition,Ti-125 FP could regulate and promote the expression of osteogenesis-related genes and proteins of HBMSCs by activating PI3K/Akt signaling pathway.These results indicated that Ti-125 FP could effectively solve the contradiction of “antibacterial activityosteointegration ability”.(4)Here,the bone defect models and bone defect-bacterial infection models were established in New Zealand white rabbits to evaluate the bioadaptability of Ti-125 FP implant.The results showed that Ti-125 FP implant displayed excellent bioadaptability in different models.Ti-125 FP implant could enhance the expression of CD31 protein,promote the vascularization and osteointegration around the surface in the absence of bacterial infection while Ti-125 FP implant displayed antibacterial activity,promoted the vascularization and osteointegration simultaneously in the presence of bacterial infection.In conclusion,in this thesis we developed a promoted CuAAC-Bor system,which was more conducive for surface functionalization than.Based on FP peptide and CuAAC-Bor,the multifunctional titanium implant Ti-125 FP was prepared.Ti-125 FP achieved bioadaptability by preventing bacterial infection,promoting the vascularization and osteointegration in animal experimental model.This relevant research study may provide an effective strategy to solve the failure implantation of titanium implants caused by bacterial infection and inefficient osseointegration.