Fabrication Of Functional Micro/nanostructured Interfaces On Titanium-based Implants For Osteogenic Regulation And The Underlying Mechanisms

Titanium and titanium alloys implants have been commonly used for bone repair because of its excellent mechanical properties and biocompatibility,but their success rate under osteoporotic conditions remains unsatisfactory due to insufficient osteointegration.From a mechanistic perspective,the abnormally accelerated osteoclast-mediated resorption under osteoporotic conditions overwhelms the compensatory osteoblast-dependent bone formation and causes a net bone loss,which would not only delay the bone defect healing but also compromise osteointegration,eventually leading to greater risk of implant loosening and detachment.Therefore,it is an important clinical significance in the optimizing of interface performance of bone-titanium implants and the studies of molecular mechanisms involved in the regulation of cell metabolism and differentiation by titanium-based interface.Considering that,a series of biofunctional micro/nano structures of titanium-based interface were constructed by micro-arc oxidation and hydrothermal treatment,which regulated biological performances and promoted osteoblasts differentiation of Mesenchymal stem cells（MSCs）..Their biological response mechanism was preliminary evaluated in vitro and in vivo.The main research contents and conclusions of this thesis are listed as follows:1.Osteogenesis regulation of MSCs via autophagy induced by bionic silica-titanium composite surfaces with different mechanical modulusThe surface structure and modulus of orthopedic implants play an important role in regulating the osseointegration properties.In this study,spherical silica nanoparticles（SSN）with different sizes were synthesized and loaded onto the surfaces of Ti via micro-arc oxidation（MAO）technique（Ti-SSNs）and the regulation mechanism of osteogenic differentiation of MSCs by composite structure was studied.The surface topography,modulus and elements of the composite structure were characterized by transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,atomic force microscopy（AFM）,X-ray diffraction（XRD）,energy dispersion spectrum（EDS）,nanomechanical test systems（NTI）and water contact angle measurements.The mechanical test indicated Ti-SSNs could effectively reduce the surface modulus of Ti substrate from 93 GPa to 6.7 Gpa,which matched that of nature bone.In vitro experiments showed that Ti-SSNs significantly stimulated the higher expression and nuclear localization of the transcription factor YAP.Meanwhile,Ti-SSNs inhibited the phosphorylation of AKT and m TOR proteins,leading to high level of LC3-II proteins expression,enhanced autophagic activity and promoted osteogenic differentiation of MSCs.2.The study of promoting osteoporotic fracture repair by Magnesium/Gallium-LDO micro-nanosheets on titanium implantsUnder osteoporotic condition,the acidic microenvironment would affect osteoblastic metabolism of MSCs and bone formation/resorption behavior.Thus,to adjust the p H of osteoporotic microenvironment and enhance osteogenic ability of MSCs,a series of Mg/Ga-LDO coatings（AT-x Mg/y Ga）were fabricated on the microrough titanium（alkali-heat-treatment,AT）via hydrothermal synthesis.The successful fabrication of the coatings was verified by SEM,EDS and XRD.The p H test and ions release results showed that the AT-Mg/Ga could prevent the burst release of ions and maintain a suitable alkaline microenvironment（p H 8.5）on the implant surface.In vitro experiments confirmed that the AT-Mg/Ga markedly promoted the autophagic activity and induced osteogenesis differentiation of MSCs,while suppressing osteoclast generation.Furthermore,in vivo tests further verified that the AT-Mg/Ga implants prominently promoted new bone formation.3.Multi-enzyme-like bio-MOF coating on titanium implants restores their mitochondrial function of MSCs and promotes osteoporotic bone regenerationElevated microenvironmental reactive oxygen species（ROS）level is a hallmark of osteoporosis that often leads to the dysfunction of bone-related MSCs,which would induce MSCs senescence and severely undermine their osteoblastic potential.Herein,we report the in-situ construction of microenvironment-responsive biofunctional bio-MOFs coatings on titanium surfaces through the coordination between p-xylylenebisphosphonate（PXBP）and Ce/Sr ions.SEM,EDS,XRD and XPS suggested that the bio-MOFs coating was successfully constructed.Ion release（p H 5.8 and p H7.4）showed that the bio-MOFs coating was responsive to the osteoporotic microenvironment.DCFH-DA dying,WB experiments and the detection of SOD,H₂O₂,DPPH and TMB showed that the bio-MOFs coating possessed on-demand superoxide dismutase and catalase-like catalytic activities to decompose ROS in MSCs and restore their mitochondrial functions.In vitro analysis showed that the bio-MOFs coating substantially restrained the mitochondrial fission,promoted mitochondrial fusion and mitophagy,indicating that the bio-MOFs could amend mitochondrial function in MSCs to reverse senescence and enhance osteogenesis differentiation of MSCs.In vivo evaluations（DHE marking,immunohistochemistry and micro-CT experiments）showed that the AHT-Ce/Sr MOF implants could reduce ROS levels in the implant site and promote new bone formation,leading to improved osteointegration in osteoporotic rat.