Micro-nano Hierarchical Structure And Photo-generated Electron On Titanium Implant Surface For Promoting Bone Regeneration

Clinically,the poor osseointegration between titanium alloy-based implant and surrounding bone tissues often leads to the final failure of implants after in vivo implantation.The common treatment is to remove the titanium implants and perform the secondary surgery.This strategy will not only bring a large financial burden to the patients,but also bring great pains to them.The main reason of the poor osseointegration between titanium implants and bone tissues is the uncertain and slow differentiation of bone marrow mesenchymal stem cells(MSCs)on the implant surface due to its biologically inert.Therefore,guiding rapid osteogenic differentiation of MSCs on the surface of titanium implants is an effective way to solve this problem.Currently,building intelligent surface system promote the rapid differentiation of cells is becoming promising strategies for guiding cells behaviors.Among them,micro-nano hierarchical topologies and electrical signals can induce cells into osteoblasts.The micro-nano hierarchical topology is a micro-nano structure that mimics the extracellular matrix.It provides cells with isotropic and anisotropic physical signals,which affect the shape of cells on their surfaces and promote osteogenic differentiation of cells.Electrical signals are a feature of the microenvironment during the life of cells.Appropriate electrical signals can also promote osteogenic differentiation of cells.Both signals are suitable for bone regeneration treatment in vivo.Therefore,this paper uses micro-ordered nano-disordered topological structure and electric field microenvironment generated by photogenerated electrons around titanium implants to promote the rapid osteogenic differentiation of MSCs on titanium implant surfaces and improve osseointegration for bone regeneration.The research content of this paper is as follows:1:The patterned structure of ordered micro wave structure and disordered nano branch structure was mainly designed and prepared.Ordered micro wave structures were produced on titanium alloys by selective laser melting,and disordered nano branch was created through alkali heat treatment.It was that in-situ localized high temperature generated by the laser on the surface of the titanium alloy.More titanium oxides were generated in the laser-treated areas,which was making the laser-treated area more difficult to be corroded by KOH solution than the laser-untreated area.A micro-nano topology was constructed on the surface of the titanium implant.Ordered micro-structures provide anisotropic signals to cells,and disordered nano-structures provide cells with isotropic signals.The two kinds of signals are merged to display appropriate polarized signals to promote osteogenic differentiation of cells.The results showed that the structure obtained by laser current of 80 A and 2 M KOH solution had the best osteogenic differentiation effect.First,the cells took advantage of integrin?5 and integrin?1on the surface of the cell membrane to sense physical cue on the surface of the patterned titanium surface.Second,the actin was oriented,and then the nucleus was oriented.MSCs and MC3T3-E1 were differentiated into osteoblasts.Ti-LA-AT₂ surface could significantly up-regulate Runx-related transcription factor 2(Runx2,a key transcription factor regulating bone formation),ALP(early marker of bone matrix remodeling process),osteocalcin(Ocn,late marker gene in embryo osteogenesis and bone reconstruction)and osteopontin(Opn,a typical bone-specific extracellular matrix protein),thereby significantly promoting bone regeneration.2:Bismuth sulfide(BS)and hydroxyapatite(HAp)composite materials were designed and prepared.BS film was deposited on the surface of titanium alloy via hydrothermal method,and then biomineralization was used to deposit HAp on the surface of BS film by electrostatic bonding.The most suitable reaction conditions for the formation of BS were assessed by the film integrity and contact angle of BS,and the optimal ratio of BS/HAp composite structure was selected through the value of photocurrent.The results show that with the increase of HAp content,the value of photocurrent of BS/HAp increased and then decreased.The yield of photogenerated electrons and holes of BS was much more under near infrared light(808 nm),but the recombination between electron and hole was too fast.PO₄^3-in HAp had a better ability to hold electrons,thus improving the separation efficiency of photo-generated electrons and holes of BS,and consequently enhancing the yields of photo-generated electrons.As HAp continued to increase,the BS was covered,which affected the absorption of near-infrared light for BS and induced the decrease of the photogenerated electrons yields,suggesting the potential application of BS/HAp as an intelligent biomaterial after evaluating the cell membrane potential and Ca²⁺flow of MSCs.3:The appreciate rate of BS and HAp was chosen as research system for in vitro cell's experiment and in vivo animal experimental.BS/HAp composite material could generate photo-generated electrons under near infrared light(808 nm).The photo-generated electrons activated the Na⁺channels on the cell membrane of MSCs and led to membrane depolarization.The shape of cell altered,and the spreading areas of the cells were increased,and adhesion and penetration of cells was enhanced,which accelerated the osteogenic differentiation of the cells.Furthermore,RNA sequencing analysis disclosed that this process was related with Wnt/Ca²⁺signaling pathway,which led to the inflow of calcium ions and further upregulated the expression of FDE1.In addition,TCF/LEF in the nucleus began to transcribe to regulate downstream genes involved in osteogenic differentiation,which in turn promoted osteogenic differentiation and bone regeneration.This study created a biotherapeutic strategy,which enables remote,precise,and non-invasive control of cell differentiation behavior in vitro by using NIR light to regulate the photoelectric microenvironment in situ.