3D Printing Of MXene Composite Hydrogel Scaffolds For Photothermal Antibacterial Activity And Bone Regeneration In Oral Infected Bone Defect Models

Background:The treatment of infected bone defects is considered as an intractable problem in the fields of oral maxillofacial surgery,oral implantology and orthopedics.When adhesion and proliferation of bacteria occur in bone defects,the self-repair ability of bone tissue will be further limited.In oral diseases,serious bone infected defect with severe infection and complex shape is especially difficult to repair,such as refractory mandibular osteomyelitis and serious infection after implantation.In clinical therapies,infected bone defects treatment measures usually include systemic or local antibiotic therapy,removal of necrotic bone fragments and debridement,and autogenous bone or synthetic bone substitutes graft.However,many problems will occur in the process of the treatment.For example,large irregular defects are difficult to personalized repair,overuse of antibiotics can cause emergence of drug-resistant strains,implantation of bone graft after elimination of infection results in a long treatment course and the pain of patient.Therefore,it is necessary to develop personalized biomaterials with antibacterial and bone regeneration capabilities.Recently,many antibiotic-independent antibacterial methods have been developed,such as antibacterial therapy based on bioactive substances,photothermal therapy,photodynamic therapy,antimicrobial peptides and so on.Photothermal therapy is used to convert light energy into heat energy under specific light by photothermal agents,thus causing thermal damage to the target area.In order to treat irregular bone defect,3D printing technique is used to construct personalized bone tissue engineering scaffolds.In clinical treatment,the application of 3D printing technology is more and more widely.It can print implants with specific shape accurately and quickly,and provide personalized tissue repair and reconstruction for patients.Cells can also be combined with bioinks to achieve 3D cell-laden printing and 3D cell culture.Proliferation and differentiation of cells depend on the interaction between cell and extracellular matrix（ECM）,and this interaction needs to be supported by 3D environment.The hydrogel is loosely crosslinked and porous networks structure,which is beneficial to the growth of cells in it.And most hydrogels have similar properties to ECM,which can promote proliferation and differentiation of stem cells into functional tissue.MXene,a transition metal carbide/nitride/carbonitride,is an emerging two-dimentional nanomaterial with ultrathin structure.It has been proved that MXene has great potential and application prospect in antibacterial properties,photothermal therapy and photodynamic therapy,biosensor,bone tissue regeneration and so on.MXene could destroy bacteria through direct physical contact or photothermal effect;and the titanium-based substances released from Ti₃C₂MXene could promote bone regeneration.Hydrogel composite ink carrier is composed of gelatin methacryloyl（Gel MA）,sodium alginate（Alg）andβ-tricalcium phosphate（β-TCP）.Gel MA is a modified gelatin with good temperature sensitivity and can be crosslinked under blue light irradiation,so it is a commonly used 3D printing hydrogel carrier;Alg can be cross-linked with divalent cations such as Ca²⁺and Sr²⁺to increase hydrogel strength and promote osteogenesis;β-TCP is a commonly used bioceramic material for bone tissue engineering with excellent osteoconduction and biodegradation.Purpose:3D printing of MXene composite hydrogel scaffolds to construct bifunctional scaffolds with individualized structure,and to optimize the treatment of infected bone defects.Methods:1.3D printing of MXene composite hydrogel scaffold GTAM(Gel MA/β-TCP/Alg(Sr²⁺)/MXene).The characterization and physicochemical properties of bioinks and scaffolds were tested.2.Evaluation of biological properties and osteogenesis of GTAM scaffolds.GTAM bioinks and rat BMSCs were co-printed to evaluate the biocompatibility and the ability to promote BMSCs proliferation and differentiation of scaffolds.3.Evaluation of antibacterial properties of GTAM scaffolds.GTAM scaffolds were co-cultured with Gram-positive Staphylococcus aureus（S.aureus）and Gram-negative Escherichia coli（E.coli）respectively.The antibacterial activity of GTAM scaffolds was evaluated by 808 nm near-infrared（NIR）laser irradiation.4.Evaluation of therapeutic effect of GTAM scaffolds in infected bone defects in vivo.Rat models of mandibular infected bone defects（chronic osteomyelitis）were established.GTAM scaffolds were implanted into the infected mandibular defects with NIR irradiation to evaluate the ability of GTAM scaffolds to resist bacteria meanwhile promote bone regeneration in vivo.Results:1.GTAM bioinks had great rheological properties to 3D print smoothly;GTAM hydrogel scaffolds were successfully fabricated though 3D printing;scaffolds possessed suitable porosity and pore size,excellent mechanical strength and stability,NIR absorption capacity and biodegradability matched with bone regeneration rate.2.BMSCs could be mixed into GTAM bioinks to co-print and 3D cultured,and GTAM scaffolds had good biocompatibility and did not induce inflammatory reaction in vitro.GTAM scaffolds had good osteogenic property in vitro,and could promote the proliferation of BMSCs and induce the expression of osteogenic differentiation genes（RUNX2,ALP,OCN）and proteins（ALP,OPN）.3.GTAM scaffolds had extraordinary antibacterial property in vitro under NIR irradiation.The bacterial membranes of S.aureus and E.coli were destroyed by photothermal-induced hyperthermia as the main method and physical damage as the supplement.4.GTAM scaffolds could reduce bacterial adhesion and inflammation under NIR irradiation,and promoted bone regeneration in mandibular defects of rats.Scaffolds had good synergistic antibacterial and osteogenic abilities.Conclusions:1.3D printed MXene composite hydrogel scaffolds GTAM possessed photothermal antibacterial and personalized precision bone regeneration abilities both in vitro and in vivo.GTAM scaffolds could treat mandibular infected bone defects with NIR irradiation in vivo.2.BMSCs could be mixed with GTAM bioinks to realize cell-laden printing and3D cell culture,which could more accurately simulate cell growth process in vivo.GTAM scaffolds were also optimized to achieve a good balance between the improvement of mechanical strength and promotion of BMSCs proliferation in the scaffolds.