OBJECTIVES: This study aims to use 3D prin-ting technology based on the principle of stereo lithography apparatus (SLA) to shape dental lithium disilicate ceramics and study the effects of different slurry proportions on the microstructure and properties of heat-treated samples. METHODS: The experimental group comprised lithium disilicate ceramics manufactured through SLA 3D printing, and the control group comprised lithium disilicate ceramics (IPS e.max CAD) fabricated through commercial milling. An array of different particle sizes of lithium disilicate ceramic powder materials (nano and micron) was selected for mixing with photocurable acrylate resin. The proportion of experimental raw materials was adjusted to prepare five groups of ceramic slurries for 3D printing (Groups S1-S5) on the basis of rheological properties, stability, and other factors. Printing, debonding, and sintering were conducted on the experimental group with the optimal ratio, followed by measurements of microstructure, crystallographic information, shrinkage, and mechanical properties. RESULTS: Five groups of lithium disilicate ceramic slurries were prepared, of which two groups with high solid content (75%) (Groups S2 and S3) were selected for 3D printing. X-ray diffraction and scanning electron microscopy results showed that lithium disilicate was the main crystalline phase in Groups S2 and S3, and its microstructure was slender, uniform, and compact. The average grain sizes of Groups S2 and S3 were (559.79±84.58) nm and (388.26±61.49) nm, respectively (P<0.05). Energy spectroscopy revealed that the samples in the two groups contained a high proportion of Si and O elements. After heat treatment, the shrinkage rate of the two groups of ceramic samples was 18.00%-20.71%. Test results revealed no statistical difference in all mechanical properties between Groups S2 and S3 (P>0.05). The flexural strengths of Groups S2 and S3 were (231.79±21.71) MPa and (214.86±46.64) MPa, respectively, which were lower than that of the IPS e.max CAD group (P<0.05). The elasticity modulus of Groups S2 and S3 were (87.40±12.99) GPa and (92.87±19.76) GPa, respectively, which did not significantly differ from that of the IPS e.max CAD group (P>0.05). The Vickers hardness values of Groups S2 and S3 were (6.53±0.19) GPa and (6.25±0.12) GPa, respectively, which were higher than that of the IPS e.max CAD group (P<0.05). The fracture toughness values of Groups S2 and S3 were (1.57±0.28) MPa·m^0.5 and (1.38±0.17) MPa·m^0.5, respectively, which did not significantly differ from that of the IPS e.max CAD group (P>0.05). CONCLUSIONS The combination of lithium disilicate ceramic powders with different particle sizes can yield a slurry with high solid content (75%) and suitable viscosity and stability. The dental lithium disilicate ceramic material is successfully prepared by using 3D printing technology. The 3D-printed samples show a small shrinkage rate after heat treatment. Their microstructure conforms to the crystal phase of lithium disilicate ceramics, and their mechanical properties are close to those of milled lithium disilicate ceramics.
Printing, Three-Dimensional ; Dental Porcelain/chemistry* ; Ceramics/chemistry* ; Materials Testing ; Particle Size

BACKGROUND:Metal-organic framework is an emerging porous material composed of metal nodes and organic ligands.Metal-organic frameworks can be both intrinsic photodynamic or photothermal and modified by photothermal agents or photosensitizers.Upon light irradiation,phototherapy effects are exerted through production of reactive oxygen species or rise in temperature,which is widely applied to antitumor and antibacterial treatments.When metal-organic frameworks possess both of above phototherapeutic effects,they can exert a synergistic therapeutic effect to compensate for the shortcomings of using a single phototherapy method.OBJECTIVE:To summarize recent proposed photodynamic-thermal synergistic strategies according to different structures of metal-organic frameworks,to provide new insights into the structural design,functionalization,and clinical scenarios of combined therapy metal-organic frameworks.METHODS:Using"metal-organic frameworks,photodynamic therapy,photothermal therapy"as Chinese search terms and"metal-organic frameworks,photodynamic therapy,photothermal therapy,phototherapy"as English search terms,articles were searched on PubMed,Web of Science,ScienceDirect,CNKI,and WanFang databases.Finally,76 articles were included for review.RESULTS AND CONCLUSION:(1)The combination of photothermal and photodynamic therapy has been shown to exert a synergistic effect.(2)Current strategies for combined photothermal and photodynamic therapy predominantly involve the modifying of metal-organic frameworks to impart photothermal and photodynamic properties,encapsulating phototherapeutic agents within metal-organic frameworks,forming core-shell structures with phototherapeutic agents and metal-organic frameworks,in-situ reduction of phototherapeutic agents within metal-organic frameworks,adhering phototherapeutic agents to metal-organic framework surfaces,and unique modification methods like pyrolyzing metal-organic frameworks to form metal-organic frameworks-derived carbon materials.(3)To construct metal-organic framework structures for specific phototherapy,it is essential to comprehensively consider the type,size,and binding of the phototherapeutic agents and metal-organic frameworks,and select different synthesis strategies accordingly.Encapsulation is a straightforward synthesis approach but is only suitable for small-sized phototherapeutic agents.Core-shell structures are stable,but their synthesis process is relatively complex.In situ reduction does not impose special restrictions on the size of phototherapeutic agents,but it is challenging to precisely control the growth of the phototherapeutic agents within the metal-organic frameworks.Surface attachment offers a simple synthesis step,but it cannot prevent the early aggregation and quenching of phototherapeutic agents.Surface attachment requires stringent conditions and can only be implemented with specific metal-organic frameworks.(4)The existing photothermal and photodynamic combined therapy approaches have been primarily applied in antimicrobial and antitumor treatments,demonstrating remarkable efficacy.The specific applications are related to the properties of the phototherapeutic agents and metal-organic frameworks.A minority of applications extend to rheumatoid arthritis and anticoagulation thrombolysis treatments,indicating a broad potential application scope.(5)The clinical translation of photothermal and photosensitizing agents is currently in its nascent stage,facing key challenges that include the evaluation of biocompatibility and biosafety,optimization of laser irradiation parameters,and the development of efficient methods for large-scale synthesis.

BACKGROUND:Bone marrow mesenchymal stem cells play a pivotal role in tissue engineering and bone regeneration.However,promoting the osteogenic differentiation of bone marrow mesenchymal stem cells poses a significant challenge.OBJECTIVE:To examine the influence of Fe3O4@ZIF-8 nanoparticles on the osteogenic differentiation of bone marrow mesenchymal stem cells under magnetic stimulation.METHODS:Zeolite imidazolate skeleton(ZIF-8)was synthesized by hydrothermal method,and magnetic Fe3O4@ZIF-8 nanoparticles were synthesized by one-pot method(2.5,5,10,and 20 μg Fe3O4 were added to the preparation materials,respectively).The Fe3O4@ZIF-8 nanoparticles were characterized by scanning electron microscopy,X-ray photoelectron spectroscopy,X-ray diffraction,and vibration sample magnetometer detection,and suitable materials were selected for subsequent experiments.Bone marrow mesenchymal stem cells of 4-week-old SD rats were extracted and co-cultured with Fe3O4@ZIF-8 nanoparticle solution with different mass concentrations(25,50,75,100,and 125 μg/mL),respectively.Cell proliferation was detected by CCK-8 assay,and the optimal material solution mass concentration was selected.After the mass concentration of the material solution was screened,magnetic stimulation was applied(magnetic field intensity was 0,50,100,and 150 MT,respectively).Cell proliferation was detected by CCK-8 assay,and the best magnetic field intensity and Fe3O4@ZIF-8 nanoparticles were selected for the experiment of induced differentiation of bone marrow mesenchymal stem cells.SD rat bone marrow mesenchymal stem cells were co-cultured with ZIF-8,Fe3O4@ZIF-8,and Fe3O4@ZIF-8(magnetic field intervention)nanoparticle solution,respectively.The single cultured cells were used as blank controls.Lipid induction was followed by oil red O staining.After osteogenesis induction,alkaline phosphatase,alizarin red staining and Runx2 protein concentration were detected.RESULTS AND CONCLUSION:(1)Under scanning electron microscopy,Fe3O4@ZIF-8 nanoparticles showed a dodecahedral structure.With the increase of Fe3O4 content in the material,the particle size of the nanoparticles increased.Fe3O4@ZIF-8 nanoparticles(5 and 10 μg Fe3O4 was added to the material preparation)with a particle size of about 250 nm(stable functional and biosafety of nanoparticles at this particle size)were selected.(2)The results of CCK-8 assay showed that 50 μg/mL Fe3O4@ZIF-8 nanoparticles(with 10 μg Fe3O4 added to the preparation of the material)could significantly promote the proliferation of bone marrow mesenchymal stem cells under a 100 MT magnetic field.The nanoparticles under this condition were selected for the osteogenic induction differentiation experiment of bone marrow mesenchymal stem cells.(3)After osteogenic induction,the alkaline phosphatase activity,extracellular matrix mineralization degree,and Runx2 protein mass concentration of bone marrow mesenchymal stem cells in Fe3O4@ZIF-8(magnetic field intervention)group were higher than those in other three groups(P<0.05).After adipogenic induction,the lipid droplet formation of bone marrow mesenchymal stem cells in Fe3O4@ZIF-8(magnetic field intervention)group was lower than that in the other three groups(P<0.05).(4)The results show that Fe3O4@ZIF-8 nanoparticles can promote osteogenic differentiation of bone marrow mesenchymal stem cells under specific magnetic field conditions.

BACKGROUND:Traditional bone tissue engineering techniques for treating critical bone defects suffer from low osteogenic efficiency and poor safety.Gene-enhanced bone tissue engineering grafts constructed with non-viral nanoparticles have attracted widespread attention from scholars both domestically and internationally due to their higher osteogenic rates and safety,leading to extensive research in this field.OBJECTIVE:To review new technologies,methods,and challenges in the research of nanoparticles in gene therapy for bone tissue engineering,aiming to provide a reference for research on gene therapy mediated by nanoparticles in bone tissue engineering.METHODS:The first author searched PubMed,Web of Science,and CNKI.The Chinese and English search terms were"bone defect repair,bone tissue engineering,gene delivery,nanoparticles,non-viral gene vector,sustained release technology,sequential release,targeted delivery."Finally,84 articles were included for summary.RESULTS AND CONCLUSION:(1)Targeted gene delivery at various physiological stages of bone defect healing can significantly enhance bone repair efficacy.In the early inflammatory stage,delivering anti-inflammatory genes via nanoparticles to regulate the inflammatory response lays the foundation for subsequent bone healing.During the angiogenesis phase,local delivery of vascularization target genes aids in forming a highly organized vascular system,significantly accelerating bone healing.As vascularization progresses,neural re-innervation of the bone begins;at this stage,delivering functional genes promoting nerve regeneration facilitates neuro-osteogenic regeneration.During the osteogenic phase,constructing nanoparticle-bone gene complexes directly enhances the efficiency of bone formation on scaffold and in vivo.(2)Non-viral nanocarriers such as various organic and inorganic nanoparticles,metal-organic frameworks,and exosomes show immense potential in gene therapy for bone tissue engineering.Each of these carriers has its unique advantages and limitations.Therefore,in practical applications,selection of the appropriate type primarily depends on factors such as gene transfection efficiency,biocompatibility,and osteogenic properties.(3)To comprehensively improve the efficiency of gene delivery,the gene transfection efficiency of nanocarriers is mainly enhanced through various functional designs,including enhancing the temporal regulation ability such as slow release and multi-gene delivery sequence,enhancing the spatial targeting ability of bone tissue and osteoblast-related cells,enhancing the transmembrane transport efficiency and nuclear targeting ability.(4)Numerous challenges need to be overcome in order to further promote the clinical application of nanoparticle-mediated gene therapy for bone tissue engineering,including improving gene transfection efficiency of organic carriers,reducing biosafety risks of inorganic carriers,optimizing the production process of new types of nanocarriers,and promoting interactions between other physiological processes and osteogenesis.These are also research hotspots and trends of gene therapy for bone tissue engineering in the future.

BACKGROUND:Metal-organic framework is an emerging porous material composed of metal nodes and organic ligands.Metal-organic frameworks can be both intrinsic photodynamic or photothermal and modified by photothermal agents or photosensitizers.Upon light irradiation,phototherapy effects are exerted through production of reactive oxygen species or rise in temperature,which is widely applied to antitumor and antibacterial treatments.When metal-organic frameworks possess both of above phototherapeutic effects,they can exert a synergistic therapeutic effect to compensate for the shortcomings of using a single phototherapy method.OBJECTIVE:To summarize recent proposed photodynamic-thermal synergistic strategies according to different structures of metal-organic frameworks,to provide new insights into the structural design,functionalization,and clinical scenarios of combined therapy metal-organic frameworks.METHODS:Using"metal-organic frameworks,photodynamic therapy,photothermal therapy"as Chinese search terms and"metal-organic frameworks,photodynamic therapy,photothermal therapy,phototherapy"as English search terms,articles were searched on PubMed,Web of Science,ScienceDirect,CNKI,and WanFang databases.Finally,76 articles were included for review.RESULTS AND CONCLUSION:(1)The combination of photothermal and photodynamic therapy has been shown to exert a synergistic effect.(2)Current strategies for combined photothermal and photodynamic therapy predominantly involve the modifying of metal-organic frameworks to impart photothermal and photodynamic properties,encapsulating phototherapeutic agents within metal-organic frameworks,forming core-shell structures with phototherapeutic agents and metal-organic frameworks,in-situ reduction of phototherapeutic agents within metal-organic frameworks,adhering phototherapeutic agents to metal-organic framework surfaces,and unique modification methods like pyrolyzing metal-organic frameworks to form metal-organic frameworks-derived carbon materials.(3)To construct metal-organic framework structures for specific phototherapy,it is essential to comprehensively consider the type,size,and binding of the phototherapeutic agents and metal-organic frameworks,and select different synthesis strategies accordingly.Encapsulation is a straightforward synthesis approach but is only suitable for small-sized phototherapeutic agents.Core-shell structures are stable,but their synthesis process is relatively complex.In situ reduction does not impose special restrictions on the size of phototherapeutic agents,but it is challenging to precisely control the growth of the phototherapeutic agents within the metal-organic frameworks.Surface attachment offers a simple synthesis step,but it cannot prevent the early aggregation and quenching of phototherapeutic agents.Surface attachment requires stringent conditions and can only be implemented with specific metal-organic frameworks.(4)The existing photothermal and photodynamic combined therapy approaches have been primarily applied in antimicrobial and antitumor treatments,demonstrating remarkable efficacy.The specific applications are related to the properties of the phototherapeutic agents and metal-organic frameworks.A minority of applications extend to rheumatoid arthritis and anticoagulation thrombolysis treatments,indicating a broad potential application scope.(5)The clinical translation of photothermal and photosensitizing agents is currently in its nascent stage,facing key challenges that include the evaluation of biocompatibility and biosafety,optimization of laser irradiation parameters,and the development of efficient methods for large-scale synthesis.

BACKGROUND:Bone marrow mesenchymal stem cells play a pivotal role in tissue engineering and bone regeneration.However,promoting the osteogenic differentiation of bone marrow mesenchymal stem cells poses a significant challenge.OBJECTIVE:To examine the influence of Fe3O4@ZIF-8 nanoparticles on the osteogenic differentiation of bone marrow mesenchymal stem cells under magnetic stimulation.METHODS:Zeolite imidazolate skeleton(ZIF-8)was synthesized by hydrothermal method,and magnetic Fe3O4@ZIF-8 nanoparticles were synthesized by one-pot method(2.5,5,10,and 20 μg Fe3O4 were added to the preparation materials,respectively).The Fe3O4@ZIF-8 nanoparticles were characterized by scanning electron microscopy,X-ray photoelectron spectroscopy,X-ray diffraction,and vibration sample magnetometer detection,and suitable materials were selected for subsequent experiments.Bone marrow mesenchymal stem cells of 4-week-old SD rats were extracted and co-cultured with Fe3O4@ZIF-8 nanoparticle solution with different mass concentrations(25,50,75,100,and 125 μg/mL),respectively.Cell proliferation was detected by CCK-8 assay,and the optimal material solution mass concentration was selected.After the mass concentration of the material solution was screened,magnetic stimulation was applied(magnetic field intensity was 0,50,100,and 150 MT,respectively).Cell proliferation was detected by CCK-8 assay,and the best magnetic field intensity and Fe3O4@ZIF-8 nanoparticles were selected for the experiment of induced differentiation of bone marrow mesenchymal stem cells.SD rat bone marrow mesenchymal stem cells were co-cultured with ZIF-8,Fe3O4@ZIF-8,and Fe3O4@ZIF-8(magnetic field intervention)nanoparticle solution,respectively.The single cultured cells were used as blank controls.Lipid induction was followed by oil red O staining.After osteogenesis induction,alkaline phosphatase,alizarin red staining and Runx2 protein concentration were detected.RESULTS AND CONCLUSION:(1)Under scanning electron microscopy,Fe3O4@ZIF-8 nanoparticles showed a dodecahedral structure.With the increase of Fe3O4 content in the material,the particle size of the nanoparticles increased.Fe3O4@ZIF-8 nanoparticles(5 and 10 μg Fe3O4 was added to the material preparation)with a particle size of about 250 nm(stable functional and biosafety of nanoparticles at this particle size)were selected.(2)The results of CCK-8 assay showed that 50 μg/mL Fe3O4@ZIF-8 nanoparticles(with 10 μg Fe3O4 added to the preparation of the material)could significantly promote the proliferation of bone marrow mesenchymal stem cells under a 100 MT magnetic field.The nanoparticles under this condition were selected for the osteogenic induction differentiation experiment of bone marrow mesenchymal stem cells.(3)After osteogenic induction,the alkaline phosphatase activity,extracellular matrix mineralization degree,and Runx2 protein mass concentration of bone marrow mesenchymal stem cells in Fe3O4@ZIF-8(magnetic field intervention)group were higher than those in other three groups(P<0.05).After adipogenic induction,the lipid droplet formation of bone marrow mesenchymal stem cells in Fe3O4@ZIF-8(magnetic field intervention)group was lower than that in the other three groups(P<0.05).(4)The results show that Fe3O4@ZIF-8 nanoparticles can promote osteogenic differentiation of bone marrow mesenchymal stem cells under specific magnetic field conditions.

BACKGROUND:Traditional bone tissue engineering techniques for treating critical bone defects suffer from low osteogenic efficiency and poor safety.Gene-enhanced bone tissue engineering grafts constructed with non-viral nanoparticles have attracted widespread attention from scholars both domestically and internationally due to their higher osteogenic rates and safety,leading to extensive research in this field.OBJECTIVE:To review new technologies,methods,and challenges in the research of nanoparticles in gene therapy for bone tissue engineering,aiming to provide a reference for research on gene therapy mediated by nanoparticles in bone tissue engineering.METHODS:The first author searched PubMed,Web of Science,and CNKI.The Chinese and English search terms were"bone defect repair,bone tissue engineering,gene delivery,nanoparticles,non-viral gene vector,sustained release technology,sequential release,targeted delivery."Finally,84 articles were included for summary.RESULTS AND CONCLUSION:(1)Targeted gene delivery at various physiological stages of bone defect healing can significantly enhance bone repair efficacy.In the early inflammatory stage,delivering anti-inflammatory genes via nanoparticles to regulate the inflammatory response lays the foundation for subsequent bone healing.During the angiogenesis phase,local delivery of vascularization target genes aids in forming a highly organized vascular system,significantly accelerating bone healing.As vascularization progresses,neural re-innervation of the bone begins;at this stage,delivering functional genes promoting nerve regeneration facilitates neuro-osteogenic regeneration.During the osteogenic phase,constructing nanoparticle-bone gene complexes directly enhances the efficiency of bone formation on scaffold and in vivo.(2)Non-viral nanocarriers such as various organic and inorganic nanoparticles,metal-organic frameworks,and exosomes show immense potential in gene therapy for bone tissue engineering.Each of these carriers has its unique advantages and limitations.Therefore,in practical applications,selection of the appropriate type primarily depends on factors such as gene transfection efficiency,biocompatibility,and osteogenic properties.(3)To comprehensively improve the efficiency of gene delivery,the gene transfection efficiency of nanocarriers is mainly enhanced through various functional designs,including enhancing the temporal regulation ability such as slow release and multi-gene delivery sequence,enhancing the spatial targeting ability of bone tissue and osteoblast-related cells,enhancing the transmembrane transport efficiency and nuclear targeting ability.(4)Numerous challenges need to be overcome in order to further promote the clinical application of nanoparticle-mediated gene therapy for bone tissue engineering,including improving gene transfection efficiency of organic carriers,reducing biosafety risks of inorganic carriers,optimizing the production process of new types of nanocarriers,and promoting interactions between other physiological processes and osteogenesis.These are also research hotspots and trends of gene therapy for bone tissue engineering in the future.

BACKGROUND:Magnetically responsive hydrogels have great advantages in bone tissue engineering,which is more conducive to the minimally invasive and efficient promotion of osteogenesis. OBJECTIVE:To review the application advances of magnetically responsive hydrogels in bone tissue engineering. METHODS:PubMed,Web of Science,WanFang and CNKI databases were used to search relevant literature.The English search terms were"Magnetic Hydrogels,Magnetic Nanoparticles,Superparamagnetic Nanoparticles,Fe3O4,SPIONs,Magnetic Fields,Bone Regeneration,Bone Repair,Bone Tissue Engineering".The Chinese search terms were"Magnetic Hydrogel,Magnetic Nanoparticles,Superparamagnetic Iron Oxide Nanoparticles,Magnetic Field,Iron Oxide Nanoparticles,Bone Regeneration,Bone Reconstruction,Bone Repair,Bone Tissue Engineering".After preliminary screening of all articles according to the inclusion and exclusion criteria,60 articles were finally retained for review. RESULTS AND CONCLUSION:(1)In recent years,due to the emergence of magnetic nanoparticles,more and more magnetic responsive scaffold materials have been developed.Among them,magnetic responsive hydrogels containing iron oxide nanoparticles and superparamagnetic iron oxide nanoparticles have outstanding mechanical properties and good biocompatibility.It can quickly respond to the external magnetic field and provide the magnetic-mechanical signals needed for seed cells to form bone.(2)Magnetic-responsive hydrogel can be used as a carrier to accurately regulate the release time of growth factors.(3)Under the three-dimensional microenvironment culture platform based on magnetically responsive hydrogel,the magnetic force at the interface between the magnetic response hydrogel and cells can activate cell surface sensitive receptors,enhance cell activity,and promote the integration of new bone and host bone.(4)The injectable magnetically responsive hydrogel can be used in the field of magnetic hyperthermia and biological imaging of bone tumors.(5)At present,magnetically responsive hydrogels are expected to mimic the anisotropic layered structure observed in natural bone tissue.However,most of the studies on magnetically responsive hydrogels focus on in vitro studies,and the mechanism of interaction between magnetically responsive hydrogels and the local microenvironment in vivo is still insufficient.(6)Therefore,based on the successful application of magnetic nanoparticles in magnetic resonance imaging,it is expected to optimize the properties of magnetic nanoparticles in the future to construct magnetic responsive hydrogels with suitable degradation properties,mechanical properties,and vascular functionalization,which can monitor changes in vivo in real time.

BACKGROUND:Due to the mechanical properties,unstable drug release,single function and other problems of pure hydrogel materials,in recent years,researchers have prepared a variety of metal organic frameworks-based hydrogel materials by introducing metal organic frameworks into hydrogel,and showed great potential in the field of soft and hard tissue regeneration. OBJECTIVE:To classify the metal organic frameworks-based hydrogel materials based on how metal organic frameworks enhance the properties of hydrogel and further summarize its recent research in the field of soft and hard tissue regeneration,in order to provide ideas and theoretical supports for the subsequent in-depth research on synthesis mechanism and clinical application of the composite material. METHODS:Using"metal organic frameworks,hydrogels,tissue engineering,tissue,bone regeneration,bone,wound"as English and Chinese search terms,we searched Web of Science,PubMed,CNKI,and Wanfang databases.The search period ranged from January 2000 to August 2023.By reading the titles and abstracts,the repetitive studies and unrelated literature of Chinese and English literature were excluded.After the literature quality evaluation,73 articles were included for review. RESULTS AND CONCLUSION:(1)Metal organic frameworks-based hydrogel materials effectively solve the problems of poor mechanical properties,unstable drug release and single function of pure hydrogel.(2)Metal organic frameworks enhance the capacity of repair and regeneration by strengthening the cross-linking of hydrogel,the drug delivery capacity of hydrogel and the multifunction of hydrogel.(3)In terms of hard tissue repair,it has shown good repair effects in animal models of diseases such as bone defects,osteoarthritis,and cartilage defects,suggesting potential application prospects in clinical repair.(4)In terms of soft tissue regeneration,it has the capacities of hemostasis,antibacterial,inflammatory state regulation,oxidative stress state regulation,promoting angiogenesis and other functions,effectively improving the microenvironment of various complex wounds and promoting soft tissue regeneration.(5)Although metal organic frameworks-based hydrogels have many excellent properties,they are still in the initial stage and there are some urgent problems to be solved in the process of clinical transformation,such as the cytotoxicity of metal organic frameworks and large-scale synthesis of metal organic frameworks.(6)With further research,metal organic frameworks-based hydrogels have broad application prospects in the field of soft and hard tissue repair.

BACKGROUND:Trauma,inflammation,tumors,and other factors commonly result in tissue defects,including damage to bones,joints,skeletal muscles,and associated blood vessels and nerves.Clinically,it is often challenging to repair all the functional injuries involving these tissues,posing great challenges for clinical treatment. OBJECTIVE:To elucidate the application of 3D-printed hydrogel biomimetic structures in motor system tissue injuries. METHODS:Relevant literature published from 2003 to 2023 was retrieved from the CNKI,Wanfang Data,and PubMed databases.The Chinese and English search terms were"3D printing,hydrogel,bone,cartilage,muscle,nerve,vasculature,tissue engineering,biomimetics".After screening,induction and summary,63 relevant articles were finally included for review. RESULTS AND CONCLUSION:(1)3D-printed hydrogels can be achieved in several different ways,such as direct 3D printing,hybrid mode 3D printing,or manufacturing 3D bio-inspired structures in hydrogels by printing intermediate molds.Among these manufacturing processes,extrusion-based printing is currently the most widely used for 3D printing hydrogels with bio-inspired structures.(2)Bioprinting hydrogels enables the production of biovascular structures with complex perfusion patterns,and it can induce the formation of biologically relevant,highly organized,and intact blood vessels.(3)By utilizing bioprinting technology,it is possible to mimic the hierarchical structure and function of natural bone,combining hydrogels with different types of cells and growth factors to create tissue engineering scaffolds that closely resemble the composition and structure of natural bone,thereby facilitating better bone regeneration.(4)Neural fiber structure can be bio-inspired by incorporating different fiber materials into the 3D-printed hydrogel conduit structure.(5)Utilizing specific hydrogel formulations,it is possible to simulate muscle bundle structures or engineer muscle tissues integrating blood vessels and nerves,which can enhance the repair of volumetric muscle injuries in vivo.(6)Based on current related research,methacrylated gelatin,which closely resembles the characteristics of the extracellular matrix,is often considered as a raw material for 3D printing various tissue bio-inspired structures.Researchers also incorporate different growth factors or cells into the hydrogels for bioprinting to achieve the desired tissue repair outcomes.(7)Although there is a lack of clinical trial reports on 3D-printed hydrogel bio-inspired structures,this indicates that the clinical translation of such materials still requires a long-term process.Further improvements are needed in terms of clinical applications,as well as comprehensive in vivo safety assessments.