Biomedical engineering of two-dimensional MXenes

In situ growth of Mn3O4 nanoparticles on accordion-like Ti3C2Tx MXene for advanced aqueous Zn-Ion batteries

Manganese-based cathodes are competitive candidates for state-of-the-art aqueous zinc-ion batteries (AZIBs) because of their easy preparation method, sufficient nature reserve, and environmental friendliness. However, their poor cycle stability and low rate performance have prevented them from practical applications. In this study, Mn3O4 nanoparticles were formed in situ on the surface and between the interlayers of Ti3C2Tx MXene, which was pretreated by the intercalation of K+ ions. Ti3C2Tx MXene not only provides abundant active sites and high conductivity but also hinders the structural damage of Mn3O4 during charging and discharging. Benefiting from the well-designed K-Ti3C2@Mn3O4 structure, the battery equipped with the K-Ti3C2@Mn3O4 cathode achieved a maximum specific capacity of 312 mAh/g at a current density of 0.3 A/g and carried a specific capacity of approximately 120 mAh/g at a current density of 1 A/g, which remained stable for approximately 500 cycles. The performance surpasses that of most reported Mn3O4-based cathodes. This study pioneers a new approach for building better cathode materials for AZIBs.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

Ti3C2Tx MXene-Decorated 3D-Printed Ceramic Scaffolds for Enhancing Osteogenesis by Spatiotemporally Orchestrating Inflammatory and Bone Repair Responses

Inflammatory responses play a central role in coordinating biomaterial-mediated tissue regeneration. However, precise modulation of dynamic variations in microenvironmental inflammation post-implantation remains challenging. In this study, the traditional β-tricalcium phosphate-based scaffold is remodeled via ultrathin MXene-Ti3C2 decoration and Zn2+/Sr2+ ion-substitution, endowing the scaffold with excellent reactive oxygen species-scavenging ability, near-infrared responsivity, and enhanced mechanical properties. The induction of mild hyperthermia around the implant via periodic near-infrared irradiation facilitates spatiotemporal regulation of inflammatory cytokines secreted by a spectrum of macrophage phenotypes. The process initially amplifies the pro-inflammatory response, then accelerates M1-to-M2 macrophage polarization transition, yielding a satisfactory pattern of osteo-immunomodulation during the natural bone healing process. Later, sustained release of Zn2+/Sr2+ ions with gradual degradation of the 3D scaffold maintains the favorable reparative M2-dominated immunological microenvironment that supports new bone mineralization. Precise temporal immunoregulation of the bone healing process by the intelligent 3D scaffold enhances bone regeneration in a rat cranial defect model. This strategy paves the way for the application of β-tricalcium phosphate-based materials to guide the dynamic inflammatory and bone tissue responses toward a favorable outcome, making clinical treatment more predictable and durable. The findings also demonstrate that near-infrared irradiation-derived mild hyperthermia is a promising method of immunomodulation.

Ti3C2Tx Coated with TiO2 Nanosheets for the Simultaneous Detection of Ascorbic Acid, Dopamine and Uric Acid

Two-dimensional MXenes have become an important material for electrochemical sensing of biomolecules due to their excellent electric properties, large surface area and hydrophilicity. However, the simultaneous detection of multiple biomolecules using MXene-based electrodes is still a challenge. Here, a simple solvothermal process was used to synthesis the Ti3C2Tx coated with TiO2 nanosheets (Ti3C2Tx@TiO2 NSs). The surface modification of TiO2 NSs on Ti3C2Tx can effectively reduce the self-accumulation of Ti3C2Tx and improve stability. Glassy carbon electrode was modified by Ti3C2Tx@TiO2 NSs (Ti3C2Tx@TiO2 NSs/GCE) and was able simultaneously to detect dopamine (DA), ascorbic acid (AA) and uric acid (UA). Under concentrations ranging from 200 to 1000 μM, 40 to 300 μM and 50 to 400 μM, the limit of detection (LOD) is 2.91 μM, 0.19 μM and 0.25 μM for AA, DA and UA, respectively. Furthermore, Ti3C2Tx@TiO2 NSs/GCE demonstrated remarkable stability and reliable reproducibility for the detection of AA/DA/UA.

Ti3C2T x -AuNP based paper substrates for label-free SERS detection of bacteria and multimodal antibacterials

Bacterial infections have become a serious global health problem due to the misuse of antibiotics which causes the emergence of antibiotic-resistant strains. Photothermal therapy (PTT) has been widely studied in recent years as a method to combat the development of bacterial resistance. However, PPT may cause damage to the human body due to excessive laser power. Therefore, it is important and urgent to develop a multifunctional platform that can sensitively detect bacteria and effectively inhibit or kill bacteria at low laser power. Herein, a novel multifunctional paper substrate of Ti3C2T x -AuNP was successfully synthesized by a self-assembly and freeze-drying method for bacterial detection and photothermal sterilization at low laser power. The typical Gram-negative Escherichia coli (E. coli) and the Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA) were used as models to perform label-free, rapid and sensitive detection of bacteria based on the surface-enhanced Raman spectroscopy (SERS) method with detection limits as low as 105 CFU mL-1 and 5 × 105 CFU mL-1, respectively, demonstrating the paper substrate's ability to detect bacteria with sensitivity and accuracy. The paper substrate of Ti3C2T x -AuNP exhibits significant antibacterial effects when irradiated with 808 nm light at a low laser power of only 300 mW cm-2 and a short irradiation time of 5 minutes, and the germicidal rates for E. coli and MRSA were 99.94% and 92.71%, respectively. At the same time, the paper substrate of Ti3C2T x -AuNP also produces a variety of reactive oxygen species under 808 nm laser irradiation, resulting in photodynamic therapy (PDT). Accordingly, this paper substrate of Ti3C2T x -AuNP can not only sensitively detect bacteria, but also has photothermal and photodynamic sterilization, providing a promising countermeasure for the clinical treatment of diseases caused by multidrug-resistant bacteria.

Insights on updates in sodium alginate/MXenes composites as the designer matrix for various applications: A review

Advancements in two-dimensional materials, particularly MXenes, have spurred the development of innovative composites through their integration with natural polymers such as sodium alginate (SA). Mxenes exhibit a broad specific surface area, excellent electrical conductivity, and an abundance of surface terminations, which can be combined with SA to maximize the synergistic effect of the materials. This article provides a comprehensive review of state-of-the-art techniques in the fabrication of SA/MXene composites, analyzing the resulting structural and functional enhancements with a specific focus on advancing the design of these composites for practical applications. A detailed exploration of SA/MXene composites is provided, highlighting their utility in various sectors, such as wearable electronics, wastewater treatment, biomedical applications, and electromagnetic interference (EMI) shielding. The review identifies the unique advantages conferred by incorporating MXene in these composites, examines the current challenges, and proposes future research directions to understand and optimize these promising materials thoroughly. The remarkable properties of MXenes are emphasized as crucial for advancing the performance of SA-based composites, indicating significant potential for developing high-performance composite materials.

Recent Advances in Two-Dimensional Nanomaterials for Healthcare Monitoring

The development of advanced technologies for the fabrication of functional nanomaterials, nanostructures, and devices has facilitated the development of biosensors for analyses. Two-dimensional (2D) nanomaterials, with unique hierarchical structures, a high surface area, and the ability to be functionalized for target detection at the surface, exhibit high potential for biosensing applications. The electronic properties, mechanical flexibility, and optical, electrochemical, and physical properties of 2D nanomaterials can be easily modulated, enabling the construction of biosensing platforms for the detection of various analytes with targeted recognition, sensitivity, and selectivity. This review provides an overview of the recent advances in 2D nanomaterials and nanostructures used for biosensor and wearable-sensor development for healthcare and health-monitoring applications. Finally, the advantages of 2D-nanomaterial-based devices and several challenges in their optimal operation have been discussed to facilitate the development of smart high-performance biosensors in the future.

Synovium microenvironment-responsive injectable hydrogel inducing modulation of macrophages and elimination of synovial fibroblasts for enhanced treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a progressive autoimmune disease accompanied by joint swelling, cartilage erosion and bone damage. Drug therapy for RA has been restricted due to poor therapeutic effect, recurrence and adverse effects. Macrophages and synovial fibroblasts both play important roles in the pathology of RA. Macrophages secrete large amount of pro-inflammatory cytokines, while synovial fibroblasts are tightly correlated with hypoxia synovium microenvironment, cytokine release, recruitment of pro-inflammatory cells, bone and cartilage erosion. Therefore, in this timely research, an injectable and pH-sensitive peptide hydrogel loading methotrexate (MTX) and bismuthene nanosheet/polyethyleneimine (BiNS/PEI) has been developed to reduce the activity of macrophages and eliminate over-proliferated synovial fibroblasts simultaneously. MTX can reduce the cytokine secretion of macrophages/anti-apoptosis property of synovial fibroblasts and BiNS/PEI can eliminate synovial fibroblasts via photodynamic therapy (PDT) and photothermal therapy (PTT) routes. The hydrogel was injected into the acidic inflammatory synovium for precise targeting and served as a drug reservoir for pH responsive and sustained drug release, while improving the bioavailability and reducing the toxicity of MTX. Excellent therapeutic efficacy has been achieved in both in vivo and in vitro studies, and this unique drug delivery system provides a new and robust strategy to eliminate synovial fibroblasts and modulate immune system for RA treatment in clinical.

Multifunctional MXene-Based Platforms for Soft and Bone Tissue Regeneration and Engineering

MXenes and their composites hold great promise in the field of soft and bone tissue regeneration and engineering (TRE). However, there are challenges that need to be overcome, such as ensuring biocompatibility and controlling the morphologies of MXene-based scaffolds. The future prospects of MXenes in TRE include enhancing biocompatibility through surface modifications, developing multifunctional constructs, and conducting in vivo studies for clinical translation. The purpose of this perspective about MXenes and their composites in soft and bone TRE is to critically evaluate their potential applications and contributions in this field. This perspective aims to provide a comprehensive analysis of the challenges, advantages, limitations, and future prospects associated with the use of MXenes and their composites for soft and bone TRE. By examining the existing literature and research, the review seeks to consolidate the current knowledge and highlight the key findings and advancements in MXene-based TRE. It aims to contribute to the understanding of MXenes' role in promoting soft and bone TRE, addressing the challenges faced in terms of biocompatibility, morphology control, and tissue interactions.

Green Synthesis and Biosafety Assessment of MXene

The rise of MXene-based materials with fascinating physical and chemical properties has attracted wide attention in the field of biomedicine, because it can be exploited to regulate a variety of biological processes. The biomedical applications of MXene are still in its infancy, nevertheless, the comprehensive evaluation of MXene's biosafety is desperately needed. In this review, the composition and the synthetic methods of MXene materials are first introduced from the view of biosafety. The evaluation of the interaction between MXene and cells, as well as the safety of different forms of MXene applied in vivo are then discussed. This review provides a basic understanding of MXene biosafety and may bring new inspirations to the future applications of MXene-based materials in biomedicine.

Transition Metal Oxide-Decorated MXenes as Drugless Nanoarchitectonics for Enriched Nanocatalytic Chemodynamic Treatment

Despite their unique characteristics, 2D MXenes with sole photothermal conversion ability are required to explore their superfluous abilities in biomedicine. The small-molecule-based chemotherapeutics suffer from various shortcomings of time-consuming and expensiveness concerning theoretical and performance (preclinical/clinical) checks. This study demonstrates the fabrication of Ti3C2 MXene nanosheets (TC-MX NSs) and subsequent decoration with transition metal oxides, that is, copper oxide (Cu2O/MX, CO-MX NCs) as drugless nanoarchitectonics for synergistic photothermal (PTT)-chemodynamic therapeutic (CDT) efficacies. Initially, the monolayer/few-layered TC-MX NSs are prepared using the chemical etching-assisted ultrasonic exfoliation method and then deposited with Cu2O nanoconstructs using the in situ reduction method. Further, the photothermal ablation under near-infrared (NIR)-II laser irradiation shows PTT effects of CO-MX NCs. The deposited Cu2O on TC-MX NSs facilitates the release of copper (Cu+) ions in the acidic microenvironment intracellularly for Fenton-like reaction-assisted CDT effects and enriched PTT effects synergistically. Mechanistically, these deadly free radicals intracellularly imbalance the glutathione (GSH) levels and result in mitochondrial dysfunction, inducing apoptosis of 4T1 cells. Finally, the in vivo investigations in BALB/c mice confirm the substantial ablation of breast carcinoma. Together, these findings demonstrate the potential synergistic PTT-CDT effects of the designed CO-MX NCs as drugless nanoarchitectonics against breast carcinoma.

MXenes for Bioinspired Soft Actuators: Advancements in Angle-Independent Structural Colors and Beyond

Soft actuators have garnered substantial attention in current years in view of their potential appliances in diverse domains like robotics, biomedical devices, and biomimetic systems. These actuators mimic the natural movements of living organisms, aiming to attain  enhanced flexibility, adaptability, and versatility. On the other hand, angle-independent structural color has been achieved through innovative design strategies and engineering approaches. By carefully controlling the size, shape, and arrangement of nanostructures, researchers have been able to create materials exhibiting consistent colors regardless of the viewing angle. One promising class of materials that holds great potential for bioinspired soft actuators is MXenes in view of their exceptional mechanical, electrical, and optical properties. The integration of MXenes for bioinspired soft actuators with angle-independent structural color offers exciting possibilities. Overcoming material compatibility issues, improving color reproducibility, scalability, durability, power supply efficiency, and cost-effectiveness will play vital roles in advancing these technologies. This perspective appraises the development of bioinspired MXene-centered soft actuators with angle-independent structural color in soft robotics.

3D Printed Photothermal Scaffold Sandwiching Bacteria Inside and Outside Improves The Infected Microenvironment and Repairs Bone Defects

Bone infection is one of the most devastating orthopedic outcomes, and overuse of antibiotics may cause drug-resistance problems. Photothermal therapy(PTT) is a promising antibiotic-free strategy for treating infected bone defects. Considering the damage to normal tissues and cells caused by high-temperature conditions in PTT, this study combines the antibacterial property of Cu to construct a multi-functional Cu2 O@MXene/alpha-tricalcium phosphate (α-TCP) scaffold support with internal and external sandwiching through 3D printing technology. On the "outside", the excellent photothermal property of Ti3 C2 MXene is used to carry out the programmed temperature control by the active regulation of 808 nm near-infrared (NIR) light. On the "inside", endogenous Cu ions gradually release and the release accumulates within the safe dose range. Specifically, programmed temperature control includes brief PTT to rapidly kill early bacteria and periodic low photothermal stimulation to promote bone tissue growth, which reduces damage to healthy cells and tissues. Meanwhile, Cu ions are gradually released from the scaffold over a long period of time, strengthening the antibacterial effect of early PTT, and promoting angiogenesis to improve the repair effect. PTT combined with Cu can deliver a new idea forinfected bone defects through in vitro and vivo application.

Ultralong Stability of Ti3 C2 Tx -MXene Dispersion Through Synergistic Regulation of Storage Environment and Defect Capping with Tris-HCl Buffering

Aqueous MXene dispersion suffers from a bottleneck issue of oxidation, leading to its gradual deterioration and ultimately compromised physicochemical characteristics. Herein, Tris-HCl buffer is employed to stabilize the diluted Ti3 C2 Tx -MXene dispersion (0.05 mg mL-1 ) through the synergy of its potent pH-regulation capability and capping effect toward oxidation-susceptible defects/edges. Tris-HCl functionalized Ti3 C2 Tx maintained its original morphology, structure, and favorable dispersity even after 150 days of aging under naturally aerated conditions. The pH-regulation nature of Tris-HCl is elucidated through solution monitoring of Ti3 C2 Tx dispersion, while the adsorption of Tris-HCl onto defects/edges is revealed by spectral analysis and multi-scale simulations. Tris-HCl at the neutral pH can bind to the negatively charged basal plane of Ti3 C2 Tx via + HTris moiety, while the other moiety (Tris) interacts with the exposed edge-based Ti atoms and/or intrinsic defects, forming a Ti─N bond that prevents MXene from attack by H2 O and O2 . Besides, Tris-HCl stabilized Ti3 C2 Tx exhibited nearly identical capacitive characteristics to its freshly-etched counterpart, indicating the minimal impact of Tris-HCl on electrochemical performance of Ti3 C2 Tx during long-term storage. This study provides practical guidance for stabilizing MXene in their native aqueous dispersion without compromising the inherent properties.

Recent advances using MXenes in biomedical applications

An MXene is a novel two-dimensional transition metal carbide or nitride, with a typical formula of Mn+1XnTx (M = transition metals, X = carbon or nitrogen, and T = functional groups). MXenes have found wide application in biomedicine and biosensing, owing to their high biocompatibility, abundant reactive surface groups, good conductivity, and photothermal properties. Applications include photo- and electrochemical sensors, energy storage, and electronics. This review will highlight recent applications of MXene and MXene-derived materials in drug delivery, tissue engineering, antimicrobial activity, and biosensors (optical and electrochemical). We further elaborate on recent developments in utilizing MXenes for photothermal cancer therapy, and we explore multimodal treatments, including the integration of chemotherapeutic agents or magnetic nanoparticles for enhanced therapeutic efficacy. The high surface area and reactivity of MXenes provide an interface to respond to the changes in the environment, allowing MXene-based drug carriers to respond to changes in pH, reactive oxygen species (ROS), and electrical signals for controlled release applications. Furthermore, the conductivity of MXene enables it to provide electrical stimulation for cultured cells and endows it with photocatalytic capabilities that can be used in antibiotic applications. Wearable and in situ sensors incorporating MXenes are also included. Major challenges and future development directions of MXenes in biomedical applications are also discussed. The remarkable properties of MXenes will undoubtedly lead to their increasing use in the applications discussed here, as well as many others.

Engineering Photo-Cross-Linkable MXene-Based Hydrogels: Durable Conductive Biomaterials for Electroactive Tissues and Interfaces

Light-cured conductive hydrogels have attracted immense interest in the regeneration of electroactive tissues and bioelectronic interfaces. Despite the unique properties of MXene (MX), its light-blocking effect in the range of 300-600 nm hinders the efficient cross-linking of photocurable hydrogels. In this study, we investigated the photo-cross-linking process of MX-gelatin methacrylate (GelMa) composites with different types of photoinitiators and MX concentrations to prepare biocompatible, injectable, conductive, and photocurable composite hydrogels. The examined photoinitiators were Eosin Y, Irgacure 2959 (Type I), and lithium phenyl-2,4,6-trimethylbenzoyl phosphinate (Type II). The light-blocking effect of MX strongly affected the thickness, pore structure, swelling ratio, degradation, and mechanical properties of the light-cured hydrogels. Uniform distribution of MX in the hydrogel matrix was achieved at concentrations up to 0.04 wt % but the film thickness and curing times varied depending on the type of photoinitiator. It was feasible to prepare thin films (0.5 mm) by employing Type I photoinitiators under a relatively long light irradiation (4-5 min) while thick films with centimeter sizes could be rapidly cured by using Type II photoinitiator (<60 s). The mechanical properties, including elastic modulus, toughness, and stress to break for the Type II hydrogels were significantly superior (up to 300%) to those of Type I hydrogels depending on the MX concentration. The swelling ratio was also remarkably higher (648-1274%). A conductivity of about 1 mS/cm was attained at 0.1 mg/mL MX for the composite hydrogel cured by the Type I photoinitiator. In vitro cytocompatibility assays determined that the hydrogels promoted cell viability, metabolic activity, and robust proliferation of C2C12 myoblasts, which indicated their potential to support muscle cell growth during myogenesis. The developed photocurable GelMa-MX hydrogels have the potential to serve as bioactive and conductive scaffolds to modulate cellular functions and for tissue-device interfacing.

Recent advances in the application of MXenes for neural tissue engineering and regeneration

Transition metal carbides and nitrides (MXenes) are crystal nanomaterials with a number of surface functional groups such as fluorine, hydroxyl, and oxygen, which can be used as carriers for proteins and drugs. MXenes have excellent biocompatibility, electrical conductivity, surface hydrophilicity, mechanical properties and easy surface modification. However, at present, the stability of most MXenes needs to be improved, and more synthesis methods need to be explored. MXenes are good substrates for nerve cell regeneration and nerve reconstruction, which have broad application prospects in the repair of nervous system injury. Regarding the application of MXenes in neuroscience, mainly at the cellular level, the long-term in vivo biosafety and effects also need to be further explored. This review focuses on the progress of using MXenes in nerve regeneration over the last few years; discussing preparation of MXenes and their biocompatibility with different cells as well as the regulation by MXenes of nerve cell regeneration in two-dimensional and three-dimensional environments in vitro. MXenes have great potential in regulating the proliferation, differentiation, and maturation of nerve cells and in promoting regeneration and recovery after nerve injury. In addition, this review also presents the main challenges during optimization processes, such as the preparation of stable MXenes and long-term in vivo biosafety, and further discusses future directions in neural tissue engineering.

A wearable electrostimulation-augmented ionic-gel photothermal patch doped with MXene for skin tumor treatment

A wearable biological patch capable of producing multiple responses to light and electricity without interfering with daily activities is highly desired for skin cancer treatment, but remains a key challenge. Herein, the skin-mountable electrostimulation-augmented photothermal patch (eT-patch) comprising transparent ionic gel with MXene (Ti3C2Tx) doping is developed and applied for the treatment of melanoma under photostimulation at 0.5 W/cm2. The eT-patch designed has superior photothermal and electrical characteristics owing to ionic gels doped with MXene which provides high photothermal conversion efficiency and electrical conductivity as a medium. Simultaneously, the ionic gel-based eT-patch having excellent optical transparency actualizes real-time observation of skin response and melanoma treatment process under photothermal and electrical stimulation (PES) co-therapy. Systematical cellular study on anti-tumor mechanism of the eT-patch under PES treatment revealed that eT-patch under PES treatment can synergically trigger cancer cell apoptosis and pyroptosis, which together lead to the death of melanoma cells. Due to the obvious advantages of relatively safe and less side effects in healthy organs, the developed eT-patch provides a promising cost-effective therapeutic strategy for skin tumors and will open a new avenue for biomedical applications of ionic gels.

Synergized photothermal therapy and magnetic field induced hyperthermia via bismuthene for lung cancer combinatorial treatment

Thanks to its intrinsic properties, two-dimensional (2D) bismuth (bismuthene) can serve as a multimodal nanotherapeutic agent for lung cancer acting through multiple mechanisms, including photothermal therapy (PTT), magnetic field-induced hyperthermia (MH), immunogenic cell death (ICD), and ferroptosis. To investigate this possibility, we synthesized bismuthene from the exfoliation of 3D layered bismuth, prepared through a facile method that we developed involving surfactant-assisted chemical reduction, with a specific focus on improving its magnetic properties. The bismuthene nanosheets showed high in vitro and in vivo anti-cancer activity after simultaneous light and magnetic field exposure in lung adenocarcinoma cells. Only when light and magnetic field are applied together, we can achieve the highest anti-cancer activity compared to the single treatment groups. We have further shown that ICD-dependent mechanisms were involved during this combinatorial treatment strategy. Beyond ICD, bismuthene-based PTT and MH also resulted in an increase in ferroptosis mechanisms both in vitro and in vivo, in addition to apoptotic pathways. Finally, hemolysis in human whole blood and a wide variety of assays in human peripheral blood mononuclear cells indicated that the bismuthene nanosheets were biocompatible and did not alter immune function. These results showed that bismuthene has the potential to serve as a biocompatible platform that can arm multiple therapeutic approaches against lung cancer.

Unveiling the tribological potential of MXenes-current understanding and future perspectives

Reducing energy consumption and CO2 emissions by improving the tribological performance of mechanical systems relies on the development of new lubrication concepts. Two-dimensional (2D) materials have been the subject of extensive tribological research due to their unique physical and chemical properties. 2D transition metal carbides, nitrides, and carbonitrides (MXenes), with their tuneable chemistry and structure, are a relatively new addition to the family of 2D materials. MXenes' good strength and stiffness, easy-to-shear ability, capability to form wear-resistant tribofilms, and the possibility to control their surface chemistry make them appealing candidates to be explored for tribological purposes. This review provides a comprehensive overview of MXenes' tribology, covering their structure-property relationship, synthesis approaches, deposition methods to generate MXene coatings for tribological purposes, and their fundamental tribological mechanisms. Furthermore, detailed insights into studies exploring MXenes' tribological performance from the nano- to the macro-scale are presented with special emphasis on their use as self-lubricating solid lubricants, lubricant additives, and reinforcement phases in composites.

Oxidation engineering triggered peroxidase-like activity of VOxC for detection of dopamine and glutathione

MXenes, two-dimensional nanomaterials, are gaining traction in catalysis and biomedicine. Yet, their oxidation instability poses significant functional constraints. Gaining insight into this oxidation dynamic is pivotal for designing MXenes with tailored functionalities. Herein, we crafted VOxC nanosheets by oxidatively engineering V4C3 MXene. Interestingly, while pristine V4C3 displays pronounced antioxidant behavior, its derived VOxC showcases enhanced peroxidase-like activity, suggesting the crossover between antioxidant and pro-oxidant capability. The mixed valence states and balanced composition of V in VOxC drive the Fenton reaction through multiple pathways to continually generate hydroxyl radicals, which was proposed as the mechanism underlying the peroxidase-like activity. Furthermore, this unique activity rendered VOxC effective in dopamine and glutathione detection. These findings underscore the potential of modulating MXenes' oxidation state to elicit varied catalytic attributes, providing an avenue for the judicious design of MXenes and derivatives for bespoke applications.

Can MXene be the Effective Nanomaterial Family for the Membrane and Adsorption Technologies to Reach a Sustainable Green World?

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and exploring methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. Therefore, the development of efficacious technology for the separation processes is of paramount importance to ensure the environmental remediation. Membrane and adsorption technologies garnered attention, especially with the use of novel and high performing nanomaterials, which provide a target-specific solution. Specifically, widespread use of MXene nanomaterials in membrane and adsorption technologies has emerged due to their intriguing characteristics, combined with outstanding separation performance. In this review, we demonstrated the intrinsic properties of the MXene family for several separation applications, namely, gas separation, solvent dehydration, dye removal, separation of oil-in-water emulsions, heavy metal ion removal, removal of radionuclides, desalination, and other prominent separation applications. We highlighted the recent advancements used to tune separation potential of the MXene family such as the manipulation of surface chemistry, delamination or intercalation methods, and fabrication of composite or nanocomposite materials. Moreover, we focused on the aspects of stability, fouling, regenerability, and swelling, which deserve special attention when the MXene family is implemented in membrane and adsorption-based separation applications.

MXene-Embedded Electrospun Polymeric Nanofibers for Biomedical Applications: Recent Advances

Recently MXenes has gained immense attention as a new and exciting class of two-dimensional material. Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for various applications such as energy, environmental, and biomedical. The ease of dispersibility and metallic conductivity of MXene render them promising candidates for use as fillers in polymer nanocomposites. MXene-polymer nanocomposites simultaneously benefit from the attractive properties of MXenes and the flexibility and facile processability of polymers. However, the potentiality of MXene to modify the electrospun nanofibers has been less studied. Understanding the interactions between polymeric nanofibers and MXenes is important to widen their role in biomedical applications. This review explores diverse methods of MXene synthesis, discusses our current knowledge of the various biological characteristics of MXene, and the synthesis of MXene incorporated polymeric nanofibers and their utilization in biomedical applications. The information discussed in this review serves to guide the future development and application of MXene-polymer nanofibers in biomedical fields.

MXene/graphene oxide nanocomposites for friction and wear reduction of rough steel surfaces

Development of solid lubricant materials that render reliable performance in ambient conditions, are amenable to industrial size and design complexities, and work on engineered surfaces is reported. These coatings are composed of Ti3C2Tx-Graphene Oxide blends, spray-coated onto bearing steel surfaces. The tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental set-up. The evaluation yielded that the use of Ti3C2Tx-Graphene-Oxide coatings led to substantial reduction in friction down to 0.065 (at 1 GPa contact pressure and 100 mm/s) in comparison to the uncoated of single-component-coated surfaces, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. In operando formation of a dense, hard and stiff, dangling-bond-saturated tribolayer was observed to be the reason for the sustained lubricity even at high test loads and sliding speeds. This report presents the holistic exploration and correlation of structure-property-processing pertaining to the advancement of solid lubrication science.

MXene-Based Nanocomposites for Piezoelectric and Triboelectric Energy Harvesting Applications

Due to its superior advantages in terms of electronegativity, metallic conductivity, mechanical flexibility, customizable surface chemistry, etc., 2D MXenes for nanogenerators have demonstrated significant progress. In order to push scientific design strategies for the practical application of nanogenerators from the viewpoints of the basic aspect and recent advancements, this systematic review covers the most recent developments of MXenes for nanogenerators in its first section. In the second section, the importance of renewable energy and an introduction to nanogenerators, major classifications, and their working principles are discussed. At the end of this section, various materials used for energy harvesting and frequent combos of MXene with other active materials are described in detail together with the essential framework of nanogenerators. In the third, fourth, and fifth sections, the materials used for nanogenerators, MXene synthesis along with its properties, and MXene nanocomposites with polymeric materials are discussed in detail with the recent progress and challenges for their use in nanogenerator applications. In the sixth section, a thorough discussion of the design strategies and internal improvement mechanisms of MXenes and the composite materials for nanogenerators with 3D printing technologies are presented. Finally, we summarize the key points discussed throughout this review and discuss some thoughts on potential approaches for nanocomposite materials based on MXenes that could be used in nanogenerators for better performance.

Advances in MXene-Based Electrochemical (Bio)Sensors for Neurotransmitter Detection

Neurotransmitters are chemical messengers that play an important role in the nervous system's control of the body's physiological state and behaviour. Abnormal levels of neurotransmitters are closely associated with some mental disorders. Therefore, accurate analysis of neurotransmitters is of great clinical importance. Electrochemical sensors have shown bright application prospects in the detection of neurotransmitters. In recent years, MXene has been increasingly used to prepare electrode materials for fabricating electrochemical neurotransmitter sensors due to its excellent physicochemical properties. This paper systematically introduces the advances in MXene-based electrochemical (bio)sensors for the detection of neurotransmitters (including dopamine, serotonin, epinephrine, norepinephrine, tyrosine, NO, and H₂S), with a focus on their strategies for improving the electrochemical properties of MXene-based electrode materials, and provides the current challenges and future prospects for MXene-based electrochemical neurotransmitter sensors.

Photoactivated MXene Nanosheets for Integrated Bone-Soft Tissue Therapy: Effect and Potential Mechanism

The bone defects caused by trauma are inevitably accompanied by soft tissue damage. The development of multifunctional bioactive biomaterials with integrated bone and soft tissue regeneration is necessary and needed urgently in orthopedics. In this work, we found that the photoactivated MXene (Ti₃C₂T_x) nanosheet showed positive effects on promoting both bone and soft tissue regeneration. We further investigated the detailed effect and potential mechanism of photoactivated MXene on tissue regeneration. Photoactivated MXene shows a good thermal effect and robust antibacterial activity to inhibit the expression of inflammation factors and methicillin-resistant Staphylococcus aureus (MRSA) infection and induces the expression of pro-angiogenic factors and soft tissue wound repair. Photoactivated MXene can also regulate the osteogenic differentiation of adipose-derived stem cells (ADSCs) through the ERK signaling pathway by activating the heat shock protein 70 (HSP70) and enhancing the repair of bone tissue. This work sheds light on the development of bioactive MXene with photothermal activation as an efficient strategy for bone and soft tissue regeneration simultaneously.

Intestine-inspired wrinkled MXene microneedle dressings for smart wound management

Composite MXene-based materials are prone to crack propagation, thus limiting their tensile properties. Numerous efforts have been devoted to removing material constraints and fabricating unitary MXene elastic films. Here, for the first time, inspired by the intestinal wrinkles and villi structure, we presented a ductile, biologically friendly, and highly conductive MXene-based microneedle (MMN) dressing composed of stacked MXene film and superfine microneedle arrays through a simple stretching and laser engraving strategy for wound healing. By utilizing photothermal responsive MXene, periodic porous structures, and a temperature-responsive polymer to construct the MMN dressing, the system can act as an effective route for facilitating controllable drug delivery controlled by near-infrared (NIR) irradiation. In addition, superior conductivity imparts them with the capacity to realize continuous and steady monitoring of motion sensing. The practical performance further demonstrated that the versatile MMN dressing showed obvious therapeutic efficacy in vivo animal wound models. Thus, it is believed that MMN dressings with biomimetic structures, controllable drug release, and conductive pathways will open a new chapter for wound management and widen other practical applications in biomedical fields, such as artificial tendons and soft robotics. STATEMENT OF SIGNIFICANCE: MXene-based materials have been demonstrated as critical tools in advancing our understanding of wound healing. However, the rapid crack propagation is a constraint on their tensile properties. Here, inspired by the intestinal wrinkles and villi structure, a single-step method has also been discussed to present a MXene-based microneedle dressing composed of unitary MXene elastic film and superfine microneedle arrays. At the same time, the dressing with biomimetic structures, controllable drug release, and conductive pathways has prospects in intelligent wound management and varieties of related biomedical fields.

Two-dimensional nanomaterial MXenes for efficient gas separation: a review

Transition metal carbides/nitrides (MXenes) are emerging two-dimensional (2D) materials that have been widely investigated in recent years. In general, these materials can be obtained from MAX phase ceramics after intercalation, etching, and exfoliation to obtain multilayer MXene nanosheet structures; moreover, they have abundant end-group functional groups on their surface. In recent years, the excellent high permeability, fine sieving ability and diverse processability of MXene series materials make the membranes prepared using them particularly suitable for membrane-based separation processes in the field of gas separation. 2D membranes enhance the diversity of the pristine membrane transport channels by regulating the gas transport channels through in-plane pores (intrinsic defects), in-plane slit-like pores, and planar to planar interlayer channels, endowing the membrane with the ability to effectively sieve gas energy efficiently. Herein, we review MXenes, a class of 2D nanomaterials, in terms of their unique structure, synthesis method, functionalization method, and the structure-property relationship of MXene-based gas separation membranes and list examples of MXene-based membranes used in the field of gas separation. By summarizing and analyzing the basic properties of MXenes and demonstrating their unique advantages compared to other 2D nanomaterials, we lay a foundation for the discussion of MXene-based membranes with outstanding carbon dioxide (CO₂) capture performance and outline and exemplify the excellent separation performances of MXene-based gas separation membranes. Finally, the challenges associated with MXenes are briefly discussed and an outlook on the promising future of MXene-based membranes is presented. It is expected that this review will provide new insights and important guidance for future research on MXene materials in the field of gas separation.

MXene-based composites against antibiotic-resistant bacteria: current trends and future perspectives

Today, finding novel nanomaterial-based strategies to combat bacterial resistance is an important field of science. MXene-based composites have shown excellent antimicrobial potential owing to their fascinating properties such as excellent photothermal effects, highly active sites, large interlayer spacing, unique chemical structures, and hydrophilicity; they have great potential to damage the bacterial cells by rupturing the bacterial cell membranes, enhancing the permeability across the membrane, causing DNA damages, reducing the metabolic activity, and generating oxidative stress. After inserting into or attaching on the surface of pathogenic bacteria, these two-dimensional structures can cause bacterial membrane disruption and cell content leakage owing to their sharp edges. Remarkably, MXenes and their composites with excellent photothermal performance have been studied in photothermal antibacterial therapy to combat antibiotic-resistant bacteria and suppress chronic wound infections, thus providing new opportunities for multidrug-resistant bacteria-infected wound healing. But, details about the possible interactions between MXene-based nanosystems and bacterial cell membranes are rather scarce. Also, the mechanisms of photothermal antibacterial therapy as well as synergistic tactics including photothermal, photodynamic or chemo-photothermal therapy still need to be uncovered. This review endeavors to delineate critical issues pertaining to the application of MXene-based composites against antibiotic-resistant bacteria, focusing on their photocatalytic inactivation, physical damage, and photothermal antibacterial therapy.

This review endeavors to delineate critical issues pertaining to the application of MXene-based composites against antibiotic-resistant bacteria.

Peptide Nanosheet-Inspired Biomimetic Synthesis of CuS Nanoparticles on Ti3C2 Nanosheets for Electrochemical Biosensing of Hydrogen Peroxide

Hydrogen peroxide (H₂O₂) is one of the intermediates or final products of biological metabolism and participates in many important biological processes of life activities. The detection of H₂O₂ is of great significance in clinical disease monitoring, environmental protection, and bioanalysis. In this study, Ti₃C₂-based nanohybrids are prepared by the biological modification and self-assembled peptide nanosheets (PNSs)-based biomimetic synthesis of copper sulfide nanoparticles (CuS NPs), which show potential application in the fabrication of low-cost and high-performance electrochemical H₂O₂ biosensors. The synthesized CuS-PNSs/Ti₃C₂ nanohybrids exhibit excellent electrochemical performance towards H₂O₂, in which CuS NPs can catalyze the decomposition of H₂O₂ and realize the transformation from a chemical signal to an electrical signal to achieve the purpose of H₂O₂ detection. The prepared CuS-PNSs/Ti₃C₂-based electrochemical biosensor platform exhibits a wide detection range (5 μM-15 mM) and a low detection limit (0.226 μM). In addition, it reveals good selectivity and stability and can realize the monitoring of H₂O₂ in a complex environment. The successful biomimetic synthesis of CuS-PNSs/Ti₃C₂ hybrid nanomaterials provides a green and friendly strategy for the design and synthesis of functional nanomaterials and also provides a new inspiration for the construction of highly effective electrochemical biosensors for practical detection of H₂O₂ in various environments.

Engineering tumor-specific catalytic nanosystem for NIR-II photothermal-augmented and synergistic starvation/chemodynamic nanotherapy

Background

As an emerging therapeutic modality, chemodynamic therapy (CDT), converting hydrogen peroxide (H2O2) into highly toxic reactive oxygen species (ROS), has been developed for tumor-specific therapy. However, the deficiency of endogenous H2O2 and high concentration of glutathione (GSH) in the tumor microenvironment (TME) weaken the CDT-based tumor-therapeutic efficacy. Herein, a photothermal-enhanced tumor-specific cascade catalytic nanosystem has been constructed on the basis of glucose oxidase (GOD)-functionalized molybdenum (Mo)-based polyoxometalate (POM) nanoclusters, termed as GOD@POMs.

Methods

GOD@POMs were synthesized by a facile one-pot procedure and covalently conjugation. Then, its structure was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, ultraviolet-visible-near-infrared (UV-vis-NIR) absorption spectrum and infrared thermal camera were applied to evaluate the catalytic and photothermal performance, respectively. Moreover, to confirm the therapeutic effects in vitro, cell counting kit-8 (CCK-8) assay, live/dead staining and ROS staining were performed. Furthermore, the biosafety of GOD@POMs was investigated via blood routine, blood biochemistry and hematoxylin and eosin (H&E) staining in Kunming mice. Besides, the C6 glioma tumor-bearing mice were constructed to evaluate its anti-tumor effects in vivo and its photoacoustic (PA) imaging capability. Notably, RNA sequencing, H&E, TdT-mediated dUTP nick end labeling (TUNEL) and Ki-67 staining were also conducted to disclose its underlying anti-tumor mechanism.

Results

In this multifunctional nanosystem, GOD can effectively catalyze the oxidation of intratumoral glucose into gluconic acid and H2O2, achieving the cancer starvation therapy. Meanwhile, the generated gluconic acid decreases the pH in TME resulting in POM aggregation, which enables PA imaging-guided tumor-specific photothermal therapy (PTT), especially in the second near-infrared (NIR-II) biological window. Importantly, the Mo (VI) sites on POM can be reduced to Mo (V) active sites in accompany with GSH depletion, and then the post-produced Mo (V) transforms in situ overproduced H2O2 into singlet oxygen (1O2) via Russell mechanism, achieving self-enhanced CDT. Moreover, the PTT-triggered local tumor temperature elevation augments the synergistic nanocatalytic-therapeutic efficacy.

Conclusions

Consequently, the integration of GOD-induced starvation therapy, H2O2 self-supply/GSH-depletion enhanced Mo-based CDT, and POM aggregation-mediated PTT endow the GOD@POMs with remarkable synergistic anticancer outcomes with neglectable adverse effects.

Advanced MXene-Based Micro- and Nanosystems for Targeted Drug Delivery in Cancer Therapy

MXenes with unique mechanical, optical, electronic, and thermal properties along with a specific large surface area for surface functionalization/modification, high electrical conductivity, magnetic properties, biocompatibility, and low toxicity have been explored as attractive candidates for the targeted delivery of drugs in cancer therapy. These two-dimensional materials have garnered much attention in the field of cancer therapy since they have shown suitable photothermal effects, biocompatibility, and luminescence properties. However, outstanding challenging issues regarding their pharmacokinetics, biosafety, targeting properties, optimized functionalization, synthesis/reaction conditions, and clinical translational studies still need to be addressed. Herein, recent advances and upcoming challenges in the design of advanced targeted drug delivery micro- and nanosystems in cancer therapy using MXenes have been discussed to motivate researchers to further investigate this field of science.

Two-dimensional MXenes: recent emerging applications

MXenes, are a rapidly growing family of two-dimensional materials exhibiting outstanding electronic, optical, mechanical, and thermal properties with versatile transition metal and surface chemistries. A wide range of transition metals and surface termination groups facilitate the properties of MXenes to be easily tuneable. Due to the physically strong and environmentally stable nature of MXenes, they have already had a strong presence in different fields, for instance energy storage, electrocatalysis, water purification, and chemical sensing. Some of the newly discovered applications of MXenes showed very promising results, however, they have not been covered in any review article. Therefore, in this review we comprehensively review the recent advancements of MXenes in various potential fields including energy conversion and storage, wearable flexible electronic devices, chemical detection, and biomedical engineering. We have also presented some of the most exciting prospects by combining MXenes with other materials and forming mixed dimensional high performance heterostructures based novel electronic devices.

Two-dimensional ultrathin Ti3C2 MXene nanosheets coated intraocular lens for synergistic photothermal and NIR-controllable rapamycin releasing therapy against posterior capsule opacification

Posterior capsule opacification (PCO) is one of the most frequent late-onset complications after cataract surgery. Several kinds of drug-eluting intraocular lenses (IOL) were designed for sustainable drug release to suppress ocular inflammation, the proliferation of lens epithelial cells (LECs) and the development of PCO after cataract surgery. Despite previous advances in this field, the drug-loaded IOLs were limited in ocular toxicity, insufficient drug-loading capacity, and short release time. To prevent PCO and to address these drawbacks, a novel drug-loaded IOL (Rapa@Ti3C2-IOL), prepared from two-dimensional ultrathin Ti3C2 MXene nanosheets and rapamycin (Rapa), was fabricated with a two-step spin coating method in this study. Rapa@Ti3C2 was prepared via electrostatic self-assembly of Ti3C2 and Rapa, with a loading capacity of Rapa at 92%. Ti3C2 was used as a drug delivery reservoir of Rapa. Rapa@Ti3C2-IOL was designed to have the synergistic photothermal and near infrared (NIR)-controllable drug release property. As a result, Rapa@Ti3C2-IOL exhibited the advantages of simple preparation, high light transmittance, excellent photothermal conversion capacity, and NIR-controllable drug release behavior. The Rapa@Ti3C2 coating effectively eliminated the LECs around Rapa@Ti3C2-IOL under a mild 808-nm NIR laser irradiation (1.0 W/cm−2). Moreover, NIR-controllable Rapa release inhibited the migration of LECs and suppressed the inflammatory response after photothermal therapy in vitro. Then, Rapa@Ti3C2-IOL was implanted into chinchilla rabbit eyes, and the effectiveness and biocompatibility to prevent PCO were evaluated for 4 weeks. The Rapa@Ti3C2-IOL implant exhibited excellent PCO prevention ability with the assistance of NIR irradiation and no obvious pathological damage was observed in surrounding healthy tissues. In summary, the present study offers a promising strategy for preventing PCO via ultrathin Ti3C2 MXene nanosheet-based IOLs with synergistic photothermal and NIR-controllable Rapa release properties.

Review of Flexible Wearable Sensor Devices for Biomedical Application

With the development of cross-fertilisation in various disciplines, flexible wearable sensing technologies have emerged, bringing together many disciplines, such as biomedicine, materials science, control science, and communication technology. Over the past few years, the development of multiple types of flexible wearable devices that are widely used for the detection of human physiological signals has proven that flexible wearable devices have strong biocompatibility and a great potential for further development. These include electronic skin patches, soft robots, bio-batteries, and personalised medical devices. In this review, we present an updated overview of emerging flexible wearable sensor devices for biomedical applications and a comprehensive summary of the research progress and potential of flexible sensors. First, we describe the selection and fabrication of flexible materials and their excellent electrochemical properties. We evaluate the mechanisms by which these sensor devices work, and then we categorise and compare the unique advantages of a variety of sensor devices from the perspective of in vitro and in vivo sensing, as well as some exciting applications in the human body. Finally, we summarise the opportunities and challenges in the field of flexible wearable devices.

MXene-Chitosan Composites and Their Biomedical Potentials

Today, MXenes with fascinating electronic, thermal, optical, and mechanical features have been broadly studied for biomedical applications, such as drug/gene delivery, photothermal/photodynamic therapy, antimicrobials/antivirals, sensing, tissue engineering, and regenerative medicine. In this context, various MXene-polymer composites have been designed to improve the characteristics such as physiological stability, sustained/controlled release behaviors, biodegradability, biocompatibility, selectivity/sensitivity, and functionality. Chitosan with advantages of ease of modification, biodegradability, antibacterial activities, non-toxicity, and biocompatibility can be considered as attractive materials for designing hybridized composites together with MXenes. These hybrid composites ought to be further explored for biomedical applications because of their unique properties such as high photothermal conversion efficiency, improved stability, selectivity/sensitivity, stimuli-responsiveness behaviors, and superior antibacterial features. These unique structural, functional, and biological attributes indicate that MXene-chitosan composites are attractive alternatives in biomedical engineering. However, several crucial aspects regarding the surface functionalization/modification, hybridization, nanotoxicological analyses, long-term biosafety assessments, biocompatibility, in vitro/in vivo evaluations, identification of optimization conditions, implementation of environmentally-benign synthesis techniques, and clinical translation studies are still need to be examined by researchers. Although very limited studies have revealed the great potentials of MXene-chitosan hybrids in biomedicine, the next steps should be toward the extensive research and detailed analyses in optimizing their properties and improving their functionality with a clinical and industrial outlook. Herein, recent developments in the use of MXene-chitosan composites with biomedical potentials are deliberated, with a focus on important challenges and future perspectives. In view of the fascinating properties and multifunctionality of MXene-chitosan composites, these hybrid materials can open significant new opportunities in the future for bio- and nano-medicine arena.

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

MXene-Graphene Composites: A Perspective on Biomedical Potentials

MXenes, transition metal carbides and nitrides with graphene-like structures, have received considerable attention since their first discovery. On the other hand, Graphene has been extensively used in biomedical and medicinal applications. MXene and graphene, both as promising candidates of two-dimensional materials, have shown to possess high potential in future biomedical applications due to their unique physicochemical properties such as superior electrical conductivity, high biocompatibility, large surface area, optical and magnetic features, and extraordinary thermal and mechanical properties. These special structural, functional, and biological characteristics suggest that the hybrid/composite structure of MXene and graphene would be able to meet many unmet needs in different fields; particularly in medicine and biomedical engineering, where high-performance mechanical, electrical, thermal, magnetic, and optical requirements are necessary. However, the hybridization and surface functionalization should be further explored to obtain biocompatible composites/platforms with unique physicochemical properties, high stability, and multifunctionality. In addition, toxicological and long-term biosafety assessments and clinical translation evaluations should be given high priority in research. Although very limited studies have revealed the excellent potentials of MXene/graphene in biomedicine, the next steps should be toward the extensive research and detailed analysis in optimizing the properties and improving their functionality with a clinical and industrial outlook. Herein, different synthesis/fabrication methods and performances of MXene/graphene composites are discussed for potential biomedical applications. The potential toxicological effects of these composites on human cells and tissues are also covered, and future perspectives toward more successful translational applications are presented. The current state-of-the-art biotechnological advances in the use of MXene-Graphene composites, as well as their developmental challenges and future prospects are also deliberated. Due to the superior properties and multifunctionality of MXene-graphene composites, these hybrid structures can open up considerable new horizons in future of healthcare and medicine.

Recent Advances of MXene-Based Electrochemical Immunosensors

Electrochemical immunosensors are the largest class of affinity biosensing devices with strong practicability. In recent years, MXenes have become hotspot materials of electrochemical biosensors for their excellent properties, including large specific surface area, good electrical conductivity, high hydrophilicity and rich functional groups. In this review, we firstly introduce the composition and structure of MXenes, as well as their properties relevant to the construction of biosensors. Then, we summarize the recent advances of MXenes-based electrochemical immunosensors, focusing on the roles of MXenes in various electrochemical immunosensors. Finally, we analyze current problems of MXenes-based electrochemical immunosensors and propose an outlook for this research field.