Cytotoxicity of MXene-based nanomaterials for biomedical applications: A mini review

MXene Hydrogels for Soft Multifunctional Sensing: A Synthesis-Centric Review

Intelligent wearable sensors based on MXenes hydrogels are rapidly advancing the frontier of personalized healthcare management. MXenes, a new class of transition metal carbon/nitride synthesized only a decade ago, have proved to be a promising candidate for soft sensors, advanced human-machine interfaces, and biomimicking systems due to their controllable and high electrical conductivity, as well as their unique mechanical properties as derived from their atomistically thin layered structure. In addition, MXenes' biocompatibility, hydrophilicity, and antifouling properties render them particularly suitable to synergize with hydrogels into a composite for mechanoelectrical functions. Nonetheless, while the use of MXene as a multifunctional surface or an electrical current collector such as an energy device electrode is prevalent, its incorporation into a gel system for the purpose of sensing is vastly less understood and formalized. This review provides a systematic exposition to the synthesis, property, and application of MXene hydrogels for intelligent wearable sensors. Specific challenges and opportunities on the synthesis of MXene hydrogels and their adoption in practical applications are explicitly analyzed and discussed to facilitate cross gemination across disciplines to advance the potential of MXene multifunctional sensing hydrogels.

Non-Ti MXenes: new biocompatible and biodegradable candidates for biomedical applications

MXenes are a class of two-dimensional nanomaterials with the general formula Mn+1XnTx, where M denotes a transition metal, X denotes either carbon or nitrogen and Tx refers to surface terminations, such as -OH, -O, -F or -Cl. The unique properties of MXenes, including their tunable surface chemistry and high surface area-to-volume ratio, make them promising candidates for various biomedical applications, such as targeted drug delivery, photothermal therapy and so on. Among the family of MXenes, titanium (Ti)-based MXenes, especially Ti3C2Tx, have been extensively explored for biomedical applications. However, despite their potential, Ti-based MXenes have shown some limitations, such as low biocompatibility. Recent studies have also indicated that Ti MXenes may disrupt spermatogenesis and accumulate in the uterus. Non-Ti MXenes are emerging as promising alternatives to Ti-based MXenes due to their superior biodegradability and enhanced biocompatibility. Recently, non-Ti MXenes have been explored for a range of biomedical applications, including drug delivery, photothermal therapy, chemodynamic therapy and sonodynamic therapy. In addition, some non-Ti MXenes exhibit enzyme-mimicking activity, such as superoxide dismutase and peroxidase-like functions, which play a major role in scavenging reactive oxygen species (ROS). This review discusses the properties of non-Ti MXenes, such as biocompatibility, biodegradability, antibacterial activity, and neuroprotective effects, highlighting their potential in various biomedical applications. These properties can be leveraged to mitigate oxidative stress and develop safe and innovative strategies for managing chronic diseases. This review provides a comprehensive analysis of the various biomedical applications of non-Ti MXenes, including their use in drug delivery and combinatorial therapies and as nanozymes for sensing and therapeutic purposes. The theranostic applications of non-Ti MXenes are also discussed. Finally, the antibacterial properties of non-Ti MXenes and the proposed mechanisms are discussed. The review concludes with a summary of the key findings and future perspectives. In short, this review provides a thorough analysis of the biomedical applications of non-Ti MXenes, emphasizing their unique properties, potential opportunities and challenges in the field.

Recent advances in the medical applications of two-dimensional MXene nanosheets

MXene-based materials are gaining significant attention due to their exceptional properties and adaptability, leading to diverse advanced applications. In 3D printing, MXenes enhance the performance of photoblockers, photocurable inks, and composites, enabling the creation of precise, flexible and durable structures. MXene/siloxane composites offer both flexibility and resilience, while MXene/spidroin scaffolds provide excellent biocompatibility and mechanical strength, making them ideal for tissue engineering. Sustainable inks such as MXene/cellulose nano inks, alginate/MXene and MXene/emulsion underscore their role in high-performance printed materials. In cancer therapy, MXenes enable innovative photothermal and photodynamic therapies, where nanosheets generate heat and reactive oxygen species to destroy cancer cells. MXene theranostic nanoprobes combine imaging and treatment, while MXene/niobium composites support hyperthermia therapy and MXene/cellulose hydrogels allow controlled drug release. Additionally, MXene-based nanozymes enhance catalytic activity, and MXene/gold nanorods enable near-infrared-triggered drug release for noninvasive treatments. In antimicrobial applications, MXene composites enhance material durability and hygiene, providing anticorrosive protection for metals. For instance, MXene/graphene, MXene/polycaprolactone nanofibers and MXene/chitosan hydrogels exhibit significant antibacterial activity. Additionally, MXene sensors have been developed to detect antibiotic residues. MXene cryogels also promote tissue regeneration, while MXene nanohybrids facilitate photocatalytic antibacterial therapy. These advancements underscore the potential of MXenes in regenerative medicine and other fields.

MXenes and artificial intelligence: fostering advancements in synthesis techniques and breakthroughs in applications

This review explores the synergistic relationship between MXenes and artificial intelligence (AI), highlighting recent advancements in predicting and optimizing the properties, synthesis routes, and diverse applications of MXenes and their composites. MXenes possess fascinating characteristics that position them as promising candidates for a variety of technological applications, including energy storage, sensors/detectors, actuators, catalysis, and neuromorphic systems. The integration of AI methodologies provides a robust toolkit to tackle the complexities inherent in MXene research, facilitating property predictions and innovative applications. We discuss the challenges associated with the predictive capabilities for novel properties of MXenes and emphasize the necessity for sophisticated AI models to unravel the intricate relationships between structural features and material behaviors. Moreover, we examine the optimization of synthesis routes for MXenes through AI-driven approaches, underscoring the potential for streamlining and enhancing synthesis processes via data-driven insights. Furthermore, the role of AI is elucidated in enabling targeted applications of MXenes across multiple domains, illustrating the correlations between MXene properties and application performance. The synergistic integration of MXenes and AI marks the dawn of a new era in material design and innovation, with profound implications for advancing diverse technological frontiers.

Cost-Effective Synthesis of MXene Cadmium Sulfide (CdS) for Heavy Metal Removal

Background Environmental contamination resulting from the release of untreated industrial wastewater has emerged as a critical worldwide issue. These effluents frequently have high levels of heavy metals and antibiotics, which are bad for aquatic ecosystems and human health. Oftentimes, conventional wastewater treatment techniques fall short of effectively eliminating these pollutants. Innovative materials that may efficiently absorb or break down contaminants from contaminated water sources are, therefore, desperately needed. Hydrothermally produced MXene cadmium sulfide (CdS) composites have shown great promise as an adsorbent material because of their special qualities, which include high surface area, chemical stability, and customizable surface functions that improve their adsorption capacity for heavy metals and antibiotics alike.  Aim The aim of this study is to produce MXene-CdS nanoparticles in a cost-effective method for the simultaneous removal of heavy metals from aqueous contaminants for water pollution control. Methods and materials MXenes were synthesized by selectively etching Ti3AlC2 MAX-phase ceramics using aqueous HF. CdS nanoparticles were synthesized separately and integrated with MXenes via a hydrothermal process. The resulting MXene CdS nanocomposites were characterized using scanning electron microscopy (SEM) for morphology, energy dispersion spectrum (EDS) for elemental composition, X-ray diffraction (XRD) study for phase identification, and removal of heavy metals via MXene CdS.  Results Consistent distribution of CdS nanoparticles on the MXene surface and the creation of MXene CdS nanomembranes with a well-defined shape were observed by SEM analysis. Ti, C, Cd, and S elements, indiciaries of a successful composite formation, were confirmed to be present by EDS. The crystalline structure of both the MXene and CdS phases was confirmed by the distinctive peaks seen in the XRD patterns. MXene-CdS composites facilitate the effective removal of chromium ions from contaminated water. The excellent hydrophilicity of the produced nanomembrane allowed for effective interaction with watery contaminants. Conclusion This study showcases the successful synthesis and characterization of MXene-CdS nanocomposites for environmental remediation, particularly in removing toxic metals like chromium from industrial effluents. SEM analysis confirmed the uniform distribution of CdS nanoparticles on the MXene surface, while elemental composition validated their integration. XRD analysis confirmed the crystalline structures of both components. The nanocomposite exhibited excellent hydrophilicity, enhancing the efficient adsorption of heavy metals. Its large surface area and chemical stability contribute to high adsorption efficiency, making it ideal for wastewater treatment. The scalable synthesis process supports practical applications. This research highlights MXene-CdS nanocomposites as a cost-effective, sustainable solution for water pollution control.

2D MXene Nanosheets with ROS Scavenging Ability Effectively Delay Osteoarthritis Progression

MXenes nanosheets with high conductivity, hydrophilicity, and excellent reactive oxygen species (ROS) scavenging ability have shown promise in treating various degenerative diseases correlated with abnormal ROS accumulation. Herein, the therapeutic potential of Ti3C2Tx nanosheets, which is the most widely investigated MXene material, in delaying osteoarthritis (OA) progression is demonstrated. In vitro experiments indicate the strong ROS scavenging capacity of Ti3C2Tx nanosheets and their acceptable biocompatibility. Ti3C2Tx nanosheets effectively protect chondrocytes from cell death induced by oxidative stress. In addition, Ti3C2Tx nanosheets demonstrate a prominent anti-inflammatory effect and the ability to restore homeostasis between anabolic activities and catabolic activities in chondrocytes. Furthermore, RNA sequencing reveals the potential mechanism underlying the Ti3C2Tx nanosheet-mediated therapeutic effect. Finally, the in vivo curative effect of Ti3C2Tx nanosheets is verified using a rat OA model. Histological staining and immunohistochemical analyses indicate that Ti3C2Tx nanosheets effectively ameliorate OA progression. Conclusively, the in vitro and in vivo experiments suggest that Ti3C2Tx nanosheets could be a promising and effective option for OA treatment.

Electrically conductive coatings in tissue engineering

Recent interest in tissue engineering (TE) has focused on electrically conductive biomaterials. This has been inspired by the characteristics of the cells' microenvironment where signalling is supported by electrical stimulation. Numerous studies have demonstrated the positive influence of electrical stimulation on cell excitation to proliferate, differentiate, and deposit extracellular matrix. Even without external electrical stimulation, research shows that electrically active scaffolds can improve tissue regeneration capacity. Tissues like bone, muscle, and neural contain electrically excitable cells that respond to electrical cues provided by implanted biomaterials. To introduce an electrical pathway, TE scaffolds can incorporate conductive polymers, metallic nanoparticles, and ceramic nanostructures. However, these materials often do not meet implantation criteria, such as maintaining mechanical durability and degradation characteristics, making them unsuitable as scaffold matrices. Instead, depositing conductive layers on TE scaffolds has shown promise as an efficient alternative to creating electrically conductive structures. A stratified scaffold with an electroactive surface synergistically excites the cells through active top-pathway, with/without electrical stimulation, providing an ideal matrix for cell growth, proliferation, and tissue deposition. Additionally, these conductive coatings can be enriched with bioactive or pharmaceutical components to enhance the scaffold's biomedical performance. This review covers recent developments in electrically active biomedical coatings for TE. The physicochemical and biological properties of conductive coating materials, including polymers (polypyrrole, polyaniline and PEDOT:PSS), metallic nanoparticles (gold, silver) and inorganic (ceramic) particles (carbon nanotubes, graphene-based materials and Mxenes) are examined. Each section explores the conductive coatings' deposition techniques, deposition parameters, conductivity ranges, deposit morphology, cell responses, and toxicity levels in detail. Furthermore, the applications of these conductive layers, primarily in bone, muscle, and neural TE are considered, and findings from in vitro and in vivo investigations are presented. STATEMENT OF SIGNIFICANCE: Tissue engineering (TE) scaffolds are crucial for human tissue replacement and acceleration of healing. Neural, muscle, bone, and skin tissues have electrically excitable cells, and their regeneration can be enhanced by electrically conductive scaffolds. However, standalone conductive materials often fall short for TE applications. An effective approach involves coating scaffolds with a conductive layer, finely tuning surface properties while leveraging the scaffold's innate biological and physical support. Further enhancement is achieved by modifying the conductive layer with pharmaceutical components. This review explores the under-reviewed topic of conductive coatings in tissue engineering, introducing conductive biomaterial coatings and analyzing their biological interactions. It provides insights into enhancing scaffold functionality for tissue regeneration, bridging a critical gap in current literature.

Fabrication Methods, Structural, Surface Morphology and Biomedical Applications of MXene: A Review

Recently, two-dimensional (2-D) layered materials have revealed outstanding properties and play a crucial role for numerous advanced applications. The emerging transition metal carbides and nitrides, known as MXene with empirical formula Mn+1XnTx, have generated widespread attention and demonstrated impressive potential in various fields. The fabrication of 2-D novel MXene and its composites and their characterizations are applicable to vast applications in different areas such as energy storage, gas sensors, catalysis, and biomedical applications. In this review, the main focus is on the various synthesis methods, their properties, and biomedical applications. This review provides detailed illustrations of MXenes for many biomedical applications, including bioimaging, drug delivery, therapies, biosensors, tissue engineering, and antibacterial reagents. The challenges and future prospects were highlighted in a comprehensive manner, and the existing problems and potential for MXene-based biomaterials were analyzed with the goal of accelerating their use in the biomedical field.

Unveiling Drimenol: A Phytochemical with Multifaceted Bioactivities

Drimenol, a phytochemical with a distinct odor is found in edible aromatic plants, such as Polygonum minus (known as kesum in Malaysia) and Drimys winteri. Recently, drimenol has received increasing attention owing to its diverse biological activities. This review offers the first extensive overview of drimenol, covering its sources, bioactivities, and derivatives. Notably, drimenol possesses a wide spectrum of biological activities, including antifungal, antibacterial, anti-insect, antiparasitic, cytotoxic, anticancer, and antioxidant effects. Moreover, some mechanisms of its activities, such as its antifungal effects against human mycoses and anticancer activities, have been investigated. However, there are still several crucial issues in the research on drimenol, such as the lack of experimental understanding of its pharmacokinetics, bioavailability, and toxicity. By synthesizing current research findings, this review aims to present a holistic understanding of drimenol, paving the way for future studies and its potential utilization in diverse fields.

Photothermal Excitation of Neurons Using MXene: Cellular Stress and Phototoxicity Evaluation

Understanding the communication of individual neurons necessitates precise control of neural activity. Photothermal modulation is a remote and non-genetic technique to control neural activity with high spatiotemporal resolution. The local heat release by photothermally active nanomaterial will change the membrane properties of the interfaced neurons during light illumination. Recently, it is demonstrated that the two-dimensional Ti3C2Tx MXene is an outstanding candidate to photothermally excite neurons with low incident energy. However, the safety of using Ti3C2Tx for neural modulation is unknown. Here, the biosafety of Ti3C2Tx-based photothermal modulation is thoroughly investigated, including assessments of plasma membrane integrity, mitochondrial stress, and oxidative stress. It is demonstrated that culturing neurons on 25 µg cm-2 Ti3C2Tx films and illuminating them with laser pulses (635 nm) with different incident energies (2-10 µJ per pulse) and different pulse frequencies (1 pulse, 1 Hz, and 10 Hz) neither damage the cell membrane, induce cellular stress, nor generate oxidative stress. The threshold energy to cause damage (i.e., 14 µJ per pulse) exceeded the incident energy for neural excitation (<10 µJ per pulse). This multi-assay safety evaluation provides crucial insights for guiding the establishment of light conditions and protocols in the clinical translation of photothermal modulation.

MXene materials in electrochemical energy storage systems

MXenes, due to their unique geometric structure, rich elemental composition, and intrinsic physicochemical properties, have multi-functional applications. In the field of electrochemical energy storage, MXenes can be used as active components, conductive agents, supports, and catalysts in ion-intercalated batteries, metal-sulfur batteries, and supercapacitors. The electrochemical performance of MXene materials is closely related to their distinctive physical and chemical properties, which depend on their geometry, surface functional groups, and elemental composition. How to regulate MXene materials to optimize electrochemical functions is a key scientific challenge. Herein, we correlated the function of MXene materials with their interlayer structure, surface functional groups, and specific catalytic sites, analyzed the electrochemical function of MXene materials, and showed how to design the electrochemical function of MXene materials based on ion/electron transport. Additionally, this feature article provides an outlook on the opportunities and challenges for MXenes, offering theoretical and technical guidance on using MXene materials in energy storage systems.

Research Progress on Metal Ion Recovery Based on Membrane Technology and Adsorption Synergy

The development of modern industry will generate more and more waste containing metal ions. It is necessary to take appropriate measures to recover these ions, whether from the perspective of environmental protection or improving economic benefits. So far, scientists have studied many methods for recovering metal ions. Among these methods, adsorption and membrane separation have received widespread attention due to their own characteristics. Combining adsorption and membrane separation methods can better leverage their respective advantages to improve the ability of recovering metal ions. This review, therefore, focuses on the synergistic recovery of metal ions by adsorption and membrane separation methods. This article first briefly explains the theoretical principles of membrane separation and adsorption synergy, and then focuses on several technologies that have received attention in different chapters. In these chapters, membrane technology is briefly introduced, followed by the situation and progress of synergistic application with adsorption technology. Then, the article compares and elaborates on the advantages and disadvantages of the above technologies, and finally summarizes and looks forward to these technologies being used to solve the difficulties and challenges in industrial application.

MXene-based composites in smart wound healing and dressings

MXenes, a class of two-dimensional materials, exhibit considerable potential in wound healing and dressing applications due to their distinctive attributes, including biocompatibility, expansive specific surface area, hydrophilicity, excellent electrical conductivity, unique mechanical properties, facile surface functionalization, and tunable band gaps. These materials serve as a foundation for the development of advanced wound healing materials, offering multifunctional nanoplatforms with theranostic capabilities. Key advantages of MXene-based materials in wound healing and dressings encompass potent antibacterial properties, hemostatic potential, pro-proliferative attributes, photothermal effects, and facilitation of cell growth. So far, different types of MXene-based materials have been introduced with improved features for wound healing and dressing applications. This review covers the recent advancements in MXene-based wound healing and dressings, with a focus on their contributions to tissue regeneration, infection control, anti-inflammation, photothermal effects, and targeted therapeutic delivery. We also discussed the constraints and prospects for the future application of these nanocomposites in the context of wound healing/dressings.

Stabilizing Ti3C2Tx MXene flakes in air by removing confined water

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti[Formula: see text]C[Formula: see text]T[Formula: see text] MXene monoflakes have exceptional thermal stability at temperatures up to 600[Formula: see text]C in air, while multiflakes readily oxidize in air at 300[Formula: see text]C. Density functional theory calculations indicate that confined water between Ti[Formula: see text]C[Formula: see text]T[Formula: see text] flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti[Formula: see text]C[Formula: see text]T[Formula: see text] films at 600[Formula: see text]C, resulting in substantial stability improvement in multiflake films (can withstand 600[Formula: see text]C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti[Formula: see text]C[Formula: see text]T[Formula: see text] oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability.

Ecotoxicity and environmental safety assessment of two-dimensional niobium carbides (MXenes)

Two-dimensional (2D) MXenes have gained great interest in water treatment, biomedical, and environmental applications. The antimicrobial activity and cell toxicity of several MXenes including Nb4C3Tx and Nb2CTx have already been explored. However, potential side effects related to Nb-MXene toxicity, especially on aquatic pneuma, have rarely been studied. Using zebrafish embryos, we investigated and compared the potential acute toxicity between two forms of Nb-MXene: the multilayer (ML-Nb4C3Tx, ML-Nb2CTx) and the delaminated (DL-Nb2CTx, and DL-Nb4C3Tx) Nb-MXene. The LC50 of ML-Nb4C3Tx, ML-Nb2CTx, DL-Nb2CTx, and DL-Nb4C3Tx were estimated to be 220, 215, 225, and 128 mg/L, respectively. Although DL-Nb2CTx, and DL-Nb4C3Tx derivatives have similar sizes, DL-Nb4C3Tx not only shows the higher mortality (LC50 = 128 mg/L Vs 225 mg/L), but also the highest teratogenic effect (NOEC = 100 mg/L Vs 200 mg/L). LDH release assay suggested more cell membrane damage and a higher superoxide anion production in DL-Nb4C3Tx than DL-Nb2CTx,. Interestingly, both DL-Nb-MXene nanosheets showed insignificant cardiac, hepatic, or behavioral toxic effects compared to the negative control. Embryos treated with the NOEC of DL-Nb2CTx presented hyperlocomotion, while embryos treated with the NOEC of DL-Nb4C3Tx presented hyperlocomotion, suggesting developmental neurotoxic effect and muscle impairment induced by both DL-Nb-MXene. According to the Fish and Wildlife Service (FSW) Acute Toxicity Rating Scale, all tested Nb-MXene nanosheets were classified as "Practically not toxic". However, DL-Nb4C3Tx should be treated with caution as it might cause a neurotoxic effect on fauna when it ends up in wastewater in high concentrations.

Staphylococcus aureus epidemiology, pathophysiology, clinical manifestations and application of nano-therapeutics as a promising approach to combat methicillin resistant Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacterium and one of the most prevalent infectious disease-related causes of morbidity and mortality in adults. This pathogen can trigger a broad spectrum of diseases, from sepsis and pneumonia to severe skin infections that can be fatal. In this review, we will provide an overview of S. aureus and discuss the extensive literature on epidemiology, transmission, genetic diversity, evolution and antibiotic resistance strains, particularly methicillin resistant S. aureus (MRSA). While many different virulence factors that S. aureus produces have been investigated as therapeutic targets, this review examines recent nanotechnology approaches, which employ materials with atomic or molecular dimensions and are being used to diagnose, treat, or eliminate the activity of S. aureus. Finally, having a deeper understanding and clearer grasp of the roles and contributions of S. aureus determinants, antibiotic resistance, and nanotechnology will aid us in developing anti-virulence strategies to combat the growing scarcity of effective antibiotics against S. aureus.

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.

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.

MXenes as emerging adsorbents for removal of environmental pollutants

MXenes are a recently emerging class of two-dimensional nanomaterials that have gained considerable interest in the field of environmental protection. Owing to their high surface area, abundant terminal groups, and unique two-dimensional layered structures, MXenes have demonstrated high efficacy as adsorbents for various pollutants. Here we focused on the latest developments in the field of MXene-based adsorbents, including the structure and properties of MXenes, their synthesis and modification methods, and their adsorption performance and mechanisms for various pollutants. Among the pollutants that have been reported to be adsorbed by MXenes are radionuclides (U(VI), Sr(II), Cs(I), Eu(III), Ba(II), Th(IV), and Tc(VII)/Re(VII)), heavy metals (Hg(II), Cu(II), Cr(VI), and Pb(II)), dyes, per- and polyfluoroalkyl substances (PFAS), antibiotics (tetracycline, ciprofloxacin, and sulfonamides), antibiotic resistance genes (ARGs), and other contaminates. Moreover, future directions in MXene research are also suggested in this review.

Recent Advances in Photothermal Therapy at Near-Infrared-II Based on 2D MXenes

The use of photothermal therapy (PTT) with the near-infrared II region (NIR-II: 1000-1700 nm) is expected to be a powerful cancer treatment strategy. It retains the noninvasive nature and excellent temporal and spatial controllability of the traditional PTT, and offers significant advantages in terms of tissue penetration depth, background noise, and the maximum permissible exposure standards for skin. MXenes, transition-metal carbides, nitrides, and carbonitrides are emerging inorganic nanomaterials with natural biocompatibility, wide spectral absorption, and a high photothermal conversion efficiency. The PTT of MXenes in the NIR-II region not only provides a valuable reference for exploring photothermal agents that respond to NIR-II in 2D inorganic nanomaterials, but also be considered as a promising biomedical therapy. First, the synthesis methods of 2D MXenes are briefly summarized, and the laser light source, mechanism of photothermal conversion, and evaluation criteria of photothermal performance are introduced. Second, the latest progress of PTT based on 2D MXenes in NIR-II are reviewed, including titanium carbide (Ti3 C2 ), niobium carbide (Nb2 C), and molybdenum carbide (Mo2 C). Finally, the main problems in the PTT application of 2D MXenes to NIR-II and future research directions are discussed.

Harnessing two-dimensional nanomaterials for diagnosis and therapy in neurodegenerative diseases: Advances, challenges and prospects

Neurodegenerative diseases (NDDs) are specific brain disorders characterized by the progressive deterioration of different motor activities as well as several cognitive functions. Current conventional therapeutic options for NDDs are limited in addressing underlying causes, delivering drugs to specific neuronal targets, and promoting tissue repair following brain injury. Due to the paucity of plausible theranostic options for NDDs, nanobiotechnology has emerged as a promising field, offering an interdisciplinary approach to create nanomaterials with high diagnostic and therapeutic efficacy for these diseases. Recently, two-dimensional nanomaterials (2D-NMs) have gained significant attention in biomedical and pharmaceutical applications due to their precise drug-loading capabilities, controlled release mechanisms, enhanced stability, improved biodegradability, and reduced cell toxicity. Although various studies have explored the diagnostic and therapeutic potential of different nanomaterials in NDDs, there is a lack of comprehensive review addressing the theranostic applications of 2D-NMs in these neuronal disorders. Therefore, this concise review aims to provide a state-of-the-art understanding of the need for these ultrathin 2D-NMs and their potential applications in biosensing and bioimaging, targeted drug delivery, tissue engineering, and regenerative medicine for NDDs.

MXene: A wonderful nanomaterial in antibacterial

Increasing bacterial infections and growing resistance to available drugs pose a serious threat to human health and the environment. Although antibiotics are crucial in fighting bacterial infections, their excessive use not only weakens our immune system but also contributes to bacterial resistance. These negative effects have caused doctors to be troubled by the clinical application of antibiotics. Facing this challenge, it is urgent to explore a new antibacterial strategy. MXene has been extensively reported in tumor therapy and biosensors due to its wonderful performance. Due to its large specific surface area, remarkable chemical stability, hydrophilicity, wide interlayer spacing, and excellent adsorption and reduction ability, it has shown wonderful potential for biopharmaceutical applications. However, there are few antimicrobial evaluations on MXene. The current antimicrobial mechanisms of MXene mainly include physical damage, induced oxidative stress, and photothermal and photodynamic therapy. In this paper, we reviewed MXene-based antimicrobial composites and discussed the application of MXene in bacterial infections to guide further research in the antimicrobial field.

Conductive 3D Ti3C2Tx MXene-Matrigel hydrogels promote proliferation and neuronal differentiation of neural stem cells

Neural stem cells (NSCs) transplantation has great potential in the field of central nervous system injury repair, but the limited differentiation efficiency of transplanted NSCs often affects the therapeutic effect. In this paper, we present a stable three-dimensional (3D) conductive hydrogel prepared by cross-linking MXenes to Matrigel hydrogel. Benefiting from 3D microporous network structure of hydrogel, the conductive hydrogel can provide an extracellular matrix-like substrate for NSCs growth. Moreover, with the addition of Ti3C2Tx MXenes, the composite has excellent electrical conductivity and biocompatibility. It is demonstrated that MXene-Matrigel hydrogels can effectively promote the proliferation and differentiation of NSCs. These findings provide experimental evidence for understanding the regulatory role of conductive hydrogels on NSCs and provides new strategies for neural tissue engineering.

Environmental implications of metal-organic frameworks and MXenes in biomedical applications: a perspective

Metal-organic frameworks (MOFs) and MXenes have demonstrated immense potential for biomedical applications, offering a plethora of advantages. MXenes, in particular, exhibit robust mechanical strength, hydrophilicity, large surface areas, significant light absorption potential, and tunable surface terminations, among other remarkable characteristics. Meanwhile, MOFs possess high porosity and large surface area, making them ideal for protecting active biomolecules and serving as carriers for drug delivery, hence their extensive study in the field of biomedicine. However, akin to other (nano)materials, concerns regarding their environmental implications persist. The number of studies investigating the toxicity and biocompatibility of MXenes and MOFs is growing, albeit further systematic research is needed to thoroughly understand their biosafety issues and biological effects prior to clinical trials. The synthesis of MXenes often involves the use of strong acids and high temperatures, which, if not properly managed, can have adverse effects on the environment. Efforts should be made to minimize the release of harmful byproducts and ensure proper waste management during the production process. In addition, it is crucial to assess the potential release of MXenes into the environment during their use in biomedical applications. For the biomedical applications of MOFs, several challenges exist. These include high fabrication costs, poor selectivity, low capacity, the quest for stable and water-resistant MOFs, as well as difficulties in recycling/regeneration and maintaining chemical/thermal/mechanical stability. Thus, careful consideration of the biosafety issues associated with their fabrication and utilization is vital. In addition to the synthesis and manufacturing processes, the ultimate utilization and fate of MOFs and MXenes in biomedical applications must be taken into account. While numerous reviews have been published regarding the biomedical applications of MOFs and MXenes, this perspective aims to shed light on the key environmental implications and biosafety issues, urging researchers to conduct further research in this field. Thus, the crucial aspects of the environmental implications and biosafety of MOFs and MXenes in biomedicine are thoroughly discussed, focusing on the main challenges and outlining future directions.

Mxene-Based Supramolecular Composite Hydrogels for Antioxidant and Photothermal Antibacterial Activities

Bacterial infections and oxidative damage caused by various reactive oxygen species (ROS) pose a significant threat to human health. It is highly desirable to find an ideal biomaterial system with broad spectrum antibacterial and antioxidant capabilities. A new supramolecular antibacterial and antioxidant composite hydrogel made of chiral L-phenylalanine-derivative (LPFEG) as matrix and Mxene (Ti3 C2 Tx ) as filler material is presented. The noncovalent interactions (H-bonding and π-π interactions) in between LPFEG and Mxene and the inversion of LPFEG chirality are verified by Fourier transform infrared and circular dichroism spectroscopy. The composite hydrogels show improved mechanical properties revealed by rheological analysis. The composite hydrogel system exhibits photothermal conversion efficiency (40.79%), which enables effective photothermal broad-spectrum antibacterial activities against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. Furthermore, the Mxene also enables the composite hydrogel to exhibit excellent antioxidant activity by efficiently scavenging free radicals like DPPH•, ABTS•+, and •OH. These results indicate that the Mxene-based chiral supramolecular composite hydrogel, with improved rheological, antibacterial, and antioxidant properties has a great potential for biomedical applications.

Enhancing the Ag-loading capacity on Ti3C2Tx sheets as hybrid fillers to form composite coatings with excellent antibacterial properties

The settlement of microorganisms is an unwanted process in various practical fields, where also the first attaching microorganisms could promote other bacterial adhesion, causing an acceleration of bioaccumulation on the solid surface and damage to the surface functions. Developing an advanced composite coating with anti-microorganism attachment features is still a big challenge, and the critical element in any such method is to find an efficient functional agent for use in the coating system that could extend the service period. MXenes have received increasing attentions owing to their unique layer structure and large specific surface area. Increasing studies have been devoted to the development of MXene/polymer composites with creatively designed structures to realize various specific functions. Herein, two-dimensional (2D) transition metal carbide material MXene as a carrier was etched and decorated with cellulose to enhance the anchor points to grasp functional Ag nanoparticles via a simple method. The MXene nanosheets (Ti3C2Tx) were modified by cellulose to graft hydroxy groups on their surface, and then they were incorporated into silver nanoparticles (Ag NPs). The results showed that the cellulose could increase the loading content of the Ag NPs on the MXene surface, and also could act as a stabilized material to form the composite filler MXene@cellulose@Ag NPs (MAC), which could serve as a functional agent. Furthermore, the obtained product MAC filler exhibited excellent dispersibility and stability among all the tested fillers (MXene and MA), and it could help avoid aggregation and promote homogenous dispersal in the coating network. Besides, MAC displayed outstanding antibacterial activities against E. coli and S. aureus at the same concentration among all the fillers. When the filler was embedded into the coating system, the composite coating PCB-MAC possessed abundant active Ag+ ions released by the Ag NPs, which could work against bacterial growth and achieve a favorable antibacterial inhibition effect. Therefore, we believe that the active MAC filler maintained high antibacterial efficiency, evincing its potential as a desirable agent for obtaining an excellent anti-adhesive behavior in numerous broad applications, such as the environment field or medical area.

Biomacromolecular and Toxicity Responses of Bacteria upon the Nano-Bio Interfacial Interactions with Ti3C2Tx Nanosheets

The biomolecular responses of bacteria to 2D nanosheets that result from nano-bio interfacial interactions remain to be thoroughly examined. Herein, Fourier transform infrared (FTIR) multivariate and 2D correlation analyses were performed to assess the composition and conformational changes in bacterial biomacromolecules (lipids, polysaccharides, and carbohydrates) upon exposure to Ti3C2Tx nanosheets. General toxicity assays, 3D excitation-emission matrix fluorescence analyses, extended Derjaguin-Landau-Verwey-Overbeek theory interaction calculations, and isothermal titration calorimetry were also performed. Our results demonstrate that Ti3C2Tx nanosheets considerably impact Gram-positive bacteria (Bacillus subtilis), causing oxidative damage and inactivation by preferentially interacting with and disrupting the cell walls. The bilayer membrane structure of Gram-negative bacteria (Escherichia coli) endows them with increased resistance to Ti3C2Tx nanosheets. The unmodified nanosheets had a higher affinity to bacterial protein components with lower toxicity due to their susceptibility to oxidation. Surface modification with KOH or hydrazine (HMH), particularly HMH, induced stronger dispersion, antioxidation, and affinity to bacterial phospholipids, which resulted in severe cell membrane lipid peroxidation and bacterial inactivation. These findings provide valuable insight into nano-bio interfacial interactions, which can facilitate the development of antimicrobial and antifouling surfaces and contribute to the evaluation of the environmental risks of nanomaterials.

Role of MXenes in advancing soft robotics

MXenes with their unique electronic, optical, chemical, and mechanical properties have shown great promise in soft robotics. MXene-based soft actuators have been designed to display ultrafast actuations and recovery speeds as well as angle-independent structural colors in response to vapor. Several studies have developed soft actuators by combining MXenes with other materials to mimic the movement of natural organisms. Thus, MXene-based soft actuators have the potential to revolutionize the field of soft robotics and flexible electronics (e.g., wearable devices and artificial muscles). MXene-based artificial muscles have been explored for use in kinetic soft robotics as actuators in microsystems requiring exceptional compliance. MXene-based sensors and actuators have already been developed for human-like sensors and photodetection. However, there are still challenges that need to be addressed in such applications, such as the design of stretchable and compliant robotic skins with a high-level functional integration for soft robotics. The integration of various devices, such as power sources, sensors, and actuators, into soft robotics is another crucial challenge. Despite the excellent stretchability and tensile strength of MXene-based composites, there is a vital need to develop their mechanical and electrochemical features and grant them multi-functionalities. Herein, recent developments pertaining to the applications of MXenes and their composites in soft robotics are discussed with a focus on the important challenges and future perspectives.

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.

Nanobio Interface Between Proteins and 2D Nanomaterials

Two-dimensional (2D) nanomaterials have significantly contributed to recent advances in material sciences and nanotechnology, owing to their layered structure. Despite their potential as multifunctional theranostic agents, the biomedical translation of these materials is limited due to a lack of knowledge and control over their interaction with complex biological systems. In a biological microenvironment, the high surface energy of nanomaterials leads to diverse interactions with biological moieties such as proteins, which play a crucial role in unique physiological processes. These interactions can alter the size, surface charge, shape, and interfacial composition of the nanomaterial, ultimately affecting its biological activity and identity. This review critically discusses the possible interactions between proteins and 2D nanomaterials, along with a wide spectrum of analytical techniques that can be used to study and characterize such interplay. A better understanding of these interactions would help circumvent potential risks and provide guidance toward the safer design of 2D nanomaterials as a platform technology for various biomedical applications.

V4 C3 MXene Immune Profiling and Modulation of T Cell-Dendritic Cell Function and Interaction

Although vanadium-based metallodrugs are recently explored for their effective anti-inflammatory activity, they frequently cause undesired side effects. Among 2D nanomaterials, transition metal carbides (MXenes) have received substantial attention for their promise as biomedical platforms. It is hypothesized that vanadium immune properties can be extended to MXene compounds. Therefore, vanadium carbide MXene (V4 C3 ) is synthetized, evaluating its biocompatibility and intrinsic immunomodulatory effects. By combining multiple experimental approaches in vitro and ex vivo on human primary immune cells, MXene effects on hemolysis, apoptosis, necrosis, activation, and cytokine production are investigated. Furthermore, V4 C3 ability is demonstrated to inhibit T cell-dendritic cell interactions, evaluating the modulation of CD40-CD40 ligand interaction, two key costimulatory molecules for immune activation. The material biocompatibility at the single-cell level on 17 human immune cell subpopulations by single-cell mass cytometry is confirmed. Finally, the molecular mechanism underlying V4 C3 immune modulation is explored, demonstrating a MXene-mediated downregulation of antigen presentation-associated genes in primary human immune cells. The findings set the basis for further V4 C3 investigation and application as a negative modulator of the immune response in inflammatory and autoimmune diseases.

MXenes and MXene-based materials for removal of pharmaceutical compounds from wastewater: Critical review

The rapid increase in the global population and its ever-rising standards of living are imposing a huge burden on global resources. Apart from the rising energy needs, the demand for freshwater is correspondingly increasing. A population of around 3.8 billion people will face water scarcity by 2030, as per the reports of the World Water Council. This may be due to global climate change and the deficiency in the treatment of wastewater. Conventional wastewater treatment technologies fail to completely remove several emerging contaminants, especially those containing pharmaceutical compounds. Hence, leading to an increase in the concentration of harmful chemicals in the human food chain and the proliferation of several diseases. MXenes are transition metal carbide/nitride ceramics that primarily structure the leading 2D material group. MXenes act as novel nanomaterials for wastewater treatment due to their high surface area, excellent adsorption properties, and unique physicochemical properties, such as high electrical conductivity and hydrophilicity. MXenes are highly hydrophilic and covered with active functional groups (i.e., hydroxyl, oxygen, fluorine, etc.), which makes them efficient adsorbents for a wide range of species and promising candidates for environmental remediation and water treatment. This work concludes that the scaling up process of MXene-based materials for water treatment is currently of high cost. The up-to-date applications are still limited because MXenes are currently produced mainly in the laboratory with limited yield. It is recommended to direct research efforts towards lower synthesis cost procedures coupled with the use of more environmentally friendly materials to avoid secondary contamination.

Recent Advances in Two-Dimensional MXene-Based Electrochemical Biosensors for Sweat Analysis

Sweat, a biofluid secreted naturally from the eccrine glands of the human body, is rich in several electrolytes, metabolites, biomolecules, and even xenobiotics that enter the body through other means. Recent studies indicate a high correlation between the analytes' concentrations in the sweat and the blood, opening up sweat as a medium for disease diagnosis and other general health monitoring applications. However, low concentration of analytes in sweat is a significant limitation, requiring high-performing sensors for this application. Electrochemical sensors, due to their high sensitivity, low cost, and miniaturization, play a crucial role in realizing the potential of sweat as a key sensing medium. MXenes, recently developed anisotropic two-dimensional atomic-layered nanomaterials composed of early transition metal carbides or nitrides, are currently being explored as a material of choice for electrochemical sensors. Their large surface area, tunable electrical properties, excellent mechanical strength, good dispersibility, and biocompatibility make them attractive for bio-electrochemical sensing platforms. This review presents the recent progress made in MXene-based bio-electrochemical sensors such as wearable, implantable, and microfluidic sensors and their applications in disease diagnosis and developing point-of-care sensing platforms. Finally, the paper discusses the challenges and limitations of MXenes as a material of choice in bio-electrochemical sensors and future perspectives on this exciting material for sweat-sensing applications.

Spin-gapless van der Waals heterostructure for spin gating through magnetic injection devices

Spin-gapless semiconductors (SGSs) are new magnetic zero-bandgap materials whose band structure is extremely sensitive to external influences (pressure or magnetic fields) and have great potential for high-speed and low-energy spintronics applications. The first-principles method was used to systematically study the heterostructures constructed of an asymmetric surface-functionalized Janus MXene material, Cr₂NOF, and a two-dimensional hexagonal lattice (2DH) semiconductor material and to study the effects of the electronic structure, Curie temperature, magnetism, and the design of unusual band structures and magnetic injection in the bilayer to obtain an SGS structure. Through the design and construction of Cr₂NOF/2DH van der Waals heterojunction spintronic devices, the spin-filtering effect of the devices can reach 100%, especially, realizing spin gating through magnetic injection. We report the transport mechanism of the heterojunction spintronic devices to achieve the goal of a controllable optimization of the device functions, which provides a theoretical basis for the design of MXene van der Waals heterojunctions for high-efficiency and low-power-consumption spintronic devices.

MXenes Antibacterial Properties and Applications: A Review and Perspective

The mutations of bacteria due to the excessive use of antibiotics, and generation of antibiotic-resistant bacteria have made the development of new antibacterial compounds a necessity. MXenes have emerged as biocompatible transition metal carbide structures with extensive biomedical applications. This is related to the MXenes' unique combination of properties, including multifarious elemental compositions, 2D-layered structure, large surface area, abundant surface terminations, and excellent photothermal and photoelectronic properties. The focus of this review is the antibacterial application of MXenes, which has attracted the attention of researchers since 2016. A quick overview of the synthesis strategies of MXenes is provided and then summarizes the effect of various factors (including structural properties, optical properties, surface charges, flake size, and dispersibility) on the biocidal activity of MXenes. The main mechanisms for deactivating bacteria by MXenes are discussed in detail including rupturing of the bacterial membrane by sharp edges of MXenes nanoflakes, generating the reactive oxygen species (ROS), and photothermal deactivating of bacteria. Hybridization of MXenes with other organic and inorganic materials can result in materials with improved biocidal activities for different applications such as wound dressings and water purification. Finally, the challenges and perspectives of MXene nanomaterials as biocidal agents are presented.

2D MXenes for controlled releases of therapeutic proteins

MXenes belong to a new class of two dimensional (2D) functional nanomaterials, mainly encompassing transition-metal carbides, nitrides and carbonitrides, with unique physical, chemical, electronic and mechanical properties for various emerging applications across different fields. To date, the potentials of MXenes for biomedical application such as drug delivery have not been thoroughly explored due to the lack of information on their biocompatibility, cytotoxicity and biomolecule-surface interaction. In this study, we developed novel drug delivery system from MXene for the controlled release of a model therapeutic protein. First, the structural, chemical and morphological properties of as synthesized MXenes were probed with electron microscopy and X-ray diffraction. Second, the potential cytotoxicity of MXene toward the proliferation and cell morphology of murine macrophages (RAW 264.7) were evaluated with MTT assays and electron microscopy, respectively. Moreover, the drug loading capacities and sustained release capabilities of MXene were assessed in conjunction with machine learning approaches. Our results demonstrated that MXene did not significantly induce cellular toxicity at any concentration below 1 mg/ml which is within the range for effective dose of drug delivery vehicle. Most importantly, MXene was efficiently loaded with FITC-catalase for subsequently achieving controlled release under different pHs. The release profiles of catalase from MXene showed higher initial rate under basic buffer (pH 9) compared to that in physiological (pH 7.4) and acidic buffers (pH 2). Taken together, the results of this study lead to a fundamental advancement toward the use of MXene as a nanocarrier for therapeutic proteins in drug delivery applications.

State-of-the-art: MXene structures in nano-oncology

Cancer nanomedicine has been investigated widely and boomed in the last two decades, resulting in designing nanostructures with biofunctionalization, giving rise to an "All-in-One" multifunctional platform. The development of rational design technology with extended functionalities brought interdisciplinary researchers to work continuously, aiming to find a prevent or effectively treat the deadly disease of the century. Thus, it led to some Food and Drug Administration (FDA)-approving nano-based formulations for cancer treatment and opening a vast area of promising discoveries by exploiting different nanomaterials. Two-dimensional (2D) materials have recently gained tremendous interest among scientists because of their outstanding structural, optical, electronic, thermal, and mechanical characteristics. Among various 2D nanomaterials, MXenes are a widely studied nanosystem because of their close similarity to graphene analogs. So, it is synthesized using multiple approaches and exploits their inherited properties. But in most cases, surface functionalization techniques are carried out for targeting, site-specific drug clearance, renal clearance, and biocompatible with healthy cells. Thus, fabricating a multimodal agent for mono or combined therapies is also an image-guided diagnostic agent. This review will explain the recent and emerging advancements of MXenes-based composites as a multifunctional theragnostic agent and discuss the possibilities of transferring laboratory research to clinical translation.

Cytocompatibility of Ti3C2Tx MXene with Red Blood Cells and Human Umbilical Vein Endothelial Cells and the Underlying Mechanisms

Two-dimensional (2D) nanomaterials have been widely used in biomedical applications because of their biocompatibility. Considering the high risk of exposure of the circulatory system to Ti3C2Tx, we studied the cytocompatibility of Ti3C2Tx MXene with red blood cells (RBCs) and human umbilical vein endothelial cells (HUVECs) and showed that Ti3C2Tx had excellent compatibility with the two cell lines. Ti3C2Tx at a concentration as high as 200 μg/mL caused a negligible percent hemolysis of 0.8%. By contrast, at the same treatment concentration, graphene oxide (GO) caused a high percent hemolysis of 50.8%. Scanning electron microscopy revealed that RBC structures remained intact in the Ti3C2Tx treatment group, whereas those in the GO group completely deformed, sunk, and shrunk, which resulted in the release of cell contents. This difference can be largely ascribed to the distinct surficial properties of the two nanosheets. In specific, the fully covered surface-terminating -O and -OH groups leading to Ti3C2Tx had a very hydrophilic surface, thereby hindering its penetration into the highly hydrophobic interior of the cell membrane. However, the strong direct van der Waals attractions coordinated with hydrophobic interactions between the unoxidized regions of GO and the lipid hydrophobic tails can still damage the integrity of the cell membranes. In addition, the sharp and keen-edged corners of GO may also facilitate its relatively strong cell membrane damage effects than Ti3C2Tx. Thus, the excellent cell membrane compatibility of Ti3C2Tx nanosheets and their ultraweak capacity to provoke excessive ROS generation endowed them with much better compatibility with HUVECs than GO nanosheets. These results indicate that Ti3C2Tx has much better cytocompatibility than GO and provide a valuable reference for the future biomedical applications of Ti3C2Tx.

Polycaprolactone-MXene Nanofibrous Scaffolds for Tissue Engineering

New conductive materials for tissue engineering are needed for the development of regenerative strategies for nervous, muscular, and heart tissues. Polycaprolactone (PCL) is used to obtain biocompatible and biodegradable nanofiber scaffolds by electrospinning. MXenes, a large class of biocompatible 2D nanomaterials, can make polymer scaffolds conductive and hydrophilic. However, an understanding of how their physical properties affect potential biomedical applications is still lacking. We immobilized Ti3C2Tx MXene in several layers on the electrospun PCL membranes and used positron annihilation analysis combined with other techniques to elucidate the defect structure and porosity of nanofiber scaffolds. The polymer base was characterized by the presence of nanopores. The MXene surface layers had abundant vacancies at temperatures of 305-355 K, and a voltage resonance at 8 × 104 Hz with the relaxation time of 6.5 × 106 s was found in the 20-355 K temperature interval. The appearance of a long-lived component of the positron lifetime was observed, which was dependent on the annealing temperature. The study of conductivity of the composite scaffolds in a wide temperature range, including its inductive and capacity components, showed the possibility of the use of MXene-coated PCL membranes as conductive biomaterials. The electronic structure of MXene and the defects formed in its layers were correlated with the biological properties of the scaffolds in vitro and in bacterial adhesion tests. Double and triple MXene coatings formed an appropriate environment for cell attachment and proliferation with mild antibacterial effects. A combination of structural, chemical, electrical, and biological properties of the PCL-MXene composite demonstrated its advantage over the existing conductive scaffolds for tissue engineering.

Neural modulation with photothermally active nanomaterials

Modulating neural electrophysiology with high precision is essential for understanding neural communication and for the diagnosis and treatment of neural disorders. Photothermal modulation offers a remote and non-genetic method for neural modulation with high spatiotemporal resolution and specificity. This technique induces highly localized and transient temperature changes at the cell membrane interfaced with photothermally active nanomaterials. This rapid temperature change affects the electrical properties of the cell membrane or temperature-sensitive ion channels. In this Review, we discuss the fundamental material properties and illumination conditions that are necessary for nanomaterial-assisted photothermal neural excitation and inhibition. We examine how this versatile technique allows direct investigation of neural electrophysiology and signalling pathways in two-dimensional and three-dimensional cell cultures and tissues, and highlight the scientific and technological challenges in terms of cellular specificity, light delivery and biointerface stability on the road to clinical translation.

Latest advances on MXenes in biomedical research and health care

The unique combination of physical and chemical properties of MXenes has propelled a growing number of applications in biomedicine and healthcare. The expanding library of MXenes with tunable properties is paving the way for high-performance, application-specific MXene-based sensing and therapeutic platforms. In this article, we highlight the emerging biomedical applications of MXenes with specific emphasis on bioelectronics, biosensors, tissue engineering, and therapeutics. We present examples of MXenes and their composites enabling novel technological platforms and therapeutic strategies, and elucidate potential avenues for further developments. Finally, we discuss the materials, manufacturing, and regulatory challenges that need to be synergistically addressed for the clinical translation of MXene-based biomedical technologies.

Graphical abstract

Preclinical safety assessment of red emissive gold nanocluster conjugated crumpled MXene nanosheets: a dynamic duo for image-guided photothermal therapy

Red emissive gold nanoclusters have potential as biological fluorescent probes, but lack sufficient light-to-heat conversion efficiency for photothermal therapy (PTT). MXene nanomaterials, on the other hand, have shown promise in PTT due to their strong near-infrared absorption abilities, but their instability caused by restacking of the sheets can decrease their available surface area. One approach to address this issue is to design sheets with wrinkles or folds. However, the crumpled or 3D MXene materials reported in the literature are actually aggregates of multiple nanosheets rather than a single sheet that is folded. In this study, a modified method for crumpling a single MXene sheet and further conjugating it with red emissive gold nanoclusters and folic acid was developed. A detailed in vitro toxicity study was performed in various cell lines and cellular uptake in cancer cells was studied using AFM to understand its interaction at the nano-bio interface. The material also demonstrated excellent utility as a bioimaging and PTT agent in vitro, with its high fluorescence allowing bioimaging at a lower concentration of 12 μg mL^-1 and a photothermal conversion efficiency of 43.51%. In vitro analyses of the cell death mechanisms induced by PTT were conducted through studies of apoptosis, cell proliferation, and ROS production. In vivo acute toxicity tests were conducted on male and female Wistar rats through oral and intravenous administration (20 mg kg^-1 dose), and toxicity was evaluated using various measures including body weight, hematology, serum biochemistry, and H&E staining. The findings from these studies suggest that the MXene gold nanoconjugate could be useful in a range of biomedical applications, with no observed toxicity following either oral or intravenous administration.

Nanocatalytic Hydrogel with Rapid Photodisinfection and Robust Adhesion for Fortified Cutaneous Regeneration

Chronic inflammation caused by invasive bacterial infections severely interferes with the normal healing process of skin regeneration. Hypoxia of the infection microenvironment (IME) seriously affects the antibacterial effect of photodynamic therapy in phototherapy. To address this serious issue, a nanocatalytic hydrogel with an enhanced phototherapy effect consisting of a hydrogel polyvinyl alcohol (PVA) scaffold, MXene/CuS bio-heterojunction, and polydopamine (PDA) for photothermal antibacterial effects and promoting skin regeneration is designed. The MXene/CuS bio-heterojunction has a benign photothermal effect. Singlet oxygen (¹O₂) and hydroxyl radicals (·OH) were generated under near-infrared light, which made the hydrogel system have good antioxidant and antibacterial properties. The addition of PDA further improves the biocompatibility and endows the nanocatalytic hydrogel with adhesion. Additionally, in vivo assays display that the nanocatalytic hydrogel has good skin regeneration ability, including ability to kill bacteria, and promotes capillary angiogenesis and collagen deposition. This work proposes an approach for nanocatalyzed hydrogels with an activated IME response to treat wound infections by enhancing the phototherapeutic effects.

Microbial electrosynthesis: carbonaceous electrode materials for CO2 conversion

Microbial electrosynthesis (MES) is a sustainable approach to address greenhouse gas (GHG) emissions using anthropogenic carbon dioxide (CO₂) as a building block to create clean fuels and highly valuable chemicals. The efficiency of MES-based CO₂ conversion is closely related to the performance of electrode material and, in particular, the cathode for which carbonaceous materials are frequently used. Compared to expensive metal electrodes, carbonaceous materials are biocompatible with a high specific surface area, wide range of possible morphologies, and excellent chemical stability, and their use can maximize the growth of bacteria and enhance electron transfer rates. Examples include MES cathodes based on carbon nanotubes, graphene, graphene oxide, graphite, graphite felt, graphitic carbon nitride (g-C₃N₄), activated carbon, carbon felt, carbon dots, carbon fibers, carbon brushes, carbon cloth, reticulated vitreous carbon foam, MXenes, and biochar. Herein, we review the state-of-the-art MES, including thermodynamic and kinetic processes that underpin MES-based CO₂ conversion, as well as the impact of reactor type and configuration, selection of biocompatible electrolytes, product selectivity, and the use of novel methods for stimulating biomass accumulation. Specific emphasis is placed on carbonaceous electrode materials, their 3D bioprinting and surface features, and the use of waste-derived carbon or biochar as an outstanding material for further improving the environmental conditions of CO₂ conversion using carbon-hungry microbes and as a step toward the circular economy. MES would be an outstanding technique to develop rocket fuels and bioderived products using CO₂ in the atmosphere for the Mars mission.

Nanomaterials and nanomaterials-based drug delivery to promote cutaneous wound healing

Various factors could damage the structure and integrity of skin to cause wounds. Nonhealing or chronic wounds seriously affect the well-being of patients and bring heavy burdens to the society. The past few decades have witnessed application of numerous nanomaterials to promote wound healing. Owing to the unique physicochemical characteristics at nanoscale, nanomaterials-based therapy has been regarded as a potential approach to promote wound healing. In this review, we first overview the wound categories, wound healing process and critical influencing factors. Then applications of nanomaterials with intrinsic therapeutic effect and nanomaterials-based drug delivery systems to promote wound healing are addressed in detail. Finally, current limitations and future perspectives of nanomaterials in wound healing are discussed.