MXenes are a class of two-dimensional transition metal carbides, nitrides, and carbonitrides that have gained significant attention in biomedical applications due to their unique physicochemical properties. Their high surface area, excellent electrical conductivity, and tunable surface chemistry make them promising candidates for various medical applications, including antibacterial therapy, drug delivery, photothermal therapy, and biosensing. Biocompatibility and toxicity studies are critical to ensuring their safe use in clinical settings.

Antibacterial Properties
MXenes exhibit strong antibacterial activity, primarily due to their sharp edges, which can physically damage bacterial membranes, and their ability to generate reactive oxygen species (ROS). Studies have shown that Ti3C2Tx MXene, one of the most widely researched MXenes, can effectively inhibit the growth of Gram-positive and Gram-negative bacteria, including Escherichia coli and Staphylococcus aureus. The antibacterial efficiency is concentration-dependent, with higher MXene concentrations leading to greater bacterial inhibition. The mechanism involves membrane disruption, oxidative stress, and eventual cell death. Surface modifications, such as functionalization with silver nanoparticles, further enhance antibacterial performance by combining the inherent properties of MXenes with the biocidal effects of silver.

Drug Delivery
MXenes have shown great potential as nanocarriers for drug delivery due to their high surface area and ease of functionalization. Their surfaces can be modified with polymers, peptides, or other biomolecules to improve stability, biocompatibility, and targeted delivery. For example, doxorubicin, a chemotherapeutic agent, has been loaded onto MXene nanosheets with high efficiency, and pH-responsive release has been demonstrated in tumor microenvironments. The drug release kinetics can be controlled by adjusting the MXene surface chemistry and external stimuli such as light or magnetic fields. Additionally, MXenes can co-deliver multiple therapeutic agents, enabling combination therapy for enhanced treatment efficacy.

Photothermal Therapy
MXenes possess strong near-infrared (NIR) absorption, making them excellent candidates for photothermal therapy (PTT). When exposed to NIR light, MXenes rapidly convert light energy into heat, inducing localized hyperthermia that can ablate cancer cells. Ti3C2Tx MXene, for instance, has demonstrated a photothermal conversion efficiency exceeding 40%, which is comparable to or better than other photothermal agents like gold nanorods. The combination of PTT with chemotherapy or immunotherapy has been explored to improve treatment outcomes. MXenes can also be engineered to enhance tumor targeting, reducing off-target effects and improving therapeutic precision.

Biosensing
The high electrical conductivity and surface functionality of MXenes make them ideal for biosensing applications. They have been incorporated into electrochemical and optical sensors for detecting biomolecules such as glucose, dopamine, and cancer biomarkers. MXene-based biosensors exhibit high sensitivity, low detection limits, and rapid response times due to their excellent electron transfer properties. For example, a Ti3C2Tx MXene-modified electrode demonstrated a glucose detection limit as low as 0.5 µM, with high selectivity against interfering substances. MXenes can also be integrated with other nanomaterials to create hybrid sensing platforms for multiplexed detection.

Biocompatibility and Toxicity Studies
The biocompatibility of MXenes is a critical factor for their biomedical applications. In vitro studies have shown that MXenes exhibit concentration-dependent cytotoxicity, with higher concentrations leading to reduced cell viability. However, surface modifications and proper dispersion techniques can mitigate toxicity. For instance, polyethylene glycol (PEG) functionalization has been shown to improve biocompatibility by reducing cellular uptake and inflammatory responses. In vivo studies in animal models have demonstrated that MXenes can be safely administered at controlled doses, with no significant systemic toxicity observed in short-term studies. However, long-term toxicity and biodistribution profiles require further investigation to ensure clinical safety.

Degradation and Clearance
Understanding the degradation and clearance pathways of MXenes is essential for their biomedical use. Studies suggest that MXenes can undergo gradual degradation under physiological conditions, particularly in the presence of enzymes or reactive oxygen species. The degradation products, such as titanium ions, are generally considered biocompatible at low concentrations. Renal and hepatic clearance pathways have been proposed, but the exact mechanisms depend on the MXene composition, size, and surface modifications. Further research is needed to optimize degradation kinetics and ensure complete clearance from the body.

Challenges and Future Perspectives
Despite their promising potential, several challenges must be addressed before MXenes can be widely adopted in clinical settings. Standardized synthesis methods are needed to ensure batch-to-batch consistency, and large-scale production techniques must be developed to meet clinical demands. Long-term toxicity studies are necessary to evaluate the safety of chronic exposure. Additionally, regulatory frameworks for MXene-based medical devices and therapies must be established. Future research should focus on optimizing MXene formulations for specific applications, improving targeting strategies, and exploring combination therapies to maximize therapeutic efficacy.

In summary, MXenes hold great promise for biomedical applications, including antibacterial therapy, drug delivery, photothermal therapy, and biosensing. Their unique properties enable innovative solutions for diagnosing and treating diseases, but thorough biocompatibility and toxicity assessments are essential to ensure their safe and effective use in medicine. Continued research and development will be crucial to overcoming current limitations and unlocking their full potential in healthcare.