Biomedical Applications of MXenes: From Nanomedicine to Biomaterials

ConspectusThe rise of two-dimensional (2D) materials has led to significant interest in their potential applications for nanomedicine and biomaterials in the hope that they can overcome some intrinsic limitations of conventional theranostic materials. MXenes, an emerging family of 2D materials mainly made of transition metal carbides/nitrides, have drawn substantial interest in biomedical applications because of their unique physicochemical properties. The remarkable photothermal energy-converting capability of MXenes allows photonic hyperthermia treatment in the second near-infrared biowindow with deep tissue penetration. The diverse choice of metal elements in MXenes endows them with the aptitudes to act as contrast agents for computed tomography and magnetic resonance imaging. As the understanding of pathological characteristics is improved, the desirable properties and performances of nanomedicine and biomaterials have become more comprehensive, which is unlikely to be accomplished with the formulation of MXenes alone.In this Account, we highlight recent progress in the biomedical applications of 2D MXenes ranging from nanomedicine and biomaterials. We will start by introducing major synthetic techniques for fabricating MXenes with ultrathin 2D structures and nanoscale sizes for biomedical purposes. We then elaborate how MXenes differ from other 2D materials, showing exclusive potential in biomedical applications. The diverse surface compositions allow the tuning of the bandgap and surface plasmon resonance effect, which is essential for nanodynamic therapy. The transition metal elements in MXenes could render them with enzymatic activities for nanocatalytic therapy. MXenes also possess favorable biodegradability and biocompatibility, facilitating the potential clinical translation.However, the intrinsic properties of MXenes might be insufficient to fulfill some specific requirements in advanced biomedical applications. For instance, the therapeutic efficiency of MXenes alone would be impaired because of the reasons such as the low tumor accumulation of nanomedicine, the inclined thermal resistance of cancer cells, and the hypoxic tumor microenvironment. In addition, the biomedical applications of MXenes are mainly limited to cancer therapy or theranostics. MXenes have been integrated with other functional components to tackle these issues. Thus, we further discuss the strategies to fabricate MXene-based biomaterials with different dimensional structures for a broad range of biomedical applications, ranging from nanomedicine to localized therapy and regeneration. Several methods to modify the surface of MXenes are demonstrated to increase the stability of MXene in physiological media. Decorating MXenes with 0D nanoparticles enables the combination of different imaging and therapeutic modalities. Integrating MXenes with other 2D layered materials for improved theranostic efficiency, or with 3D implantable materials for advanced applications are also discussed.