MXene Hydrogels as Soft Bioelectronic Interfaces

Biological tissues and organs, such as the cardiac tissue and the brain, are mechanically soft and exhibit viscoelastic behavior. Real-time diagnosis and treatment of diseases of such electrically active tissues requires continuous electrophysiological monitoring stimulation. This has been achieved through implantable bioelectronic platforms. However, current implantable bioelectronics are composed of mechanically rigid materials such as metals (Au, Pt), metal oxides (IrOx), and semiconductors (Si). The large mechanical mismatch between the target tissues and the bioelectronics interfaces has been a bottleneck for chronic clinical applications. Although metal nanoparticles and carbon nanomaterials have been leveraged to fabricate electrically conductive hydrogel bioelectronics, they are limited by their electrochemical functionality, biocompatibility, and processability.<br/>Here we leverage safe liquid-phase processing of two-dimensional Ti₃C₂T_x MXene to fabricate MXene-based hydrogels for implantable bioelectronic interfaces. We achieve a high-density network of MXene flakes by directly crosslinking individual MXene flakes using transition metal ions. The matrix-free structure of the MXene hydrogels endows them with high electrical conductivity and low electrochemical impedances, thus facilitating their integration into soft bioelectronics for electrophysiological recordings with high signal-to-noise ratio. The capacitive nature of Ti₃C₂T_x further allows the hydrogels to exhibit high charge injection capacities for safe delivery of electrical stimulation to target tissues. Finally, we demonstrate modulation of the mechanical properties of the packaged hydrogels by altering the composition and degree of cross-linking of the alginate-based insulation. Our results underscore the application of MXene-based soft bioelectronics in studying neural function and disease pathologies, as well as developing neuromodulation paradigms.