Soft and Transient Bioelectronics from MXene Hydrogels

Biological tissues, such as cardiac and neural tissues, are inherently soft and exhibit viscoelastic behavior. Monitoring and modulating such tissues through bioelectronic implants can enable real-time diagnosis and adaptive therapies for a growing and diverse number of disorders. Current bioelectronic interfaces are composed of mechanically rigid materials that trigger stiffness-related inflammatory and toxic reactions. Hydrogels have emerged as promising materials for soft and flexible bioelectronic interfaces due to their similarities with mechanical properties of biological tissues. Existing hydrogel-based bioelectronics are designed to facilitate chronic operation and require surgical extractions when necessary. Biodegradable bioelectronics might circumvent the need for surgical extraction; however, their material library and interface geometry has been limited to two-dimensional metal and polymeric thin films.<br/>Here we leverage liquid-phase processing of two-dimensional Ti₃C₂T_x MXene to fabricate MXene-based hydrogels for soft and transient bioelectronics. We directly crosslink individual MXene flakes using transition metal ions to achieve soft matrix-free hydrogels high electrical conductivity of up to 790 ± 150 S/m. The high capacitance and surface area of Ti₃C₂T_x MXene flakes allows us to fabricate electrodes that exhibit electrochemical impedance as low as 540 ± 130 Ω at 1 kHz (2 mm diameter), thus facilitating their application in low-noise electrophysiological recordings with high signal-to-noise ratio. Ti₃C₂T_x hydrogel electrodes further exhibit up to 50-fold greater high charge storage capacity and up to 7-fold greater charge injection capacity than conventional Pt-based rigid electrodes of the same size. By optimizing the structure and degree of cross-linking of the gelatin-based encapsulation and Ti₃C₂T_x conductive hydrogel, we have fabricated a biodegradable electrode array. Our unique approach facilitates safe delivery of therapeutic electrical stimulation and recording of electrophysiological signals from target tissues. Our results underscore the application of MXene-based soft hydrogel bioelectronics in studying neural function and disease pathologies, as well as developing transient electroceutical approaches.