Soft and Transient Bioelectronics Enabled by Polymer-Free Ti₃C₂T_x MXene Hydrogels

Implantable bioelectronics for acute neural applications must combine tissue-like mechanics with high electrochemical performance while enabling safe biodegradation to avoid risks associated with explant surgeries. Here, we present MXgel bioelectronics, a soft and fully transient hydrogel platform that enables high-fidelity electrophysiological recordings and effective stimulation with programmable degradation under physiological conditions. The platform employs polymer-free Ti₃C₂T_x MXene hydrogels (MXgel) that achieve exceptional electrical conductivities (hydrated: 790 ± 150 S m^-1, freeze-dried: 4420 ± 576 S m^-1). Integrated on biodegradable gelatin-based substrates, MXgel bioelectronics exhibit low electrochemical impedance (1.06 ± 0.37 kΩ at 1 kHz), 25-fold higher cathodic charge storage (207.1 ± 48.8 mC cm^-2), and 10-fold greater charge injection capacity (0.24 ± 0.08 mC cm^-2) than conventional clinical electrodes. We demonstrate that these properties enable cortical and peripheral neural recordings with ∼60 dB signal-to-noise ratio and effective neuromodulation. Moreover, MXgel bioelectronics undergo safe degradation under physiological conditions with predictable and tunable kinetics. Importantly, MXgel bioelectronics do not trigger severe foreign body reaction, and their degradation byproducts do not accumulate in the body, confirming safe systemic clearance. Together, these results establish MXgel bioelectronics as a clinically relevant platform for soft, high-performance, and transient neural interfaces.