Soft multifunctional materials that seamlessly integrate bioelectronics with therapeutic functionality are critical for next-generation human-machine interface (HMI) systems. Herein, we report a three-dimensional (3D)-printable, biodegradable, and piezoionic/conductive hydrogel ‘E-skin’ based on a double-network gelatin methacrylate/alginate reinforced with TEMPO-oxidized cellulose nanocrystals (TOCNCs) and Ti3C2Tx (MXene) nanosheets (=GACM hydrogel). The as-fabricated nanocomposite hydrogel exhibits higher compressive strength (∼21 kPa), stable adhesion on diverse dry and wet substrates, and shear-thinning property that allows high-resolution direct ink writing (DIW) printing of complex architectures. Owing to the MXene-enabled conductive/piezoionic features, the GACM hydrogel functions as a self-powered sensor with a gauge factor of ∼1.77 at 80% compressive strain. It generates physiologically relevant voltage outputs (∼36.35 mV) under mechanical deformation. Beyond sensing, the platform acts as a smart wound dressing, supporting robust in vivo wound healing, enabling pH-responsive drug release, and exhibiting strong bactericidal activity. Importantly, the GACM hydrogel is successfully integrated into a wireless HMI, enabling real-time robotic control from human motion. This work establishes a versatile and sustainable hydrogel biointerface that integrates 3D printability, self-powered sensing, infection management, and accelerated wound healing, offering a compelling materials framework for future bioelectronic skins and regenerative healthcare technologies.