In situ formation of adaptive electronic skin in 2 seconds enabled by metal coordination

Epidermal electronics, which are flexible and conformable electronic systems designed to interact seamlessly with human skin, hold great promise for healthcare monitoring and personal electronics. However, traditional fabrication methods face challenges of reliance on non-sustainable materials, intricate and time-consuming processes, and material softness-induced fragile transfer to target substrates. Inspired by the "milk skin" phenomenon, we developed a rapid dipping-dipping molecular assembly method to fabricate cellulose-based bio-skin in situ within seconds, exhibiting ultra-thin, highly conformal, shape-customizable, degradable, and low-impedance performances. This technique immerses substrates sequentially into carboxymethyl cellulose (CMC) and Cu(II) solutions, leveraging strong metal-coordination interactions. Membrane formation efficiency, influenced by the oxidation and coordination characteristics of metal ions, follows the order: Cu(II) > Fe(II) > Ca(II). CMC-Ag(I)/CMC-Cu(II) form stable membranes, whereas CMC-Fe(II) forms fragmented structures, and CMC-Mg(II)/CMC-Ca(II) remain in solution. This adaptable method can also be extended to other biomacromolecules like methylcellulose and carboxymethyl chitosan, broadening applications. The bio-skin enables real-time monitoring of electrocardiograms (ECG), electrooculograms (EOG), electroencephalograms (EEG), and electromyograms (EMG), showcasing its potential for wearable, biocompatible electronics in healthcare.