Intimate encapsulation of non-planar electrodes via a viscoplastic interlayer.

Implantable electronics often adopt non-planar electrodes to resolve the conflict between conductivity and deformability. Encapsulation of these electrodes becomes a critical challenge for conventional elastic seals due to the elastic-contact-induced interfacial voids and consequential fluid ingress. Here, we present a viscoplastic interlayer that can adapt to the three-dimensional structures of non-planar electrodes, resulting in intimate contact and hermetic encapsulation. This interlayer is a polymeric composite that consists of a long-chain polyisobutylene as the matrix, a short-chain polyisobutylene as the plasticizer, and maleic anhydride-grafted polypropylene as the foreign domains. Its viscoplasticity originates from the chain slippage and permanent disentanglement of the long-chain polyisobutylene, promoted by the plasticizers and confining domains, respectively. When synergized with covalent bonding, the interlayer derives defect-free interfaces between the sealing elastomer and various non-planar electrodes, such as microwires, micropillars, and serpentine electrodes. This intimate encapsulation stabilizes the signal-to-noise ratio of an electromechanical device for 50 weeks in acidic, neutral, and alkaline solutions and extends the in vivo duration of signal fidelity for stretchable bioelectronics to a record of 45 weeks. This viscoplastic interlayer provides fruitful implications for improving the long-term stability of implantable bioelectronics.