Liquid-Based Encapsulation for Implantable Bioelectronics Across Broad pH Environments

Implantable bioelectronics designed for interfacing with highly mobile organs across a broad pH range (1.5-7.4) has a wide range of applications in basic biomedical research and clinical medicine. The encapsulation of these systems represents a key challenge as they require encapsulation materials not only to have superior barrier performance in diverse pH environments but also to maintain stretchability. However, the existing encapsulation materials for implantable bioelectronics typically possess superior barrier performance or high stretchability, but not both. Here, we present a waterproof yet stretchable liquid-based encapsulation material, named oil-infused elastomer, by infusing a thin oil layer on a rough elastomer, which not only maintains the transparent and stretchable properties of the elastomer but also offers additional waterproof properties of the oil layer. Importantly, the oil-infused elastomer demonstrates outstanding waterproof properties over 550 days across various pH environments (pH = 1.5, 4.5, and 7.4) in a set of implantable wireless bioelectronics, including near-field communication antennas and wireless optoelectronic devices. Additionally, <i>in vivo</i> immunohistochemistry reveals the biocompatibility of oil encapsulation. Finally, the wireless optoelectronics encapsulated with an oil-infused elastomer show robust operation over the duration of testing (three months) <i>in vivo </i>in freely moving mice. Overall, this new class of encapsulation layer offers the desired mechanical stretchability and softness, optical transparency, biocompatibility, and waterproof properties in diverse biological environments (pH = 1.5 to 7.4). All these properties suggest potential applications in implantable bioelectronics for emerging applications ranging from gastrointestinal monitoring to bioelectronic medicine.