Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m2) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

For the last decade, researchers have studied the creation of self-healable polymeric materials with desired properties for advanced applications. Since the polymeric network governs the overall behavior, precise control over the polymer morphology is important. Among the controlling strategies, the chemical structure of dynamic stickers in polymer chains can determine the polymer networks, which directly affect the macroscopic properties. However, it has been rarely understood how the sticker structure determines the polymer properties. Here, we systematically modulated dynamic mechanical responses of the polymer networks by adjusting the angles that a single sticker unit makes. From this study, we found that the polymer with periodic 180° stickers stacks well and forms a strong network, while the polymer with 120° stickers is twisted and forms a vulnerable network. Therefore, the 180° stickers induce high toughness and non-self-healable properties. On the other hand, polymers with 120° stickers are soft but easily self-healed. Finally, we mixed these two different angled stickers to have both mechanically tough and self-healable properties. This study of an angular factor in polymeric materials will be an important consideration for future materials for achieving superior properties.

Pressure-sensitive adhesives (PSAs) have been a workhorse in diverse applications from the repair of objects to heavy-duty industrial use due to their unique capability to form near-instant and robust yet repeatable adhesion to a wide range of engineering solids via physical bonding. While these characteristics of PSAs are highly favorable in various biomedical applications, commercial PSAs lack adhesion to wet tissue surfaces. Moreover, existing bioadhesives are mostly limited to single-use applications incapable of repeated adhesion and repositioning due to the irreversible nature of chemical adhesion. In this work, we introduce a pressure-sensitive bioadhesive (PSB) that synergistically combines the advantages of viscoelastic PSAs and bioadhesives. Enabled by a one-pot scalable copolymerization of a poly(glycerol sebacate)-co-poly(ethylene glycol) (PGS-co-PEG) block copolymer, the PSB provides near-instant (~ 1 s), robust, and repeatable (over 1,000 times) adhesion to wet biological tissues (i.e., skin, lung, heart) and engineering (i.e., metals, plastics) substrates without prior surface functionalization. We further demonstrate in vitro and in vivo biocompatibility and biodegradability of the PSB and its potential applications as a surgical sealant and the rapid, robust, and repositionable integration of biomedical devices with wet dynamic organs in rat and porcine models.