Soft Tissue-Adhesive Epicardial Bioelectronics for Chronic On-Site Signaling

Soft bioelectronics for stable and multifunctional cardiac implants have been developed. However, using inorganic materials through wavy/buckled structural designs for stretchability and softness cannot perfectly match the tissue deformations of the heart under the dynamic contraction-relaxation cycles. Therefore, intrinsically stretchable bioelectronics for epicardial interfacing have been paid remarkable attention to make stable tissue-device interface on the epicardium for reducing tissue deformations of the heart due to applied pressure. In addition, tissue adhesion is needed for avoiding suture, conventional fixation methodology, which causes bleeding, continuous shear stress and an inflammation in the stitched regions. However, the bioadhesive devices still remain challenges due to instability of adhesion, non-uniform coverage on the curved tissue, and the breakdown of the fatigue-accumulated electrodes. In this work, we report soft and stretchable cardiac patch with instantaneous adhesion on the tissue. This patch composed of three layers: a tissue-adhesive catechol-conjugated alginate (Alg-CA) hydrogel, an electrospun fibre-interlocked viscoelastic network-type polymer substrate, and an electrically durable liquid metal nano-/micro-particles composite electrode. The patch immediately adheres to the curved tissue with spontaneous modulus matching according to no need for external stimuli or long time for adhesion and an efficient strain adaptation of SHP (Self-healing polymer). Especially, fibrous network structure mechanically enhances not only the stress relaxation property of the polymer itself but also the tissue adhesiveness of the patch through interlocked interface via penetration of the Alg-CA into the micropores on the substrate. Also, compared to the composite of solid-state conductive fillers, liquid-state of the EGaIn (Eutectic gallium-indium) particles is suitable for reducing the issues related to fatigue-induced electrical malfunctions during long-term cardiac monitoring. Lastly, the chemical coordination between carboxylate and catechol groups in adhesive hydrogel and metal ions on the oxide layer of the liquid metal particles in electrode enables precise electrical stimulation besides stable ECG (Electrocardiogram) signal recording even in rodent with myocardial infarction (MI) and drug-induced bradycardia-/arrhythmia-triggering model. Therefore, the approach can be of potential use in precise diagnostics and feedback treatment for patients with cardiovascular diseases.