From grape seed extract to highly sensitive sensors with adhesive, self-healable and biocompatible properties

Conductive hydrogels are widely applied in artificial intelligences, wearable devices, health-monitoring systems, etc. However, it remains long-sought yet largely unmet to fabricate multifunctional sensors via a facile method. To achieve this goal, grape seed extract (GSE) and polyvinyl alcohol (PVA) were adopted to form the gel matrix, and carbon nanotube (CNTs) were selected as conductive fillers. Due to the free catechol groups from GSE, the hydrogel could spontaneously adhere to the skin, wrist, elbow and other parts, avoiding interfacial delamination and friction between contact areas. The introduction of CNTs endowed the hydrogel with high sensitivity (gauge factor = 31.2 near 140 % strain) as well as low limit of detection (0.2 % strain). Thus, the resultant sensor could reliably detect full-range movements of human body, including frowning smiling, running and working. Because of the hydrogen bonds, the hydrogel exhibited self-healing capability (healing efficiency = 60.0 %). The biocompatible materials and green process led to excellent biocompatibility (cell viability near 100 %). All these features make it an ideal candidate for tissue engineering materials.