The remarkable ability of human skin to self-repair allows it to function as a protective barrier, despite being subjected to constant damage, while continuously sensing the external environment. An ideal biomimetic electronic sensor skin should demonstrate similar mechanical sensing and repeatable self-healing capabilities, the fulfillment of which will simultaneously require self-healing electrodes (conductivity >1 S cm−1) and tactile sensors. For practical use, both electrodes and sensors must further demonstrate repeatable electrical and mechanical healing at room temperature, even at the same damage location, much like human skin. Electronic skins are approaching human skin-like properties and performance in terms of mechanical sensing and form factor1,2,3,4,5,6,7,8,9, but the ability to repeatably self-heal has not been demonstrated in electronic skins so far. Such ambient repeatable self-healing and mechanical-sensing capability will be useful in bioprosthetics and the emerging field of soft robotics10,11, where robots are made entirely of soft, flexible and conformable materials.

In recent years there has been intense research into self-healing materials, but this has largely focused on designing unique stimulus-responsive polymer systems for the restoration of mechanical properties. Chen and colleagues used thermally reversible Diels–Alder reactions with dynamic covalent bonds to create a tough epoxy-like polymer that can structurally heal when heat-treated above 120 °C (ref. 12), whereas Burnworth and colleagues showed that a metallo-supramolecular polymer can be selectively healed by converting an optical stimulus to localized heat13. Recently, Leibler and co-workers pioneered a repeatably healable thermoplastic elastomer material based on the use of supramolecular interactions for spontaneous healing14,15. In the area of fault-tolerant soft electronics, Yuan and colleagues first demonstrated the use of high-strain-capable carbon-nanotube electrodes that can selectively combust or ‘self-clear’ in localized short circuits to maintain constant operation of the dielectric elastomer actuators16,17. These smart material systems are tremendously useful for enhancing structural safety12, enabling new biological applications18,19, creating long-lived super-hydrophobic coatings20,21, increasing the lifespan of materials and improving environmental sustainability12,16,22.

In spite of the great promise these systems provide, there is one striking omission in their properties—a lack of high bulk electrical conductivity in the self-healing materials. This shortcoming limits their potential use in electronic applications. Bielawski and colleagues proposed the use of organometallic polymer thin films as self-healing conductors, but these demonstrated very low conductivities (10−3 S cm−1) and required high temperatures and organic solvents for cracks to be healed23. White, Moore and co-workers pioneered the use of microcapsules containing various types of liquid-precursor healing agents for structural healing24,25, and have recently used capsules filled with various conductive agents or solvents for autonomous electrical healing of thin metal films26,27. In these systems, the local healing agent is depleted after capsule rupture, having actioned just a single local healing event28. In addition, these conductive healing agents do not allow simultaneous structural healing. To impart conductive healing to thin films, Li and colleagues recently used water as the self-healing agent29. However, the use of potentially volatile plasticizers as additives or healing agents is undesirable in electronic systems because of the risk of contamination or electronic short circuits arising from escaped additives. Furthermore, no self-healing tactile sensors have been reported30,31. Clearly, combining repeatable self-healing, force sensitivity and high bulk electrical conductivity remains a challenge.

Here, we show the first repeatable, room-temperature self-healing electronic sensor skin, using a supramolecular organic–inorganic composite. A conductivity as high as 40 S cm−1 was measured for our composite, which is four orders of magnitude higher than previously reported self-healing conductive organometallic polymer films23. The composite material is mechanically flexible, and is capable of sensing tactile and flexion forces. Although there has been substantial research into conductive polymer composites, this is the first demonstration of a self-healing conductive composite made using a supramolecular polymer host.