Electronic skin is expected to sense pressure, temperature and other signals

Electronic skin (E-skin) is an important application for flexible sensors. Skin is one of the most important organs of the human body, with ductility, self-healing, high mechanical toughness and other characteristics, can KJ3222X1-BA1 sense a variety of shapes and textures, temperature changes and contact pressure, and devices that mimic the characteristics of human skin and have similar sensory functions are often referred to as electronic skin. Similar to human skin, electronic skin has the characteristics of flexibility, comfort and safety, which is regarded as the emerging development direction of future electronic technology, and has received more attention in the haptic scheme of humanoid robots.

The electronic skin is generally composed of electrodes, dielectric materials, active functional layers and flexible substrates. When the external pressure is felt, the active functional layer converts the strain, humidity, temperature and other signals into detectable electrical signals, and receives and transmits them at the electrode layer on both sides of the functional layer, and finally transmits them to the target area, thus achieving “tactile” transmission. Flexible substrates can carry electronic skin and ensure its compatibility with materials such as biological skin. Excellent flexible materials can provide sensors with high sensitivity, wide sensing range, high dynamic response and high repeatability.

Electronic skin has four characteristics: stretchability, self-healing, KJ3222X1-BA1 biocompatibility and biodegradability. 1) Stretchability: Under the action of various mechanical stresses, the electronic skin will deform in different directions. There are two main technological paths to improving e-skin stretchability – material innovation (developing new stretchable materials in single or polymerized form to create e-skin) or structural design (modifying the structure of a brittle material to absorb the applied strain). In terms of material innovation, the following materials are usually taken into consideration: ① Hydrogel: Three-dimensional mesh gels with mixed solvents such as water as dispersants have good stretchability, self-healing ability, biocompatibility and ionic conductivity. After modification, high mechanical properties can be obtained, but the stability is poor. The development of hydrogels with high stability and frost resistance is the current research focus.

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Liquid metal: Liquid metal has excellent electrical conductivity and deformability, among which gallium and its alloys have been widely used in the field of electronic skin because of its low toxicity and high conductivity. Its disadvantage is that the surface tension is high, difficult to process and compatible with other materials, need to be overcome by the interface material modification; (3) Conductive polymers: polymers are the basic components of most flexible electronic devices, and the selection of intrinsically conductive polymers as the construction unit can achieve flexibility, electrical conductivity and better mechanical properties at the same time. At present, the polymer materials that have been successfully applied in the preparation of electronic skin include PEDOT:PSS, polypyrrole, poly-acetylene, poly-thiophene, etc. (4) Nanomaterials: The stretchable conductor based on nanomaterials forms a permeable network in the elastomer by mixing conductive fillers in the stretchable polymer matrix, thereby providing a current path for the composite material, and its thin shape and excellent mechanical compliance have great application prospects in the field of flexible electronic devices. The commonly used nano-fillers are zero-vinamil particles, one-Vinamil wires with high aspect ratio and two-dimensional nano-sheets with large KJ3222X1-BA1 surface area. Polymers such as degradable plastics, polydimethylsiloxanes and polyvinyl alcohol are commonly used as elastic substrates to give stretchability to permeable networks.

In structural design, the following types of structures are usually considered: ① waveform structure: By applying the pre-stress force to the substrate of the plane structure, the pre-stress force is released after modifying the required active material, so that the upper conductive or active material layer is transformed into a wave structure, so that it can release part of the pressure during deformation. The disadvantage is that the tensile property provided by the structure is extremely limited; (2) island-bridge structure: composed of conductive lines (Bridges) and fixed position functional components (islands), of which the snake structure is more common, its shape is simple, easy to process, can achieve high stretchability of electronic skin; (3) KJ3222X1-BA1 Origami/paper-cut structure: Origami contains a pre-arranged folding structure, which can effectively slow down the stress changes generated in the process of folding, bending, stretching, etc., so as to provide high versatility, large deformation and comparable performance with rigid electrons; The paper-cut structure transforms the plane structure into a regular hollow structure, which is able to fully release the stress generated in the deformation of the substrate and achieve stronger tensile deformation ability; ④ Fabric structure: most of the fabric is composed of polymer materials, naturally has excellent mechanical properties, only need to be supplemented by appropriate conductive and other functional materials, you can build excellent flexible electronic products.