Preparation And Properties Of Artificial Intelligence Skin Based On Ionically Conductive Hydrogels

The human skin is the largest sensing organ of the body and provides various kinds of seamless information about the surrounding environment sensitively and reliably throughout the years.With the rise of flexible electronics,wearable electronics and artificial intelligence,artificial smart skins,based on high-performance wearable sensors that can play similar roles as human skins are in high demand in advanced applications such as personal health monitoring,human-machine interfaces,wearable and implantable devices,and soft robotics.According to the type of signal feedback,artificial smart skins can be divided into electronic skins（e-skins）and photonic skins（p-skins）.Currently reported e-skins can quantitatively convert various external signals into electrical signals with the help of external additional circuit modules.Although remarkable progress has been made in improving sensitivity,flexibility and detection range,it is reported that the response of e-skins to external stimuli is highly dependent on external circuit modules and lacks an intuitive feedback mechanism that can be perceived by organisms.P-skin can simulate or enhance the function of real skin through the change of light signals under external stimulation.However,the ability to develop its quantitative perception is often overlooked.So far,there has been no report on the construction of artificial smart skin with multi-dimensional sensing capability based on p-skin.1.A new artificial smart skin,which integrates the functions of e-skin and p-skin in one device,has been developed.By introducing a one-dimensional photonic crystal structure into the hydrogel conductor,the integration of quantitative sensing,intuitive response and multi-dimensional sensing functions is realized.Due to its anisotropic structure,the prepared artificial smart skin demonstrated anisotropic electrical,optical,and mechanical properties.By further utilizing the mechanical anisotropic behavior characteristics,the novel optoelectronic skin can make distinguishable response signals to vector stimuli such as stress types,motion directions and the like to meet the needs of multi-dimensional perception.On this basis,combined with micro-electromechanical systems,this new type of optoelectronic skin can make appropriate feedback according to external stimuli,and has advanced functions such as information display and adaptive stealth.2.In this contribution,we report a brand-new type of vehicle intelligent skin,which integrates the advantages of both traditional vehicle intelligent skins and gel-based vehicle intelligent in a single skin device.By introducing a one-dimensional photonic crystal structure into an organohydrogel conductor,the integration of multi-sensing functions,self-adaptive feedback functions,simple fabrication process and extreme environmental stability is realized.Briefly,a highly ordered layered structure was self-assembled in a solvent aided by a nonionic surfactant with specific self-assembly ability.Then the special structure was immobilized within a polyacrylamide network through in-situ polymerization and the synthesized photonic crystal hydrogel was bathed into a soaking solution of Glycerol/H₂O mixed solution.The obtained vehicle intelligent skin has multiple sensing functions,not only responding to multiple stimuli such as stress,strain,temperature,but also can effectively distinguish the stress direction and realize the decoupling of shear force and normal force because of the inherent anisotropic structure in photonic crystal organohydrogel.Taking advantage of the confinement effect of glycerol and photonic crystal layered structure in the system,the prepared vehicle intelligent skin shows the ability to maintain stable operation in extreme environments.Therefore,the vehicle intelligent skin can adapt to the wide working environment,including high temperatures and extremely cold temperatures,which shows excellent and non-fading working ability after being placed at room temperature for 140 days.And the self-assembled lamellar structure in the vehicle intelligent skin system not only improves the environmental stability but also promotes its ionic conductivity in the electrochemical process because of the similar size-confinement phenomena.Its ionic conductivity reaches as high as 1.01 S m^-1 in the blistering temperature of 100℃after 7h.Combined with the micro-electro-mechanical system,the vehicle intelligent skin also demonstrates advanced intelligent functions such as display and self-adaptive camouflage according to the changing environment,without additional information feedback devices and function drivers.3.Here,we designed and synthesized a new type of artificial bionic skin for the HMI system,breaking through the limitations of traditional artificial bionic skin in the application of human-computer interaction interface in terms of environmental stability,damage reconstruction and mechanical ductility.The artificial bionic skin was conveniently prepared by random copolymerization of acrylic acid（AAc）,3-[dimethyl-[3-（2-methylprop-2-enoylamino）propyl]azaniumyl]propane-1-sulfonate（DP）in the mixed solution of deionized water and choline chloride（CCL）without chemical crosslinking.CCL as a free molecule not only provides the necessary ionic conductivity for artificial bionic skin,but also reduces the freezing point and improves the boiling point of pure water solvent in the system,and obtains excellent environmental stability（-80～80°C）.Due to the large binding energy between CCL molecules and the polymer network in the system,CCL molecules can be uniformly distributed in the polymer network under large strain conditions,which is beneficial to the effective dissipation of stress in the deformation process,so that the prepared artificial bionic skin has excellent mechanical ductility（>13000%strain）.More importantly,the shielding effect of CCL effectively reduces the bonding probability between polymer chains,resulting in a large number of unpaired hydrogen bonds and ionic binding sites in the system.Therefore,when the artificial bionic skin is damaged,it can be dissolved in water and reconstructed in air to achieve long-term repeated recycling of artificial bionic skin,reducing power waste and environmental pressure.In addition,the artificial bionic skin has multiple sensory properties towards stress,strain,temperature,solvent and bioelectricity,similar to natural skin.Finally,the stimulus signals from the artificial bionic skin are collected,filtered and programmed to be compatible with the integrated electronic equipment.Wireless motion capture and information feedback are carried out through Bluetooth,Wi-Fi,and the Internet.The high-degree-of-freedom robot after receiving the signal can synchronize human motion,which can be used for extreme environmental operations,fire rescue,prosthetics,exoskeleton control,and other scenarios to reduce the risk of human accidents.We provide an interactive platform,through material selection,device design,integration strategy and system layout,to obtain an excellent HMI based on artificial bionic skin with outstanding environmental stability and damaged reconstruction function.