Preparation And Properties Of Polyvinyl Alcohol-based Hydrogel Electronic Skins

Polyvinyl alcohol（PVA）-based hydrogels have good water solubility,biocompatibility,mechanical properties,and environmental degradability.Conductive hydrogel has good mechanical properties,excellent biocompatibility,and adjustable conductive channels.It is a promising raw material candidate for preparing bionic skin.In addition,the development of anti-freezing and anti-dryness hydrogels is critical to increasing the useful life of hydrogels.More importantly,the collection of multiple outside signal of the electronic skin and the performance of the self-power collector are also important.In this paper,starting from the application of biomimetic electronic skin of hydrogel,a series of biomimetic electronics with different structures and properties were developed by using biocompatible PVA as a hydrogel base substrate and using physical and chemical bionic means.It is expected to be used in the fields of wearable electronics.（1）To completely mimic the tactile sensing of natural skin,flexible conductive hydrogels（CHs）have been assembled into bionic skin.Here,we innovatively incorporated a proanthocyanins/reduced graphene oxide（PC/r GO）composite with a nerve-like nanonetwork into a glycerol-plasticized polyvinyl alcohol-borax（PVA-borax）hydrogel system to obtain a bionic tactile PC/r GO/PVA hydrogel-based electronic skin,which perfectly simulates the tactual sensation of human skin and integrates excellent stretchability（>5000%）,compliance（1mm）,self-healing（3s,95.73%）ability for the first time.Due to its unique structure and mechanical properties,this electronic skin has remarkable wearable and strain-sensitive（GF=14.14）properties,which can mimic and detect some real skin epidermis movements such as finger bending,facial expression changes,and throat vocalization.Interestingly,the hydrogel can also be used as an adhesive electrode for the accurate detection of electrocardiograph（ECG）and electromyography（EMG）signals.（2）Herein,we innovatively designed and fabricated a transparent,conductive polyvinyl alcohol-tannic acid@talc（PVA-TA@talc）organohydrogel via molecular-level ion conductive channels in ethylene glycol/H₂O（EG/H₂O）,and this organohydrogel integrates excellent conductive,transparent,anti-freezing,moisture-retention,toughness,and stretchable properties for the first time.Moreover,this organohydrogel possesses remarkable light filtering capabilities and can effectively filter ultraviolet（UV）light.Interestingly,this organohydrogel can act as a wearable dressing to protect skin from frostbite and ultraviolet radiation.Notably,based on molecular-level ion transport channels,this organohydrogel has great strain sensitivity（gauge factor=9.17,0–1.2%strain）that enables recognition of limb movement,pulse,language,and handwriting.The organohydrogel can collect electromyography（EMG）signals as a bioelectrode and be applied to prepare a T-pen for controlling smartphones.（3）Herein,we developed a smart ionic skin on the basis of ion-conducting organohydrogel assemblies,which enables achieving various stimulus responses via chemical and electrical signals transmission.This organohydrogel substrate renders the electronic skin with great transparency（93.8%）,haze（27.8%）,stretchability（450%）,softness（8.2mm）,antifreeze（-63.28°C）,anti-dryness,conductivity,as well as thermal self-healing properties.While,its customized and kirigami-inspired pressure/strain-sensing component of electronic skin make skin adaptability and high stimuli sensitivity.The resulting ionic skin also exhibits the sensitive stimulating detection capabilities including temperature and moisture,within the wide ranges of temperature（-30-70°C）and humidity（45-85%RH）.Moreover,the spontaneous moist-electric-generating component produced a voltage potential of up to～0.17V,available for imitating the energy station of natural skin.