Construction And Sensing Performance Of All-ion Self-powered Sensor Based On Gradient Polyelectrolyte Hydrogel

Flexible self-powered sensors that can simulate human body sensing characteristics are widely used in soft robots,bionic medicine,artificial intelligence and other fields.Self-powered sensors based on triboelectricity and piezoelectric nanogenerators transmit signals electronically,unlike the signal carriers（ions）of human sensory systems.While for ion diodes,they may be suffer from layering problem,as well as limited stretchability and transparency due to the use of metal electrodes.In addition,ion diode-based sensors respond only to mechanical stimuli and do not sense the thermal and chemical stimuli associated with human activity.Therefore,designing scalable,multifunctional self-powered ion sensors that replicate human sensory systems remains a huge challenge.In order to solve the above problems,this paper proposes to construct a bionic gradient polyelectrolyte hydrogel self-powered ion sensor.The main results are as follows:1.Gradient polycationic electrolyte Chitosan（CS）hydrogels were prepared with the aid of electric field,and polyacrylamide/sodium chloride（PAM/Na Cl）ionic hydrogels were in-situ prepared on the upper and lower sides of the gradient hydrogels as ion electrodes,respectively.All-ion self-powered ionic receptors（SPI receptor）with bionic cell membrane structure were finally obtained.The SPI sensor not only has a self-induced potential,but also has good stretchability and transparency.The SPI hydrogel sensor can accurately sense small changes in pressure and can respond to pressure up to 0.05 k Pa;And has a wide strain sensing range（≥120%）,high strain sensitivity（2.72）;In addition,the sensor has good stability and can realize repeated waveform in a certain range.The self-powered sensor can also accurately detect human activities such as finger bending,pulse,arm swing,which is expected to have broad application prospects such as in the fields of human activity monitoring and intelligent medical treatment.2.Fold structures exist widely in nature and are usually deformed due to uneven stress.Inspired by this,we successfully prepared gradient polyacrylamide/polyacrylic acid（PAM/PAA）hydrogel with fold structures under ultraviolet light,and the fold structures were controlled by altering the tensile ratio of PAM/PAA hydrogel in ferric chloride（Fe Cl₃）solution.A regular flexible pressure sensor with continuous gradient fold structures has been finallu obtained.The pressure sensor with folds increases the stress sensing range and can respond to a small pressure of 0.025 k Pa.At the same time,the potential can be increased or decreased according to the size of stress,higher sensitivity stress sensing is realized.3.Receptors on the skin and tongue can sense chemical stimuli through potential changes in cell membranes,which are then transmitted by nerves to the brain,creating sensory feedback.Inspired by human sensing system,the gradient polyelectrolyte hydrogel is used as polarized cell membrane,and ionic hydrogels are used as extracellular and intracellular electrolyte,respectively.The ambient temperature fields and chemical stimulation such as salinity and p H values are explored by gradient hydrogel sensors with bionic cell membrane structure,respectively.The temperature field（2.9℃）can be accurately perceived in a non-contact manner according to the potential changes caused by thermal diffusion.And the salinity(10^-5 M-10 M)and p H(10^-5 M-10^-2 M)of the additional solution can be accurately sensed by salinity gradient ion diffusion.Unlike the ion-electron hybrid strategy,this self-powered sensor consisting entirely of ionic conductors will be more conducive for the development of complex human-like sensing systems in the future.