Preparation And Application Of Multifunctional Wearable Tactile Sensor

Wearable tactile sensors are able to monitor human health,which has become an effective method for preventing sudden diseases and ensure healthy life.However,the mechanical incompatibility between the sensing materials and skin,the trade-off issue between the sensitivity and detection range,as well as the mono-function of sensing devices,hamper the real application of wearable tactile sensors.To tackle the above issue,in this study,we prepared the novel double network hydrogel membranes which contains the covalent bonds and hydrogen bonds via photopolymerization,and tailored the stretchability and toughness of the hydrogel membrane by controlling its hydrogen bond intensity.Electronic conductive hydrogels(ECH)and ionic conductive hydrogels(ICH)were obtained by doping conducting polymers and inorganic salts into the hydrogels,respectively.Then,the ECH and ICH were employed for fabrication of wearable strain sensors and wearable pressure sensors which offer both the high sensitivity and wide detection range.Finally,the quick response(QR)code was integrated into the microsensors by using the stereolithography technique,realizing preparation of the multifunctional microdevices,i.e.,health monitoring and information storage.Firstly,double network elastic hydrogel membranes were prepared by photopolymerization,which contains covalent crosslinked polyacrylamide(PAAm),serving as the first network,and the hydrogen-bonded polyvinylpyrrolidone(PVP)and PAAm,as the second network.Stretchable ECH was then obtained by photopolymerizing the poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid(PEDOT: PSS)doped hydrogel precursor solutions.Scanning electron microscopy(SEM),low-field nuclear magnetic resonance(LF-NMR),Fourier transform infrared spectroscopy(FTIR),and universal material testing machine et al.were utilized for characterization of the crosslinking network,microstructures,and mechanical properties of hydrogel membranes,confirming the tunability of stretchability via hydrogen bonds.The ECH was employed for fabrication of wearable stain sensors.The effect of PEDOT: PSS content on the sensing performance was investigated.The experimental results showed that the reversible hydrogen bonds significantly boosted the stretchability of hydrogel membrane(λ=21),which extends the detection range of the ECH strain sensor.Besides,the uniform dispersion of PEDOT: PSS in the hydrogel membrane enhanced the sensitivity(GF≈16.6)of ECH strain sensor.The optimized ECH strain sensor could stably run more than 1300 cycles,and perform well after storage for 37 days without obvious signal degradation.Additionally,QR code was manufactured into the microsensor via maskless lithography technique,realizing integration of multifunctional devices,i.e.,health monitoring and information storage.Subsequently,LiCl was added into the above optimized PAAm/PVP hydrogel membrane for preparation of ICH which was employed for construction of capacitive pressure sensors.FT-IR,LF-NMR,SEM,and differential scanning calorimetry(DSC)et al.were adopted for tracing the molecular interaction and microstructure evolution of ICH with different LiCl contents,which assisted optimization of the ionic conductivity and mechanical properties of ICH.The results demonstrated that the LiCl addition enhanced ionic conductivity and mechanical properties of ICH,and reduced the freezing point of hydrogel membrane,which endowed the hydrogel membrane with high ionic conductivity even at-20 ℃.Next,maskless lithography technique was employed for fabrication of micropatterned ICH.The influence of microstructures on the sensitivity of capacitive pressure sensors was studied,which discovered that: 1)high LiCl content enhanced the capacitance and reduced the energy consumption of the sensing device;2)microstructures boosted the sensitivity of the sensors and the highest sensitivity reached 15.4 n F/k Pa.In summary,PAAm/PVP double-network hydrogel membranes were prepared,which were employed for fabrication of electronic strain sensors or ionic pressure sensors after doping with conducting polymers or inorganic salts,respectively.Moreover,according to the high sensitivity of the device and photo-crosslinking features of the hydrogels,multifunctional integrated wearable sensors were fabricated,which promoted the development of electronic diagnosis.