Stretchable and Self-Healable Conductive Hydrogels for Wearable Multimodal Touch Sensors with Thermoresponsive Behavior

Abstract

Multifunctional hydrogels with properties including transparency, flexibility, self-healing, and high electrical conductivity have attracted great attention for their potential application to soft electronic devices. The presence of an ionic species can make hydrogels conductive in nature. However, the conductivity of hydrogels is often influenced by temperature, due to the change of the internal nano/microscopic structure when temperature reaches the sol−gel phase transition temperature. In this regard, by introducing a novel surface-capacitive sensor device based on polymers with lower critical solution temperature (LCST) behavior, near-perfect stimulus discriminability of touch and temperature may be realized. Here, we demonstrate a multimodal sensor that can monitor the location of touch points and temperature simultaneously, using poly(N-isopropylacrylamide) (PNIPAAm) in hybrid poly(vinyl alcohol) (PVA) and sodium tetraborate decahydrate cross-linked hydrogels doped with poly(sodium acrylate) (SA) [w/w/w = 5:2.7:1−3]. This multimodal sensor exhibits a response time of 0.3 s and a temperature coefficient of resistance of −0.58% K −1 from 20 to 40 °C. In addition, the LCST behavior of PNIPAAmincorporated PVA/SA gels is investigated. Incorporation of LCST polymers into high-end hydrogel systems may contribute to the development of temperature-dependent soft electronics that can be applied in smart windows.

Self‐healing Polyol/Borax Hydrogels: Fabrications, Properties and Applications

“…[89] Stretchable, thermoresponsive and self-healing conductive hydrogels composed of PVA/PSA/PNIPAAm/B (PSA = poly sodium acrylate) were produced for application as wearable multimodal touch sensors. [90] Increasing the PSA content reduced transparency of the hydrogel due to the aggregation and heterogeneous distribution of PSA in the hydrogel matrix which leads to higher light scattering, refraction, or reflection. It was shown by increasing the PSA content, Young's modulus and maximum tensile stress were increased.…”

“…The high boiling point of EG and its strong interaction with water increased the stability and strength of the hydrogel. [90]…”

“…However, due to the weak mechanical property of the PVA/PSA/PNIPAAm hydrogel, which limited practical applications, the water was exchanged by swelling the hydrogel in EG : H 2 O (25 : 75 wt/wt, EG=ethylene glycol). The high boiling point of EG and its strong interaction with water increased the stability and strength of the hydrogel …”

Flexible wearable sensors - an update in view of touch-sensing

“…Following this trend, wearable sensors also become popular. Among them, there are devices capable of monitoring human motions, designing human-machine interfaces, detecting the toxic agents in the environment, or applying in the healthcare/therapeutic [1][2][3]. are superior to traditional rigid devices.…”

In-Situ Forming pH and Thermosensitive Injectable Hydrogels to Stimulate Angiogenesis: Potential Candidates for Fast Bone Regeneration Applications

“…A sol-gel fabrication of antibacterial peptide nanofibrils with PNIPAM have shown great promise for minimally invasive drug delivery [25]. A combination of PNIPAM in hybrid PVA and sodium tetraborate decahydrate composite hydrogels have potential in the development of artificial electronic skins and temperature dependent soft electronics applications [26]. Sertaconazole-loaded nanostructured lipid carriers (Sertaconazole-NLCs) incorporated HPMC nanocomposite hydrogels have shown good results in vitro studies in the treatment of fungal keratitis [27].…”