Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

Abstract

such as carbon nanotubes, graphene, nanowires) into soft elastomer composites. [8][9][10][11][12][13][14][15][16] Nevertheless, most of these reported flexible strain sensors could only display one single electrical signal output, which might have some practical use limitations. Especially with the development of human-machine interactive systems, there has been an increasing demand for dual-channel reporting flexible sensors, which are capable of exhibiting both strain-dependent electrical and optical changes. [17][18][19][20][21] Among various optical means, fluorescence is believed to quite promising for wearable stretchable sensing uses because of its high sensitivity, fast response and operational simplicity. The most convenient strategy is to develop the mechanofluorescent elastomer materials with strain-dependent electrical signal response. One famous example was reported by Zhang and colleagues who draw inspiration from the muscle-controlled display tactics of cephalopods to present the robust nanostructured self-healable and mechanoluminescent elastomer composites, which were capable of displaying reversible strain-dependent luminescence and resistance response to tensile strain. [21] Meanwhile, there has also been a growing interest to explore soft polymeric hydrogels for flexible sensors. [22][23][24][25][26][27][28][29][30][31][32] Different from elastomers, polymeric hydrogels usually have a 3D crosslinked hydrophilic network that is highly swollen by water. [5,33] Thus they are endowed with many unique advantages, including intrinsic soft wet nature, good biocompatibility, and especially tissue-like mechanical properties, which have made polymeric hydrogels promising candidates for flexible sensors. [34] In this context, considerable progresses have been recently achieved in soft conductive hydrogels with strain-dependent electronic signal changes. However, it still remains challenging to develop the promising dual-channel hydrogel systems with both sensitive conductivity and interactive fluorescence color changes to dynamic activities, which would show potentials to enable both electronic and visual monitoring of human motions. This is possibly because it is quite difficult to construct robust multifunctional materials with continuous and synergistic fluorescence/electronic signal responses over a wide strain range.Flexible strain sensors are of great importance in many emerging applications for human motion monitoring, implanted devices, and humanmachine interactive systems. However, the dual-channel sensing systems that enable both strain-dependent electronic and visually optical signal responses still remain underdeveloped, but such systems are of great interest for human-machine interactive uses. Here, inspired by the mechanically modulated skin color changes of squids via muscle contracting/releasing movements, a class of mechanofluorescent and conductive hydrogel laminates for visually flexible electronics is presented. The sensing laminates consist of interfacially bonded red fluorescent hyd...

Mimicking Color-Changing Organisms to Enable the Multicolors and Multifunctions of Smart Fluorescent Polymeric Hydrogels

“…All of these advantages further encouraged us to demonstrate an artificial Atolla jellyfish that is capable of interacting with a model predator and displaying switched fluorescent patterns for an alarming purpose. Besides electricity, light and force stimuli have also been used to trigger fluorescence color changes of hydrogels for smart display applications . In a study shown in Figure c, Zhang and co-workers utilized the photothermal effect of liquid metal nanoparticles to achieve real-time and reversible light writing that enables the on-demand display of different fluorescence information …”

“…Besides electricity, light and force stimuli have also been used to trigger fluorescence color changes of hydrogels for smart display applications. 45 In a study shown in Figure 6c, Zhang and co-workers utilized the photothermal effect of liquid metal nanoparticles to achieve real-time and reversible light writing that enables the on-demand display of different fluorescence information. 46 Despite these advances, the pattern display capacity of artificial systems is still far inferior to that of natural cephalopod skins, which features a concerted integration of spatial/temporal precision for multicolor patterns and reversible/rapid switching upon stimulation.…”

Biocompatible Conductive Hydrogels: Applications in the Field of Biomedicine

“…This kind of CHs can stably and sensitively monitor human motion status even in extreme environments (−20 • C), which has great application potential in healthcare monitoring. For motion monitoring, Lin et al [138] combined red fluorescent hydrogels, polydimethylsiloxane, and CNTs to make a dual-channel flexible biosensor for human motion monitoring.…”

Smart Soft Materials with Multiscale Architecture and Dynamic Surface Topographies

“…By slight design adjustment, this system can be applied as a finger motion sensor, encryption device, dynamic display, and thermal camouflage. This mechanochromism design strategy based on the strain-dependent crack width has been widely adopted by other researchers − after its first report, leading to widespread applications in photonic-electronic skins, , triboelectric nanogenerators with motion sensing, , and optical strain sensors. ,− For example, Guo et al invented a mechanoluminescent material, consisting of a carbon nanotube/cellulose nanocrystal composite film and a self-healable supramolecular elastomer substrate . This material can exhibit mechanical-responsive PL for strain sensing because of the presence of dynamic strain-dependent microcracks on the film layer.…”