A Skin‐Inspired Substrate with Spaghetti‐Like Multi‐Nanofiber Network of Stiff and Elastic Components for Stretchable Electronics

Abstract

Mimicking the skin's non‐linear self‐limiting mechanical characteristics is of great interest. Skin is soft at low strain but becomes stiff at high strain and thereby can protect human tissues and organs from high mechanical loads. Herein, the design of a skin‐inspired substrate is reported based on a spaghetti‐like multi‐nanofiber network (SMNN) of elastic polyurethane (PU) nanofibers (NFs) sandwiched between stiff poly(vinyldenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) NFs layers embedded in polydimethylsiloxane elastomer. The elastic moduli of the stretchable skin‐inspired substrate can be tuned in a range that matches well with the mechanical properties of skins by adjusting the loading ratios of the two NFs. Confocal imaging under stretching indicates that PU NFs help maintain the stretchability while adding stiff P(VDF‐TrFE) NFs to control the self‐limiting characteristics. Interestingly, the Au layer on the substrate indicates a negligible change in the resistance under cyclic (up to 7000 cycles at 35% strain) and dynamic stretching (up to 35% strain), which indicates the effective absorption of stress by the SMNN. A stretchable chemoresistive gas sensor on the skin‐inspired substrate also demonstrates a reasonable stability in NO2 sensing response under strain up to 30%. The skin‐inspired substrate with SMNN provides a step toward ultrathin stretchable electronics.

Skin-like mechanoresponsive self-healing ionic elastomer from supramolecular zwitterionic network

“…Stretching such a dynamic network is usually accompanied by crosslinking density reduction and stress relaxation, leading to the remarkable attenuation of material modulus as well as poor elastic recovery from large deformations 14 , 16 – 19 . On the other hand, strain-stiffening materials normally involve two distinct networks with different rigidities that unfold progressively for synergizing softness and firmness 20 – 23 . For instance, bottlebrush elastomers could replicate the strain-stiffening characteristics of biological tissues by unfolding flexible strands at lower forces followed by stretching rigid backbone at higher forces 9 , 21 – 24 .…”

Ion‐Conductive Hydrogel‐Based Stretchable, Self‐Healing, and Transparent NO2 Sensor with High Sensitivity and Selectivity at Room Temperature

“…The low LOD of the sensor met the requirement of thresholds of annual average NO 2 (53 ppb) proclaimed by the US Environmental Protection Agency. [ 28 ] Furthermore, the LOD was lower than those of state‐of‐the‐art stretchable NO 2 sensors based on other sensing materials, including MoS 2 @rGO, [ 51 ] Al‐doped ZnO/AgNWs, [ 52 ] GaSe, [ 53 ] rGO/ZnO hybrid fiber, [ 38 ] MWNT/SnO 2 , [ 54 ] [EMIM] + [TFSI] − /TPU, [ 39 ] vertically aligned 2D MoS 2 , [ 37 ] rGO, [ 55 ] PbS colloidal quantum dots, [ 56 ] and Eg‐organohydrogel [ 46 ] ( Table 1 ). The above results collectively indicate the highly competitive NO 2 sensing performance of the CaCl 2 ‐infiltrated hydrogel.…”

Skin-Compatible Amorphous Oxide Thin-Film-Transistors with a Stress-Released Elastic Architecture

“…The corresponding models for a-IGZO TFTs on elastomeric PDMS are shown in Figure 1. In this modelling, a 30% lateral strain was applied to the a-IGZO TFT by considering the maximum strain of the epidermis [23,24]. As shown in Figure 1, the highest stress was induced in the gate dielectric layer for the conventional PDMS substrate because of the large Young's modulus of Al 2 O 3 (Table 1) [25].…”