Omnidirectional Printing of Soft Elastomer for Liquid-State Stretchable Electronics

Abstract

Stretchable electronics has emerged as a new class of electronic technology to expand the applications of conventional electronics built on rigid wafers. Among various systems, liquid-state devices utilize electronically active liquids to achieve excellent stretchability and durability. The widespread adaption to such attractive form of device is hindered by the lack of robust fabrication approach to precisely and efficiently assemble liquid-state materials into functional systems. In this study, an additive manufacturing platform for digital fabrication of three-dimensional elastomeric structures is reported. The shear-thinning ink is formulated to enable omnidirectional printing process. Various elastic features with complex architectures are generated without using sacrificial materials, which consist of overhanging parts, suspended structures, and embedded channels. Harnessing the unique printability allows facile creation of elastomeric sensors with strain-and pressure-sensing capabilities by simply filling the embedded microchannels with liquid metal. A smart glove to capture hand gestures is also demonstrated as a fully integrated electronic system with liquid-state components. The liquid-state stretchable electronics developed here may find potential applications in biomedical instruments, wearable devices, and soft robotics.

Nacre‐Inspired, Liquid Metal‐Based Ultrasensitive Electronic Skin by Spatially Regulated Cracking Strategy

“…The combination of these two cracking strategies contributed to a much improved sensor performance. Compared with previously reported liquid metal‐based counterparts (Figure 1f; Table S2, Supporting Information), [ 17,29,35–40 ] this sensor design resulted in two orders of magnitude of sensitivity amplification in term of maximum and overall gauge factor ( GF , Note 1, Supporting Information), while maintaining a wide working range (>85%). As shown in Figure 1g, to our knowledge, this is the first liquid metal‐based sensor that rivals the state‐of‐art counterparts on sensitivity.…”

“…Working range can be regulated by adjusting liquid metal pattern configurations. f,g) Compared with previous liquid metal‐based counterparts, [ 17,29,35–40 ] the proposed sensor improves the sensitivity by two orders of magnitude. By this improvement, liquid metal‐based sensors rival the state‐of‐art counterparts.…”

A Review of 3D Printing Technologies for Soft Polymer Materials

“…Inspired by them, Kokkinis et al [21] used fumed silica as a rheology modifier in polymer systems and successfully printed different resins including epoxies, silicones, and acrylics. Increasing studies [148,149,166] have proven that silica can act as a universal rheology modifier for polymer systems (Figure 5A,B). Besides silica, other particle additives are also widely used in existing practices.…”

“…Many impressive results in developing new printable materials reinforced by nano/micro particles and fibers have been demonstrated. Typical nano/ micro particles and fibers include nano silica, [51,83,149,166,174] nanoclay, [175][176][177] aluminum/alumina (Al 2 O 3 ), [21,104,[178][179][180] and C/SiC fiber. [168,181,182] Figure 5.…”

Progress in wearable electronics/photonics—Moving toward the era of artificial intelligence and internet of things

“…Although these traditional micro‐electro‐mechanical systems (MEMS) based sensors can achieve high‐precision measurement of continuous finger motions in 3D space, sensor‐wise they are rigid and complicated to be fabricated, thus limiting their applications in light and flexible wearable situations. Flexibility, stretchability and light‐weight of wearable electronics, as the key factors determining the comfort level of users and the portability of devices, have drawn tremendous attention across the world for developing finger/glove sensors with such characteristics 122‐125 . The common flexible strain sensors are normally based on resistive sensing 123,126‐137 or capacitive sensing, 138,139 whose output signals can dynamically respond to the variation of applied force or strain under continuous motions.…”