Washable, breathable, and stretchable e-textiles wirelessly powered by omniphobic silk-based coils

Highlights

• Scalable fabrication of low-cost, biodegradable, Omniphobic Silk-based Coils (OSCs).

• OSCs continuously power e-textiles wirelessly via magnetic resonance coupling (MRC).

• E-textiles powered by OSCs are breathable, washable, and can be used under water.

• OSC-powered e-textiles are flexible, stretchable, and operate within wireless power safety limits.

• OSCs enable the low-cost manufacturing of reliable, battery-free, wireless e-textiles.

Abstract

The commercial development of smart garments is currently hindered by significant challenges, such as dependence on batteries, reduced washability, and difficult incorporation into existing large-scale textile manufacturing technologies. This work describes an industrially scalable approach to transform conventional fabrics into smart textiles—wirelessly powered by omniphobic silk-based coils (OSCs). OSCs are stretchable and lightweight power-receiving coils that can be easily sewn onto any textile, enabling the safe wireless powering of wearable electronics via magnetic resonance coupling without compromising the comfort of the user. OSCs are composed of microfibers made of a novel silk-nanocarbon composite that benefits from the stretchability of silk fibroin and the high conductivity of multiwall carbon nanotubes and chitin carbon nanoflakes. The surface of the OSC-powered electronic textiles (e-textiles) is rendered omniphobic—both hydrophobic and oleophobic—using a spray-based silanization method, which imbues the e-textile with waterproof and stain repellent properties without compromising its flexibility, stretchability, or breathability. OSCs exhibit excellent stability in high moisture environments and under mechanical deformations, allowing them to undergo up to 50 standard machine-washing cycles without degradation in performance. Moreover, OSC-powered e-textiles can be fabricated at a low cost using scalable manufacturing processes, paving the way toward the rapid development and commercialization of machine-washable and battery-free smart clothing and reusable wearable electrophysiological sensors.

Introduction

The ubiquity of textiles in daily life and the recent miniaturization of electronic systems using flexible substrates have led to a fast-growing and advanced interdisciplinary research field that aims to incorporate wearable devices into electronic textiles called “e-textiles” [1], [2], [3]. E-textiles have demonstrated to serve as convenient platforms for human-machine interfacing [4], [5], the embedding of wearable sensors [6], [7], and the development of conformable robotic sensory skin [8]. While e-textiles are commonly powered using conventional rechargeable batteries, their weight and rigidity often compromise the bendability and stretchability of the textile, reducing the comfort of the user. To circumvent this limitation, several researchers have demonstrated the fabrication of flexible, fiber-shaped batteries such as coaxial or twinned yarn-like Li‐ion [9] and Zn‐ion [10] rechargeable batteries equipped with bendable carbon or metal-based anodes. Unfortunately, these fiber-shaped batteries require to be encapsulated to prevent the evaporation and leakage of their liquid electrolytes, incrementing their radius and making them difficult to interface with conventional sewing equipment [11].

Several approaches to integrate advanced energy harvesting technologies into traditional textiles and other flexible platforms have been proposed as lightweight and flexible alternatives to power e-textiles [12], [13], [14]. Efficient fiber-based photovoltaic systems using perovskite nanolayers have been successfully used to power e-textiles [15], [16], [17]. Unfortunately, the deteriorating performance of these solar cells upon stretching and their dependence on environmental illumination compromise the continuity of the power generation, limiting their reliability to power e-textiles [18]. The transformation of the biomechanical energy of the wearer into electrical energy also constitutes a promising strategy to fabricate self-powered e-textiles [19]. Materials with piezoelectric properties such as ZnO [5] and PVDF [20], [21] have been deposited or grown directly onto textiles for the fabrication of flexible and stretchable piezoelectric nanogenerators (PENGs) capable of powering wearable devices without compromising the comfort of the user. Unfortunately, the conversion efficiency of piezoelectric materials degrades rapidly in high relative humidity environments [22], hindering the launderability of piezoelectric e-textiles. Yarn-based triboelectric nanogenerators (TENGs) capable of converting user-device interaction into electrical outputs via contact electrification have also been explored as a battery-less strategy to power wearable sensors [23], [24], [25], [26], [27] and e-textiles [28], [29], [30], [31], [32]. TENGs, similar to PENGs, still depend on rigid power storage systems to continuously power wearable devices while the user is not moving. Moreover, the complex processes required to fabricate and incorporate TENGs into e-textiles are often incompatible with current textile mass production technologies [33].

Flexible and lightweight wireless power systems have emerged as an ideal battery-free strategy to power e-textiles [34], [35]. Radio frequency identification (RFID) antennas have been extensively attached to consumable products [36], [37], textiles [38], and even human skin as a cost-effective approach for the real-time collection of wireless measurements [39]. The relatively low distance range of operation of RFID technology, however, has limited its applicability to continuously powering wearables and e-textiles. Additionally, the laminating materials often required to protect RFID antennas and circuits from oxidation hamper the breathability of these sensors [38].

Wireless power transmission (WPT) using resonant inductive coupling has demonstrated to be a promising strategy to continuously power e-textiles without significantly increasing their rigidity or weight [40], [41]. To maximize WPT efficiency, the coils embedded into e-textiles require to both exhibit low ohmic losses and match the impedance of the external resonant coil [42], [43]. Several nanomaterial-based inks with high electrical conductivity have been used to rapidly pattern—via inkjet [44], [45] or screen printing [46], [47]—2D WPT coils over the surface of different e-textiles. While these conductive inks exhibit a high degree of flexibility and adhesion to the surface of fibrous textiles, the prolonged exposure of e-textiles to mechanical strains from wearer use often cause ink cracking and delamination, compromising WPT performance [48]. Silk fibroin protein, due to its biocompatibility, low-cost, and high mechanical strength and toughness, has served as support and reinforcement for conductive nanomaterials in a variety of stretchable wearable sensors [49], [50], biodegradable thread-like conductors [51], and transient implantable electronics [52], [53]. Unfortunately, the degradation of silk fibroin composites after prolonged contact with water has limited their application in washable e-textiles [54]. To benefit from the intrinsic flexibility and stretchability of textiles, a variety of thread-based WPT coils incorporating highly conductive metallic filaments have been directly knitted [55], embroidered [56], or sewn [57], [58] onto e-textiles. Unfortunately, the hygroscopic behavior of most textiles and garments makes the metallic components of these thread-based coils susceptible to moisture-induced corrosion in humid environments, upon contact with the sweat of the user, or during washing cycles [57]. A rapid, cost-effective, and scalable process to transform conventional fabrics into e-textiles would therefore be desirable to accelerate the development and commercialization of smart garments that do not depend on batteries for their power and are robust enough to be washed with everyday laundry.

Here, we present a scalable method to fabricate omniphobic silk-based coils (OSCs), which can be integrated into conventional textiles by sewing and can be used for the continuous wireless powering of electronic components via magnetic resonance coupling (MRC). By judiciously combining multiwall carbon nanotubes (MWCNTs) and chitin carbon (ChC) with silk fibroin (SF), we were able to electrospin conductive silk-based fibers that could be easily twisted into thread. This stretchable and conductive thread can be sewn onto a variety of textiles in the shape of a flat spiral coil and rendered omniphobic by the spray‐based deposition of fluoroalkylated organosilanes, creating OSCs. We demonstrate that OSCs are flexible, stretchable, washable, and capable of continuously providing power to e-textiles via wireless power transfer. We also demonstrate that the power output of OSCs does not diminish significantly after repeated mechanical deformation and washing cycles, enabling the continuous wireless powering of wearable sensors embedded into e-textiles. The combination of stretchability, high conductivity, independence from environmental moisture, and relative low cost, outperforms the WPT capabilities of several silver and carbon-based yarns proposed for the manufacturing of washable e-textiles [59]. We expect the WPT efficiency of OSCs to expedite the sustainable development and commercialization of emerging, battery-free, wearable electronics and e-textiles.