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Wei et al. Soft Sci 2023;3:17 https://dx.doi.org/10.20517/ss.2023.09 Page 3 of 38

In this review, we logically present the progress of multimodal electronic textiles and summarize their
applications in human-machine interfaces, as shown in Figure 1. We first introduce functional fiber
fabrication techniques and electronic textile forming strategies. Then, the multimodal electronic textiles
with multifunctional sensing capabilities in physical signals, physiological signals, chemical signals, and
hybrid signals are summarized. Next, the applications of multimodal electronic textiles in intelligent
human-machine interfaces are discussed, including healthcare monitoring, motion recognition, gesture
interaction, VR and AR control, and smart home. In the end, we point out the key challenges and future
development trends of multimodal electronic textiles in human-machine interface research.

FUNCTIONAL FIBER FABRICATION AND ELECTRONIC TEXTILE FORMING
With the rapid development of smart textiles, increasing fabric manufacturing technologies are used in
electronic textiles. According to the required function, the appropriate sensing material, micro-nano
processing, and fiber manufacturing technology are selected to prepare the functional fibers. Subsequently,
multifunctional fibers are integrated into textiles through various textile processing technologies to form
multimodal electronic textiles. In this section, we discuss the common functional fiber fabrication
techniques and electronic textile-forming methods in detail.

Fiber fabrication
Fiber is the basic component unit of textiles, so the preparation of functional fiber is the basis for building
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multimodal electronic textiles. In recent years, various manufacturing technologies, such as coating ,
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injecting , twisting , spinning , thermal drawing , and coaxial extrusion , have been used in the
development of fiber. These technologies can combine one or more functional materials to continuously
produce multifunctional fibers, as shown in Figure 2.
Coating
The coating is a universal, convenient, and effective fiber manufacturing technology which can transfer
functional materials to fiber or yarn substrate . The most common coating methods include spraying ,
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dipping , electrochemical coating , and more. Chen et al. used the common textile material polyamide
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(PA) yarn as the substrate and coated silver on its surface as the conductive electrode . The silver-coated
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PA yarn was coated with silicone rubber to obtain PA composite yarn with negative friction, as shown in
Figure 2A. Park et al. also used coating silicone rubber as a negative friction material to design a
triboelectric nanogenerator (TENG), which generates electric energy by continuous contact and separation
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between human skin and silicone rubber . In addition, Liu et al. prepared a pressure-sensing fabric based
on MXene coating, using cotton fabric as a substrate .
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Injecting
Injecting is the simplest functional fiber manufacturing technology, which is usually used to inject
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conductive liquid materials (such as liquid metal , conductive ink , conductive ionic liquid , etc.) into
hollow polymer tubes to form functional fibers. Liquid metal (such as gallium, EGaIn, Galinstan, etc.) is
widely used in liquid electrodes due to its low Young’s modulus, high conductivity, and non-toxicity. As the
good fluidity of liquid metals, Wang et al. continuously pumped them into homogeneous ultra-fine polymer
hollow fibers to propose a large-scale textile-based TENG , as shown in Figure 2B. The liquid metal/
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polymer core/shell fiber structure served as the basic unit of a textile-based TENG for energy harvesting,
sensing, and home control. Based on Galinstan, a eutectic alloy consisting of gallium, indium, and tin, Yang
et al. proposed a TENG with a super-stretchable and structural design .
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