Soft and Highly Integrated Electronic Fibers

Stretchable optical and electronic fibers constitute increasingly important building blocks for a myriad of emerging applications, such as in robotics, sensing, medical implants or e-textiles. They are particularly suitable for wearables and smart textiles as seamlessly integrated devices that can bring high added values for monitoring, energy harvesting, haptic and even actuation functionalities. Yet, it remains challenging to fabricate efficient and advanced soft fiber-base devices that can undergo significant mechanical deformation in a simple and scalable way. The preform-to-fiber thermal drawing technique is a powerful platform to fabricate multi-material fibers with complex architectures and functionalities. Until recently, this fabrication approach has been restricted to rigid thermoplastic or glass fibers, preventing their use for mechanical sensing or actuation, and rendering difficult their use in wearable approaches or within textiles.<br/>In this contribution we will show how we could revisit the selection criteria for cladding materials compatible with the thermal drawing process, and fabricate super-elastic fibers with advanced electronic functionalities. We will demonstrate how, thanks to a deeper rheological characterization, we could identify thermoplastic elastomers that could be drawn from a solid preform at high viscosity (Advanced Materials, 2018, 201707251). Subsequently, we will demonstrate that thermoplastics, liquid metals, and conductive polymer composites could be co-drawn with prescribed architectures within thermoplastic elastomer cladding. This allowed us to successfully fabricate stretchable optical but also electronic fibers that are used as precise and robust pressure, strain or more generally deformation and haptic sensors. We will in particular show examples of electronic fibers for strain or pressure sensing, that can be integrated into textiles and fabrics for large area pressure mapping (Adv. Funct. Mat. 30, 1904274 (2019)), and for polymer composite part monitoring (Adv. Mat. Technologies 6, 2000957 (2021)). We will also introduce an original strategy based on fibers that integrate tens of liquid metal electrodes that can act as a soft transmission line for sensing multiple mechanical deformation events along the entire fiber length (Nature Electronics 3, 316 (2020)). Based on the same combination of micro-structured thermoplastic elastomers and liquid metal electrodes, we will present self-powered strategies via soft triboelectric fibers (Nature Communications. 11, 3537 (2020)). These examples of fibers enable to realize, with a few connections at fiber ends, robust large area sensing fabrics, paving the way towards novel opportunities for advanced yet scalable soft electronics, soft prosthesis, wearable devices and electronic textiles. We will conclude with a hint on recent developments (currently under review) of steerable multi-material soft fibers to realize highly integrated thin catheters with micro-channels, optical waveguides and electrodes, paving the way towards novel opportunities in soft robotics.