Liquid crystal elastomer (LCE) fiber actuators are promising candidates for smart textiles owing to their reversible large-stroke actuation and high aspect ratios. However, current LCEs require ultraviolet (UV) curing and are not recyclable. In addition, research is mainly focused on flat knitted thermo-responsive textiles. Here, a scalable recycling route for smart LCE textiles is developed by melt-extruding a thermoplastic LCE containing a near-infrared photothermal dye. The LCE fibers exhibit ∼30% reversible actuation strain and display light-driven rolling motions with left- or right-turning trajectories according to their programmed twist handedness. Using commercial knitting machines, multi-material plain- and rib-knit textiles are fabricated that exhibit in-plane contraction and out-of-plane deformations including bending and twisting under thermal and photo stimuli. Circularly knitted tubular structures exhibit reversible contraction in both radial and axial directions, reaching approximately 16% in outer diameter, 19% in inner diameter, and 14% in length, enabling applications in autonomous climbing, controlled liquid release, and micro pumping. Finally, thermo-mechanical recycling yields recycled fibers and both flat and circularly knitted textile structures with nearly unchanged actuation performance and comparable mechanical properties, demonstrating robust recyclability. Our results demonstrate the creation of smart textiles that are simultaneously intelligent in function and sustainable in design.

In recent years, knitted strain sensors have been developed that aim to achieve reliable sensing and high wearability, but they are associated with difficulties due to high hysteresis and low gauge factor (GF) values. This study investigated the electromechanical performance of the weft-knitted strain sensors with a systematic approach to achieve reliable knitted sensors. For two elastic yarn types, six conductive yarns with different resistivities, the knitting density as well as the number of conductive courses were considered as variables in the study. We focused on the 1 × 1 rib structure and in the sensing areas co-knit the conductive and elastic yarns and observed that positioning the conductive yarns at the inside was crucial for obtaining sensors with low hysteresis values. We show that using this technique and varying the knitting density, linear sensors with a working range up to 40% with low hysteresis can be obtained. In addition, using this technique and varying the knitting density, linear sensors with a working range up to 40% strain, hysteresis values as low as 0.03, and GFs varying between 0 and 1.19 can be achieved.

Eleven phase change materials (PCMs) for cooling humans in heat-stressed conditions were evaluated for their cooling characteristics. Effects of packaging material and segmentation were also investigated. Sample packs with a different type PCM (water- and oil-based PCMs, cooling gels, inorganic salts) or different packaging (aluminum, TPU, TPU + neoprene) were investigated on a hotplate. Cooling capacity, duration, and power were determined. Secondly, a PCM pack with hexagon compartments was compared to an unsegmented version with similar content. Cooling power decreased whereas cooling duration increased with increasing melting temperature. The water-based PCMs showed a >2x higher cooling power than other PCMs, but were relatively short-lived. The flexible gels and salts did not demonstrate a phase change plateau in cooling power, compromising their cooling potential. Using a TPU or aluminum packaging was indifferent. Adding neoprene considerably extended cooling duration, while decreasing power. Segmentation has practical benefits, but substantially lowered contact area and therefore cooling power.