Smart textiles from liquid crystal elastomer fibers can now be melted down and reknitted with nearly identical shape-shifting performance.
(Nanowerk Spotlight) Smart textiles built from liquid crystal elastomer fibers can contract, bend, twist, and pump. But until now, no one has shown that these textiles can be recycled into new fibers and fabrics without losing their ability to actuate.
The reason is structural. Liquid crystal elastomers, or LCEs, are rubbery polymers whose rod-shaped molecules align in an ordered phase. Heat them past a critical temperature, and that alignment collapses, forcing the material to contract by as much as a third of its length. Cool it, and the order returns. The shape change is powerful, repeatable, and fully reversible. That makes LCE fibers excellent building blocks for fabrics that move on command.
Researchers have knitted, woven, braided, and embroidered them into prototype smart textiles that respond to heat, light, and electric fields. But virtually all of these fibers rely on ultraviolet curing to form permanent chemical cross-links. Once set, the polymer network cannot be melted, reshaped, or reprocessed.
While recyclable LCE concepts have been demonstrated in simple, non-textile formats, and certain dynamic chemistries can enable network rearrangement, no one has recycled LCE fibers and smart textiles while quantifying whether the recycled material still performs.
That gap matters in an industry where global fiber production reached roughly 132 million tonnes in 2024 and less than 1% was recycled back into new textile fibers. A second limitation has also held the field back: most LCE textile work has stayed flat, confined to two-dimensional knitted or woven swatches. Three-dimensional tubular structures, the kind required for compression garments or miniature fluid pumps, have remained largely unexplored.
A study published in Advanced Functional Materials (“Thermo‐Mechanically Recyclable Smart Textiles from Circularly Knitted Liquid Crystal Elastomer Fibers”) now addresses both issues. An international team led from Eindhoven University of Technology, with collaborators in Switzerland, China, the Netherlands, and Singapore, reports thermoplastic LCE fibers that respond to heat and near-infrared light, run on commercial knitting machines to form flat and tubular textile structures, and can be melted down and re-extruded into new fibers and fabrics with nearly unchanged performance.
This is the first demonstration of a complete recycling loop for smart LCE textiles with quantified retention of both mechanical properties and actuation capacity.
Fabrication of the NIR light–responsive thermoplastic PTU LCE fibers. (a) Chemical structure of the PTU LCE. (b) Schematic of the fiber fabrication process using a capillary rheometer followed by drawing. The liquid crystal mesogens are aligned along the fiber’s axial direction. (c) Tens-of-meters-long LCE fibers. Scale bar, 1 cm. (d) Longitudinal and cross-sectional views of the LCE fiber. Scale bars, 5 mm (top) and 500 µm (bottom). (e) Demonstration of the fiber flexibility via knotting. Scale bar, 5 mm. (f) 2D X-ray diffraction pattern of the LCE fiber. The arrow indicates the alignment of mesogens. (g) Length and width changes of the LCE fiber under thermal stimulus. Inset pictures show the fiber at 25 and 110°C, respectively. Scale bars, 5 mm. (Image: Reproduced from DOI:10.1002/adfm.202530973, CC BY) (click on image to enlarge)
The fiber starts as a thermoplastic polythiourethane polymer composed of 90 wt% liquid crystal “soft” segments and 10 wt% hydrogen-bonding “hard” segments. The critical difference from conventional LCEs is the nature of the cross-links. Instead of permanent covalent bonds, this material relies on dynamic hydrogen bonds that weaken above 130 °C, allowing the molecular network to be reshaped or melted entirely. The researchers blended in 1 wt% of a commercial near-infrared-absorbing dye, Lumogen IR 765, to enable light-driven heating. They then melt-extruded the composite at 190 °C through a capillary die and drew it into continuous fiber tens of meters long, with a uniform diameter of 1.3 ± 0.2 mm.
When heated from 25 to 110 °C, the fiber contracts by approximately 31% along its length as it passes through the liquid crystal phase transition at 84 °C. The thermally driven actuation force reaches 0.20 N at approximately 100 °C under fixed-strain conditions. Under near-infrared illumination, the embedded dye converts light to heat, producing up to ~30% reversible actuation strain and a photo-driven force of 0.09 N at a power density of 625 mW cm⁻².
The fiber sustained stable light-driven contraction of around 27% over 30 cycles and demonstrated good reversible thermal actuation over 50 heating-cooling cycles. A single fiber wound helically around a soft tube also served as a light-activated locking device: illumination contracted the fiber, squeezed the tube shut around an inserted object, and switching the light off released it.
The dynamic hydrogen bonds allow the fiber to be reprogrammed into new shapes. Heating to 130 °C for 30 min while twisting locks in a helical geometry. When placed on a flat surface and illuminated from one side, a straight fiber rolls toward the light source. A right-hand-twisted fiber curves left; a left-hand-twisted fiber curves right. The rolling direction is encoded by the twist, at speeds between 0.72 and 1.43 mm s⁻¹.
The fibers proved compatible with standard domestic knitting machines. Using single-bed and double-bed setups, the team produced plain-knit and rib-knit textiles incorporating LCE fibers alongside conventional cotton yarns. Plain-knit structures curled into three-dimensional shapes upon heating, while rib-knit structures, where alternating loop types cancel internal torques, stayed flat and contracted in-plane. A slanted multi-material textile combined both patterns, shrinking by approximately 18% in length and 15% in width at 110 °C. Because only the dye-containing fibers absorb near-infrared light, the researchers could selectively actuate specific regions of the fabric with a light beam, leaving neighboring zones unchanged.
The hydrogen-bonding network also enabled reprogramming of finished textiles. A rib-knit swatch could be stretched and heat-set into a new elongated shape that then exhibited reversible actuation strains of 13.7% and 6.6% along length and width, respectively. This represents the first reported demonstration of reshaping an already-knitted LCE textile into a new geometry without disassembling the fibers and re-knitting them.
The team then moved beyond flat fabrics. They hand-knitted circular tubes on four double-pointed needles, with 4, 6, and 8 stitches per round. When heated, these hollow tubes contracted in both the radial and axial directions simultaneously, a behavior distinct from previously reported LCE tubes, which typically shrank in one dimension while expanding in the other.
The 4-stitch-per-round tube delivered the largest shape changes: an average inner diameter shrinkage of 19.4 ± 1.5%, an outer diameter shrinkage of 16.3 ± 0.9%, and a length shrinkage of 14.0 ± 0.4% over 5 cycles. Finite-element simulations confirmed that the mechanism relies on axial fiber contraction tightening the knitted stitches.
These tubular structures enabled several functional demonstrations. As a soft robotic climber, a tube placed over a rod inched upward through sequential heating and cooling: the top section contracted first, gripping the rod, while the bottom section then pulled upward. Adding localized near-infrared illumination to strengthen the grip increased total upward displacement from 11.4 mm to 19.9 mm over 4 cycles.
The tubes also functioned as fluid-handling devices. Fitted around a soft silicone insert connected to a glass pipette, the tube acted as a smart dropper: heating caused radial compression that squeezed liquid out, and cooling released it. Operated repeatedly, the same setup worked as a micro pump, cycling liquid volume between 0 and ~0.11 mL over 5 heating-cooling cycles.
In a separate test, the tube was placed on a mannequin leg and illuminated locally, producing an estimated compressive pressure of ~1.3–1.8 kPa. That figure is comparable to shape memory polymer-based smart stockings and is classified as light compression under European standards.
The recyclability tests delivered the study’s central result. The researchers disassembled knitted textiles, mechanically fragmented the fibers, and re-fed the pieces into the melt extruder using identical processing parameters. The recycled fibers showed a slightly smaller diameter (1.1 ± 0.2 mm) and a modest shift in mechanical properties: higher stiffness (Young’s modulus of 8.5 ± 0.9 MPa) and tensile strength (16.0 ± 0.2 MPa), with a slight reduction in stretchability (fracture strain of 995.0 ± 33.8%).
The recycled fiber maintained ~25% reversible actuation strain over 50 cycles, closely comparable to the pristine fiber’s ~30%. When re-knitted into circular tubes, the recycled fibers produced actuation strains of 14.0 ± 1.4%, 16.1 ± 1.8%, and 15.8 ± 1.0% in the outer diameter, inner diameter, and length, closely matching the pristine tubes. Multi-cycle reprocessing tests on hot-pressed films confirmed that the material retains its actuation capacity through repeated recycling.
The approach does not yet address challenges such as wash durability, integration with electronics, or scaling to industrial circular knitting machines. But by replacing permanent cross-links with reversible hydrogen bonds, this work demonstrates that smart LCE textiles can be melted down and rebuilt with the same fibers delivering closely comparable performance. That closes a loop the field has left open until now.
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Albert P. H. J. Schenning (Eindhoven University of Technology)
, 0000-0002-3485-1984 corresponding author
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