This work presents a new class of thermoplastic liquid crystal elastomer (LCE) soft actuators that combine large, reversible deformations with recyclability and processability—addressing sustainability and scalability limitations of conventional thermoset LCEs [1]. By incorporating dynamic hydrogen-bonding crosslinks, these materials are melt-processable, reusable, and structurally programmable. Segmented polythiourethane LCEs were synthesized via a one-pot thiol-addition method using commercially available components. Tuning the length of liquid crystal oligomers allowed precise optimization of mechanical and actuation properties. The materials exhibited rapid, reversible actuation strains up to 32%, matching thermoset analogues while offering full recyclability.

A direct ink writing (DIW) technique was developed to 3D print actuators without post-curing. Thermoreversible H-bonding enabled extrusion and solidification into functional constructs exhibiting contraction and bending, which could be reprocessed multiple times—supporting circular material use. Light-activated LCEs incorporating azobenzene photoswitches enabled dual photothermal and photochemical actuation in air and underwater. DIW facilitated complex geometries such as spirals and honeycombs, producing spatially directed, reversible deformations.

Versatility was further enhanced by embedding a charge-transfer complex (CTC) into the H-bonded matrix, enabling spatially programmable near-infrared (NIR) actuation via selective disruption of H-bonds. This allowed localized shape and color changes, with metastable patterns recoverable on demand. Finally, melt-extrusion and fiber drawing yielded rotating fiber actuators and triple-helical ropes capable of delivering amplified torque and force. These retained programmability, self-healing, and recyclability, demonstrating readiness for industrial-scale use.

This work establishes a new paradigm in sustainable, reprocessable LCE-based soft actuators—poised for impactful applications in soft robotics, smart textiles, artificial muscles, and adaptive devices.

Thermo-responsive polymers are typically the systems of choice when smart systems are aspired that respond reversibly to a non-invasive trigger. The most popular example is poly(N-isopropyl acrylamide) PNIPAM in aqueous media that exhibits a lower critical solution temperature (LCST) of around 32 °C. Yet, for many contexts, such smart systems should be operated at constant temperature. This can be realized by integrating additional photo-responsive groups into inherently thermo-responsive polymers, which modulate reversibly the polymer's hydrophilicity upon irradiation. The light-triggered E-Z (or trans-cis) isomerization of azodyes represents the most reliable and resilient photo-switch available so far. Nonetheless, the more polar Z-state is prone to a rather fast thermal relaxation to the E-state. Also, the changes of LCST that can be achieved are limited (mostly ≤ 5 K), and the considerable spectral overlap of the E- and Z-states in the UV-vis range reduces the switching efficiency even further. We shall report on new azodye-functionalized polyacrylamides bearing arylazopyrazoles that mitigate these shortcomings, thus allowing reversible changes of the LCST of up to 25 K while simultaneously showing highly stable Z-states and little spectral overlap. Also, we shall show that by appropriate design of the polymers, LCST-shifts of up to 15 K can be induced even when incorporating simple azobenzene dyes. Moreover, we shall demonstrate that their light-triggered E-Z isomerization may not only lead to the (according to common wisdom) expected increase of the LCST but, alternatively, may also result in a drastic decrease of the LCST for yet unclear reasons.

To facilitate the ongoing transition towards a circular economy, renewable 3D printed materials that are both sustainable and competitive must be accessible. [1] Global capacity for biobased materials is expected to grow significantly over the next few years. However, the growing demand for (biobased) thermosetting resins, which are used as ink for vat photopolymerization, raises environmental concerns regarding to plastic waste management. [2] Therefore, photocurable materials that are renewable and recyclable at the same time are needed. We have developed a mechanically robust and reprocessable photopolymer for 3D printing, based on malic acid which has been selected as one of the 12 most promising chemicals that can be derived from sugar by the U.S. Department of Energy. [3] The reaction of malic acid with glycidyl methacrylate introduces both methacrylate moieties that can undergo photopolymerization in the printer, and β-hydroxyester linkages that can function as dynamic crosslinks via associative bond exchange reactions. The resin formulations demonstrate good layer fusion and accurate print quality, while the 3D printed specimen are robust and thermally stable. Notably, the printed object with the shortest relaxation time displayed Arrhenius flow (vitrimer) behavior with an activation energy of 36.0 kJ mol^-1, and its mechanical performance was maintained after being recycled three times. [1] The use of renewable building blocks together with the design for recyclability will promote the precise and waste-free production of a new generation of 3D materials, supporting a more sustainable plastics economy in the near future. [4]

Soft robots are a type of robotic system composed of flexible materials with an inherent ability to deform, allowing them to interact with and adapt to their surroundings in a versatile and safe manner. Liquid crystal elastomers (LCEs) present a unique opportunity for creating soft robotic systems due to their ability to undergo reversible shape changes in response to external stimuli.(1) The integration of 3D printing with the LCEs in soft robotics allows for precise programming of the robotic structures.
Here, we explore the use of 3D printed LCEs in combination with photothermal actuation at the water/air interface, realizing a soft robot that mimics a swimming frog. Specifically, optimization and customization of the liquid crystal oligomer ink was investigated by modifying its chemical composition including the type of mesogen and the thiol linker or changing the reaction time, to determine the composition with the most suitable printability, allowing for alignment through extrusion-based 3D printing. The actuation and alignment of 3D printed rectangles with different numbers of layers was systematically compared. Graphene oxide was added to the ink, with the aim to use photothermal actuation when the 3D printed structures were illuminated with near infrared light. In addition, a UV-curable polydimethylsiloxane-based ink was developed to create the passive outer matrix. Finally, a 3D-printed, frog-like structure was created by combining passive PDMS ink for the body with LCEs functioning as muscles, enabling controlled leg movements at the water/air interface when exposed to near infrared light.