skip to main content

Title: 4D Printing of Freestanding Liquid Crystal Elastomers via Hybrid Additive Manufacturing

Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable and rapid actuation capabilities. Recent progress has been made on direct ink writing (DIW) or Digital Light Processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, a novel method to 4D print freestanding LCEs on‐the‐fly by using laser‐assisted DIW with an actuation strain up to −40% is proposed. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one‐step additive process. Various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW‐printed functionally freestanding LCEs with the DLP‐printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices.

more » « less
Award ID(s):
2145601 2142789
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Advanced Materials
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Digital Light Processing (DLP) 3D printing enables the creation of hierarchical complex structures with specific micro‐ and macroscopic architectures that are impossible to achieve through traditional manufacturing methods. Here, this hierarchy is extended to the mesoscopic length scale for optimized devices that dissipate mechanical energy. A photocurable, thus DLP‐printable main‐chain liquid crystal elastomer (LCE) resin is reported and used to print a variety of complex, high‐resolution energy‐dissipative devices. Using compressive mechanical testing, the stress–strain responses of 3D‐printed LCE lattice structures are shown to have 12 times greater rate‐dependence and up to 27 times greater strain–energy dissipation compared to those printed from a commercially available photocurable elastomer resin. The reported behaviors of these structures provide further insight into the much‐overlooked energy‐dissipation properties of LCEs and can inspire the development of high‐energy‐absorbing device applications.

    more » « less
  2. Abstract

    Liquid crystal elastomers (LCEs) are a class of stimuli‐responsive materials that have been intensively studied for applications including artificial muscles, shape morphing structures, and soft robotics due to their capability of large, programmable, and fully reversible actuation strains. To fully take advantage of LCEs, rapid, untethered, and programmable actuation methods are highly desirable. Here, a liquid crystal elastomer‐liquid metal (LCE‐LM) composite is reported, which enables ultrafast and programmable actuations by eddy current induction heating. The composite consists of LM sandwiched between two LCE layers printed via direct ink writing (DIW). When subjected to a high‐frequency alternating magnetic field, the composite is actuated in milliseconds. By moving the magnetic field, the eddy current is spatially controlled for selective actuation. Additionally, sequential actuation is achievable by programming the LM thickness distribution in a sample. With these capabilities, the LCE‐LM composite is further exploited for multimodal deformation of a pop‐up structure, on‐ground omnidirectional robotic motion, and in‐water targeted object manipulation and crawling.

    more » « less
  3. Abstract

    Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So far, most 3D‐printed LCEs are thermally actuated. Herein, a 3D‐printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D‐printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near‐infrared (NIR) light (808 nm) at 1.4 W cm−2(corresponding to 160 °C) under optimal printing conditions. The 3D‐printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light‐responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s−1(on a flat surface) and 0.216 mm s−1(on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm).

    more » « less
  4. Abstract

    The ability to manufacture highly intricate designs is one of the key advantages of 3D printing. Achieving high dimensional accuracy requires precise, often time‐consuming calibration of the process parameters. Computerized feedback control systems for 3D printing enable sensing and real‐time adaptation and optimization of these parameters at every stage of the print, but multiple challenges remain with sensor embedment and measurement accuracy. In contrast to these active control approaches, here, the authors harness frontal polymerization (FP) to rapidly cure extruded filament in tandem with the printing process. A temperature gradient present along the filament, which is dependent on the printing parameters, can impose control over this exothermic reaction. Experiments and theory reveal a self‐regulative mechanism between filament temperature and cure kinetics that allows the frontal cure speed to autonomously match the print speed. This self‐regulative printing process rapidly adapts to changes in print speed and environmental conditions to produce complex, high‐fidelity structures and freestanding architectures spanning up to 100 mm, greatly expanding the capabilities of direct ink writing (DIW).

    more » « less
  5. Abstract

    Direct ink writing (DIW) has demonstrated great potential as a multimaterial multifunctional fabrication method in areas as diverse as electronics, structural materials, tissue engineering, and soft robotics. During DIW, viscoelastic inks are extruded out of a 3D printer's nozzle as printed fibers, which are deposited into patterns when the nozzle moves. Hence, the resolution of printed fibers is commonly limited by the nozzle's diameter, and the printed pattern is limited by the motion paths. These limits have severely hampered innovations and applications of DIW 3D printing. Here, a new strategy to exceed the limits of DIW 3D printing by harnessing deformation, instability, and fracture of viscoelastic inks is reported. It is shown that a single nozzle can print fibers with resolution much finer than the nozzle diameter by stretching the extruded ink, and print various thickened or curved patterns with straight nozzle motions by accumulating the ink. A quantitative phase diagram is constructed to rationally select parameters for the new strategy. Further, applications including structures with tunable stiffening, 3D structures with gradient and programmable swelling properties, all printed with a single nozzle are demonstrated. The current work demonstrates that the mechanics of inks plays a critical role in developing 3D printing technology.

    more » « less