Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F21: Soft Robotic Matter II: Shape-Morphing and Responsive MaterialsFocus Recordings Available
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Sponsoring Units: DSOFT Chair: Hamed Shahsavan, University of Waterloo Room: McCormick Place W-185D |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F21.00001: Bioinspired light-driven soft robots based on liquid crystal polymers Invited Speaker: Albert Schenning
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Tuesday, March 15, 2022 8:36AM - 8:48AM |
F21.00002: Plasticized Liquid Crystal Networks for the Active Control of Power Transmission in Gear Train Natalie P Pinchin, Abdon Pena-Francesch, Hamed Shahsavan There is growing interest in the development of small-scale machines and devices across a variety of fields, including sensing, bioengineering, and robotics. As current methods of powering and control have inherent size limitations, there is a demonstrated need for mechanisms that operate at small scales. One approach of interest is untethered control of self-powering systems. This can be achieved using protein motors in conjunction with liquid crystal networks (LCNs). Protein motors provide high efficiency, sustained power without hazardous chemical reactions. LCNs are molecularly anisotropic and demonstrate shape-change programmability when external stimuli, such as light or heat, are applied. In this work we showcase the use of these materials for the untethered control and powering of a multi-component mechanical device. We design and fabricate a milli-scale gear train with integrated motor and clutch functionalities. The driving gear contains protein motors and uses the Marangoni effect to generate a propulsive force. A clutch gear composed of plasticized LCNs uses photothermal actuation of the gear teeth to disengage from the gear train, halting the chain of motion on demand. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F21.00003: Shape-memory and shrink-on-demand aquabots Shipei Zhu, Huanqing Cui, Ho Cheung Shum, Thomas P Russell Current soft robots are mainly fabricated from soft solid materials. The deformability is limited by the underlying solid bulk rheology. It remains challenging for current soft robots to navigate and reconfigure their shapes for diverse tasks inside very clustered and constrained spaces. Building on an ultra-soft liquid robot, termed aquabots, we have developed an approach to achieve reversible dimensional shrinkage and shape memory functions. Using photo-crosslinking-assisted water-in-water printing, thermal and magnetic multi-responsive membranes of aquabots are produced. Our shape-memory and shrink-on-demand aquabots can in situ adapt theirs size and shapes to navigate through and conduct tasks in very constrained spaces narrower than the size of aquabots. These unprecedented cooperative abilities of aquabots create new opportunities in the applications of medical manipulation, biosensing, endoscopy and microsurgery. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F21.00004: Liquid Crystal Elastomer based artificial neuromuscular unit with electrically controllable ultrafast actuation Yang Wang Neuromuscular unit is the basic block for animals to convert their intentions into real movements. The similarity between ionic signal of action potential and electronic signal of electric circuit lures people to build an electronically controllable soft actuating system to rebuild the neuromuscular unit. Our work provides a new solution with a stretchable ultrathin gold-sputtered liquid crystal elastomer (LCE) film as artificial muscle which can be actuated by short voltage pulses (< 5ms) just like action potentials. Its actuation frequency range can cover the natural frequency of the mechanical system it is actuating. Therefore, it can amplify the output power density through resonance. Such energy-favorable amplification strategy is commonly used in animals’ locomotion and many robotic designs. During test, our artificial muscle (self-weight of 1.2 mg) can lift a weight of 3.1 g with actuation strain of 25% (peak strain rate of 400%/s) and frequency of 6 Hz. The power density of LCE artificial muscle in this case is 1300 W/kg, which outperforms most of the biological muscles. We believe such electrically controllable artificial neuromuscular system can inspire many new designs in the future. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F21.00005: Digital light processing of liquid crystal elastomers for self-sensing artificial muscles Shuo Li, Hedan Bai, Robert F Shepherd Artificial muscles based on stimuli-responsive polymers usually exhibit mechanical compliance, versatility, and high power-to-weight ratio, showing great promise to potentially replace conventional rigid motors for next-generation soft robots, wearable electronics, and biomedical devices. In particular, thermomechanical liquid crystal elastomers (LCEs) constitute artificial muscle-like actuators that can be remotely triggered for large stroke, fast response, and highly repeatable actuations. Here, we introduce a digital light processing (DLP)–based additive manufacturing approach that automatically shear aligns mesogenic oligomers, layer-by-layer, to achieve high orientational order in the photocrosslinked structures; this ordering yields high specific work capacity (63 J kg−1) and energy density (0.18 MJ m−3). We demonstrate actuators composed of these DLP printed LCEs’ applications in soft robotics, such as reversible grasping, untethered crawling, and weightlifting. Furthermore, we present an LCE self-sensing system that exploits thermally induced optical transition as an intrinsic option toward feedback control. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F21.00006: Flexo-ionic effect of Ionic Liquid Crystal Elastomers for Soft Robotic Applications Chathuranga Prageeth H Rajapaksha, M D Tharindupriya Gunathilaka, Suresh Narute, Hamad A Albehaijan, Camilo Piedrahita, Pushpa R Paudel, P M Sineth G Kodikara, Chenrun Feng, Bjorn Lussem, Thein Kyu, Antal I Jakli Strain gradient induced electricity (flexoelectricity) has been potential of a wide variety of applications such as bending sensors and micropower generators [1] [2]. Liquid crystals are fascinating materials with long-range molecular orientation, used for various applications [3] [4] [5]. Liquid crystal elastomers are polymers, which exhibit liquid crystal properties. The first study of the flexo-ionic effect of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported [6]. The measured flexo- ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m [7]. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The shortest response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in soft robotics. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F21.00007: 3D Printing of Electrically Responsive PVC Gel Actuator Shengqiang Cai, Zijun Wang Additive manufacturing of electrically responsive soft actuators is greatly desired for designing and constructing novel soft machines. However, there are very limited options for 3D printable and electrically responsive soft materials. Recently we have developed a strategy of 3D printing polyvinyl chloride (PVC) gel actuators that are electrically controllable. We print a jellyfish-like actuator from PVC ink which can deform rapidly and reversibly with an applied voltage. With the multi-material 3D printing technique, we further demonstrate a soft actuator with a stiffness gradient that can generate undulatory motion. As a proof-of-concept demonstration, we show that a 3D printed PVC gel-based smart window can change its transparency upon the application of voltage. Some simulations of the PVC gel actuation will also be discussed. We hope our work can provide a facile way to fabricate electric field-responsive soft actuators with multiple actuation modes and expand their potential applications in diverse engineering fields. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F21.00008: Composite Wearable Textile Materials with Spatial Control of Joule Heating Marquise D Bell, Te Faye Yap, Anoop Rajappan, Jason Hsu, Colter J Decker, Vivian Tat, Chien-Te K Tseng, Daniel J Preston Flexible heaters have gained interest as a viable option for thermal management and heat generation in wearable devices. Various conductive polymers, fibers, and textiles have been studied for their effectiveness as Joule heaters. Most existing methods provide uniform heating over an area but do not allow a spatially varying heat flux. In this work, we designed a low-profile composite textile material that enables spatial control of the localized level of heating by tailoring the geometry of an integrated serpentine conductive textile pathway. The composite material is composed of three layers bonded by heat sealing—a thermoplastic polyurethane (TPU)-coated supportive backing textile, a serpentine-patterned conductive textile, and an electrically insulating TPU top layer—enabling facile fabrication. Using an analytical approach to determine the relationship between power density and material design, a desired spatial distribution of heat flux can be achieved. This material provides a customizable and repeatable heating method for applications in wearable devices for thermoregulation and thermotherapy, actuation mechanisms for soft robots, and climate control devices for temporary or portable shelters. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F21.00009: Statistical field theory for the free energy of an electro-mechanical polymer chain: non-local dipole-dipole interactions in the fixed applied field ensemble Pratik Khandagale, Carlos Garcia Cervera, Gal deBotton, Carmel Majidi, Kaushik Dayal Existing theoretical approaches for polarizable polymers subject to a combined applied electric field and stretch are based on discrete monomer models. It is challenging to account for the non-local dipole-dipole interaction in this framework, and prior work typically consider only the interaction between the applied field and dipoles. To go beyond this approximation, we apply the statistical field theoretic framework that is based on a continuous description of the polymer chain in terms of density fields. We introduce a self-consistent formulation that enables us to address the setting of constant applied electric field ensembles that transforms the nonlocal interactions into a PDE constraint corresponding to the Gauss’ equation. We implement the model in a finite element method to compute the free energy, average density, and average polarization distribution at equilibrium. We use this to study the impact of dipole-dipole interactions on the equilibrium properties. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F21.00010: Self-healing and reconfigurable protein-based magnetic actuators Zenghao Zhang, Abdon Pena-Francesch Soft microrobots can achieve controlled motion and shape changing upon actuation, and thus are capable of performing non-invasive surgery in the human body. Among soft actuation systems, magnetic actuation is advantageous for healthcare applications since magnetic fields can penetrate tissue, and can generate both pulling forces and torques remotely. One current challenge is that magnetic microrobots typically have limited actuation modes, which are determined by the actuation field and the internal magnetization profile of the robot. In this study, we developed a magnetic soft composite based on squid-derived proteins and rare-earth magnetic particles with discrete magnetization profiles, and used self-healing to reconfigure their magnetization and actuation modes. The self-healing properties of the squid-derived protein matrix enables the rearrangement of modular components with different magnetic properties. By tailoring the composition, the anisotropy of the thermo-mechanical properties, the geometrical robot design, and the actuation magnetic field, we demonstrate control over complex robot deformations, and reversible reconfiguration of actuation modes. This work opens up the design space of magnetic soft robots and their reconfigurable actuation modes via the discrete programming of the magnetization directions and intensities throughout the microrobot body. This freedom in design can provide key advantages in soft and small-scale actuation to perform specific tasks in confined environments, with application in healthcare and industrial micromanipulation. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F21.00011: Particle-resolved description of a soft magnetoelastic actuator Lukas Fischer, Andreas M Menzel Soft magnetoactive elastomers contain magnetic or magnetizable particles in a soft elastic matrix. They react to external magnetic fields by changes in their overall rheological properties (magnetorheological effect) and by overall deformation (magnetostriction). |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F21.00012: Physically cross-linked healable zwitterionic hydrogel for soft robotics Negin Bouzari, Rasool Nasseri, Natalie P Pinchin, Tizazu Mekonnen, Hamed Shahsavan Self-Healing, anti-fouling, and biocompatible hydrogels are highly desirable for soft robotics. The self-healing of chemically cross-linked hydrogels requires external energy or guest molecules to facilitate the reformation of dynamic covalent bonds. It can adversely affect the functionality of micro-robots or impose undesirable limitations on their real-world medical applications. This project aims to introduce a bio-compatible, anti-fouling, physically cross-linked hydrogel that shows inherent self-healing properties by incorporating a zwitterionic component into the hydrogel. Our system is based on random copolymers of sulfobetaine (SB) and acrylic acid (AA). The electrostatic interactions between the positively and negatively charged sections of the SB monomers and the intra- and inter-molecular hydrogen bonds present in the network provide the hydrogel with self-healing properties. We have also employed cellulose nanocrystal (CNC) to enhance the mechanical properties of the hydrogel without compromising its healing efficiency. The system demonstrates a self-healing ability that is independent of the duration the segments are separated before healing. |
Tuesday, March 15, 2022 10:48AM - 11:00AM |
F21.00013: Macromolecular Radical Networks as a Novel Magnetic Material Leah Marks, Abdon Pena-Francesch The corrosion, toxicity, and sustainability concerns that beset traditional magnetic materials containing heavy metals and rare-earth elements may be abated through replacement with petroleum-derived organic radicals. Previous work has investigated doping polymer gel networks with an organic radical solution to induce a paramagnetic response in lieu of metals. However, this system proved vulnerable to rapid solution leeching and a corresponding loss of magnetic properties. To facilitate a prolonged retention of organic radicals, we have alternatively developed intrinsically magnetic polymer gels that can yield nitroxide radicals upon oxidation. This project specifically looks at networks of TMPM monomers (a TEMPO methacrylate precursor) connected by common difunctional crosslinkers such as EGDMA, bisacrylamide, bisphenol A, and PEGDA. |
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