Soft Materials for Soft Actuators
Inspired by living organisms, soft material robotics hold great promise for areas where robots need to contact and interact with humans, such as manufacturing and healthcare. Unlike rigid robots, soft robots can replicate natural motion—grasping and manipulation—to provide medical and other types of assistance, perform delicate tasks, or pick up soft objects.
To achieve an actuator with high strain and high stress coupled with low density, lead author of the study Aslan Miriyev, a postdoctoral researcher in the Creative Machines lab, used a silicone rubber matrix with ethanol distributed throughout in micro-bubbles. The solution combined the elastic properties and extreme volume change attributes of other material systems while also being easy to fabricate, low cost, and made of environmentally safe materials.
After being 3D-printed into the desired shape, the artificial muscle was electrically actuated using a thin resistive wire and low-power (8V). It was tested in a variety of robotic applications where it showed significant expansion-contraction ability, being capable of expansion up to 900% when electrically heated to 80°C. Via computer controls, the autonomous unit is capable of performing motion tasks in almost any design.
“Our soft functional material may serve as robust soft muscle, possibly revolutionizing the way that soft robotic solutions are engineered today,” said Miriyev. “It can push, pull, bend, twist, and lift weight. It’s the closest artificial material equivalent we have to a natural muscle.”
The researchers will continue to build on this development, incorporating conductive materials to replace the embedded wire, accelerating the muscle’s response time and increasing its shelf life. Long-term, they will involve artificial intelligence to learn to control the muscle, which may be a last milestone towards replicating natural motion.
About the Study
Journal: Nature Communications
Title: Soft Material for Soft Actuators
Authors: Aslan Miriyev, Kenneth Stack & Hod Lipson
The study was funded by Columbia University and an Israeli Ministry of Defense (IMoD) grant for 3D-printed robotics.
COI: The authors declare no financial or other conflicts of interest.
Columbia Engineering
Columbia Engineering is one of the top engineering schools in the U.S. and one of the oldest in the nation. Based in New York City, the School offers programs to both undergraduate and graduate students who undertake a course of study leading to the bachelor's, master's, or doctoral degree in engineering and applied science. Columbia Engineering’s nine departments offer 16 majors and more than 30 minors in engineering and the liberal arts, including an interdisciplinary minor in entrepreneurship with Columbia Business School. With facilities specifically designed and equipped to meet the laboratory and research needs of faculty and students, Columbia Engineering is home to a broad array of basic and advanced research initiatives, from the Columbia Nano Initiative to the Columbia Genome Center. These interdisciplinary centers in science and engineering, big data, nanoscience, and genomic research are leading the way in their respective fields while our engineers and scientists collaborate across the University to solve theoretical and practical problems in many other significant areas.
Making Paints Whiter and Cooler
Passive daytime radiative cooling (PDRC) involves simultaneously reflecting sunlight and radiating heat into the cold sky to achieve a net heat loss. The process, which is spontaneous, can cool down structures to sub-ambient temperatures.
The team—Yuan Yang, assistant professor of materials science and engineering; Nanfang Yu, associate professor of applied physics; and Jyotirmoy Mandal, lead author of the study and a doctoral student in Yang’s group (all department of applied physics and applied mathematics)—built upon earlier work that demonstrated that simple plastics and polymers, including acrylic, silicone, and PET, are excellent heat radiators and could be used for PDRC. The challenges were how to get these normally transparent polymers to reflect sunlight without using silver mirrors as reflectors and how to make them easily deployable.
They decided to use phase-inversion because it is a simple, solution-based method for making light-scattering air-voids in polymers. Polymers and solvents are already used in paints, and the Columbia Engineering method essentially replaces the pigments in white paint with air voids that reflect all wavelengths of sunlight, from UV to infrared.
“This simple but fundamental modification yields exceptional reflectance and emittance that equal or surpass those of state-of-the-art PDRC designs, but with a convenience that is almost paint-like,” says Mandal.
The researchers found their polymer coating’s high solar reflectance (R > 96%) and high thermal emittance (Ɛ ~ 97%) kept it significantly cooler than its environment under widely different skies, e.g. by 6˚C in the warm, arid desert in Arizona and 3˚C in the foggy, tropical environment of Bangladesh. “The fact that cooling is achieved in both desert and tropical climates, without any thermal protection or shielding, demonstrates the utility of our design wherever cooling is required,” Yang notes.
The team also created colored polymer coatings with cooling capabilities by adding dyes. “Achieving a superior balance between color and cooling performance over current paints is one of the most important aspects of our work,” Yu notes. “For exterior coatings, the choice of color is often subjective, and paint manufacturers have been trying to make colored coatings, like those for roofs, for decades.”
The group took environmental and operational issues, such as recyclability, bio-compatibility, and high-temperature operability, into consideration, and showed that their technique can be generalized to a range of polymers to achieve these functionalities. “Polymers are an amazingly diverse class of materials, and because this technique is generic, additional desirable properties can be conveniently integrated into our PDRC coatings, if suitable polymers are available,” Mandal adds.
“Nature offers many ways for heating and cooling, some of which are extremely well known and widely studied and others that are poorly known. Radiative cooling—by using the sky as a heat sink—belongs to the latter group, and its potential has been strangely overlooked by materials scientists until a few years ago,” says Uppsala University Physics Professor Claes-Göran Granqvist, a pioneer in the field of radiative cooling, who was not involved with the study. “The publication by Mandal et al. highlights the importance of radiative cooling and represents an important breakthrough by demonstrating that hierarchically porous polymer coatings, which can be prepared cheaply and conveniently, give excellent cooling even in full sunlight.”
Yang, Yu, and Mandal are refining their design in terms of applicability, while exploring possibilities such as the use of completely biocompatible polymers and solvents. They are in talks with industry about next steps.
“Now is a critical time to develop promising solutions for sustainable humanity,” Yang notes. “This year, we witnessed heat waves and record-breaking temperatures in North America, Europe, Asia, and Australia. It is essential that we find solutions to this climate challenge, and we are very excited to be working on this new technology that addresses it.”
Yu adds that he used to think that white was the most unattainable color: “When I studied watercolor painting years ago, white paints were the most expensive. Cremnitz white or lead white was the choice of great masters, including Rembrandt and Lucian Freud. We have now demonstrated that white is in fact the most achievable color. It can be made using nothing more than properly sized air voids embedded in a transparent medium. Air voids are what make snow white and Saharan silver ants silvery.”
About the Study
Journal: Science
Title: Hierarchically Porous Polymer Coatings for Highly Efficient Passive Daytime Radiative Cooling
Authors: J. Mandal*, Y. Fu*, A. Overvig*, M. Jia**, K. Sun*, N. Shi*, H. Zhou***, X. Xiao***, N. Yu*, Y. Yang*
Affiliations: *Department of Applied Physics and Applied Mathematics, Columbia Engineering. **Department of Mechanical Engineering, Columbia Engineering ***Advanced Photon Source, Argonne National Laboratory, Lemony, IL 60439, USA
The study was supported by startup funding from Columbia University, the NSF MRSEC program through Columbia University’s Center for Precision Assembly of Superstratic and Superatomic Solids (Y.Y. DMR-1420634), AFOSR MURI (Multidisciplinary University Research Initiative) program (N.Y. grant # FA9550-14-1-0389), AFOSR DURIP (Defense University Research Instrumentation Program) (N.Y. grant # FA9550-16-1-0322), and the National Science Foundation (N.Y. grant # ECCS-1307948). A.C.O. acknowledges support from the NSF IGERT program (# DGE-1069240). We acknowledge support from the Advanced Photon Source in Argonne National Laboratory (under Contract No. DE-AC02-06CH11357) and the Brookhaven National Laboratory (under Contract No. DE-AC02-98CH10886.)
COI: The authors have no competing interests. The authors have filed a provisional patent application with Columbia Technology Ventures for this study.
Columbia Engineering
Columbia Engineering, based in New York City, is one of the top engineering schools in the U.S. and one of the oldest in the nation. Also known as The Fu Foundation School of Engineering and Applied Science, the School expands knowledge and advances technology through the pioneering research of its more than 250 faculty, while educating undergraduate and graduate students in a collaborative environment to become leaders informed by a firm foundation in engineering. The School’s faculty are at the center of the University’s cross-disciplinary research, contributing to the Data Science Institute, Earth Institute, Zuckerman Mind Brain Behavior Institute, Precision Medicine Initiative, and the Columbia Nano Initiative. Guided by its strategic vision, “Columbia Engineering for Humanity,” the School aims to translate ideas into innovations that foster a sustainable, healthy, secure, connected, and creative humanity.
Seated Postural and Reaching Control Training with the Trunk Support Trainer (TruST)
“We wanted to scientifically demonstrate how robotic TruST can be used to deliver an intense activity-based postural and reaching training to improve the functional sitting abilities of children with CP and trunk control problems”, says Victor Santamaria, a physical therapist and associate researcher scientist in Agrawal’s Robotics and Rehabilitation Laboratory, and first author of the paper.
Recent developments in robotic equipment have enabled clinicians to address engagement, repetition, and intensity for their patients to practice task-oriented movements in CP. A team led by Agrawal, together with other researchers at Teacher’s College and the Columbia University Irving Medical Center, recently won a five-year National Institutes of Health R01 award (#1R01 HD101903-01) to conduct a randomized clinical trial.
The project—"Improving seated postural control and upper extremity function in bilateral CP with a robotic Trunk-Support-Trainer (TruST)"—will involve up to 80 children with poor trunk control. Some will use the TruST robotic rehabilitation while others will try conventional rehabilitation. This new NIH study will compare the efficacy of the motorized TruST to engage children in play-oriented practice while advancing their skill progression with static trunk support.
“Our new NIH project is a randomized clinical trial with a large sample size to study the efficacy of TruST-intervention as a unique therapeutic solution to promote seated functional abilities in children with bilateral CP,” Agrawal adds.
About the Study
Journal: IEEE Transactions of Neural Systems and Rehabilitation Engineering
Title: Promoting Functional and Independent Sitting in Children with Cerebral Palsy Using the Robotic Trunk Support Trainer
Authors: Victor Santamaria, Moiz Khan, Tatiana Luna, Jiyeon Kang, Joseph Dutkowsky, Andrew Gordon, and Sunil Agrawal, Department of Mechanical Engineering, Columbia Engineering.
The pilot study was partially funded by the Langer Foundation as administered by The Order of Malta.
COI: The authors declare no financial or other conflicts of interest.
Columbia Engineering
Columbia Engineering, based in New York City, is one of the top engineering schools in the U.S. and one of the oldest in the nation. Also known as The Fu Foundation School of Engineering and Applied Science, the School expands knowledge and advances technology through the pioneering research of its more than 220 faculty, while educating undergraduate and graduate students in a collaborative environment to become leaders informed by a firm foundation in engineering. The School’s faculty are at the center of the University’s cross-disciplinary research, contributing to the Data Science Institute, Earth Institute, Zuckerman Mind Brain Behavior Institute, Precision Medicine Initiative, and the Columbia Nano Initiative. Guided by its strategic vision, “Columbia Engineering for Humanity,” the School aims to translate ideas into innovations that foster a sustainable, healthy, secure, connected, and creative humanity.
Header image: Trunk Support Trainer (TruST).
Thermal camera and visible photos of a hickory hairstreak
Thermal camera and visible photos of a hickory hairstreak (Satyrium caryaevorus) basking in the sun. Because of their small thermal capacity, the wings can overheat rapidly.
New York, NY—January 28, 2020—A new study from Columbia Engineering and Harvard University identified the critical physiological importance of suitable temperatures for butterfly wings to function properly, and discovered that the insects exquisitely regulate their wing temperatures through both structural and behavioral adaptations.
Contrary to common belief that butterfly wings consist primarily of lifeless membranes, the new study demonstrated that they contain a network of living cells whose function requires a constrained range of temperatures for optimal performance. Given their small thermal capacity, wings can overheat rapidly in the sun when butterflies cease flight, and they can cool down too much during flight in a cold environment. The study, published online today by Nature Communications, is the first to explore the implications of temperature in shaping the wing structure and behavior of butterflies.
Beat the Heat in the Living Wings of Butterflies
Video on new study from Columbia engineers and Harvard biologists who have found that butterflies have specialized behaviors and wing scales to protect the living parts of their wings; nanostructures found in the wing scales could inspire the design of radiative-cooling materials to help manage excessive heat conditions; sensory network in the wings could inspire the design of advanced flying machines.
“Butterfly wings are essentially vector light-detecting panels by which butterflies can accurately determine the intensity and direction of sunlight, and do this swiftly without using their eyes,” says Nanfang Yu, associate professor of applied physics at Columbia Engineering and co-PI of the study.
The team, which was co-led by Naomi E. Pierce, Hessel Professor of Biology in the department of organismic and evolutionary biology, and Curator of Lepidoptera at the Museum of Comparative Zoology, Harvard, used their expertise in biology and optics to make a number of significant discoveries. By carefully removing the wing scales to enable them to peer into the interior of the wings, and by staining the neurons found within the wing, they found that butterfly wings are loaded with a network of mechanical and temperature sensors. The living tissues in the wings are actively supplied by circulatory and tracheal systems throughout the adult lifetime—in the case of painted lady butterflies, for more than three weeks.
They also discovered a “wing heart” that beats a few dozen times per minute to facilitate the directional flow of insect blood, or hemolymph, through a “scent pad” or an androconial organ located on the wings of some species of butterflies.
“Most of the research on butterfly wings has focused on colors used in signaling between individuals,” says Pierce. “This work shows that we should reconceptualize the butterfly wing as a dynamic, living structure rather than as a relatively inert membrane. Patterns observed on the wing may also be shaped in important ways by the need to modulate temperatures of living parts of the wing.”
Yu’s lab designed a noninvasive technique based on infrared hyperspectral imaging, with each pixel of an image representing one infrared spectrum, that enabled them to make—for the first time—accurate measurements of the temperature distributions over butterfly wings. “This has been difficult to do until now,” Pierce notes, “because of the thinness and delicacy of butterfly wings.”
“This imaging technique enables us to examine physical adaptations that decouple the wing’s visible appearance from its thermodynamic properties,” Yu adds. “We discovered that diverse scale nanostructures and non-uniform cuticle thicknesses create a heterogeneous distribution of radiative cooling—heat dissipation through thermal radiation—that selectively reduces the temperature of living structures such as wing veins and scent pads.”
The effect of this regional and selective enhancement of thermal radiation was amply demonstrated in the team’s thermodynamic experiments on butterfly wings. Experimental conditions that mimic the butterflies’ natural environment were created in Yu’s lab, and allowed the researchers to quantify the relative contributions of several environmental factors to the wing temperature. These included the intensity of sunlight, the temperature of the terrestrial environment, and the “coldness” of the sky, which can serve as an efficient heat sink of thermal radiation from heated wings. The team found that in all simulated environmental conditions, despite diverse visible colors and patterns, the areas of butterfly wings that contain live cells (wing veins and scent pads) are always cooler than the “lifeless” regions of the wing due to enhanced radiative cooling.
“The nanostructures found in the wing scales could inspire the design of radiative-cooling materials to cope with excessive heat conditions,” says Cheng-Chia Tsai, a PhD student in Yu’s group who was lead author of the study.
The researchers conducted a series of behavioral studies of living butterflies from six of the seven recognized butterfly families, to investigate responses to simulated sunlight applied to the wings. The team discovered that the insects use their wings to sense the direction and intensity of sunlight—the main source of warmth or overheating—and to respond with specialized behaviors to prevent overheating or overcooling of their wings. For example, all species studied exhibited a relatively constant “trigger” temperature of approximately 40oC (104oF), turning within a few seconds to avoid overheating of wings from a small light spot shone upon them.
Yu and Pierce are now conducting a large-scale systematic optical study of the lepidopteran collections in Harvard’s Museum of Comparative Zoology. These include thousands of individual specimens of hundreds of butterfly species across the entire phylogenetic tree, each specimen with full hyperspectral imaging data taken from the ultraviolet to the mid-infrared.
In 1863, Henry Walter Bates, an English naturalist and explorer, wrote about butterfly wings in his book The Naturalist on the River Amazons, “On these expanded membranes Nature writes, as on a tablet, the story of the modifications of species …” Just like deciphering enigmatic symbols on a tablet, the team hopes to gain a comprehensive understanding of the wing coloration and pattern, which are the results of many (and often conflicting) biological and physical factors: sexual selection, warning coloration, mimicry, camouflage, and thermoregulation.
“Each wing of a butterfly is equipped with a few dozen mechanical sensors that provide real-time feedback to enable complex flying patterns,” Yu says. “This is an inspiration for designing the wings of flying machines: perhaps wing design should not be solely based on considerations of flight dynamics, and wings designed as an integrated sensory-mechanical system could enable flying machines to perform better in complex aerodynamic conditions.”
About the Study
Journal: Nature Communications
Title: Physical and Behavioral Adaptations to Prevent Overheating of the Living Wings of Butterflies
Authors: Cheng-Chia Tsai 1; Richard A. Childers 2; Norman Nan Shi 1§; Crystal Ren 1; Julianne N. Pelaez 2†; Gary D. Bernard 3; Naomi E. Pierce 2, 4; and Nanfang Yu 1.
- Department of Applied Physics and Applied Mathematics, Columbia Engineering
- Department of Organismic and Evolutionary Biology, Harvard University
- Department of Electrical Engineering, University of Washington
- Museum of Comparative Zoology, Harvard University
† Currently at Department of Integrative Biology, University of California, Berkeley
§ Currently at Western Digital
The study was supported by the National Science Foundation (no. PHY-1411445 awarded to N. Yu and N. Pierce, no. DEB-0447242 awarded to N. Pierce), and the Air Force Office of Scientific Research (no. FA9550-14-1-0389 through the Multidisciplinary University Research Initiative program and no. FA9550-16-1-0322 through the Defense University Research Instrumentation Program awarded to N. Yu). R. A. Childers was supported by the Graduate Research Fellowship Program of the National Science Foundation. Measurements were carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-SC0012704.
COI: The authors declare no competing interests.
Columbia Engineering
Columbia Engineering, based in New York City, is one of the top engineering schools in the U.S. and one of the oldest in the nation. Also known as The Fu Foundation School of Engineering and Applied Science, the School expands knowledge and advances technology through the pioneering research of its more than 220 faculty, while educating undergraduate and graduate students in a collaborative environment to become leaders informed by a firm foundation in engineering. The School’s faculty are at the center of the University’s cross-disciplinary research, contributing to the Data Science Institute, Earth Institute, Zuckerman Mind Brain Behavior Institute, Precision Medicine Initiative, and the Columbia Nano Initiative. Guided by its strategic vision, “Columbia Engineering for Humanity,” the School aims to translate ideas into innovations that foster a sustainable, healthy, secure, connected, and creative humanity.
ABOUT THE STUDY
Journal: IEEE Open Journal of Engineering in Medicine and Biology
Authors: Youngbin Kim, Kunlun Wang, Roberta I. Lock, Trevor R. Nash, Sharon Fleischer, Bryan Z. Wang, and Gordana Vunjak-Novakovic, Department of Biomedical Engineering, Columbia Engineering; and Barry M. Fine, Department of Medicine, Division of Cardiology, Columbia University Medical Center.
FUNDING: The work of Gordana Vunjak-Novakovic was supported by the National Institutes of Health under Grants P41 EB027062 and 5R01HL076485-15, in part by the National Science Foundation under Grant NSF1647837, and in part by National Aeronautics and Space Administration under Grant NNX16AO69A. The work of Barry M. Fine was supported in part by the National Institutes of Health under Grant R01HL166387 and in part by Abramova Foundation.
The authors declare no financial or other conflicts of interest.
Human-Robot Facial Co-expression
Go inside the Creative Machines Lab to watch Emo's facial co-expression. Video Credit: Yuhang Hu, Columbia Engineering
What’s next
The researchers are now working to integrate verbal communication, using a large language model like ChatGPT into Emo. As robots become more capable of behaving like humans, Lipson is well aware of the ethical considerations associated with this new technology.
“Although this capability heralds a plethora of positive applications, ranging from home assistants to educational aids, it is incumbent upon developers and users to exercise prudence and ethical considerations,” says Lipson, James and Sally Scapa Professor of Innovation in the Department of Mechanical Engineering at Columbia Engineering, co-director of the Makerspace at Columbia, and a member of the Data Science Institute. “But it’s also very exciting -- by advancing robots that can interpret and mimic human expressions accurately, we're moving closer to a future where robots can seamlessly integrate into our daily lives, offering companionship, assistance, and even empathy. Imagine a world where interacting with a robot feels as natural and comfortable as talking to a friend.”
About the Study
Journal: Science Robotics
Title: “Human-Robot Facial Co-expression”
Authors: Yuhang Hu (1); Boyuan Chen (2, 3, 4); Jiong Lin (1); Yunzhe Wang (5); Yingke Wang (5); Cameron Mehlman (1); and Hod Lipson (1, 6)
- Creative Machines Laboratory, Mechanical Engineering Department, Columbia University,
- Mechanical Engineering and Materials Department, Duke University
- Electrical and Computer Engineering Department, Duke University
- Computer Science Department, Duke University
- Computer Science Department, Columbia University
- Data Science Institute, Columbia University
Funding: The study was supported by the National Science Foundation AI Institute for Dynamical Systems (DynamicsAI.org ) grant 2112085, and an Amazon grant through the Columbia Center of AI Technology (CAIT).
COI: The authors declare that they have no competing interests.