Tag Archives: Michael Bartlett

A robot that morphs from a ground vehicle to an air vehicle using liquid metal

This video starts slow but the part where the robot morphs is pretty good stuff,

A February 9, 2022 news item on ScienceDaily announces a new approach to shape-changing materials,

Imagine a small autonomous vehicle that could drive over land, stop, and flatten itself into a quadcopter. The rotors start spinning, and the vehicle flies away. Looking at it more closely, what do you think you would see? What mechanisms have caused it to morph from a land vehicle into a flying quadcopter? You might imagine gears and belts, perhaps a series of tiny servo motors that pulled all its pieces into place.

If this mechanism was designed by a team at Virginia Tech led by Michael Bartlett, assistant professor in mechanical engineering, you would see a new approach for shape changing at the material level. These researchers use rubber, metal, and temperature to morph materials and fix them into place with no motors or pulleys. The team’s work has been published in Science Robotics. Co-authors of the paper include graduate students Dohgyu Hwang and Edward J. Barron III and postdoctoral researcher A. B. M. Tahidul Haque.

A February 9, 2022 Virginia Tech news release (also on EurekAlert) by Alex Parrish, which originated the news item, provides more detail,

Getting into shape

Nature is rich with organisms that change shape to perform different functions. The octopus dramatically reshapes to move, eat, and interact with its environment; humans flex muscles to support loads and hold shape; and plants move to capture sunlight throughout the day. How do you create a material that achieves these functions to enable new types of multifunctional, morphing robots?

“When we started the project, we wanted a material that could do three things: change shape, hold that shape, and then return to the original configuration, and to do this over many cycles,” said Bartlett. “One of the challenges was to create a material that was soft enough to dramatically change shape, yet rigid enough to create adaptable machines that can perform different functions.”

To create a structure that could be morphed, the team turned to kirigami, the Japanese art of making shapes out of paper by cutting. (This  method differs from origami, which uses folding.) By observing the strength of those kirigami patterns in rubbers and composites, the team was able to create a material architecture of a repeating geometric pattern.

Next, they needed a material that would hold shape but allow for that shape to be erased on demand. Here they introduced an endoskeleton made of a low melting point alloy (LMPA) embedded inside a rubber skin. Normally, when a metal is stretched too far, the metal becomes permanently bent, cracked, or stretched into a fixed, unusable shape. However, with this special metal embedded in rubber, the researchers turned this typical failure mechanism into a strength. When stretched, this composite would now hold a desired shape rapidly, perfect for soft morphing materials that can become instantly load bearing.

Finally, the material had to return the structure back to its original shape. Here, the team incorporated soft, tendril-like heaters next to the LMPA mesh. The heaters cause the metal to be converted to a liquid at 60 degrees Celsius (140 degrees Fahrenheit), or 10 percent of the melting temperature of aluminum. The elastomer skin keeps the melted metal contained and in place, and then pulls the material back into the original shape, reversing the stretching, giving the composite what the researchers call “reversible plasticity.” After the metal cools, it again contributes to holding the structure’s shape.

“These composites have a metal endoskeleton embedded into a rubber with soft heaters, where the kirigami-inspired cuts define an array of metal beams. These cuts combined with the unique properties of the materials were really important to morph, fix into shape rapidly, then return to the original shape,” Hwang said.

The researchers found that this kirigami-inspired composite design could create complex shapes, from cylinders to balls to the bumpy shape of the bottom of a pepper. Shape change could also be achieved quickly: After impact with a ball, the shape changed and fixed into place in less than 1/10 of a second. Also, if the material broke, it could be healed multiple times by melting and reforming the metal endoskeleton.

One drone for land and air, one for sea

The applications for this technology are only starting to unfold. By combining this material with onboard power, control, and motors, the team created a functional drone that autonomously morphs from a ground to air vehicle. The team also created a small, deployable submarine, using the morphing and returning of the material to retrieve objects from an aquarium by scraping the belly of the sub along the bottom.

“We’re excited about the opportunities this material presents for multifunctional robots. These composites are strong enough to withstand the forces from motors or propulsion systems, yet can readily shape morph, which allows machines to adapt to their environment,” said Barron.

Looking forward, the researchers envision the morphing composites playing a role in the emerging field of soft robotics to create machines that can perform diverse functions, self-heal after being damaged to increase resilience, and spur different ideas in human-machine interfaces and wearable devices.

Here’s link to and a citation for the paper,

Shape morphing mechanical metamaterials through reversible plasticity by Dohgyu Hwang, Edward J. Barron III, A. B. M. Tahidul Haque and Michael D. Bartlett. Science Robotics • 9 Feb 2022 • Vol 7, Issue 63 • DOI: 10.1126/scirobotics.abg2171

This paper is behind a paywall.

From flubber to thubber

Flubber (flying rubber) is an imaginary material that provided a plot point for two Disney science fiction comedies, The Absent-Minded Professor in 1961 which was remade in 1997 as Flubber. By contrast, ‘thubber’ (thermally conductive rubber) is a real life new material developed at Carnegie Mellon University (US).

A Feb. 13, 2017 news item on phys.org makes the announcement (Note: A link has been removed),

Carmel Majidi and Jonathan Malen of Carnegie Mellon University have developed a thermally conductive rubber material that represents a breakthrough for creating soft, stretchable machines and electronics. The findings were published in Proceedings of the National Academy of Sciences this week.

The new material, nicknamed “thubber,” is an electrically insulating composite that exhibits an unprecedented combination of metal-like thermal conductivity, elasticity similar to soft, biological tissue, and can stretch over six times its initial length.

A Feb.13, 2017 Carnegie Mellon University news release (also on EurekAlert), which originated the news item, provides more detail (Note A link has been removed),

“Our combination of high thermal conductivity and elasticity is especially critical for rapid heat dissipation in applications such as wearable computing and soft robotics, which require mechanical compliance and stretchable functionality,” said Majidi, an associate professor of mechanical engineering.

Applications could extend to industries like athletic wear and sports medicine—think of lighted clothing for runners and heated garments for injury therapy. Advanced manufacturing, energy, and transportation are other areas where stretchable electronic material could have an impact.

“Until now, high power devices have had to be affixed to rigid, inflexible mounts that were the only technology able to dissipate heat efficiently,” said Malen, an associate professor of mechanical engineering. “Now, we can create stretchable mounts for LED lights or computer processors that enable high performance without overheating in applications that demand flexibility, such as light-up fabrics and iPads that fold into your wallet.”

The key ingredient in “thubber” is a suspension of non-toxic, liquid metal microdroplets. The liquid state allows the metal to deform with the surrounding rubber at room temperature. When the rubber is pre-stretched, the droplets form elongated pathways that are efficient for heat travel. Despite the amount of metal, the material is also electrically insulating.

To demonstrate these findings, the team mounted an LED light onto a strip of the material to create a safety lamp worn around a jogger’s leg. The “thubber” dissipated the heat from the LED, which would have otherwise burned the jogger. The researchers also created a soft robotic fish that swims with a “thubber” tail, without using conventional motors or gears.

“As the field of flexible electronics grows, there will be a greater need for materials like ours,” said Majidi. “We can also see it used for artificial muscles that power bio-inspired robots.”

Majidi and Malen acknowledge the efforts of lead authors Michael Bartlett, Navid Kazem, and Matthew Powell-Palm in performing this multidisciplinary work. They also acknowledge funding from the Air Force, NASA, and the Army Research Office.

Here’s a link to and a citation for the paper,

High thermal conductivity in soft elastomers with elongated liquid metal inclusions by Michael D. Bartlett, Navid Kazem, Matthew J. Powell-Palm, Xiaonan Huang, Wenhuan Sun, Jonathan A. Malen, and Carmel Majidi.  Proceedings of the National Academy of Sciences of the United States of America (PNAS, Proceedings of the National Academy of Sciences) doi: 10.1073/pnas.1616377114

This paper is open access.

Geckskin and Z-Man

Z-Man or do I mean SpiderMan? They used to make reference to SpiderMan and/or geckos when there was some research breakthrough or other concerning adhesion (specifically, bioadhesion) but these days, it’s all geckos, all the time.

I’m going to start with the first announcement from the research team at the University of Massachusetts at Amherst, from the Feb. 17, 2012 news item on Nanowerk,

For years, biologists have been amazed by the power of gecko feet, which let these 5-ounce lizards produce an adhesive force roughly equivalent to carrying nine pounds up a wall without slipping. Now, a team of polymer scientists and a biologist at the University of Massachusetts Amherst have discovered exactly how the gecko does it, leading them to invent “Geckskin,” a device that can hold 700 pounds on a smooth wall. Doctoral candidate Michael Bartlett in Alfred Crosby’s polymer science and engineering lab at UMass Amherst is the lead author of their article describing the discovery in the current online issue of Advanced Materials (“Looking Beyond Fibrillar Features to Scale Gecko-Like Adhesion”). The group includes biologist Duncan Irschick, a functional morphologist who has studied the gecko’s climbing and clinging abilities for over 20 years. Geckos are equally at home on vertical, slanted, even backward-tilting surfaces.

Here’s a picture illustrating the material’s strength,

A card-sized pad of Geckskin can firmly attach very heavy objects such as this 42-inch television weighing about 40 lbs. (18 kg) to a smooth vertical surface. The key innovation by Bartlett and colleagues was to create a soft pad woven into a stiff fabric that includes a synthetic tendon. Together these features allow the stiff yet flexible pad to “drape” over a surface to maximize contact. Photo courtesy of UMass Amherst

This image is meant as an illustration of what the product could do and not as a demonstration, i.e., the tv is not being held up by ‘geckskin’.

There are other research teams around the world working on ways to imitate the properties of gecko feet or bioadhesion (my Nov. 2, 2011 posting mentions some work on robots with ‘gecko feet’ at Simon Fraser University [Canada] and my March 19, 2012 posting mentions in passing some work being done at the University of Waterloo [Canada] are two recent examples).

The University of Massachusetts team’s innovation (from the Feb. 17, 2012 news item),

The key innovation by Bartlett and colleagues was to create an integrated adhesive with a soft pad woven into a stiff fabric, which allows the pad to “drape” over a surface to maximize contact. Further, as in natural gecko feet, the skin is woven into a synthetic “tendon,” yielding a design that plays a key role in maintaining stiffness and rotational freedom, the researchers explain.

Importantly, the Geckskin’s adhesive pad uses simple everyday materials such as polydimethylsiloxane (PDMS), which holds promise for developing an inexpensive, strong and durable dry adhesive.

The UMass Amherst researchers are continuing to improve their Geckskin design by drawing on lessons from the evolution of gecko feet, which show remarkable variation in anatomy. “Our design for Geckskin shows the true integrative power of evolution for inspiring synthetic design that can ultimately aid humans in many ways,” says Irschick.

The research at the University of Massachusetts is being funded, in part, by DARPA (US Defense Advanced Research Projects Agency) through its Z-man program. From the March 2, 2012 news item on Nanowerk,

“Geckskin” is one output of the Z-Man program. It is a synthetically-fabricated reversible adhesive inspired by the gecko’s ability to climb surfaces of various materials and roughness, including smooth surfaces like glass. Performers on Z-Man designed adhesive pads to mimic the gecko foot over multiple length scales, from the macroscopic foot tendons to the microscopic setae and spatulae, to maximize reversible van der Waals interactions with the surface.

Here’s the reasoning for the Z-Man program, from the March 2, 2012 news item,

The Defense Advanced Research Projects Agency (DARPA)’s “Z-Man program” aims to develop biologically inspired climbing aids to enable soldiers to scale vertical walls constructed from typical building materials, while carrying a full combat load, and without the use of ropes or ladders.

Soldiers operate in all manner of environments, including tight urban terrain. Their safety and effectiveness demand maximum flexibility for maneuvering and responding to circumstances. To overcome obstacles and secure entrance and egress routes, soldiers frequently rely on ropes, ladders and related climbing tools. Such climbing tools cost valuable time to use, have limited application and add to the load warfighters are forced to carry during missions.

The Z-Man program provides more information, as well as, images here, where you will find this image, which is not as pretty as the one with the tv screen but this one is a demonstration,

A proof-of-concept demonstration of a 16-square-inch sheet of Geckskin adhering to a vertical glass wall while supporting a static load of up to 660 pounds. (from the Z-Man Program website)

In the very latest news, the University of Massachusetts team has won international funding for its (and Cambridge University’s) work on bioadhesion. From the University of Massachusetts at Amherst March 28, 2012 [news release],

Duncan Irschick, Biology, and Al Crosby, Polymer Science and Engineering, with Walter Federle of Cambridge University, have been awarded a three-year, $900,000 grant from the Human Frontiers Science Program (HFSP) in Strasbourg, France, to study bioadhesion in geckos and insects.

Theirs was one of only 25 teams from among approximately 800 to apply worldwide. HFSP is a global organization that funds research at the frontiers of the life sciences.

Crosby, Irschick and colleagues received international scientific and media attention over the past several weeks for their discovery reported in the journal Advanced Materials, of how gecko feet and skin produce an adhesive force roughly equivalent to the 5-ounce animal carrying nine pounds up a wall without slipping. This led them to invent “Geckskin,” a device that can hold 700 pounds on a smooth wall. Irschick, a functional morphologist who has studied the gecko’s climbing and clinging abilities for over 20 years, says the lizards are equally at home on vertical, slanted and even backward-tilting surfaces.

Not having heard of the Human Science Frontier Program (HSFP) previously, I was moved to investigate further. From the About Us page,

The Human Frontier Science Program is a program of funding for frontier research in the life sciences. It is implemented by the International Human Frontier Science Program Organization (HFSPO) with its office in Strasbourg.

The members of the HFSPO, the so-called Management Supporting Parties (MSPs) are the contributing countries and the European Union, which contributes on behalf of the non-G7 EU members.

The current MSPs are Australia, Canada, France, Germany, India, Italy, Japan, Republic of Korea, Norway, New Zealand, Switzerland the United Kingdom, the United States of America and the European Union.

I wonder how much impact all the publicity had on the funding decision. In any event, it’s good to find out about a new funding program and I wish anyone who applies the best of luck!