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This flat structure morphs into shape of a human face when temperature changes

This flat structure morphs into shape of a human face when temperature changes

Researchers at MIT and elsewhere have designed 3-D printed mesh-like structures that morph from flat layers into predetermined shapes, in response to changes in ambient temperature. The new structures can transform into configurations that are more complex than what other shape-shifting materials and structures can achieve.

As a demonstration, the researchers printed a flat mesh that, when exposed to a certain temperature difference, deforms into the shape of a human face. They also designed a mesh embedded with conductive liquid metal, that curves into a dome to form an active antenna, the resonance frequency of which changes as it deforms.

The team’s new design method can be used to determine the specific pattern of flat mesh structures to print, given the material’s properties, in order to make the structure transform into a desired shape.

The researchers say that down the road, their technique may be used to design deployable structures, such as tents or coverings that automatically unfurl and inflate in response to changes in temperature or other ambient conditions.

Such complex, shape-shifting structures could also be of use as stents or scaffolds for artificial tissue, or as deformable lenses in telescopes. Wim van Rees, assistant professor of mechanical engineering at MIT, also sees applications in soft robotics.

“I’d like to see this incorporated in, for example, a robotic jellyfish that changes shape to swim as we put it in water,” says van Rees. “If you could use this as an actuator, like an artificial muscle, the actuator could be any arbitrary shape that transforms into another arbitrary shape. Then you’re entering an entirely new design space in soft robotics.”

Van Rees and his colleagues are publishing their results this week in the Proceedings of the National Academy of Sciences. His co-authors are J. William Boley of Boston University; Ryan Truby, Arda Kotikian, Jennifer Lewis, and L. Mahadevan of Harvard University; Charles Lissandrello of Draper Laboratory; and Mark Horenstein of Boston University.

Gift wrap’s limit

Two years ago, van Rees came up with a theoretical design for how to transform a thin flat sheet into a complex shape such as a human face. Until then, researchers in the field of 4-D materials — materials designed to deform over time — had developed ways for certain materials to change, or morph, but only into relatively simple structures.

“My goal was to start with a complex 3-D shape that we want to achieve, like a human face, and then ask, ‘How do we program a material so it gets there?’” van Rees says. “That’s a problem of inverse design.”

He came up with a formula to compute the expansion and contraction that regions of a bilayer material sheet would have to achieve in order to reach a desired shape, and developed a code to simulate this in a theoretical material. He then put the formula to work, and visualized how the method could transform a flat, continuous disc into a complex human face.

But he and his collaborators quickly found that the method wouldn’t apply to most physical materials, at least if they were trying to work with continuous sheets. While van Rees used a continuous sheet for his simulations, it was of an idealized material, with no physical constraints on the amount of expansion and contraction it could achieve. Most materials, in contrast, have very limited growth capabilities. This limitation has profound consequences on a property known as double curvature, meaning a surface that can curve simultaneously in two perpendicular directions — an effect that is described in an almost 200-year-old theorem by Carl Friedrich Gauss called the Theorema Egregium, Latin for “Remarkable Theorem.”

If you’ve ever tried to gift wrap a soccer ball, you’ve experienced this concept in practice: To transform paper, which has no curvature at all, to the shape of a ball, which has positive double curvature, you have to crease and crumple the paper at the sides and bottom to completely wrap the ball. In other words, for the paper sheet to adapt to a shape with double curvature, it would have to stretch or contract, or both, in the necessary places to wrap a ball uniformly.

To impart double curvature to a shape-shifting sheet, the researchers switched the basis of the structure from a continuous sheet to a lattice, or mesh. The idea was twofold: first, a temperature-induced bending of the lattice’s ribs would result in much larger expansions and contractions of the mesh nodes, than could be achieved in a continuous sheet. Second, the voids in the lattice can easily accommodate large changes in surface area when the ribs are designed to grow at different rates across the sheet.

The researchers also designed each individual rib of the lattice to bend by a predetermined degree in order to create the shape of, say, a nose rather than an eye-socket.

For each rib, they incorporated four skinnier ribs, arranging two to line up atop the other two. All four miniribs were made from carefully selected variations of the same base material, to calibrate the required different responses to temperature.

When the four miniribs were bonded together in the printing process to form one larger rib, the rib as a whole could curve due to the difference in temperature response between the materials of the smaller ribs: If one material is more responsive to temperature, it may prefer to elongate. But because it is bonded to a less responsive rib, which resists the elongation, the whole rib will curve instead.

The researchers can play with the arrangement of the four ribs to “preprogram” whether the rib as a whole curves up to form part of a nose, or dips down as part of an eye socket.

Shapes unlocked

To fabricate a lattice that changes into the shape of a human face, the researchers started with a 3-D image of a face — to be specific, the face of Gauss, whose principles of geometry underly much of the team’s approach. From this image, they created a map of the distances a flat surface would require to rise up or dip down to conform to the shape of the face. Van Rees then devised an algorithm to translate these distances into a lattice with a specific pattern of ribs, and ratios of miniribs within each rib.

The team printed the lattice from PDMS, a common rubbery material which naturally expands when exposed to an increase in temperature. They adjusted the material’s temperature responsiveness by infusing one solution of it with glass fibers, making it physically stiffer and more resistant to a change in temperature. After printing lattice patterns of the material, they cured the lattice in a 250-degree-Celsius oven, then took it out and placed it in a saltwater bath, where it cooled to room temperature and morphed into the shape of a human face.

Courtesy of the researchers

The team also printed a latticed disc made from ribs embedded with a liquid metal ink — an antenna of sorts, that changed its resonant frequency as the lattice transformed into a dome.

Van Rees and his colleagues are currently investigating ways to apply the design of complex shape-shifting to stiffer materials, for sturdier applications, such as temperature-responsive tents and self-propelling fins and wings.

This research was supported, in part, by the National Science Foundation, and Draper Laboratory.

Materials provided by Massachusetts Institute of Technology

industrial robot

Danish designers envision autonomous 3D printing robots for fixing the environment

Three Danish companies, GXN Innovation, the research wing of 3XN; Map Architects and The Danish AM Hub, the additive manufacturer have collaborated to form an initiative named Break the Grid. According to Break the Grid, coastlines and buildings could be maintained by autonomous 3D printers that have the ability to fix problems. It has proposed that by making 3D printers which can move and act independently problems such as damaged infrastructures and erosion of coastlines can be tackled. The 3D printers are visioned to have the power to move across all three forms of physical communication, land, sea and air.

Kasper Jensen, GXN founder said that it could be a revolution if 3D printers would be “freed” for tackling the challenges. If 3D printing robots are made to crawl, fly and swim then environmental threats can be handled at much lower costs with increased efficiency.

For tackling three separate cases, the companies have developed three different concept designs. In all the situations, the environment is scanned autonomously by the robots and the problems are then identified for the implementation of solutions.

In one of the designs, the robot can move underwater and construct artificial reefs. This can protect the coastlines from erosion and also provide habitat to aquatic creatures. It would function by extruding a mixture of sand from the ocean floor and glue which is inspired by a natural adhesive produced by oysters. In the meantime, a six-legged robot would scan the cities for micro-cracks and repair them. By detecting them early, the damage could be fixed before water further creeps in causing corrosion.

The land-based robots are visioned to 3D print a porous filler with a mixture of Trichoderma reesei, promoting the formation of calcium carbonate which creates a self-healing material. It can also patrol the infrastructure in urban areas remotely.

Another concept is drones operated in the air which can detect the damages in old buildings and then swoop in to repair the damages. It is based on the research that thermal insulation can be built using a customized composite of polymers and glass. The team has already been working on modifying the existing 3D printers for building the prototypes.

Mads Kjøller Damkjær, CEO of Danish AM Hub said that new approaches to construction can be built using converging technologies. New possibilities can be visualized only by the change of current ways of thinking which needs a combination of technology and design. Recent 3D printing developments have involved a plan for the 3D printed village and a stage for dance performances built by ETH Zurich students.

The Bukobot Reprap 3D Printer

Graphene based ink that could be used for printing energy storage devices

Scientists have developed an ink based on graphene nanosheets and also demonstrated that this ink can be used for printing 3D structures. This ink based on graphene can be produced on a large scale at very low costs in an eco-friendly manner. This can result in the wide-scale development of a large variety of printable energy storage equipment.

The group of researchers led by Jingyu Sun and Zhongfan Liu from Soochow University and  Beijing Graphene Institute respectively have published a study on their work in ACS Nano journal.

Sun said that their work makes use of the green synthesis of graphene nanosheets that are nitrogen-doped on a salt template with the help of chemical vapour deposition. This gives the room for exploring derived inks in the field of printable energy storage in a greater way.

A major goal in the research of graphene is to make the production of graphene possible at a wide scale assuring both high quality and affordable costs. The production methods used so far resulted in a low quality of graphene with a high number of structural defects and chemical based impurities. Thus it has not been possible to prepare good quality graphene inks.

In this new technique, researchers have used NaCl crystals for growing nitrogen-doped graphene nanosheets with the help of chemical vapour deposition technique as a result of which nitrogen and carbon molecules diffuse on the surface of NaCl crystals. NaCl was chosen due to its wide availability, low cost and high water solubility. For removing sodium chloride, the coated crystals are dipped in water as a result of which NaCl dissolves leaving behind the very pure nitrogen-doped graphene cages. The last step involves giving treatment to the cages with ultrasound as a result of which they transform to two-dimensional nanosheets that are nearly 5-7 layers of graphite in thickness.

These nanosheets have very fewer defects and they are of the perfect size for printing as they are of 5 micrometres in length, whereas the bigger flakes block the nozzle. For putting to test, the actual effectiveness of the ink, a large number of 3D structures were built using the inks. Scientists used the ink as a conductive additive for electrode and then used the composite ink for printing flexible electrodes to be used in supercapacitors with a large power density.

Additionally, scientists also used the ink for printing interlayers for the Li-S batteries. These batteries showed better-enhanced performance with increased conductivity.

soft total artifical heart

For the first time scientists successfully create a complete heart by 3D printing

A team of researchers at the Tel Aviv University has managed to successfully 3D print a small heart by using human tissues which includes blood vessels, biological molecules and collagens. This is considered to be a remarkable achievement as the scientists hope that with the help of this, they can make organ donation to be a thing of the past.

This achievement was reported by head researchers from TAU’s Faculty of Life Sciences, Professor Tal Dvir, Dr. Assaf Shapira and his doctoral student Nadav Noor in the Advanced Science journal.

The 3D printed heart is the size of a rabbit’s and it is not fully functional yet. However, the team has pointed out that the technology involved in 3D printing the heart for a human body is essentially the same. There are several steps of improvement left in the heart as the cells need to possess the pumping ability, a crucial working of the heart. Currently, the group of cells can contract but they need to work together. The scientists believe that they can succeed in increasing the efficiency of the method.

So the next step in the line is to make the printed heart grow and mature in the laboratory and make it learn how to function like an actual heart. Only after then can scientists take the decision to use it for transplant in animals for testing their functionality. This is a very time-consuming process and it may take years before this technology can create actual functioning organs that are ready to transplant. Nevertheless, this is a significant progress, as three-dimensional printing has managed to print tissues but not the blood vessels, which is very important for its working.

Dr. Dvir said that this is the first time, a team has successfully managed to engineer and print an entire heart with all the components inside it, the cells, blood vessels, chambers.

Scientists have previously printed cartilage and aortal tissues, but the main challenge was not accomplished, which is to create tissues with complete vascularization, blood vessels, capillaries. In the absence of these, the organs would not survive.

The scientists began the process with fatty tissues extracted from the human body and then they separated the cellular components from the non-cellular components. After that, they programmed these cells to undifferentiated stem cells which can be nudged to form cardiac cells or endothelial cells. The non-cellular materials such as the proteins galore were processed to form a personalized hydrogel which served as printing ink.

Organ printing basically involves three stages. The first stage is called the pre-print stage, which involves scanning the organ. The second stage is printing the organ and the third stage is maturing the organ in a proper environment.