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TU Delft: Researchers 3D Printing Minimal Surface Structures Inspired by Origami

Although Japan is famous for their creations in origami, the craft is appreciated around the world, and recently by TU Delft researchers in the Netherlands who sought to understand more about folding mechanisms for complex efficient structures. Their findings are fully outlined in ‘Hyperbolic origami-inspired folding of triply periodic minimal surface structures,’ by Sebastien J.P. Callens, Nazlı Tümer, and  Amir A. Zadpoor.

The Dutch researchers point out at the beginning of their study that geometries from triply periodic minimal surfaces—those that locally minimize an area, with vanishing mean curvatures present—have received a great amount of attention lately due to their potential for:

  • High yield stress
  • Low elastic modulus
  • High fatigue resistance
  • Bone-mimicking transport properties

And while TPMS structures are found to be ‘ideal for bone substitutes,’ the researchers explain that they are also suitable for creating a variety of structures that may be photonic, architected, or porous. They see obstacles in creating cellular structures, however, that can only be 3D printed in the form of lattices and are ‘incompatible with the planar functionality-inducing processes.’ As a result, the point of their research is to reduce constraints, while encouraging folding mechanisms, and innovating with new structures via sheet stretching. The authors also tweak the title of this new form of production from origami to origomu, since they are folding rubber instead of paper sheets—with ‘gomu’ meaning rubber.

Minimal material programming is required, and complex porous structures can be created this novel folding method:

“The rationale behind our approach consists of realizing curved minimal surface patches from a flat state, by combining rigid foldable frames with pre-strained elastomer sheets. Multiple of these foldable patches could then be connected together in a net and used as building blocks to fold a myriad of 3D TPMS-based architectures, ranging from single unit cells to larger assemblies consisting of multiple unit cells and 3D stackable minimal surface layers,” state the authors.

Geometry of TPMS and patch folding. (a) A translational P unit cell decorated with the hyperbolic *246 tiling of the fundamental asymmetrical patch. (b) Alternative patches to tile the P surface, shown together with the conventional unit cell. (c) The four TPMS considered here. From left to right: P, D, CLP, and C(P) surface. (d) Folding kinematics for the straight-edged skew polygonal patches of the P, D, CLP, and C(P) surfaces, respectively.

The concept of creating a TPMS structure in a saddle-shaped 3D puzzle form is the focus of the research, with their work using surfaces tiled by ‘straight-edged skew polygonal patches (homeomorphic to a disk).’

“A necessary (but not sufficient) condition therefore is the existence of embedded straight lines in the TPMS, which are axes of two-fold rotation and form the “linear skeletal net” of the surface,” state the researchers.

Polygonal patches are flattened with hinges attaches to boundary frame vertices, with edge lengths constant. This type of engineering allows for continuous folding of the frame to a flat polygon.

Connecting patches. (a) The edge-connection of two P patches. (b) The vertex-connection of two D patches. A transparent patch indicates a patch that fits in between two vertex-connected patches. (c) When trying to conform the hyperbolic (6,4) tiling of the D surface to the flat plane, one frequently encounters overlaps in the 2D net. (d–g) The folding of TPMS unit cells consisting of vertex-connected patches.

The patches can be connected to form more substantial minimal surfaces, resulting in a foldable 2D net, which then results in a 3D portion of the TPMS. Taking that one step further, the nets can continue to be connected, making even larger assemblies. Frames were 3D printed on an Ultimaker 2+ FDM printer, using PLA, with a 0.25 mm diameter nozzle and a layer thickness of 0.6 mm.

“We physically realized our self-folding minimal surface structures by attaching stretched elastomer sheets to 3D printed foldable frames,” said the researchers. “Upon release, the strain energy in the sheets causes the flat polygonal frame to self-fold into the desired skew polygonal configuration, and the sheet spanning the frame adopts an energy-minimizing saddle-shaped geometry, approximating the minimal surface.”

For this study, the authors narrowed their focus to four different TPMS types, but other minimal surfaces could be constructed if desired; in fact, they predict that a variety of different morphologies could be created.

“In this work, we focused on sheet-based structures, but beam-based lattices derived from the boundary frames could also be folded,” concluded the researchers. “Finally, our approach is not strictly bound by a specific length scale, meaning that it could also inspire the self-folding of architectural-scale tensile structures, nor is it limited to specific constituent materials, as long as a sufficient area distortion of the sheet surfaces and the rigidity of the boundary frames can be obtained.”

Self-folded physical models. (a) 3D-printed foldable frames for the four patch types in flat (top row) and folded (bottom row) configurations after the stretched latex sheets have been attached. (b) The mean curvature estimated using the 3D reconstructions of the four patch types obtained from micro-computed tomography data. (c) 3D-printed foldable TPMS unit cells in the flat (top row) and folded (bottom row) configurations. (d) The self-folding of the CLP unit cell through the pre-tension present in the latex sheet. (e) An assembly of four D unit cells in the flat (left) and folded (right) configurations. All scale bars are 20 mm.

Origami is an Asian craft so ancient that no one is sure whether it began in China or Japan, but Japanese artists have certainly made it their own over time. And because so many creative and scientific endeavors revolve around the creation of complex geometries and structures, origami has been an ongoing inspiration. In 3D printing, designers have also been inspired by the folding paper shapes to create complex structures for surgical implants, soft robotics, and even 4D printing to fabricate stronger metamaterials. Find out more about how origami is improving triply periodic minimal surface structures here.

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[Source / Images: Hyperbolic origami-inspired folding of triply periodic minimal surface structures]

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Researchers Make Strong, 3D Printed Expandable Origami Structures for Engineering Applications

Rearranging the same units can change a structure from one that can support a load 100 times its weight to one that will fold flat under the same load. [Image: Soft Matter]

A collaborative team of researchers from the Georgia Institute of Technology, the Beijing Institute of Technology, and Peking University are using 3D printing to directly build reconfigurable origami assemblages that can expand and fold. But even better, the 3D printed structures also have enough load-bearing capability and strength to be used in engineering applications.

In a paper published in Soft Matters, titled “3D printing of complex origami assemblages for reconfigurable structures,” the researchers explained how they used digital light processing (DLP) 3D printing to fabricate structures with hollow features.

With this method, far less support material is required for 3D printing hollow features, and softer materials, necessary for flexible structures, can be used.

The abstract of the paper reads, “Origami engineering principles have recently been applied to a wide range of applications, including soft robots, stretchable electronics, and mechanical metamaterials. In order to achieve the 3D nature of engineered structures (e.g. load-bearing capacity) and capture the desired kinematics (e.g., foldability), many origami-inspired engineering designs are assembled from smaller parts and often require binding agents or additional elements for connection. Attempts at direct fabrication of 3D origami structures have been limited by available fabrication technologies and materials. Here, we propose a new method to directly 3D print origami assemblages (that mimic the behavior of their paper counterparts) with acceptable strength and load-bearing capacity for engineering applications. Our approach introduces hinge-panel elements, where the hinge regions are designed with finite thickness and length. The geometrical design of these hinge-panels, informed by both experimental and theoretical analysis, provides the desired mechanical behavior. In order to ensure foldability and repeatability, a novel photocurable elastomer system is developed and the designs are fabricated using digital light processing-based 3D printing technology. Various origami assemblages are produced to demonstrate the design flexibility and fabrication efficiency offered by our 3D printing method for origami structures with enhanced load bearing capacity and selective deformation modes.”

Many 3D printed structures with unique properties have been inspired by origami, opening up applications in soft robotics and self-folding structures. While most origami structures mean thin sheets being joined together with binding elements like glue, the research team found a way to make several 3D assemblies in one step, without needing to connect smaller parts together. The team, led by Zeang Zhao, developed a new polymer and used geometrical design to move towards using origami for engineering structures.

To build the origami, the team developed a novel new elastomer, which makes it possible for the structure to be created from a single component. The elastic polymer material can be 3D printed at room temperature and set with UV light, which forms a soft, foldable material that can be stretched up to 100%. This material was used for the whole 3D assembly. DLP 3D printing was used to build structures, made up of various combinations of individual units of origami, without requiring any extra assembly steps.

By altering how each origami unit is connected, the structures can be designed to have different load-bearing capabilities: vitally important for applications in engineering. One of the test structures was even able to support a load that weighed 100 times more than the structure itself did. But here’s the really interesting part – just by rearranging the same individual units in a different way, the team was able to build a bridge that, under the same heavy load, would fold flat.

The structures were designed with thick panels, which were separated by hinges not unlike the creases in a piece of paper. The hinges made it possible for the angle between the panels to vary between 0° and 90°. Hinge thickness is important for a structure’s mechanical properties: if it’s too thick, it won’t fold well, while if it’s too thin, it might not be able to support the structure’s weight. In addition, the researchers made sure that the high strain and stress the structures experienced during folding was localized specifically to the hinges, so the panels would not end up deformed.

Co-authors of the paper are Zhao, Xiao Kuang, Jiangtao Wu, Qiang Zhang, Glaucio H. Paulino, H. Jerry Qi, and Daining Fang.

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[Source: Physics World]

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3D Printed Origami Device Safely Traps Soft-Bodied Sea Creatures for Study

Many 3D printing applications and innovations, like self-folding objects, robots, and face masks, have been inspired by the Japanese paper folding art of origami. Now, a collaborative group of scientists from Harvard University, the University of Rhode Island, and City University of New York (CUNY) have combined the principles of 3D printing and origami to find a less damaging way to capture delicate, soft-bodied sea creatures like squids, anemones, and jellyfish.

While soft forms like these are adapted to ocean pressures, it’s hard to catch them for the purposes of study without injuring the very subjects you want to learn more about. Marine biologist David Gruber, who helped design the capture device, says that these creatures are often called the “forgotten fauna” because their study has been so neglected. But the multi-university research team recently introduced its 3D printed, 12-sided trap, inspired by origami, that can fold around these animals gently, without harming them.

The RAD device, which is short for rotary actuated dodecahedron, is far better equipped for handling these delicate creatures than nets or suction samplers. It can be attached to the arm of an underwater rover, then triggered remotely, and has already successfully trapped jellyfish and small squid and octopuses at a depth of 700 meters. However, the design can work at depths up to 11 kilometres, with the possibility of being scaled up even further for larger creatures.

Still images showing the capture of three different types of soft-bodied sea life using the RAD. [Image: Wyss Institute at Harvard University]

Zhi Ern Teoh, a mechanical engineer at Harvard, said the most important part of the design was getting it to unfold with just one motor so that the system has fewer points of failure. The team had to create a complex series of linkages, lightweight enough so as not to cause motor strain but still able to hold up underwater, which would connect each of the 12 panels back to the motor.

The RAD has several other important design touches, including making the edges of the panels softer than the rest of the plastic device so creatures struggling to get out (which makes me sad to think about but I know it’s important to study these animals so I’ll just get over it) aren’t accidentally amputated. Additionally, there are gaps between each of the panels to pressure doesn’t build up inside when the RAD travels back up to the surface.

“I view this as a platform technology that we hope will continue to evolve. The dream is to enclose delicate deep-sea animals, take 3D imagery that includes properties like hardness, 3D-print that animal at the surface, and also have a ‘toothbrush’ tickle the organism to obtain its full genome. Then, we’d release it,” Gruber told the Verge.

L-R: Zhi Ern Teoh inspects the RAD when attached to an underwater rover; a closeup of the RAD folded shut. [Image: Kaitlyn Becker, Wyss Institute at Harvard]

The basic RAD organism, as previously mentioned, can be scaled up for the capture of larger species, and Teoh even says it could one day be possible to develop a version that’s human-sized, which could have applications in self-building habitats in outer space. In addition, the current remote-controlled RAD could be turned into an automated trap in the future that uses sensors to detect when a creature is passing by.

3D printing has helped us sample the floor of the ocean and clean up debris from its shores, give coral reefs a helping hand, and quietly observe marine life. Now, this basic 3D printed origami mechanism can help us safely capture soft-bodied organisms for the purposes of study.

Gruber believes, and I tend to agree, that this kind of advanced technology is absolutely imperative to exploring our oceans without causing further harm to the myriad creatures that call them home. We are only just scratching the surface when it comes to figuring out just how important of a role marine life – from the tiniest sea cucumber to the most massive of coral reefs – can play in the overall ecosystem of the ocean.

The RAD device capturing a squid in the ocean. ]Image: Wyss Institute at Harvard University]

The team published a paper on their development of the RAD in the Science Robotics journal, which you can read here. Co-authors are Teoh, Brennan T. Phillips, Kaitlyn P. Becker, Griffin Whittredge, James C. Weaver, Chuck Hoberman, Gruber, and Robert J. Wood.

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