LLNL Researchers Develop New Class of 3D PRINTED METAMATERIALS that Strengthen “On Demand” – Applications for armor that responds on impact; car seats that reduce whiplash and NextGen Neck braces


Combining 3D printing with a magnetic ink injection, researchers at Lawrence Livermore National Laboratory (LLNL) have created a new class of metamaterial – engineered with behaviors outside their nature.

Like 4D printed objects, LLNL’s 3D printed lattices rely on the fourth element of time to become something “other” than their natural resting state. However, in contrast to its relatives, that often transform in response to temperatures or water, the change in LLNL’s new structures is almost instantaneous – they stiffen when a magnetic field is applied.

This unique class is the next step forward in metamaterials that can be tuned “on-the-fly” to achieve desired properties, and applied to make intuitive objects: e.g. armor that responds on impact; car seats that reduce whiplash; and next generation neck braces.

A 3D printed lattice injected with magnetic fluid. Image via Science Advances, supplementary materials/LLNL

A 3D printed lattice injected with magnetic fluid. Image via Science Advances, supplementary materials/LLNL

Harnessing the power of lattices

In the first stage of this development, the LLNL team performed a digital simulation of their metamaterial lattices. By doing so, the team could determine how the shape would respond to a magnetic field, and therefore optimize its structure for desired mechanical properties.

Mark Messner, former LLNL researcher and co-author of a study presenting the new metamaterial, explains, “The design space of possible lattice structures is huge, so the model and the optimization process helped us choose likely structures with favorable properties before [it was] printed, filled and tested the actual specimens, which is a lengthy process.”

After optimization, experimental lattices were 3D printed using a method of Large Area Projection Microstereolithography (LAPµSL). With microscale precision, LAPµSL enabled the team to create thin walls that could support injected fluid.

Lead author Julie Jackson Mancini explains, “In this paper we really wanted to focus on the new concept of metamaterials with tunable properties, and even though it’s a little more of a manual fabrication process,” i.e. with the injection of material, “it still highlights what can be done, and that’s what I think is really exciting.”

Materials with “on-the-fly” tunability 

The ink inside the LLNL lattice is a magnetorheological fluid, containing minute magnetic particles.

Like a “dancing” iron filing experiment, when a magnetic field is applied to this lattice, the particles realign, making the structure stiff and supportive of added weight.

This newfound strength is demonstrated through a test in which a 10g weight is added to the top of the lattice. As the magnet beneath the lattice is moved away, the structure gradually gives way, and eventually drops the weight.

Demonstration showing a 3D printing magnetic metamaterial lattice, and its response to the removal of a magnetic field. Image via Science Advance, supplementary materials/LLNL

Demonstration showing a 3D printing magnetic metamaterial lattice, and its response to the removal of a magnetic field. Image via Science Advance, supplementary materials/LLNL

“What’s really important,” explains Mancini, “is it’s not just an on and off response, by adjusting the magnetic field strength applied we can get a wide range of mechanical properties,”

“THE IDEA OF ON-THE-FLY, REMOTE TUNABILITY OPENS THE DOOR TO A LOT OF APPLICATIONS.”

Future development

The next steps for the LLNL metamaterial team is to develop a means of integrating the ink-injection stage of lattice fabrication, and to increase the size of objects that can be 3D printed.

Results of the lab’s most recent study, “Field responsive mechanical metamaterials” are published online in Science Advances journal. It’s co-authors are listed as Julie A. JacksonMark C. MessnerNikola A. Dudukovic, William L. SmithLogan BekkerBryan MoranAlexandra M. GolobicAndrew J. PascallEric B. DuossKenneth J. Loh, and Christopher M. Spadaccini.

Nominate 3D Printing Research Team of the Year and more now for the 2019 3D Printing Industry Awards.

Preventing greenhouse gas from entering the atmosphere


Harvard greenhouse gas microcapatmospherex250A novel class of materials that enable a safer, cheaper and more energy-efficient process for removing greenhouse gas from power plant emissions has been developed by a multi-institution team of researchers. The approach could be an important advance in carbon capture and sequestration (CCS).

The team, led by scientists from Harvard Univ. and Lawrence Livermore National Laboratory, employed a microfluidic assembly technique to produce microcapsules that contain liquid sorbents encased in highly permeable polymer shells. They have significant performance advantages over the carbon-absorbing materials used in current CCS technology.

The work is described in a paper published online in Nature Communications.

“Microcapsules have been used in a variety of applications–for example, in pharmaceuticals, food flavoring, cosmetics and agriculture–for controlled delivery and release, but this is one of the first demonstrations of this approach for controlled capture,” says Jennifer A. Lewis, the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences (SEAS) and a co-lead author. Lewis is also a core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard.

Harvard greenhouse gas microcapatmospherex250

This is an optical image of the cured silicone microcapsules, each with a diameter of approximately 600 microns. Image: John Vericella, Chris Spadaccini, and Roger Aines, LLNL; James Hardin and Jennifer Lewis, Harvard Univ.; and Nature

Power generating plants are the single largest source of carbon dioxide (CO2), a greenhouse gas that traps heat and makes the planet warmer. According to the U.S. Environmental Protection Agency, coal- and natural gas-fired plants were responsible for one-third of U.S. greenhouse gas emissions in 2012.

That’s why the agency has proposed rules mandating dramatically reduced carbon emissions at all new fossil fuel-fired power plants. Satisfying the new standards will require operators to equip plants with carbon-trapping technology.

Current carbon capture technology uses caustic amine-based solvents to separate CO2 from the flue gas escaping a facility’s smokestacks. But state-of-the-art processes are expensive, result in a significant reduction in a power plant’s output, and yield toxic byproducts. The new technique employs an abundant and environmentally benign sorbent: sodium carbonate, a.k.a. kitchen-grade baking soda. The microencapsulated carbon sorbents (MECS) achieve an order-of-magnitude increase in CO2 absorption rates compared to sorbents currently used in carbon capture. Another advantage: amines break down over time, while carbonates have a virtually limitless shelf life.

“MECS provide a new way to capture carbon with fewer environmental issues,” says Roger D. Aines, leader of the fuel cycle innovations program at Lawrence Livermore National Laboratory (LLNL) and a co-lead author. “Capturing the world’s carbon emissions is a huge job; we need technology that can be applied to many kinds of carbon dioxide sources with the public’s full confidence in the safety and sustainability.”

Researchers at LLNL and the U.S. Dept. of Energy (DOE)’s National Energy Technology Lab are now working on enhancements to the capture process to bring the technology to scale.

The emission-scrubbing potential of CCS is not limited to the electric generation sector; Aines says that the MECS-based approach can also be tailored to industrial processes like steel and cement production, significant greenhouse gas sources.

“These permeable silicone beads could be a ‘sliced-bread’ breakthrough for CO2 capture–efficient, easy-to-handle, minimal waste, and cheap to make,” says Stuart Haszeldine, professor of carbon capture and storage at the University of Edinburgh, who was not involved in the research. “Durable, safe, and secure capsules containing solvents tailored to diverse applications can place CO2 capture for CCS firmly onto the cost-reduction pathway.”

MECS are produced using a double capillary device in which the flow rates of three fluids–a carbonate solution combined with a catalyst for enhanced CO2 absorption, a photocurable silicone that forms the capsule shell, and an aqueous solution–can be independently controlled.

“Encapsulation allows you to combine the advantages of solid capture media and liquid capture media in the same platform,” says Lewis. “It is also quite flexible, in that both the core and shell chemistries can be independently modified and optimized.”

“This innovative gas separation platform provides large surface areas while eliminating a number of operational issues including corrosion, evaporative losses, and fouling,” notes Ah-Hyung (Alissa) Park, chair in applied climate science and associate professor of Earth and environmental engineering at Columbia Univ., who was not involved in the research.

Lewis has previously conducted groundbreaking research in the 3D printing of functional materials, including tissue constructs with embedded vasculature, lithium-ion microbatteries, and ultra-lightweight carbon-fiber epoxy materials.

Source: Harvard Univ.