Carbon Nanotube Second Skin Protects First Responders and Warfighters against Chem, Bio Agents – Lawrence Livermore National Laboratory

Published 8 May 2020

Recent events such as the COVID-19 pandemic and the use of chemical weapons in the Syria conflict have provided a stark reminder of the plethora of chemical and biological threats that soldiers, medical personnel and first responders face during routine and emergency operations. Researchers have developed a smart, breathable fabric designed to protect the wearer against biological and chemical warfare agents. Material of this type could be used in clinical and medical settings as well.

Recent events such as the COVID-19 pandemic and the use of chemical weapons in the Syria conflict have provided a stark reminder of the plethora of chemical and biological threats that soldiers, medical personnel and first responders face during routine and emergency operations.

Personnel safety relies on protective equipment which, unfortunately, still leaves much to be desired. For example, high breathability (i.e., the transfer of water vapor from the wearer’s body to the outside world) is critical in protective military uniforms to prevent heat-stress and exhaustion when soldiers are engaged in missions in contaminated environments.

The same materials (adsorbents or barrier layers) that provide protection in current garments also detrimentally inhibit breathability.

To tackle these challenges, a multi-institutional team of researchers led by Lawrence Livermore National Laboratory (LLNL) scientist Francesco Fornasiero has developed a smart, breathable fabric designed to protect the wearer against biological and chemical warfare agents. Material of this type could be used in clinical and medical settings as well.

The work was recently published online in Advanced Functional Materials and represents the successful completion of Phase I of the project, which is funded by the Defense Threat Reduction Agency through the Dynamic Multifunctional Materials for a Second Skin “D[MS]“ program.

“We demonstrated a smart material that is both breathable and protective by successfully combining two key elements: a base membrane layer comprising trillions of aligned carbon nanotube pores and a threat-responsive polymer layer grafted onto the membrane surface,” Fornasiero said.

LLNL notes that these carbon nanotubes (graphitic cylinders with diameters more than 5,000 times smaller than a human hair) could easily transport water molecules through their interiors while also blocking all biological threats, which cannot fit through the tiny pores.

This key finding was previously published in Advanced Materials.

The team has shown that the moisture vapor transport rate through carbon nanotubes increases with decreasing tube diameter and, for the smallest pore sizes considered in the study, is so fast that it approaches what one would measure in the bulk gas phase.

This trend is surprising and implies that single‐walled carbon nanotubes (SWCNTs) as moisture conductive pores overcome a limiting breathability/protection trade-off displayed by conventional porous materials, according to Fornasiero. Thus, size-sieving selectivity and water-vapor permeability can be simultaneously enhanced by decreasing SWCNT diameters.

Contrary to biological agents, chemical threats are smaller and can fit through the nanotube pores. To add protection against chemical hazards, a layer of polymer chains is grown on the material surface, which reversibly collapses in contact with the threat, thus temporarily blocking the pores.

“This dynamic layer allows the material to be ‘smart’ in that it provides protection only when and where it is needed,” said Timothy Swager, a collaborator at the Massachusetts Institute of Technology who developed the responsive polymer. These polymers were designed to transition from an extended to a collapsed state in contact with organophosphate threats, such as sarin. “We confirmed that both simulants and live agents trigger the desired volume change,” Swager added.

The team showed that the responsive membranes have enough breathability in their open-pore state to meet the sponsor requirements. In the closed state, the threat permeation through the material is dramatically reduced by two orders of magnitude. The demonstrated breathability and smart protection properties of this material are expected to translate in a significantly improved thermal comfort for the user and enable to greatly extend the wear time of protective gears, whether in a hospital or battlefield.

“The safety of warfighters, medical personnel and first responders during prolonged operations in hazardous environments relies on personal protective equipment that not only protects but also can breathe,” said Kendra McCoy, the DTRA program manager overseeing the project.

“DTRA Second Skin program is designed to address this need by supporting the development of new materials that adapt autonomously to the environment and maximize both comfort and protection for many hours.”

In the next phase of the project, the team will aim to incorporate on-demand protection against additional chemical threats and make the material stretchable for a better body fit, thus more closely mimicking the human skin.

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

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

“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. Jackson, Mark C. Messner, Nikola A. Dudukovic, William L. Smith, Logan Bekker, Bryan Moran, Alexandra M. Golobic, Andrew J. Pascall, Eric B. Duoss, Kenneth 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

A 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.

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.