LLNL and UC Berkeley Researchers Continue Work on Their Promising Volumetric 3D Printing Method

It’s been said that volumetric 3D printing has more speed, flexibility, and geometric versatility than other methods, with a lower cost. In late 2017, researchers at Lawrence Livermore National Laboratory (LLNL) in California teamed up with collaborators from MIT, the University of Rochester, and UC Berkeley to develop this method, which flashes laser-generated, hologram-like 3D images into photosensitive resin.

It seems this collaborative work has continued, since a team of researchers from LLNL and UC Berkeley just published another paper about volumetric 3D printing, titled “Volumetric additive manufacturing via tomographic reconstruction.” Co-authors of the paper are Brett E. Kelly, Indrasen Bhattacharya, Hossein Heidari, Maxim Shusteff, Christopher M. Spadaccini, and Hayden K. Taylor. This has overexcited a lot of press into miraculous claims for the nascent technology.

“This is the first case where we don’t need to build up custom 3D parts layer by layer. It makes 3D printing truly three-dimensional, “explained Kelly, who completed research on the project while a graduate student working jointly at UC Berkeley and LLNL.

The team nicknamed its new 3D printer ‘the Replicator,’ after the fictional Star Trek device that’s able to materialize any object at the push of a button, and filed a patent application on their method.

Jeremy Thomas, a spokesman for LLNL, said, “It looks like something you might find aboard the Starship Enterprise.

“Though it seems like science fiction, it’s not, thanks to scientists and engineers at LLNL and UC Berkeley, who have developed a brand-new high-speed 3D printing method called Computed Axial Lithography (CAL).”

Thomas is referring to a projector that beams a 3D video into a container of viscous, gooey photosensitive resin, which briefly rotates and then lets the fluids drain, leaving behind a complete, fully formed 3D object in minutes. A rotating cylinder of the material reacts to a certain threshold of projected light, which can be crafted into various patterns, to quickly form a solid shape…no layering required.

“Basically, you’ve got an off-the-shelf video projector, which I literally brought in from home, and then you plug it into a laptop and use it to project a series of computed images, while a motor turns a cylinder that has a 3D-printing resin in it. Obviously there are a lot of subtleties to it — how you formulate the resin, and, above all, how you compute the images that are going to be projected, but the barrier to creating a very simple version of this tool is not that high,” explained Taylor, assistant professor of mechanical engineering at UC Berkeley.

The new 3D printer is able to make smoother, more complex, and flexible objects, and can also be used to encase another object with a different material, like putting a handle around the shaft of a metal screwdriver…bringing mass customization further into the realm of possibility.

The 3D printer works by shining changing patterns of light through a rotating vial of liquid. A computer algorithm calculates the exact patterns of light needed to shape a specific object.

Taylor said, “I think this is a route to being able to mass-customize objects even more, whether they are prosthetics or running shoes.

“The fact that you could take a metallic component or something from another manufacturing process and add on customizable geometry, I think that may change the way products are designed.”

CT scans, which project X-rays or electromagnetic radiation into the body from various angles, actually inspired this method, as those patterns of transmitted energy need to be analyzed in order to reveal the geometry of an object, like a tumor.

“Essentially we reversed that principle. We are trying to create an object rather than measure an object, but actually a lot of the underlying theory that enables us to do this can be translated from the theory that underlies computed tomography,” Taylor explained.

In addition to completing complex calculations to perfect the exact intensities and shapes of various light patterns, the team also had to determine how to develop a material that would stay liquid when exposed to a small amount of light, but would react and form a solid when exposed to a significant amount.

Taylor said, “The liquid that you don’t want to cure is certainly having rays of light pass through it, so there needs to be a threshold of light exposure for this transition from liquid to solid.”

The resulting resin is made up liquid polymers, mixed with photosensitive molecules and dissolved oxygen. The molecules are activated by light, which drains the oxygen, and only in the 3D regions that have been depleted of oxygen will the polymers from cross-links turn the liquid resin into a solid.

CAL volumetric fabrication.

The team can also 3D print objects that appear opaque with a dye that transmits light at the curing wavelength, but will absorb most others.

“This is particularly satisfying for me, because it creates a new framework of volumetric or ‘all-at-once’ 3D printing that we have begun to establish over the recent years. We hope this will open the way for many other researchers to explore this exciting technology area,” LLNL staff engineer Shusteff said.

Additionally, unused resin can be recycled by heating it up in an oxygen atmosphere.

Heidari, a graduate student in Taylor’s lab at UC Berkeley, said, “Our technique generates almost no material waste and the uncured material is 100 percent reusable. This is another advantage that comes with support-free 3D printing.”

The researchers created many objects, like a customized jawbone model and a tiny model of Rodin’s “The Thinker” statue, to test out their 3D printer.

While this is definitely an exciting development, it’s important to note that further engineering and polymer chemistry need to be completed in order to improve the resin properties, so more stable structures can be fabricated. In addition, the LLNL and UC Berkeley team can only 3D print objects up to four inches in diameter at the moment, so large-scale objects are off the table right now. Our take is that this is indeed an interesting technology on whose development we’ve been reporting for two years now. But, this is still very much a lab technology that is not close to being commercialized at the moment. A good development and a good thing for 3D printing but it remains to be seen how long it will take to commercialize this properly and then how it will perform. Media tend to forget that 3D printing is a manufacturing technology and therefore will need to work on the concrete floor not just in the press release.

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[Source: Science Daily / Images: Stephen McNally and Hayden Taylor, UC Berkeley]

UC Berkeley researchers develop a projection-based 3D printer from CT scans

Researchers from the University of California (UC), Berkeley have developed a 3D printer which projects CT scans onto a rotating volume of photosensitive resin. Named after Star Trek’s Replicator, a device that can materialize any object on demand, this system uses Computed Axial Lithography (CAL) for smooth, flexible and more complex 3D models. In the […]

Patent filed for metal 3D printing without layers

The patent for a metal 3D printing method reportedly capable of  producing entire objects in a single step has been published online by the World Intellectual Property Organization (WIPO). Invented by Nataša Muševič, director of Research and Development at small-scale manufacturing provider and consultancy Zavod Park in Slovenia, the system is a method of support-free 3D printing […]

3D Printing Industry review of the year December 2018

News from the 3D printing world did not slow down in the last month of the calendar. December brought developments in materials, software, and European Space Agency’s ambitious plans for interplanetary missions. Marie the phantom A Louisiana State University student Meagan Moore, 3D printed a full-body phantom (and she named it Marie) which can be […]

LLNL: Magnetically Responsive Metamaterials Instantly Stiffen 3D Printed Structures

Lawrence Livermore National Laboratory (LLNL) frequently does impressive work with 3D printing materials, including metamaterials. Now the lab has introduced a new class of metamaterial that can almost instantly respond and stiffen 3D printed structures when exposed to a magnetic field. LLNL calls the materials “field-responsive mechanical metamaterials” or FRMMs. They involve a viscous, magnetically responsive fluid that is injected into the hollow struts and beams of 3D printed lattices. Unlike other 4D printed materials, the FRMMs’ overall structure does not change. The fluid’s ferromagnetic particles located in the core of the beams form chains in response to the magnetic field, stiffening the fluid and the lattice structure. This happens in less than a second.

The research is documented in a paper entitled “Field responsive mechanical metamaterials.

“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, it still highlights what can be done, and that’s what I think is really exciting,” said lead author Julie Jackson Mancini, an LLNL engineer who has worked on the project since 2014. “It’s been shown that through structure, metamaterials can create mechanical properties that sometimes don’t exist in nature or can be highly designed, but once you build the structure you’re stuck with those properties. A next evolution of these metamaterials is something that can adapt its mechanical properties in response to an external stimulus. Those exist, but they respond by changing shape or color and the time it takes to get a response can be on the order of minutes or hours. With our FRMM’s, the overall form doesn’t change and the response is very quick, which sets it apart from these other materials.”

The researchers injected a magnetorheological fluid into hollow lattice structures built on LLNL’s Large Area Projection Microstereolithography (LAPµSL) platform, which is capable of 3D printing objects with microscale features over wide areas using light and a photosensitive polymer resin. According to Mancini, the LAPµSL machine played a big role in the development of the new metamaterials, as the complex tubular structures needed to be manufactured with thin walls and be capable of keeping the fluid contained while withstanding the pressure generated during the infill process and the response to a magnetic field.

The stiffening of the fluid and, in turn, the 3D printed structures, is reversible and tunable by varying the strength of the applied magnetic field.

“What’s really important 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,” Mancini said. “The idea of on-the-fly, remote tunability opens the door to a lot of applications.”

Those applications include impact absorption, such as automotive seats that have fluid-responsive metamaterials integrated inside of them along with sensors that can detect a crash. The seats would stiffen upon impact, possibly reducing whiplash. Other applications include helmets, neck braces, housing for optical components or soft robotics.

To predict how lattice structures would respond to an applied magnetic field, former LLNL researcher Mark Messner, who now works for Argonne National Laboratory, developed a model from single strut tests. Starting with a model he developed to predict the mechanical properties of non-tunable static lattice-structured materials, he added a representation of how magenetically responsive fluid affects a single lattice member under a magnetic field and incorporated the model of a single strut into designs for unit cells and lattices. He then calibrated the model to experiments Mancini performed on fluid-filled tubes similar to the struts in the lattices. The researchers used the model to optimize the topology of the lattice, finding the structures that would result in large changes in mechanical properties as the magnetic field was varied.

“We looked at elastic stiffness, but the model (or similar models) can be used to optimize different lattice structures for different sorts of goals,” Messner said. “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 (Mancini) printed, filled and tested the actual specimens, which is a lengthy process.”

Mancini began the work at the University of California, Davis under her adviser, materials and engineering professor Ken Loh, who is now at the University of California, San Diego. According to Loh, the concept was partially inspired by automotive-based suspension systems. They began by investigating ways to develop flexible armor that could morph or change its mechanical properties as needed.

“One of the criteria is to achieve fast response, and magnetic fields and MR materials offer that capability,” said Loh.

He also said that the researchers will explore new ways to develop a single-phase material, instead of having a liquid embedded in a solid, and higher performance-to-weight rations. Future work, he continued, “could lead to new technologies, such as flexible armor for the warfighter that stiffen instantaneously when a threat is detected.”

Authors of the paper include 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.

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3D Printed Graphene Aerogel May Lead to Powerful Supercapacitors

Supercapacitors are energy storage devices that charge very rapidly and can retain their storage capacity through tens of thousands of charge cycles. Their applications include regenerative braking systems in electric vehicles. They hold less energy in the same amount of space as batteries, and they don’t hold a charge for quite as long – but advances in supercapacitor technology could make them competitive with batteries in a wider range of applications. In a study entitled “Efficient 3D Printed Pseudocapacitive Electrodes with Ultrahigh MnO2 Loading,” a group of researchers at UC Santa Cruz and Lawrence Livermore National Laboratory have achieved unprecedented performance from a supercapacitor electrode. The electrode was fabricated from a 3D printable graphene aerogel, which was used to build a porous 3D scaffold loaded with pseudocapacative material.

In tests, the electrodes achieved the highest areal capacitance ever reported for a supercapacitor. In an earlier study, the researchers achieved extremely fast supercapacitor electrodes 3D printed from graphene aerogel. This time, they used an improved graphene aerogel to build a porous scaffold which was loaded with manganese oxide.

A pseudocapacitor is a type of supercapacitor that stores energy through a reaction at the electrode surface, giving it more battery-like performance than supercapacitors that store energy primarily through an electrostatic mechanism (called electric double-layer capacitance, or EDLC).

“The problem for pseudocapacitors is that when you increase the thickness of the electrode, the capacitance decreases rapidly because of sluggish ion diffusion in bulk structure,” said UC Santa Cruz Professor of Chemistry and Biochemistry Yat Li. “So the challenge is to increase the mass loading of pseudocapacitor material without sacrificing its energy storage capacity per unit mass or volume.”

The study demonstrates a breakthrough in balancing mass loading and capacitance in a pseudocapacitor. The researchers increased mass loading to record levels of more than 100 milligrams of manganese oxide per square centimeter without compromising performance, a major increase compared to commercial devices, which have levels of about 10 milligrams per square centimeter.

The areal capacitance also increased linearly with mass loading of manganese oxide and electrode thickness, while the capacitance per gram (gravimetric capacitance) remained almost unchanged. This indicates that the electrode’s performance is not limited by ion diffusion even at such a high mass loading.

In the traditional fabrication of supercapacitors, according to graduate student Bin Lao, a thin coating of electrode material is applied to a thin metal sheet that serves as a current collector. Increasing the thickness of the coating causes performance to decline, so multiple sheets are stacked to build capacitance, increasing weight and material cost.

“With our approach, we don’t need stacking because we can increase capacitance by making the electrode thicker without sacrificing performance,” Yao said.

The researchers managed to increase the thickness of the electrodes to four millimeters without sacrificing performance. The electrodes were designed with a periodic pore structure that allows for both uniform deposition of the material and efficient ion distribution for charging and discharging. The printed structure itself is a lattice made from cylindrical porous rods of the graphene aerogel. Manganese oxide is then deposited onto the lattice.

“The key innovation in this study is the use of 3D printing to fabricate a rationally designed structure providing a carbon scaffold to support the pseudocapacitive material,” Li said. “These findings validate a new approach to fabricating energy storage devices using 3D printing.”

Supercapacitor devices made with the electrodes showed good cycling stability, retaining more than 90 percent of initial capacitance after 20,000 cycles of charging and discharging. The 3D printed electrodes allow for a large amount of design flexibility, and the graphene-based inks offer ultrahigh surface area, lightweight properties, elasticity, and superior electrical conductivity.

Authors of the paper include Bin Yao, Swetha Chandrasekaran, Jing Zhang, Wang Xiao, Fang Qian, Cheng Zhu, Eric B. Duoss, Christopher M. Spadaccini, Marcus A. Worsley and Yat Li.

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LLNL machine learning detects 3D printer failures with 10ms of video

Engineers and scientists at Lawrence Livermore National Laboratory (LLNL), California, have applied an algorithm to detect flaws in parts as they are 3D printed. Convolutional neural networks (CNNs), used with real-time in situ monitoring cameras present the next step toward an ability to “fix it on the fly” and improve the reliability of metal additive systems. “This […]

LLNL Researchers Use Laser Beam Shaping to Enhance Properties During Metal 3D Printing

Custom laser powder bed fusion test setup for producing single track samples in an argon flow and capturing high speed image data of the process.

From bioprinting blood vessels and using 3D printing to control reactive materials to 3D printing nanoporous gold and researching metal 3D printing flaws, the scientists at Lawrence Livermore National Laboratory (LLNL) are well known for their impressive work with 3D printing materials. Recently, a group of LLNL researchers explored the use of spatial laser modulation in enhancing the processability and properties of 3D printing metals. The team created a custom laser powder bed fusion (LPBF) test bed, which can produce single tracks of steel 316L under various conditions.

Top and transversal cross-sectional views of simulated melt-track formation by the Gaussian (a, b) and longitudinal elliptical (c, d) beams, where laser scanning occurs in the positive x-direction.

The alloys used most often for metal 3D printing, like 316L stainless steel, titanium alloys like Ti6Al4V, Inconel 718/625 superalloys, and aluminum alloys such as AlCuMgScSi, are more developed for standard manufacturing than they are for AM processing; reasons for this include unsuitable materials feedstocks, little control over local thermal histories that drive microstructure control, and deficient predictive capabilities due to limited data from in situ process monitoring.

In addition, while metal LPBF 3D printing has a lot of potential for a wide variety of applications, it lacks the degree of control that’s necessary to produce parts that can meet exacting, performance-driven criteria. In order to continue driving 3D printing from a rapid prototyping mindset to rapid manufacturing, it’s important to have in-depth knowledge of the AM process and the structures it can create. To do this, the LLNL researchers are working to develop a new science-based AM design strategy that can control thermal history by using tailored and simulation-driven light sources.

M.J. Matthews, T.T. Roehling, S.A. Khairallah, G. Guss, S.Q. Wu, M.F. Crumb, J.D. Roehling, and J.T. McKeown with LLNL recently published a paper, titled “Spatial modulation of laser sources for microstructural control of additively manufactured metals,” where they demonstrate how beam ellipticity can be used for microstructural control during LPBF 3D printing.

The abstract reads, “In this work, we explore spatial laser modulation to enhance the properties and processability of AM metals. Experiments are carried out with the goals of demonstrating control of the columnar-to-equiaxed transition, identify methods to reduce surface roughness, and extend processing windows for AM alloys. Results show that beam modulation provides site-specific microstructural control, and these results are interpreted using finite element modeling of the melt pool dynamics and thermal profiles.”

The team used simple beam shaping optical elements which could, in theory, be implemented on a commercial AM system someday.

“Thus, through engineering of the thermal gradients with such optics, it may be possible to control equiaxed or columnar grains at specified locations by modulating beam shape during a build,” the researchers wrote.

Conceptual framework for tuning material properties in AM using tailored light sources like shaped beams.

316L stainless steel powder from Concept Laser on 316L stainless steel substrates was used during the single-track laser melting experiments. In their LPBF testbed, the team used a 50 mm FL lens to make rays of light from of a 600 W fiber laser parallel. Using LLNL’s ALE3D numerical simulation software tool, the researchers modeled the actual particle size distribution and random particle packing, before using a laser ray tracing algorithm to simulate laser interaction with the actual powder bed.

“The three-dimensional model was addressed using a hybrid finite element and finite volume formulation on an unstructured grid,” the researchers wrote. Simulations were run using each beam shape at Size S for P = 550 W. To conserve computational time, the scan velocity was set at 1800 mm/s, resulting in an energy density of 61 J/mm3. This energy density is slightly lower than the minimum value used in the experiments (80 J/mm3).”

Microstructure cross-sections as a function of beam shape: (a) Gaussian, (b) longitudinal elliptical and (c) transverse elliptical.

Using LLNL’s ALE3D code to model laser-model interactions made it possible to investigate beam shape effects on track macro- and microstructures. The researchers determined that “equiaxed solidification was favored at lower laser powers,” independently of beam ellipticity or size; this was observed particularly when substrate penetration by the melt was poor or even absent.

The concentration of columnar grains generally increases when the power and scan speed goes up as well, and the parameter space, “over which equiaxed or mixed equiaxed-columnar microstructures” were made,” was larger for elliptical beams than it was for Gaussian ones. This shows that it it is possible to achieve site-specific microstructural control by varying the beam ellipticity. Additionally, even more complex microstructures are possible with full builds that use alternate beam shapes.

“The effects of Gaussian and elliptical laser intensity profiles on single-track microstructures were investigated. Beam ellipticity demonstrated a strong effect on solidification microstructure. The elliptical intensity profiles produced equiaxed or mixed equiaxed-columnar grains over a much larger parameter space than the circular profiles when conduction-mode laser heating occurred. This indicates that grain morphology can be tailored by varying beam intensity spatial profile while maintaining constant laser power and scan speed,” the researchers concluded.

Because the research showed that it’s possible to locally tune microstructures, users can now engineer site-specific properties right into 3D printed parts, which ultimately means more design flexibility.

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Lawrence Livermore National Laboratory Makes 3D Printed Nanoporous Gold That Could Change the Design of Electrochemical Reactors

[Image: Ryan Chen/LLNL]

Lawrence Livermore National Laboratory (LLNL) is known for doing impressive work with materials, particularly related to 3D printing. Whether it’s nanoscale 3D printing or 3D printed glass, the organization is constantly making new discoveries. In its latest study, entitled “Toward digitally controlled catalyst architectures: Hierarchical nanoporous gold via 3D printing,” LLNL researchers along with those from Harvard University discuss the hierarchical printing of nanoporous gold. According to the researchers, this work could have a major impact on the design of chemical reactors.

Nanoporous metals are strong catalysts for chemical reactions, as they have a large surface area and high electrical conductivity. This makes them well-suited to applications such as electrochemical reactors, sensors and actuators.

“If you consider traditional machining processes, it’s time consuming and you waste a lot of materials — also, you don’t have the capability to create complex structures,” said LLNL postdoctoral researcher Zhen Qi, a co-author on the paper. “By using 3D printing we can realize macroporous structures with application-specific flow patterns. By creating hierarchical structures, we provide pathways for fast mass transport to take full advantage of the large surface area of nanoporous materials. It’s also a way to save materials, especially precious metals.”

[Image: Ryan Chen/LLNL]

The researchers combined an extrusion-based direct ink writing process with an alloying and dealloying process to engineer nanoporous gold into three distinct scales, from the microscale to the nanoscale. According to the team, the hierarchical structure “dramatically improves mass transport and reaction rates for both liquid and gases.” Being able to manipulate the catalyst’s surface area to generate electrochemical reactions through 3D printing could have a big impact on electrochemical plants, which currently rely mostly on thermal energy.

“By controlling the multiscale morphology and surface area of 3D porous materials, you can start to manipulate the mass transport properties of these materials,” said LLNL researcher Eric Duoss. “With hierarchal structures you have channels that can handle transfer of reactants and products for different reactions. It’s like transportation systems, where you go from seven-lane expressways down to multiple lane highways to thoroughfares and side streets, but instead of transporting vehicles we’re transporting molecules.”

LLNL researcher Cheng Zhu and former postdoctoral student Wen Chen made inks out of gold and silver nanoparticles, which were then 3D printed. The printed parts were placed into a furnace to allow the particles to coalesce into a gold-silver alloy. The team then put the parts into a chemical bath that removed the silver in a process called dealloying, leaving porous gold behind.

“The final part is a 3D hierarchical gold architecture comprising the macroscale printed pores and the nanoscale pores that result from dealloying,” said Chen, who is currently a professor at the University of Massachusetts-Amherst. “Such hierarchical 3D architectures allow us to digitally control the morphology of the macropores, which allowed us to realize the desired rapid mass transport behavior.”

According to Zhu and Chen, the method can also be applied to other metals such as magnesium, nickel and copper, opening up 3D printing applications in fields such as catalysis, batteries, supercapacitors and carbon dioxide reduction.

The challenge in catalysis, according to LLNL researcher Juergen Biener, is in combining high surface area with rapid transport.

“While additive manufacturing is an ideal tool to create complex macroscale structures, it remains extremely difficult to directly introduce the nanostructures that provide the required high surface area,” Biener said. “We overcame this challenge by developing a metallic ink-based approach that allowed us to introduce nanoporosity through a selective corrosion process called dealloying.”

Biener said that the team’s extrusion-based approach is universal and scalable, provides tooling-free control over the macroscopic sample shape, and enables integration of nanoporosity in an application-specific engineered macroporous network structure. These advantages open new design possibilities for chemical reactor and energy storage and conversion devices.

The project is part of a feasibility study into a proposed strategic initiative to create 3D electrochemical reactors in which scientists could have greater control over catalysts and reduce transport limitations. Instead of large electrochemical plants, which are located near oil refineries or in remote areas, modular reactor networks could be created in a series that could be easily replaceable and transportable to locations near sources of abundant renewable energy or carbon dioxide.

“There are a whole lot of scientific and engineering challenges left, but it could have significant impact,” said Chris Spadaccini, director of LLNL’s Center for Engineered Materials and Manufacturing. “Scaling up should be easier with small-scale reactors because you can parallelize. You could have an array of small 3D reactors together instead of one large vessel enabling you to control the chemical reaction process more effectively.”

The researchers are also starting to explore other materials that could be catalysts for other reactions.

Authors of the paper include Cheng Zhu, Zhen Qi, Victor A. Beck, Mathilde Luneau, Judith Lattimer, Wen Chen, Marcus A. Worsley, Jianchao Ye, Eric B. Duoss, Christopher M. Spadaccini,  Cynthia M. Friend and Juergen Biener. 

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[Source: Newswise]

Virginia Tech and LLNL develop light based method of 3D printing graphene

Virginia Tech and Lawrence Livermore National Laboratory (LLNL) have developed a high resolution method of 3D printing graphene that is “an order of magnitude greater” than any 3D printed before. Aiming to unlock ways to make graphene in any shape or quantity, the researchers have moved one step closer to harnessing its true potential as the strongest […]