How To Strengthen 3-D Printed Parts

From aerospace and defense to digital dentistry and medical devices, 3-D printed parts are used in a variety of industries. Currently, 3-D printed parts are very fragile and traditionally used in the prototyping phase of materials or as a toy for display. A doctoral student in the Department of Materials Science and Engineering at Texas A&M University has pioneered a countermeasure to transform the landscape of 3-D printing today.

Brandon Sweeney and his advisor Dr. Micah Green, associate professor in the Department of Chemical Engineering, discovered a way to make 3-D printed parts stronger and immediately useful in real-world applications. Sweeney and Green applied the traditional welding concepts to bond the submillimeter layers in a 3-D printed part together, while in a microwave.

I was able to see the amazing potential of the technology, such as the way it sped up our manufacturing times and enabled our CAD designs to come to life in a matter of hours,” Sweeney said. “Unfortunately, we always knew those parts were not really strong enough to survive in a real-world application.

3-D printed objects are comprised of many thin layers of materials, plastics in this case, deposited on top of each other to form a desired shape. These layers are prone to fracturing, causing issues with the durability and reliability of the part when used in a real-world application, for example a custom printed medical device. “I knew that nearly the entire industry was facing this problem,” Sweeney said. “Currently, prototype parts can be 3-D printed to see if something will fit in a certain design, but they cannot actually be used for a purpose beyond that.”

When Sweeney started his doctorate, he was working with Green in the Department of Chemical Engineering at Texas Tech University. Green had been collaborating with Dr. Mohammad Saed, assistant professor in the electrical and computer engineering department at Texas Tech, on a project to detect carbon nanotubes using microwaves. The trio crafted an idea to use carbon nanotubes in 3-D printed parts, coupled with microwave energy to weld the layers of parts together.

The basic idea is that a 3-D part cannot simply be stuck into an oven to weld it together because it is plastic and will melt,” Sweeney said. “We realized that we needed to borrow from the concepts that are traditionally used for welding parts together where you’d use a point source of heat, like a torch or a TIG welder to join the interface of the parts together. You’re not melting the entire part, just putting the heat where you need it.” The technology is patent-pending and licensed with a local company, Essentium Materials.

The team recently published a paper “Welding of 3-D Printed Carbon Nanotube-Polymer Composites by Locally Induced Microwave Heating,” in Science Advances.


How To Repair Connections Between Nerve Cells

Carbon nanotubes exhibit interesting characteristics rendering them particularly suited to the construction of special hybrid devices – consisting of biological tissue and synthetic material – planned to re-establish connections between nerve cells, for instance at spinal level, lost on account of lesions or trauma. This is the result of a piece of research published on the scientific journal Nanomedicine: Nanotechnology, Biology, and Medicine conducted by a multi-disciplinary team comprising SISSA (International School for Advanced Studies), the University of Trieste, ELETTRA Sincrotrone and two Spanish institutions, Basque Foundation for Science and CIC BiomaGUNE. More specifically, researchers have investigated the possible effects on neurons of the interaction with carbon nanotubes. Scientists have proven that these nanomaterials may regulate the formation of synapses, specialized structures through which the nerve cells communicate, and modulate biological mechanisms, such as the growth of neurons, as part of a self-regulating process. This result, which shows the extent to which the integration between nerve cells and these synthetic structures is stable and efficient, highlights the great potentialities of carbon nanotubes as innovative materials capable of facilitating neuronal regeneration or in order to create a kind of artificial bridge between groups of neurons whose connection has been interrupted. In vivo testing has actually already begun.

Scientists have proven that these nanomaterials may regulate the formation of synapses, specialized structures through which the nerve cells communicate, and modulate biological mechanisms, such as the growth of neurons, as part of a self-regulating process

Interface systems, or, more in general, neuronal prostheses, that enable an effective re-establishment of these connections are under active investigation” explain Laura Ballerini (SISSA) and Maurizio Prato (UniTSCIC BiomaGUNE), coordinating the research project. “The perfect material to build these neural interfaces does not exist, yet the carbon nanotubes we are working on have already proved to have great potentialities. After all, nanomaterials currently represent our best hope for developing innovative strategies in the treatment of spinal cord injuries“. These nanomaterials are used both as scaffolds, a supportive framework for nerve cells, and as means of interfaces releasing those signals that empower nerve cells to communicate with each other.


Carbon Nanotubes Self-Assemble Into Tiny Transistors

Carbon nanotubes can be used to make very small electronic devices, but they are difficult to handle. University of Groningen (Netherlands) scientists, together with colleagues from the University of Wuppertal and IBM Zurich, have developed a method to select semiconducting nanotubes from a solution and make them self-assemble on a circuit of gold electrodes. The results look deceptively simple: a self-assembled transistor with nearly 100 percent purity and very high electron mobility. But it took ten years to get there. University of Groningen Professor of Photophysics and Optoelectronics Maria Antonietta Loi designed polymers which wrap themselves around specific carbon nanotubes in a solution of mixed tubes. Thiol side chains on the polymer bind the tubes to the gold electrodes, creating the resultant transistor.

polymer wrapped nanotube

In our previous work, we learned a lot about how polymers attach to specific carbon nanotubes, Loi explains. These nanotubes can be depicted as a rolled sheet of graphene, the two-dimensional form of carbon. ‘Depending on the way the sheets are rolled up, they have properties ranging from semiconductor to semi-metallic to metallic.’ Only the semiconductor tubes can be used to fabricate transistors, but the production process always results in a mixture.

We had the idea of using polymers with thiol side chains some time ago‘, says Loi. The idea was that as sulphur binds to metals, it will direct polymer-wrapped nanotubes towards gold electrodes. While Loi was working on the problem, IBM even patented the concept. ‘But there was a big problem in the IBM work: the polymers with thiols also attached to metallic nanotubes and included them in the transistors, which ruined them.’

Loi’s solution was to reduce the thiol content of the polymers, with the assistance of polymer chemists from the University of Wuppertal. ‘What we have now shown is that this concept of bottom-up assembly works: by using polymers with a low concentration of thiols, we can selectively bring semiconducting nanotubes from a solution onto a circuit.’ The sulphur-gold bond is strong, so the nanotubes are firmly fixed: enough even to stay there after sonication of the transistor in organic solvents.

Over the last years, we have created a library of polymers that select semiconducting nanotubes and developed a better understanding of how the structure and composition of the polymers influences which carbon nanotubes they select’, says Loi. The result is a cheap and scalable production method for nanotube electronics. So what is the future for this technology? Loi: ‘It is difficult to predict whether the industry will develop this idea, but we are working on improvements, and this will eventually bring the idea closer to the market.’

The results were published in the journal Advanced Materials on 5 April.

Stem Cells Boost Bones Repair

A recent study, affiliated with UNIST (South Korea) has developed a new method of repairing injured bone using stem cells from human bone marrow and a carbon material with photocatalytic properties, which could lead to powerful treatments for skeletal system injuries, such as fractures or periodontal disease. In the study, the research team reported that the use of human bone marrow-derived mesenchymal stem cells (hBMSCs) has been tried successfully in fracture treatment due to their potential to regenerate bone in patients who have lost large areas of bone from either disease or trauma. Recently, many attempts have been made to enhance the function of stem cells using carbon nanotubes, graphenes, and nano-oxides.

Professor Kim and Professor Suh (UNIST) examined the C₃N₄sheets. They discovered that this material absorbs red light and then emits fluorescence, which can be used to speed up bone regeneration. Professor Suh conducted a biomedical application of this material. After two days of testing, the material showed no cytotoxicity, making it useful as biomaterials.

bone-repairUpper left) Chemical bonding and physical structure of C₃N₄4 sheets. (Lower left) In a liquid state, red light is transmitted at a maximum of 450nm and emitted at a wavelength of 635 nm. (Right) After 4 weeks of loading C₃N₄4 sheets into the skull-damaged mice, the skull was regenerated by more than 90%.

This research has opened up the possibility of developing a new medicine that effectively treats skeletal injuries, such as fractures and osteoporosis,” said Professor Young-Kyo Seo. “It will be a very useful tool for making artificial joints and teeth with the use of 3D printing. This is an important milestone in the analysis of biomechanical functions needed for the development of biomaterials, including adjuvants for hard tissues such as damaged bones and teeth.”

This research has been jointly conducted by Professor Youngkyo Seo of Life Sciences and Dr. Jitendra N. Tiwari of Chemistry in collaboration with Professor Kwang S. Kim of Natural Science, Professor Pann-Ghill Suh of Life Sciences, and seven other researchers from UNIST.  The results of the study has been published in the January issue of ACS Nano journal.


3D Printing and Nanotechnology To Detect Toxic Liquids

Carbon nanotubes have made headlines in scientific journals for a long time, as has 3D printing. But when both combine with the right polymer, in this case a thermoplastic, something special occurs: electrical conductivity increases and makes it possible to monitor liquids in real time. This is a breakthrough for Polytechnique Montréal.

In practical terms, the result of this research, led by  Professor Daniel Therriault, looks like a cloth; but as soon as a liquid comes into contact with it, said cloth is able to identify its nature. In this case, it is ethanol, but it might have been another liquid. Such a process would be a terrific advantage to heavy industry, which uses countless toxic liquids.

carbon nanotubes

While deceptively simple, the recipe is so efficient that Professor Therriault protected it with a patent. In fact, a U.S. company is already looking at commercializing this material printable in 3D, which is highly conductive and has various potential applications. The first step: take a thermoplastic and, with a solvent, transform it into a solution so that it becomes a liquid. Second step: as a result of the porousness of this thermoplastic solution, carbon nanotubes can be incorporated into it like never before, somewhat like adding sugar into a cake mix. The result: a kind of black ink that’s fairly viscous and whose very high conductivity approximates that of some metals. Third step: this black ink, which is in fact a nanocomposite, can now move on to 3D printing. As soon as it comes out of the printing nozzle, the solvent evaporates and the ink solidifies. It takes the form of filaments slightly bigger than a hair. The manufacturing work can then begin.

Findings are described in the journal Small.


“Liquid Biopsy” Chip Detects Metastatic Cancer Cells in a Drop of Blood

A chip developed by mechanical engineers at Worcester Polytechnic Institute (WPI) can trap and identify metastatic cancer cells in a small amount of blood drawn from a cancer patient. The breakthrough technology uses a simple mechanical method that has been shown to be more effective in trapping cancer cells than the microfluidic approach employed in many existing devices.


The chip is tested in the lab. The electrodes detect electrical changes that occur when cancer cells are captured (click on the image to enjoy the video)

The WPI device uses antibodies attached to an array of carbon nanotubes at the bottom of a tiny well. Cancer cells settle to the bottom of the well, where they selectively bind to the antibodies based on their surface markers (unlike other devices, the chip can also trap tiny structures called exosomes produced by cancers cells). This “liquid biopsy,”  could become the basis of a simple lab test that could quickly detect early signs of metastasis and help physicians select treatments targeted at the specific cancer cells identified.

Metastasis is the process by which a cancer can spread from one organ to other parts of the body, typically by entering the bloodstream. Different types of tumors show a preference for specific organs and tissues; circulating breast cancer cells, for example, are likely to take root in bones, lungs, and the brain. The prognosis for metastatic cancer (also called stage IV cancer) is generally poor, so a technique that could detect these circulating tumor cells before they have a chance to form new colonies of tumors at distant sites could greatly increase a patient’s survival odds.

The focus on capturing circulating tumor cells is quite new,” said Balaji Panchapakesan, associate professor of mechanical engineering at WPI and director of the Small Systems Laboratory. “It is a very difficult challenge, not unlike looking for a needle in a haystack. There are billions of red blood cells, tens of thousands of white blood cells, and, perhaps, only a small number of tumor cells floating among them. We’ve shown how those cells can be captured with high precision.

The findings have been described in  the journal Nanotechnology,


Adhesive Holds From Extreme Cold To Extreme Heat

Researchers from Case Western Reserve University, Dayton Air Force Research Laboratory and China have developed a new dry adhesive that bonds in extreme temperatures—a quality that could make the product ideal for space exploration and beyond.

The gecko-inspired adhesive loses no traction in temperatures as cold as liquid nitrogen or as hot as molten silver, and actually gets stickier as heat increases, the researchers report.

The research, which builds on earlier development of a single-sided dry adhesive tape based on vertically aligned carbon nanotubes, is published in the journal Nature Communications.

Liming Dai, professor of macromolecular science and engineering at Case Western Reserve and an author of the study teamed with Ming Xu, a senior research associate at Case School of Engineering and visiting scholar from Huazhong University of Science and Technology.


Ming Xu, senior research associate at Case Western Reserve, hangs from two wooden blocks held to a painted wall with six small pieces of the double-sided adhesive.

Vertically aligned carbon nanotubes with tops bundled into nodes replicate the microscopic hairs on the foot of the wall-walking reptile and remain stable from -320 degrees Fahrenheit to 1,832 degrees, the scientists say.

When you have aligned nanotubes with bundled tops penetrating into the cavities of the surface, you generate sufficient van der Waal’s forces to hold,” Xu said. “The dry adhesive doesn’t lose adhesion as it cools because the surface doesn’t change. But when you heat the surface, the surface becomes rougher, physically locking the nanotubes in place, leading to stronger adhesion as temperatures increase.”

Because the adhesive remains useful over such a wide range of temperatures, the inventors say it is ideally suited for use in space, where the shade can be frigid and exposure to the sun blazing hot.

In addition to range, the bonding agent offers properties that could add to its utility. The adhesive conducts heat and electricity, and these properties also increase with temperature. “When applied as a double-sided sticky tape, the adhesive can be used to link electrical components together and also for electrical and thermal management,”said Ajit Roy, of the Materials and Manufacturing Directorate, Air Force Research Laboratory.

This adhesive can thus be used as connecting materials to enhance the performance of electronics at high temperatures,” Dai comments. “At room temperature, the double-sided carbon nanotube tape held as strongly as commercial tape on various rough surfaces, including paper, wood, plastic films and painted walls, showing potential use as conducting adhesives in home appliances and wall-climbing robots.”


Diamond NanoThread, The New Wonder Material

Would you dress in diamond nanothreads? It’s not as far-fetched as you might think. And you’ll have a Brisbane-based carbon chemist and engineer to thank for it. QUT’s Dr Haifei Zhan is leading a global effort to work out how many ways humanity can use a newly-invented material with enormous potential – diamond nanothread (DNT). First created by Pennsylvania State University last year, one-dimensional DNT is similar to carbon nanotubes, hollow cylindrical tubes 10,000 times smaller than human hair, stronger than steel – but brittle.


DNT, by comparison, is even thinner, incorporating kinks of hydrogen in the carbon’s hollow structure, called Stone-Wale (SW) transformation defects, which I’ve discovered reduces brittleness and adds flexibility,” said Dr Zhan, from QUT’s School of Chemistry, Physics and Mechanical Engineering.

That structure makes DNT a great candidate for a range of uses. It’s possible DNT may become as ubiquitous a plastic in the future, used in everything from clothing to cars.

DNT does not look like a rock diamond. Rather, its name refers to the way the carbon atoms are packed together, similar to diamond, giving it its phenomenal strength. Dr Zhan has been modelling the properties of DNT since it was invented, using large-scale molecular dynamics simulations and high-performance computing. He was the first to realise the SW defects were the key to DNT’s versatility.

While both carbon nanotubes and DNT have great potential, the more I model DNT properties, the more it looks to be a superior material,” Dr Zhan said. “The SW defects give DNT a flexibility that rigid carbon nanotubes can’t replicate – think of it as the difference between sewing with uncooked spaghetti and cooked spaghetti. “My simulations have shown that the SW defects act like hinges, connecting straight sections of DNT. And by changing the spacing of those defects, we can a change – or tune – the flexibility of the DNT.

That research is published in the peer-reviewed publication Nanoscale.


How To Turn Plants Into Bomb-Sniffing Machines

Spinach is no longer just a superfood: By embedding leaves with carbon nanotubes, MIT engineers have transformed spinach plants into sensors that can detect explosives and wirelessly relay that information to a handheld device similar to a smartphone. This is one of the first demonstrations of engineering electronic systems into plants, an approach that the researchers call “plant nanobionics”.


The goal of plant nanobionics is to introduce nanoparticles into the plant to give it non-native functions,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the leader of the research team.

In this case, the plants were designed to detect chemical compounds known as nitroaromatics, which are often used in landmines and other explosives. When one of these chemicals is present in the groundwater sampled naturally by the plant, carbon nanotubes embedded in the plant leaves emit a fluorescent signal that can be read with an infrared camera. The camera can be attached to a small computer similar to a smartphone, which then sends an email to the user.

This is a novel demonstration of how we have overcome the plant/human communication barrier,” says Strano, who believes plant power could also be harnessed to warn of pollutants and environmental conditions such as drought.

Strano is the senior author of a paper describing the nanobionic plants in  Nature Materials. The paper’s lead authors are Min Hao Wong, an MIT graduate student who has started a company called Plantea to further develop this technology, and Juan Pablo Giraldo, a former MIT postdoc who is now an assistant professor at the University of California at Riverside.

Michael McAlpine, an associate professor of mechanical engineering at the University of Minnesota, says this approach holds great potential for engineering not only sensors but many other kinds of bionic plants that might receive radio signals or change color. “When you have manmade materials infiltrated into a living organism, you can have plants do things that plants don’t ordinarily do,” says McAlpine, who was not involved in the research. “Once you start to think of living organisms like plants as biomaterials that can be combined with electronic materials, this is all possible.”

In the 2014 plant nanobionics study, Strano’s lab worked with a common laboratory plant known as Arabidopsis thaliana. However, the researchers wanted to use common spinach plants for the latest study, to demonstrate the versatility of this technique. “You can apply these techniques with any living plant,” Strano says. So far, the researchers have also engineered spinach plants that can detect dopamine, which influences plant root growth, and they are now working on additional sensors, including some that track the chemicals plants use to convey information within their own tissues. “Plants are very environmentally responsive,” Strano says. “They know that there is going to be a drought long before we do. They can detect small changes in the properties of soil and water potential. If we tap into those chemical signaling pathways, there is a wealth of information to access.”

These sensors could also help botanists learn more about the inner workings of plants, monitor plant health, and maximize the yield of rare compounds synthesized by plants such as the Madagascar periwinkle, which produces drugs used to treat cancer. “These sensors give real-time information from the plant. It is almost like having the plant talk to us about the environment they are in,” Wong says. “In the case of precision agriculture, having such information can directly affect yield and margins.”


Self-Healable Lithium Ion Battery For Electronic Textile

Electronics that can be embedded in clothing are a growing trend. However, power sources remain a problem. In the journal Angewandte Chemie, scientists have now introduced thin, flexible, lithium ion batteries with self-healing properties that can be safely worn on the body. Even after completely breaking apart, the battery can grow back together without significant impact on its electrochemical properties.

Existing lithium ion batteries for wearable electronics can be bent and rolled up without any problems, but can break when they are twisted too far or accidentally stepped on—which can happen often when being worn. This damage not only causes the battery to fail, it can also cause a safety problem: Flammable, toxic, or corrosive gases or liquids may leak out.

A team led by Yonggang Wang and Huisheng Peng from  Fudan University in Shanghai – China, has now developed a new family of lithium ion batteries that can overcome such accidents thanks to their amazing self-healing powers. In order for a complicated object like a battery to be made self-healing, all of its individual components must also be self-healing. The scientists from Fudan University  the Samsung Advanced Institute of Technology (South Korea), and the Samsung R&D Institute China, have now been able to accomplish this.

self-healing-batteryThe electrodes in these batteries consist of layers of parallel carbon nanotubes. Between the layers, the scientists embedded the necessary lithium compounds in nanoparticle. In contrast to conventional lithium ion batteries, the lithium compounds cannot leak out of the electrodes, either while in use or after a break. The thin layer electrodes are each fixed on a substrate of self-healing polymer. Between the electrodes is a novel, solvent-free electrolyte made from a cellulose-based gel with an aqueous lithium sulfate solution embedded in it. This gel electrolyte also serves as a separation layer between the electrodes.

After a break, it is only necessary to press the broken ends together for a few seconds for them to grow back together. Both the self-healing polymer and the carbon nanotubes “stick” back together perfectly. The parallel arrangement of the nanotubes allows them to come together much better than layers of disordered carbon nanotubes. The electrolyte also poses no problems. Whereas conventional electrolytes decompose immediately upon exposure to air, the new gel is stable. Free of organic solvents, it is neither flammable nor toxic, making it safe for this application.

The capacity and charging/discharging properties of a batteryarmband” placed around a doll’s elbow were maintained, even after repeated break/self-healing cycles.


Nanocomputer Confirms The Moore’s Law

A research team led by faculty scientist Ali Javey at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has done just that by creating a transistor with a working 1-nanometer gate. For comparison, a strand of human hair is about 50,000 nanometers thick. The development could be key to keeping alive Intel co-founder Gordon Moore’s prediction that the density of transistors on integrated circuits would double every two years, enabling the increased performance of our laptops, mobile phones, televisions, and other electronics. For more than a decade, engineers have been eyeing the finish line in the race to shrink the size of components in integrated circuits. They knew that the laws of physics had set a 5-nanometer threshold on the size of transistor gates among conventional semiconductors, about one-quarter the size of high-end 20-nanometer-gate transistors now on the market.


We made the smallest transistor reported to date,” said Javey, lead principal investigator of the Electronic Materials program in Berkeley Lab’s Materials Science Division. “The gate length is considered a defining dimension of the transistor. We demonstrated a 1-nanometer-gate transistor, showing that with the choice of proper materials, there is a lot more room to shrink our electronics.” The key was to use carbon nanotubes and molybdenum disulfide (MoS2), an engine lubricant commonly sold in auto parts shops. MoS2 is part of a family of materials with immense potential for applications in LEDs, lasers, nanoscale transistors, solar cells, and more.

The findings were published in the journal Science.


Nanocomputer: Carbon Nanotube Transistors Outperform Silicon

For decades, scientists have tried to harness the unique properties of carbon nanotubes to create high-performance electronics that are faster or consume less power — resulting in longer battery life, faster wireless communication and faster processing speeds for devices like smartphones and laptops. But a number of challenges have impeded the development of high-performance transistors made of carbon nanotubes, tiny cylinders made of carbon just one atom thick. Consequently, their performance has lagged far behind semiconductors such as silicon and gallium arsenide used in computer chips and personal electronics.

Now, for the first time, University of Wisconsin–Madison materials engineers have created carbon nanotube transistors that outperform state-of-the-art silicon transistors. Led by Michael Arnold and Padma Gopalan, UW–Madison professors of materials science and engineering, the team’s carbon nanotube transistors achieved current that’s 1.9 times higher than silicon transistors. The researchers reported their advance in a paper published in the journal Science Advances.

carbon nanotube integrated circuits

This achievement has been a dream of nanotechnology for the last 20 years,” says Arnold. “Making carbon nanotube transistors that are better than silicon transistors is a big milestone. This breakthrough in carbon nanotube transistor performance is a critical advance toward exploiting carbon nanotubes in logic, high-speed communications, and other semiconductor electronics technologies.”

This advance could pave the way for carbon nanotube transistors to replace silicon transistors and continue delivering the performance gains the computer industry relies on and that consumers demand. The new transistors are particularly promising for wireless communications technologies that require a lot of current flowing across a relatively small area.