Northwestern University researchers have developed a way to print large, robust 3-D structures with graphene-based ink.

The new method could allow for using graphene-printed scaffolds for regenerative medicine and other medical and electronic  applications.

“People have tried to print graphene before,” said Ramille Shah, assistant professor of materials science and engineering at the McCormick School of Engineering and of surgery in the Feinberg School of Medicine.  “But it’s been a mostly polymer composite with graphene making up less than 20 percent of the volume.”

Adding higher volumes of graphene flakes to the mix in these ink systems typically results in printed structures too brittle and fragile to manipulate. At 60–70 percent graphene, the new ink preserves the material’s unique properties, including its electrical conductivity. And it’s flexible and robust enough to print robust macroscopic structures.

The secret: graphene nanoflakes are mixed with a biocompatible elastomer and fast-evaporating solvents.

“After the ink is extruded, one of the solvents in the system evaporates right away, causing the structure to solidify nearly instantly,” Shah explained. “The presence of the other solvents and the interaction with the specific polymer binder chosen also has a significant contribution to its resulting flexibility and properties. Because it holds its shape, we are able to build larger, well-defined objects.”

Could allow neurons to grow and communicate

Shah said her team populated one of the scaffolds with stem cells to surprising results. Not only did the cells survive; they divided, proliferated, and morphed into neuron-like cells.

The printed graphene structure is also flexible and strong enough to be easily sutured to existing tissues, so it could be used for biodegradable sensors and medical implants. Shah said the biocompatible elastomer and graphene’s electrical conductivity most likely contributed to the scaffold’s biological success.

“Cells conduct electricity inherently — especially neurons,” Shah said. “So if they’re on a substrate that can help conduct that signal, they’re able to communicate over wider distances.”

Supported by a Google Gift and a McCormick Research Catalyst Award, the research is described in the paper published in the April 2015 issue of ACS Nano.

Abstract of Three-Dimensional Printing of High-Content Graphene Scaffolds for Electronic and Biomedical Applications

The exceptional properties of graphene enable applications in electronics, optoelectronics, energy storage, and structural composites. Here we demonstrate a 3D printable graphene (3DG) composite consisting of majority graphene and minority polylactide-co-glycolide, a biocompatible elastomer, 3D-printed from a liquid ink. This ink can be utilized under ambient conditions via extrusion-based 3D printing to create graphene structures with features as small as 100 μm composed of as few as two layers (<300 μm thick object) or many hundreds of layers (>10 cm thick object). The resulting 3DG material is mechanically robust and flexible while retaining electrical conductivities greater than 800 S/m, an order of magnitude increase over previously reported 3D-printed carbon materials. In vitro experiments in simple growth medium, in the absence of neurogenic stimuli, reveal that 3DG supports human mesenchymal stem cell (hMSC) adhesion, viability, proliferation, and neurogenic differentiation with significant upregulation of glial and neuronal genes. This coincides with hMSCs adopting highly elongated morphologies with features similar to axons and presynaptic terminals. In vivo experiments indicate that 3DG has promising biocompatibility over the course of at least 30 days. Surgical tests using a human cadaver nerve model also illustrate that 3DG has exceptional handling characteristics and can be intraoperatively manipulated and applied to fine surgical procedures. With this unique set of properties, combined with ease of fabrication, 3DG could be applied toward the design and fabrication of a wide range of functional electronic, biological, and bioelectronic medical and nonmedical devices.

Northwestern University scientists have developed the first entirely artificial molecular pump, in which molecules pump other molecules. The pump might one day be used to power other molecular machines, such as artificial muscles.

The new machine mimics the pumping mechanism of proteins that move small molecules around living cells to metabolize and store energy from food. The artificial pump draws power from chemical reactions, driving molecules step-by-step from a low-energy state to a high-energy state — far away from equilibrium.

While nature has had billions of years to perfect its complex molecular machinery, modern science is now beginning to scratch the surface of what might be possible in tomorrow’s world.

Imitating how nature transfers energy

“Our molecular pump is radical chemistry — an ingenious way of transferring energy from molecule to molecule, the way nature does,” said Sir Fraser Stoddart, the senior author of the study. Stoddart is the Board of Trustees Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences.

“All living organisms, including humans, must continuously transport and redistribute molecules around their cells, using vital carrier proteins,” he said. “We are trying to recreate the actions of these proteins using relatively simple small molecules we make in the laboratory.”

“In some respects, we are asking the molecules to behave in a way that they would not do normally,” Cheng said. “It is much like trying to push two magnets together. The ring-shaped molecules we work with repel one another under normal circumstances. The artificial pump is able to syphon off some of the energy that changes hands during a chemical reaction and uses it to push the rings together.”

The tiny molecular machine threads the rings around a nanoscopic chain — a sort of axle — and squeezes the rings together, with only a few nanometers separating them. At present, the artificial molecular pump is able to force only two rings together, but the researchers believe it won’t be long before they can extend its operation to tens of rings and store more energy.

Compared to nature’s system, the artificial pump is very simple, but it is a start, the researchers say. They have designed a novel system, using kinetic barriers, that allows molecules to flow “uphill” energetically.

Powering artificial muscles

“This is non-equilibrium chemistry, moving molecules far away from their minimum energy state, which is essential to life,” said Paul R. McGonigal, an author of the study. “Conducting non-equilibrium chemistry in this way, with simple artificial molecules, is one of the major challenges for science in the 21st century.”

Ultimately, they intend to use the energy stored in their pump to power artificial muscles and other molecular machines. The researchers also hope their design will inspire other chemists working in non-equilibrium chemistry.

“This is completely unlike the process of designing the machinery we are used to seeing in everyday life,” Stoddart said. “In a way, one must learn to see things from the molecules’ point of view, considering forces such as random thermal motion that one would never consider when building an agricultural water pump or any other mechanical device.”

The National Science Foundation supported the research, published May 18 in the journal Nature Nanotechnology.

Animation shows the steps of the pumping mechanism, which operates in response to redox cycling, with simplified illustrations of the corresponding energy profiles. The dumbbell and the ring repel each other initially, then reduction favors complexation both thermodynamically and kinetically. Oxidation restores the repulsion between the components and causes the ring to be trapped around the dumbbell during thermal relaxation. When another reduction step is performed, attraction of a second ring from the bulk solution is kinetically favored. After oxidation and thermal relaxation, the second ring falls into the same kinetic trap as the first, resulting in the mutually repulsive rings being held in close proximity to one another.

Abstract of An artificial molecular pump

Carrier proteins consume fuel in order to pump ions or molecules across cell membranes, creating concentration gradients. Their control over diffusion pathways, effected entirely through noncovalent bonding interactions, has inspired chemists to devise artificial systems that mimic their function. Here, we report a wholly artificial compound that acts on small molecules to create a gradient in their local concentration. It does so by using redox energy and precisely organized noncovalent bonding interactions to pump positively charged rings from solution and ensnare them around an oligomethylene chain, as part of a kinetically trapped entanglement. A redox-active viologen unit at the heart of a dumbbell-shaped molecular pump plays a dual role, first attracting and then repelling the rings during redox cycling, thereby enacting a flashing energy ratchet mechanism with a minimalistic design. Our artificial molecular pump performs work repetitively for two cycles of operation and drives rings away from equilibrium toward a higher local concentration.

University of Melbourne animal welfare researcher Jean-Loup Rault, PhD says pets will soon become a luxury in an overpopulated, high-density world and the future may lie in robot pets that mimic the real thing.

“It might sound surreal for us to have robotic or virtual pets, but it could be totally normal for the next generation,” Rault said. “If 10 billion human beings live on the planet in 2050 as predicted, it’s likely to occur sooner than we think. We are already seeing people form strong emotional bonds with robot dogs in Japan.

“Pet robotics has come a long way from the Tamagotchicraze of the mid-1990s. In Japan, people are becoming so attached to their robot dogs that they hold funerals for them when the circuits die.

“You won’t find a lot of research on pet robotics out there, but if you Google robot dogs, there are countless patents. Everyone wants to get ahead of this thing because there is a market and it will take off in the next 10 to 15 years.”

“Robots can, without a doubt, trigger human emotions,” Rault added. “If artificial pets can produce the same benefits we get from live pets, does that mean that our emotional bond with animals is really just an image that we project on to our pets?

“Of course we care about live animals, but if we become used to a robotic companion that doesn’t need food, water or exercise, perhaps it will change how humans care about other living beings.”

Rault says robot pets of the future could learn to think and respond on their own.

“When engineers work on robotic dogs, they work on social intelligence, they address what people need from their dogs: companionship, love, obedience, dependence,” he said.

“They want to know everything about animal behavior so they can replicate it as close as possible to a real pet.”

And what about robotic cats? “Well, that’s a little harder because you have to make them unpredictable,” he concluded.

His open access paper is in the latest edition of Frontiers in Veterinary Science

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Playing natural sounds such as flowing water in offices could boost worker moods and improve cognitive abilities in addition to providing speech privacy, according to a new study from researchers at Rensselaer Polytechnic Institute.

An increasing number of modern open-plan offices employ sound masking systems such as “white noise” that raise the background sound of a room so that speech is rendered unintelligible beyond a certain distance and distractions are less annoying.

“If you’re close to someone, you can understand them. But once you move farther away, their speech is obscured by the masking signal,” said Jonas Braasch, an acoustician and musicologist at the Rensselaer Polytechnic Institute in New York.

Braasch and his team are currently testing whether masking signals inspired by natural sounds might work just as well, or better, than white noise. The idea was inspired by previous work by Braasch and his graduate student Mikhail Volf, which showed that people’s ability to regain focus improved when they were exposed to natural sounds versus silence or machine-based sounds.

Recently, Braasch and his graduate student Alana DeLoach built upon those results to start a new experiment.

They are exposing 12 human participants to three different sound stimuli while performing a task that requires them to pay close attention: typical office noises with the conventional random electronic signal; an office soundscape with a “natural” masker; and an office soundscape with no masker. The test subjects only encounter one of the three stimuli per visit.

The natural sound used in the experiment was designed to mimic the sound of flowing water in a mountain stream. “The mountain stream sound possessed enough randomness that it did not become a distraction,” DeLoach said. “This is a key attribute of a successful masking signal.”

They want to find out if workers who are listening to natural sounds are more productive and overall in better moods than the workers exposed to traditional masking signals.

Braasch said using natural sounds as a masking signal could have benefits beyond the office environment. “You could use it to improve the moods of hospital patients,” for example, Braasch said.

Abstract of Tuning the cognitive environment: sound masking with “natural” sounds in open-plan offices

With the gain in popularity of open-plan office design and the engineering efforts to achieve acoustical comfort for building occupants, a majority of workers still report dissatisfaction in their workplace environment. Office acoustics influence organizational effectiveness, efficiency, and satisfaction through meeting appropriate requirements for speech privacy and ambient sound levels. Implementing a sound masking system is one tried-and-true method of achieving privacy goals. Although each sound masking system is tuned for its specific environment, the signal – random steady state electronic noise, has remained the same for decades. This session explores how “natural” sounds may be used as an alternative to this standard masking signal employed so ubiquitously in sound masking systems in the contemporary office environment. As an unobtrusive background sound, possessing the appropriate spectral characteristics, this proposed use of “natural” sounds for masking challenges the convention that masking sounds should be as meaningless as possible. Based on psychophysical data and a sound-field analysis through an auditory model, we hypothesize that “natural” sounds as masking sounds have the ability (with equal success as conventional masking sounds) to meet standards and criteria for speech privacy while enhancing cognitive functioning, optimizing the ability to concentrate, and increasing overall worker satisfaction.

Infusing the polymer in a laser-induced graphene supercapacitor (used to rapidly store and discharge electricity) with boric acidquadrupled the supercapacitor’s ability to store an electrical charge while greatly boosting its energy density (energy per unit volume), Rice University researchers have found.

The Rice lab of chemist James Tour uses commercial lasers to create thin, flexible supercapacitors by burning patterns into common polymers. The laser burns away everything but the carbon to a depth of 20 microns on the top layer, which becomes a foam-like matrix of interconnected graphene flakes.

Capacitors charge quickly and release their energy in a burst when needed, as in a camera flash. Supercapacitors add the high energy capacity of batteries and have potential for electric vehicles and other heavy-duty applications. But the potential to shrink them into a small, flexible, easily produced package could make them suitable for many more applications, including catalysts, field emission transistors, and components for solar cells and lithium-ion batteries, the researchers said.

In their earlier work, the team led by Rice graduate student Zhiwei Peng tried many polymers and discovered that a commercial polyimide was the best for the process. For the new work, the lab dissolved boric acid into polyamic acid and condensed it into a boron-infused polyimide sheet, which was then exposed to the laser.

Industrial-scale production

The two-step process produces microsupercapacitors with four times the ability to store an electrical charge and five to 10 times the energy density of the earlier, boron-free version.

The new devices proved highly stable over 12,000 charge-discharge cycles, retaining 90 percent of their capacitance. In stress tests, they handled 8,000 bending cycles with no loss of performance, the researchers reported.

Tour said the technique lends itself to industrial-scale, roll-to-roll production of microsupercapacitors. “What we’ve done shows that huge modulations and enhancements can be made by adding other elements and performing other chemistries within the polymer film prior to exposure to the laser,” he said.

Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of materials science and nanoengineering and of computer science and a member of Rice’s Richard E. Smalley Institute for Nanoscale Science and Technology.

The research is detailed in the journal ACS Nano.

The Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative supported the research.

Abstract of Flexible Boron-Doped Laser Induced Graphene Microsupercapacitors

Heteroatom-doped graphene materials have been intensely studied as active electrodes in energy storage devices. Here, we demonstrate that boron-doped porous graphene can be prepared in ambient air using a facile laser induction process from boric acid containing polyimide sheets. At the same time, active electrodes can be patterned for flexible microsupercapacitors. As a result of boron doping, the highest areal capacitance of as-prepared devices reaches 16.5 mF/cm^2, three times higher than non-doped devices, with concomitant energy density increases of 5 to 10 times at various power densities. The superb cyclability and mechanical flexibility of the device is well-maintained, showing great potential for future microelectronics made from this boron-doped laser induced graphene material.

A team of MIT researchers has come up with a way to reduce immune-system rejection of implantable devices used for for drug delivery, tissue engineering, or sensing.

Previous research found that smooth surfaces, especially spheres, are better — but counterintuively, larger spheres actually work better at reducing scar tissue, the researchers discovered.

“We were surprised by how much the size and shape of an implant can affect its triggering of an immune response. What it’s made of is still an important piece of the puzzle, but it turns out if you really want to have the least amount of scar tissue you need to pick the right size and shape,” says Daniel Anderson, the Samuel A. Goldblith Associate Professor in MIT’s Department of Chemical Engineering, a member of MIT’s Koch Institute for Integrative Cancer Research and Institute for Medical Engineering and Science (IMES), and the paper’s senior author.

Tests of spheres

The study grew out of the researchers’ efforts to build an artificial pancreas. The goal is to deliver pancreatic islet cells encapsulated within a particle made of alginate — a polysaccharide (sugar) naturally found in algae — or another material. These implanted cells could replace patients’ pancreatic islet cells, which are nonfunctional in Type I diabetes.

The researchers tested spheres in two sizes — 0.5 and 1.5 millimeters in diameter. In tests of diabetic mice, the spheres were implanted within the abdominal cavity and the researchers tracked their ability to accurately respond to changes in glucose levels. The devices prepared with the smaller spheres were completely surrounded by scar tissue and failed after about a month, while the larger ones were not rejected and continued to function for more than six months.

The larger spheres also evaded the immune response in tests in nonhuman primates. Smaller spheres implanted under the skin were engulfed by scar tissue after only two weeks, while the larger ones remained clear for up to four weeks.

A universal size effect

This effect was seen not only with alginate, but also with spheres made of stainless steel, glass, polystyrene, and polycaprolactone, a type of polyester. “We realized that regardless of what the composition of the material is, this effect still persists, and that made it a lot more exciting because it’s a lot more generalizable,” said Koch Institute postdoc Omid Veiseh, one of the lead authors of a paper in the May 18 issue of Nature Materials.

The researchers believe this finding could also be applicable to any other type of implantable device, including drug-delivery vehicles and sensors for glucose and insulin, which could also help improve diabetes treatment. Optimizing particle size and shape could also help guide scientists in developing other types of implantable cells for treating diseases other than diabetes.

The research was funded by the Juvenile Diabetes Research Foundation, the Leona M. and Harry B. Helmsley Charitable Trust Foundation, the National Institutes of Health, the Koch Institute Support Grant from the National Cancer Institute, and the Tayebati Family Foundation. Veiseh was also supported by the Department of Defense.

Abstract of Size- and shape-dependent foreign body immune response to materials implanted in rodents and non-human primates

The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.