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Compact new microscope chemically identifies micrometer-sized particles

Multiple types of micrometer-sized particles are simultaneously illuminated by a far-infrared laser and a green laser beam. Absorption of the infrared laser energy by the particles increases their temperatures, causing them to expand and slightly altering their visible-light optical properties. These changes are unique to the material composition of each particle and can be measured by examining the modulation of scattered green light from each particle. (credit: Ryan Sullenberger, MIT Lincoln Laboratory)

MIT researchers have developed a radical design for a low-cost, miniaturized microscope that can chemically identify individual micrometer-sized particles. It could one day be used in airports or other high-security venues as a highly sensitive and low-cost way to rapidly screen people for microscopic amounts of potentially dangerous materials. It could also be used for scientific analysis of very small samples or for measuring the optical properties of materials.

Optical setup for PMMS measurement scheme. A tunable far-IR laser (QCL) or pump projects laser light (shown in this illustration as red, but actually invisible far-IR, or thermal energy) and a 532 nm laser (probe) projects green light onto the same location on a sample, which consists of microspheres deposited onto a ZnSe substrate in this experiment. A visible-light camera fitted with a 16× microscopic lens images the particles directly. The white LED is used to help locate the particles. (credit: R. M. Sullenberger et al./ Optics Letters)

In an open-access paper in the journal Optics Letters, from The Optical Society (OSA), the researchers demonstrated their new “photothermal modulation of Mie scattering” (PMMS) microscope by measuring infrared spectra of individual 3-micrometer spheres made of silica or acrylic. The new technique uses a simple optical setup consisting of compact components that will allow the instrument to be miniaturized into a portable device about the size of a shoebox.

The new microscope’s use of visible wavelengths for imaging gives it a spatial resolution of around 1 micrometer, compared to the roughly 10-micrometer resolution of traditional infrared spectroscopy methods. This increased resolution allows the new technique to distinguish and identify individual particles that are extremely small and close together.*

“If there are two very different particles in the field of view, we’re able to identify each of them,” said Stolyarov. “This would never be possible with a conventional infrared technique because the image would be indistinguishable.”

“The most important advantage of our new technique is its highly sensitive, yet remarkably simple design,” said Ryan Sullenberger, associate staff at MIT Lincoln Labs and first author of the paper. “It provides new opportunities for nondestructive chemical analysis while paving the way towards ultra-sensitive and more compact instrumentation.”

Probing spectral fingerprints

A typical far-IR spectrometer (credit: NYU)

Infrared spectroscopy is typically used to identify unknown materials because almost every material can be identified by its unique far-infrared absorption spectrum, or fingerprint. The new method detects this fingerprint without using actual far-infrared detectors, which add significant bulk to traditional instruments. That limits their use as portable devices — also because of their requirement for cooling.

The new technique works by illuminating particles with both an far-infrared laser and a green laser. The far-infrared laser deposits energy into the particles, causing them to heat up and expand. The green laser light is then scattered by these heated particles. A visible-wavelength camera is used to monitor this scattering, tracking physical changes of the individual particles through the microscope’s lens.

The instrument can be used to identify the material composition of individual particles by tuning the far-infrared laser to different wavelengths and collecting the visible scattered light at each wavelength. The slight heating of the particles doesn’t impart any permanent changes to the material, making the technique ideal for non-destructive analysis.

The ability to excite particles with infrared light and then look at their scattering with visible wavelengths — a process called photothermal modulation of Mie scattering — has been used since the 1980s. This new work uses more advanced optical components to create and detect the Mie scattering and is the first to use an imaging configuration to detect multiple species of particles.

“We’re actually imaging the area that we’re interrogating,” said Alexander Stolyarov, technical staff and a co-author of the paper. “This means we can simultaneously probe multiple particles on the surface at the same time.”

Compact, tunable infrared laser

The development of compact, tunable quantum-cascade infrared lasers was a key enabling technology for the new technique. The researchers combined a quantum-cascade laser with a very stable visible laser source and a commercially available scientific-grade camera.

“We are hoping to see an improvement in high-power wavelength-tunable quantum cascade lasers,” said Sullenberger. “A more powerful infrared laser enables us to interrogate larger areas in the same amount of time, allowing more particles to be probed simultaneously.”

The researchers plan to test their microscope on additional materials, including particles that are not spherical in shape. They also want to test their setup in more realistic environments that might contain interfering particles.

The work was supported by the U.S. Assistant Secretary of Defense for Research and Engineering under an Air Force contract.

* “By using a visible probe beam and camera for registering the particle absorption, we are able to spectroscopically identify individual particles that are spaced closer than the IR diffraction limit, which represents a significant improvement over conventional IR spectroscopic imaging techniques,” the authors note.

Abstract of Spatially-resolved individual particle spectroscopy using photothermal modulation of Mie scattering

We report a photothermal modulation of Mie scattering (PMMS) method that enables concurrent spatial and spectral discrimination of individual micron-sized particles. This approach provides a direct measurement of the “fingerprint” infrared absorption spectrum with the spatial resolution of visible light. Trace quantities (tens of picograms) of material were deposited onto an infrared-transparent substrate and simultaneously illuminated by a wavelength-tunable intensity-modulated quantum cascade pump laser and a continuous-wave 532 nm probe laser. Absorption of the pump laser by the particles results in direct modulation of the scatter field of the probe laser. The probe light scattered from the interrogated region is imaged onto a visible camera, enabling simultaneous probing of spatially-separated individual particles. By tuning the wavelength of the pump laser, the IR absorption spectrum is obtained. Using this approach, we measured the infrared absorption spectra of individual 3 μm PMMA and silica spheres. Experimental PMMS signal amplitudes agree with modeling using an extended version of the Mie scattering theory for particles on substrates, enabling the prediction of the PMMS signal magnitude based on the material and substrate properties.

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Intricate microdevices that can be safely implanted

Fabrication and assembly of an iMEMS microdevice. Left: layer-by-layer fabrication of support structures and assembly of gear components. Right: the complete device after the layers have been sealed, with ferromagnetic iron material (black) to enable external magnetic control. (credit: SauYin Chin/Columbia Engineering)

Columbia Engineering researchers have invented a technique for manufacturing complex microdevices with three-dimensional, freely moving parts made from biomaterials that can safely be implanted in the body. Potential applications include a drug-delivery system to provide tailored drug doses for precision medicine, catheters, stents, cardiac pacemakers, and soft microbotics.

Most current implantable microdevices have static components rather than moving parts and, because they require batteries or other toxic electronics, they have limited biocompatibility.

The new technique stacks a soft biocompatible hydrogel material in layers, using a fast manufacturing method the researchers call “implantable microelectromechanical systems” (iMEMS).

iMEMS drug-delivery system. The payload delivery system was tested in a bone cancer mouse model, finding that the triggering of releases of doxorubicin from the device over 10 days showed high treatment efficacy and low toxicity, at 1/10th of the standard systemic chemotherapy dose. The device contains iron nanoparticle–doped components, which respond to external magnetic actuation. Actuation of the device triggers release of payloads from reservoirs. (credit: Sau Yin Chin et al./Science Robotics)

“Our iMEMS platform enables development of biocompatible implantable microdevices with a wide range of intricate moving components that can be wirelessly controlled on demand, and solves issues of device powering and biocompatibility,” says Biomedical Engineering Professor Sam Sia, senior author of an open-access paper published online January 4, 2017, in Science Robotics).

The researchers were able to trigger the iMEMS device to release payloads over days to weeks after implantation, with precise actuation by using magnetic forces to induce gear movements that, in turn, bend structural beams made of hydrogels with highly tunable properties. (Magnetic iron particles are commonly used and are FDA-approved for human use as contrast agents.)

Batteryless implantable medical devices or sensors

Sia’s iMEMS technique addresses several issues in building biocompatible microdevices, micromachines, and microrobots: how to power small robotic devices without using toxic batteries; how to make small, biocompatible, moveable components that are not silicon, which has limited biocompatibility; and how to communicate wirelessly once implanted (radio-frequency microelectronics require power, are relatively large, and are not biocompatible).

The researchers developed a “locking mechanism” for precise actuation and movement of freely moving parts, which can function as valves, manifolds, rotors, pumps, and drug delivery systems. They were able to tune the biomaterials within a wide range of mechanical and diffusive properties and to control them after implantation without a sustained power supply, such as a toxic battery.

“We can make small implantable devices, sensors, or robots that we can talk to wirelessly. Our iMEMS system could bring the field a step closer to developing soft miniaturized robots that can safely interact with humans and other living systems,” said Sia.

The team developed a drug delivery system and tested it on mice with bone cancer. The iMEMS system delivered chemotherapy adjacent to the cancer, and limited tumor growth while showing less toxicity than with chemotherapy administered throughout the body.

The study was supported by the National Science Foundation, NIH, and the Agency for Science, Technology and Research (Singapore).

* The team used light to polymerize sheets of gel and incorporated a stepper mechanization to control the z-axis and pattern the sheets layer by layer, giving them three-dimensionality. Controlling the z-axis enabled the researchers to create composite structures within one layer of the hydrogel while managing the thickness of each layer throughout the fabrication process. They were able to stack multiple layers that are precisely aligned and, because they could polymerize a layer at a time, one right after the other, the complex structure was built in under 30 minutes.

“Hydrogels are difficult to work with, as they are soft and not compatible with traditional machining techniques,” says Sau Yin Chin, lead author of the study, who worked with Sia. “We have tuned the mechanical properties and carefully matched the stiffness of structures that come in contact with each other within the device. Gears that interlock have to be stiff in order to allow for force transmission and to withstand repeated actuation. Conversely, structures that form locking mechanisms have to be soft and flexible to allow for the gears to slip by them during actuation, while at the same time they have to be stiff enough to hold the gears in place when the device is not actuated. We also studied the diffusive properties of the hydrogels to ensure that the loaded drugs do not easily diffuse through the hydrogel layers.”

Abstract of Additive manufacturing of hydrogel-based materials for next-generation implantable medical devices

Implantable microdevices often have static components rather than moving parts and exhibit limited biocompatibility. This paper demonstrates a fast manufacturing method that can produce features in biocompatible materials down to tens of micrometers in scale, with intricate and composite patterns in each layer. By exploiting the unique mechanical properties of hydrogels, we developed a “locking mechanism” for precise actuation and movement of freely moving parts, which can provide functions such as valves, manifolds, rotors, pumps, and delivery of payloads. Hydrogel components could be tuned within a wide range of mechanical and diffusive properties and can be controlled after implantation without a sustained power supply. In a mouse model of osteosarcoma, triggering of release of doxorubicin from the device over 10 days showed high treatment efficacy and low toxicity, at 1/10 of the standard systemic chemotherapy dose. Overall, this platform, called implantable microelectromechanical systems (iMEMS), enables development of biocompatible implantable microdevices with a wide range of intricate moving components that can be wirelessly controlled on demand, in a manner that solves issues of device powering and biocompatibility.

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Synthetic stem cells offer benefits of natural stem cells without the risks

A synthetic cardiac stem cell (left) mirroring a real cardiac stem cell (right), offering therapeutic benefits without the associated risks (credit: Alice Harvey/NC State University)

Scientists have created the first synthetic version of a cardiac stem cell, offering therapeutic benefits comparable to those from natural stem cells — but without the risks and limitations, according to researchers from North Carolina State University, the University of North Carolina at Chapel Hill, and First Affiliated Hospital of Zhengzhou University in China.

The newly created “synthetic stem cells” (not actual stem cells — not even cells — just clever mimics) cannot replicate. That means they could reduce some of the risks associated with natural stem-cell therapies — including tumor growth and immune rejection. The synthetic stem calls would also avoid the fragility of natural stem cells, which require careful storage and a multi-step process of typing and characterization before they can be used.

Simulating cardiac stem cells with synthetic stem cells: a cargo-shell strategy

In an in vitro (test tube) experiment described in an open-access paper in Nature Communications, the scientists created synthetic “cell-mimicking microparticles” (CMMPs) and tested them on a mouse model with myocardial infarction.

The scientists found that the CMMPs’ ability to bind to cardiac tissue and promote growth after a heart attack was comparable to that of cardiac stem cells. But unlike cardiac (and other) natural stem cells, the synthetic stem cells have better preservation stability, and the technology is also generalizable to other types of stem cells, according to the researchers.

A cargo-and-shell strategy. The therapeutic potential of CMMPs was successfully tested in tissue repair of a mouse model of myocardial infarction. To create the synthetic stem cell, a microparticle (MP) was first fabricated from PLGA, or poly(lactic-co-glycolic acid) — a biodegradable, biocompatible polymer that serves as a dissolvable carrier. The MP contained conditioned media and growth factors* (the “cargo”) from cardiac stem cells (CSC) in its polymeric core — forming a synthetic cell-mimicking microparticle (CMMP). To prevent an immune reaction, the researchers also cloaked the CMMP with a coating from the cardiac stem-cell membrane (forming the “shell”). (credit: Junnan Tang et al./Nature Communications)

“The synthetic cells operate much the same way a deactivated vaccine works,” explains research-team leader Ke Cheng, associate professor of molecular biomedical sciences at NC State, associate professor in the joint biomedical engineering program at NC State and UNC, and adjunct associate professor at the UNC Eshelman School of Pharmacy. “[The synthetic cells'] membranes allow them to bypass the immune response, bind to cardiac tissue, release the growth factors, and generate repair, but they cannot amplify [and thus risk out-of-control growth, leading to tumors] by themselves. So you get the benefits of stem cell therapy without risks.”

Multiple stem-cell types and organs

The synthetic stem cells are also much more durable than human stem cells, they can tolerate harsh freezing and thawing, and they don’t have to be derived from the patient’s own cells, the researchers note.

“Although our first application targeted the heart, the CMMP strategy represents a platform technology that can be applied to multiple stem cell types and the repair of various organ systems,” the authors state in the paper.

The work was funded in part by the National Institutes of Health, NC State Chancellor’s Innovation Fund, and University of North Carolina General Assembly Research Opportunities Initiative grant.

* Stem-cell therapies work by secreting “paracrine factors,” including proteins and genetic materials, that aid damaged tissue in repairing itself.

Abstract of Therapeutic microparticles functionalized with biomimetic cardiac stem cell membranes and secretome

Stem cell therapy represents a promising strategy in regenerative medicine. However, cells need to be carefully preserved and processed before usage. In addition, cell transplantation carries immunogenicity and/or tumorigenicity risks. Mounting lines of evidences indicate that stem cells exert their beneficial effects mainly through secretion (of regenerative factors) and membrane-based cell-cell interaction with the injured cells. Herein, we fabricated a synthetic cell-mimicking microparticle (CMMP) that recapitulates stem cell functions in tissue repair. CMMPs carries similar secreted proteins and membranes as genuine cardiac stem cells do. In a mouse model of myocardial infarction, injection of CMMPs leads to preservation of viable myocardium and augmentation of cardiac functions similar to cardiac stem cell therapy. CMMPs (derived from human cells) do not stimulate T cells infiltration in immuno-competent mice. In conclusion, CMMPs act as “synthetic stem cells” which mimic the paracrine and biointerfacing activities of natural stem cells in therapeutic cardiac regeneration.

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Nanowire ‘inks’ enable low-cost paper- or plastic-based printable electronics

Duke University chemists have found that silver nanowire films like these conduct electricity well enough to form functioning circuits without applying high temperatures, enabling printable electronics on materials like paper or plastic. (credit: Ian Stewart and Benjamin Wiley)

By suspending tiny metal nanoparticles in liquids, Duke University scientists can use conductive ink-jet-printed conductive “inks” to print inexpensive, customizable RFID and other electronic circuit patterns on just about any surface — even on paper and plastics.

Printed electronics, which are already being used widely in devices such as the anti-theft radio frequency identification (RFID) tags you might find on the back of new DVDs, currently have one major drawback: for the circuits to work, they first have to be heated to 200° C (392°F) to melt all the nanoparticles together into a single conductive wire.

But Duke researchers have now found that electrons are conducted through films made of silver nanowires much more easily than with films made from other shapes (like nanospheres or microflakes). And the nanowire films can now function in printed circuits without the need to melt them first — heating at only 70° C (158°F) is required — and that means the circuits can be printed on cheaper plastics or paper.

“The nanowires [in their research] had a 4,000 times higher conductivity than the more commonly used silver nanoparticles that you would find in printed antennas for RFID tags,” said Benjamin Wiley, assistant professor of chemistry at Duke.

The technology could also be used to make lower-cost solar cells, printed displays, LEDs, touchscreens, amplifiers, batteries, and even some implantable bio-electronic devices. The results appeared online Dec. 16 in ACS Applied Materials and Interfaces.

The team is now experimenting with using aerosol jets to print silver nanowire inks in usable circuits. Wiley says they also want to explore whether silver-coated copper nanowires, which are significantly cheaper to produce than pure silver nanowires, will give the same effect.

This research was supported by funding from the National Science Foundation and a GAANN Fellowship through the Duke Chemistry Department.

Abstract of Effect of Morphology on the Electrical Resistivity of Silver Nanostructure Films

The relatively high temperatures (>200 °C) required to sinter silver nanoparticle inks have limited the development of printed electronic devices on low-cost, heat-sensitive paper and plastic substrates. This article explores the change in morphology and resistivity that occurs upon heating thick films of silver nanowires (of two different lengths; Ag NWs), nanoparticles (Ag NPs), and microflakes (Ag MFs) at temperatures between 70 and 400 °C. After heating at 70 °C, films of long Ag NWs exhibited a resistivity of 1.8 × 10–5 Ω cm, 4000 times more conductive than films made from Ag NPs. This result indicates the resistivity of thick films of silver nanostructures is dominated by the contact resistance between particles before sintering. After sintering at 300 °C, the resistivity of short Ag NWs, long Ag NWs, and Ag NPs converge to a value of (2–3) × 10–5 Ω cm, while films of Ag MFs remain ∼10× less conductive (4.06 × 10–4 Ω cm). Thus, films of long Ag NW films heated at 70 °C are more conductive than Ag NP films sintered at 300 °C. Adding 10 wt % nanowires to a film of nanoparticles results in a 400-fold improvement in resistivity.

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A transparent, self-healing, highly stretchable conductive material

This illustration shows use of an ion-dipole interaction and self-healing material. (credit: University of Colorado, Boulder)

A team of scientists has developed a transparent, self-healing, highly stretchable conductive material that can be electrically activated to power artificial muscles or used to improve batteries, electronic devices, and robots.

The findings, published Dec. 23 in the journal Advanced Materials, combine the fields of self-healing materials and ionic conductors (a material that ions can flow through). Ionic conductors are a class of materials with key roles in energy storage, solar energy conversion, sensors, and electronic devices.

The material has potential applications in a wide range of fields. It could give robots the ability to self-heal after mechanical failure, extend the lifetime of lithium ion batteries used in electronics and electric cars, and improve biosensors used in the medical field and environmental monitoring, the scientists say.

Inspired by wound healing in nature, the idea for self-healing materials is to repair damage caused by wear, lower the cost of materials and devices, and extend their lifetime.

“Creating a material with all these properties has been a puzzle for years,” said Chao Wang*, a University of California, Riverside adjunct assistant professor of chemistry who is one of the authors of a paper published in December in Advanced Materials.

Another author of the paper, Christoph Keplinger, an assistant professor at the University of Colorado, Boulder, previously demonstrated that stretchable, transparent, ionic conductors can be used to power artificial muscles and to create transparent loudspeakers — devices that feature several of the key properties of the new material (transparency, high stretchability, and ionic conductivity).

Limitations of current self-healing polymers

Conventionally, self-healing polymers make use of non-covalent bonds, which creates a problem because those bonds are affected by electrochemical reactions that degrade the performance of the materials.

Design concept for a transparent, self-healing, highly stretchable ionic conductor using ion–dipole interaction (credit: Yue Ca et al./Advanced Materials)

Wang helped solve that problem by using a mechanism called ion-dipole interactions, which are forces between charged ions and polar molecules that are highly stable under electrochemical conditions. He combined a polar, stretchable polymer with a mobile, high-ionic-strength salt to create the material with the desired properties.

The soft rubber-like material they created is low-cost, easy to produce, and can stretch 50 times its original length. After being cut, it can completely re-attach, or heal, in 24 hours at room temperature. (After only five minutes of healing, the material can be stretched two times its original length.)

Artificial muscles

The scientists demonstrated that the material could be used to power an artificial muscle, or dielectric elastomer actuator. “Artificial muscle” is a generic term used for materials or devices that can reversibly contract, expand, or rotate due to an external stimulus such as voltage, current, pressure or temperature.

The dielectric elastomer actuator is actually three individual pieces of polymer that are stacked together. The top and bottom layers are the new material developed at UC Riverside, which is able to conduct electricity and is self-healable, and the middle layer is a transparent, non-conductive rubber-like membrane.

The researchers used electrical signals to get the artificial muscle to move. So, just like how a human muscle (such as a bicep) moves when the brain sends a signal to the arm, the artificial muscle also reacts when it receives a signal.

Most importantly, the researchers were able to demonstrate that the ability of the new material to self-heal can be used to mimic a preeminent survival feature of nature: wound-healing. After parts of the artificial muscle were cut into two separate pieces, the material healed without relying on external stimuli, and the artificial muscle returned to the same level of performance as before being cut.

* Wang developed an interest in self-healing materials because of his lifelong love of Wolverine, the comic book character who has the ability to self-heal.

Abstract of A Transparent, Self-Healing, Highly Stretchable Ionic Conductor

Self-healing materials can repair damage caused by mechanical wear, thereby extending lifetime of devices. Here, a transparent, self-healing, highly stretchable ionic conductor is presented that autonomously heals after experiencing severe mechanical damage. The design of this self-healing polymer uses ion–dipole interactions as the dynamic motif. The unique properties of this material when used to electrically activate transparent artificial muscles are demonstrated.

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MIT researchers design one of the strongest, lightest materials known

3-D-printed “gyroid” models such as this one were used to test the strength and mechanical properties of a new lightweight material (credit: Melanie Gonick/MIT)

MIT scientists said today they’ve just created one the strongest materials known (ten times stronger than steel, but also one of the lightest, with a density of just 5 percent of that of steel) by compressing and fusing flakes of graphene, a two-dimensional form of carbon.

In its two-dimensional form, graphene is thought to be the strongest of all known materials. But researchers until now have had a hard time translating that two-dimensional strength into useful three-dimensional materials.

It’s all about the geometrical configuration

But it’s not about the material itself; it’s about their unusual 3-D geometrical configuration, the researchers discovered. That suggests that similar strong, lightweight materials (in addition to graphene) could be made from a variety of materials by creating similar geometric features.

“You can replace the material itself with anything,” says Markus Buehler, the head of MIT’s Department of Civil and Environmental Engineering (CEE) and the McAfee Professor of Engineering. “The geometry is the dominant factor. It’s something that has the potential to transfer to many things.”

The findings were reported today an open-access paper in the journal Science Advances.

This illustration shows the simulation results of  compression (top left and i) and tensile (bottom left and ii) tests on 3-D graphene (credit: Zhao Qin)

By analyzing the material’s behavior down to the level of individual atoms within the structure, the engineers were able to produce a mathematical framework that very closely matches experimental observations.

Two-dimensional materials — basically flat sheets that are just one atom in thickness but can be indefinitely large in the other dimensions — have exceptional strength as well as unique electrical properties. But because of their extraordinary thinness, “they are not very useful for making 3-D materials that could be used in vehicles, buildings, or devices,” says Buehler. “What we’ve done is to realize the wish of translating these 2-D materials into three-dimensional structures.”

The trick: heat + pressure

The solution for compressing small flakes of graphene turned out to be a combination of heat and pressure. This process produced a strong, stable structure whose form resembles that of some corals and microscopic creatures called diatoms. These new shapes, which have an enormous surface area in proportion to their volume, proved to be remarkably strong.

Buehler says the process resembles what would happen with sheets of paper. Paper has little strength along its length and width, and can be easily crumpled up. But when made into certain shapes, for example rolled into a tube, suddenly the strength along the length of the tube is much greater and can support substantial weight. Similarly, the geometric arrangement of the graphene flakes after treatment naturally forms a very strong configuration.


Melanie Gonick/MIT | One of the strongest, lightweight materials known

Other applications

But many other possible applications of the material could eventually be feasible, the researchers say, for uses that require a combination of extreme strength and light weight. “You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals,” Buehler says, to gain similar advantages of strength combined with advantages in cost, processing methods, or other material properties (such as transparency or electrical conductivity).

The unusual geometric shapes that graphene naturally forms under heat and pressure look something like a Nerf ball — round, but full of holes. These shapes, known as “gyroids,” are so complex that “actually making them using conventional manufacturing methods is probably impossible,” Buehler says.

The team used 3-D-printed models of the structure, enlarged to thousands of times their natural size, for testing purposes. For actual synthesis, the researchers say, one possibility is to use the polymer or metal particles as templates, coat them with graphene by chemical vapor deposit before heat and pressure treatments, and then chemically or physically remove the polymer or metal phases to leave 3-D graphene in the gyroid form.

The same geometry could even be applied to large-scale structural materials, they suggest. For example, concrete for a structure such a bridge might be made with this porous geometry, providing comparable strength with a fraction of the weight. This approach would have the additional benefit of providing good insulation because of the large amount of enclosed airspace within it.

Because the shape is riddled with very tiny pore spaces, the material might also find application in some filtration systems, for either water or chemical processing. The mathematical descriptions derived by this group could facilitate the development of a variety of applications, the researchers say.

The research was supported by the Office of Naval Research, the Department of Defense Multidisciplinary University Research Initiative, and BASF-North American Center for Research on Advanced Materials.

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Rogue Two

Carrie Fisher just died but she will likely come back to life because the Singularity is Near and is bringing Singularity CGI with it!

Bringing the dead back to life

In the latest Star Wars movie, Rogue One, five characters were brought back as they would have looked between episodes 3 and 4 of Star Wars. They were Princess Leia, Grand Moff Tarkin, Dr. Cornelius Evazan (who said “I have the death sentence on twelve systems” in episode 4), General Dodonna, and Mon Mothma. General Dodonna and Mon Mothma were brought back with the traditional method of using actors who looked similar to the original actors. The other three were brought back with CGI (computer-generated imagery), more specifically CGI enhanced with motion capture.

Princess Leia (Carrie Fisher) created by computer in Rogue One (credit: Lucasfilm)

Grand Moff Tarkin created by computer in Rogue One (credit: Lucasfilm)

Motion capture has been used for a while including depicting Gollum in Lord of the Rings and all the apes in the latest Planet of the Apes movies but Grand Moff Tarkin was considered possibly too hard to do with today’s technology because people are better at seeing flaws in CGI humans than CGI apes and CGI twisted hobbits.

Here is how Grand Moff Tarkin was created:

English actor Guy Henry (Harry Potter) wore motion capture materials on his head so that his face could eventually be replaced with a digital likeness of Cushing’s (the original actor for Moff Tarkin). He was picked because he had a similar build and stature as Cushing and was able to speak in a similar manner.

Guy Henry looked a little different before the CGI was placed on top of him.
(credit: Industrial Light & Magic/Lucasfilm)

John Knoll, the chief creative officer at Industrial Light & Magic, wasn’t sure they were going to be able to pull this off. He said, “We did talk about Tarkin participating in conversations via hologram, or transferring that dialogue to other characters.” Tarkin ended up looking pretty good (actually fooling some critics!) although Dr. Evazan looked even better for his scene mostly because his distorted face doesn’t look completely human.

It takes a lot of work to make CGI look realistic! (credit: Industrial Light & Magic/Lucasfilm)

Nvidia

Was this CGI good enough to envision Princess Leia having a significant role using this technology? Probably not. But something amazing happened earlier this year. Nvidia completed an over $2 billion project to develop a new class of graphics/AI chips. An example of how good they were is that the new version of the Nvidia Titan X can do AI (artificial intelligence) 566% faster than the previous Titan X that was only released a year before. This $1,200 card is so popular that five months after its release Nvidia is still rationing this card to two per customer. (Disney gets to use Nvidia cards that are even more powerful than the Titan X!)

Why does Nvidia matter to Star Wars fans? Because Nvidia’s chips power the CGI in virtually all movies. Nvidia is now making 100% of the profits of all companies selling graphics cards, with their chips being put into everything from Nintendo’s newest console to every Tesla car currently being built. This has caused Nvidia to soar in value, with their stock over tripling in 2016. This means that Nvidia is going to be able to spend a lot more than $2 billion on their next generation of graphics/AI chips! (Nvidia has found a way to use about the same architecture for AI chips and regular graphics chips.)

Not only is Nvidia’s new graphics/AI chip design affecting movies but they are helping make Ray Kurzweil’s prediction of human equivalent AI by 2029 a reality. Nvidia’s CEO Jen-Hsun Huang said, “AI is going to increase in capability faster than Moore’s Law. I believe it’s a kind of a hyper Moore’s Law phenomenon because it has the benefit of continuous learning. It has the benefit of large-scale networked continuous learning. Today, we roll out a new software package, fix bugs, update it once a year. That rhythm is going to change. Software will learn from experience much more quickly. Once one smart piece of software on one device learns something, then you can over-the-air (OTA) it across the board. All of a sudden, everything gets smarter.”

Singularity CGI

Nvidia’s improved chips are part of a three layer accelerating returns juggernaut that is affecting CGI and which we will call Singularity CGI.

Layer one of Singularity CGI is better hardware with Nvidia having just switched from 28 nanometer transistors to 16/14 nanometer transistors. (They are getting 16 nanometer technology from TSMC and 14 nanometer from Samsung.) A 14 nanometer part is only 140 atoms wide! Both Samsung and TSMC will be producing 10 nanometer parts in 2017, with large Nvidia parts likely in 2018. (The 10 nanometer parts in 2017 will be for companies like Apple who don’t need large, complex chips as Nvidia does.)

Layer two of Singularity CGI is better Nvidia designs which is what Nvidia just spent over two billion dollars on. Layer three of Singularity CGI is better software. An example of this exponentially improved software is that Disney Research and Carnegie Mellon University scientists have found that three computer vision methods commonly used to reconstruct 3D scenes produce superior results in capturing facial details when they are performed simultaneously, rather than independently.

“The quality of a 3D model can make or break the perceived realism of an animation,” said Paulo Gotardo, an associate research scientist at Disney Research. “That’s particularly true for faces; people have a remarkably low threshold for inaccuracies in the appearance of facial features. PGSF (photogeometric scene flow) could prove extremely valuable because it can capture dynamically moving objects in high detail and accuracy.”

Conclusion

The growing power of Singularity CGI means that when Disney is ready to release episode 9 in 2019, Disney will be able to use much more powerful Nvidia cards and more sophisticated software to bring Carrie Fisher back to life to finish her story whose first two parts were in The Force Awakens (episode 7) in 2015 and episode 8 in 2017. (Carrie already filmed her scenes for episode 8.)

To increase the chance of success of creating a realistic Carrie Fisher, Disney will even be given $50 million thanks to insurance through Lloyd’s of London to fund this effort. May the force be with us!

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Tesla Autopilot predicts collision ahead seconds before it happens

Hans Noordsij, a Dutch Tesla driver, uploaded a Dec. 27 dashcam video that dramatically shows the new radar processing capacity of Tesla’s Autopilot and resulting auto-breaking, DarkVision Hardware reports. The system’s radar saw ahead of the car in front and tracked two cars ahead on the road. Note the audible warning a second or so before the accident.

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How to form the world’s smallest self-assembling nanowires — just 3 atoms wide

This animation shows molecular building blocks joining the tip of a growing self-assembling nanowire. Each block consists of a diamondoid — the smallest possible bit of diamond — attached to sulfur and copper atoms (yellow and brown spheres). Like LEGO blocks, they only fit together in certain ways that are determined by their size and shape. The copper and sulfur atoms form a conductive wire in the middle, and the diamondoids form an insulating outer shell. (credit: SLAC National Accelerator Laboratory)

Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids* — the smallest possible bits of diamond — to self-assemble atoms, LEGO-style, into the thinnest possible electrical wires, just three atoms wide.

The new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results last week in Nature Materials.

The researchers started with the smallest possible diamondoids —interlocking cages of carbon and hydrogen — and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion — creating a semiconducting combination of copper and sulfur known as a chalcogenide.

A conventional insulated electrical copper wire (credit: Alibaba)

That created the basic nanowire building blocks, which then drifted toward each other, drawn by “unusually strong” van der Waals attraction between the diamondoids, and attached themselves to the growing tip of the nanowire. The attached diamondoids formed an insulating shell — creating the nanoscale equivalent of a conventional insulated electrical wire.

Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.

The team also included researchers from Lawrence Berkeley National Laboratory, the National Autonomous University of Mexico (UNAM) and Justus-Liebig University in Germany. The work was funded by the DOE Office of Science and the German Research Foundation.

* Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory.

Citation: Yan et al., Nature Materials, 26 December 2016 (10.1038/nmat4823)

Press Office Contact: Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

Abstract of Hybrid metal–organic chalcogenide nanowires with electrically conductive inorganic core through diamondoid-directed assembly

Controlling inorganic structure and dimensionality through structure-directing agents is a versatile approach for new materials synthesis that has been used extensively for metal–organic frameworks and coordination polymers. However, the lack of ‘solid’ inorganic cores requires charge transport through single-atom chains and/or organic groups, limiting their electronic properties. Here, we report that strongly interacting diamondoid structure-directing agents guide the growth of hybrid metal–organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. The strong van der Waals attraction between diamondoids overcomes steric repulsion leading to a cis configuration at the active growth front, enabling face-on addition of precursors for nanowire elongation. These nanowires have band-like electronic properties, low effective carrier masses and three orders-of-magnitude conductivity modulation by hole doping. This discovery highlights a previously unexplored regime of structure-directing agents compared with traditional surfactant, block copolymer or metal–organic framework linkers.

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MRI breakthroughs include ultra-sensitive MRI magnetic field sensing, more-sensitive monitoring without chemical or radioactive labels

Highly sensitive magnetic field sensor (credit: ETH Zurich/Peter Rüegg)

Swiss researchers have succeeded in measuring changes in strong magnetic fields with unprecedented precision, they report in the open-access journal Nature Communications. The finding may find widespread use in medicine and other areas.

In their experiments, the researchers at the Institute for Biomedical Engineering, which is operated jointly by ETH Zurich and the University of Zurich, magnetized a water droplet inside a magnetic resonance imaging (MRI) scanner, a device used for medical imaging. The researchers were able to detect even the tiniest variations of the magnetic field strength within the droplet. These changes were up to 10-12 (1 trillion) times smaller than the 7 tesla field strength of the MRI scanner used in the experiment.

“Until now, it was possible only to measure such small variations in weak magnetic fields,” says Klaas Prüssmann, Professor of Bioimaging at ETH Zurich and the University of Zurich. An example of a weak magnetic field is that of the Earth, where the field strength is just a few dozen microtesla. For fields of this kind, highly sensitive measurement methods are already able to detect variations of about a trillionth of the field strength, says Prüssmann. “Now, we have a similarly sensitive method for strong fields of more than one tesla, such as those used … in medical imaging.”

The scientists based the sensing technique on the principle of nuclear magnetic resonance (NMR), which also serves as the basis for magnetic resonance imaging and the spectroscopic methods that biologists use to elucidate the 3D structure of molecules, but with 1000 times greater sensitivity than current NMR methods.

Ultra-sensitive recordings of heart contractions in an MRI machine

Real-time magnetic field recordings of cardiac activity. Magnetic field dynamics generated by the beating human heart in a background of 7 tesla, recorded at three different positions on the chest and neck, along with simultaneous electrocardiogram (ECG). (credit: Simon Gross et al./Nature Communications)

The scientists carried out an experiment in which they positioned their sensor in front of the chest of a volunteer test subject inside an MRI scanner. They were able to detect periodic changes in the magnetic field, which pulsated in time with the heartbeat. The measurement curve is similar to an electrocardiogram (ECG), but measures a mechanical process (the contraction of the heart) rather than electrical conduction.

“We are in the process of analyzing and refining our magnetometer measurement technique in collaboration with cardiologists and signal processing experts,” says Prüssmann. “Ultimately, we hope that our sensor will be able to provide information on heart disease — and do so non-invasively and in real time.”

The new measurement technique could also be used in the development of new contrast agents for magnetic resonance imaging and improved nuclear magnetic resonance (NMR) spectroscopy for applications in biological and chemical research.

A radiation-free approach to imaging molecules in the brain

Scientists hoping to see molecules that control brain activity have devised a probe that lets them image such molecules without using chemical or radioactive labels. The sensors consist of proteins that detect a particular target, which causes them to dilate blood vessels, producing a change in blood flow that can be imaged with magnetic resonance imaging (MRI) or other techniques. (credit: Mitul Desai et al./ Nature Communications)

In a related development, MIT scientists hoping to get a glimpse of molecules that control brain activity have devised a new sensor that allows them to image these molecules without using any chemical or radioactive labels (which feature low resolution and can’t be easily used to watch dynamic events).

The new sensors consist of enzymes called proteases designed to detect a particular target, which causes them to dilate blood vessels in the immediate area. This produces a change in blood flow that can be imaged with magnetic resonance imaging (MRI) or other imaging techniques.*

A peptide called calcitonin gene-related peptide (CGRP) acts on a receptor in smooth muscle cells (left) to induce cAMP production, resulting in relaxation of vascular smooth muscle cells and consequent vasodilation (middle). That induces haemodynamic effects visible by MRI and other imaging methods (right). (credit: Mitul Desai et al./ Nature Communications)

“This is an idea that enables us to detect molecules that are in the brain at biologically low levels, and to do that with these imaging agents or contrast agents that can ultimately be used in humans,” says Alan Jasanoff, an MIT professor of biological engineering and brain and cognitive sciences. “We can also turn them on and off, and that’s really key to trying to detect dynamic processes in the brain.”

Monitoring neurotransmitters at 100 times lower levels

In a paper appearing in the Dec. 2 issue of open-access Nature Communications, Jasanoff and his colleagues explain that they used proteases (sometimes used as biomarkers to diagnose diseases such as cancer and Alzheimer’s disease) to demonstrate the validity of their approach. But now they’re working on adapting these imaging agents to monitor neurotransmitters, such as dopamine and serotonin, which are critical to cognition and processing emotions.

“What we want to be able to do is detect levels of neurotransmitter that are 100-fold lower than what we’ve seen so far. We also want to be able to use far less of these molecular imaging agents in organisms. That’s one of the key hurdles to trying to bring this approach into people,” Jasanoff says.

“Many behaviors involve turning on genes, and you could use this kind of approach to measure where and when the genes are turned on in different parts of the brain,” Jasanoff says.

His lab is also working on ways to deliver the peptides without injecting them, which would require finding a way to get them to pass through the blood-brain barrier. This barrier separates the brain from circulating blood and prevents large molecules from entering the brain.

Jeff Bulte, a professor of radiology and radiological science at the Johns Hopkins School of Medicine, described the technique as “original and innovative,” while adding that its safety and long-term physiological effects will require more study.

“It’s interesting that they have designed a reporter without using any kind of metal probe or contrast agent,” says Bulte, who was not involved in the research. “An MRI reporter that works really well is the holy grail in the field of molecular and cellular imaging.”

The research was funded by the National Institutes of Health BRAIN Initiative, the MIT Simons Center for the Social Brain, and fellowships from the Boehringer Ingelheim Fonds and the Friends of the McGovern Institute.

* To make their probes, the researchers modified a naturally occurring peptide called calcitonin gene-related peptide (CGRP), which is active primarily during migraines or inflammation. The researchers engineered the peptides so that they are trapped within a protein cage that keeps them from interacting with blood vessels. When the peptides encounter proteases in the brain, the proteases cut the cages open and the CGRP causes nearby blood vessels to dilate. Imaging this dilation with MRI allows the researchers to determine where the proteases were detected.

Another possible application for this type of imaging is to engineer cells so that the gene for CGRP is turned on at the same time that a gene of interest is turned on. That way, scientists could use the CGRP-induced changes in blood flow to track which cells are expressing the target gene, which could help them determine the roles of those cells and genes in different behaviors. Jasanoff’s team demonstrated the feasibility of this approach by showing that implanted cells expressing CGRP could be recognized by imaging.

Abstract of Dynamic nuclear magnetic resonance field sensing with part-per-trillion resolution

High-field magnets of up to tens of teslas in strength advance applications in physics, chemistry and the life sciences. However, progress in generating such high fields has not been matched by corresponding advances in magnetic field measurement. Based mostly on nuclear magnetic resonance, dynamic high-field magnetometry is currently limited to resolutions in the nanotesla range. Here we report a concerted approach involving tailored materials, magnetostatics and detection electronics to enhance the resolution of nuclear magnetic resonance sensing by three orders of magnitude. The relative sensitivity thus achieved amounts to 1 part per trillion (10−12). To exemplify this capability we demonstrate the direct detection and relaxometry of nuclear polarization and real-time recording of dynamic susceptibility effects related to human heart function. Enhanced high-field magnetometry will generally permit a fresh look at magnetic phenomena that scale with field strength. It also promises to facilitate the development and operation of high-field magnets.

Abstract of Molecular imaging with engineered physiology

In vivo imaging techniques are powerful tools for evaluating biological systems. Relating image signals to precise molecular phenomena can be challenging, however, due to limitations of the existing optical, magnetic and radioactive imaging probe mechanisms. Here we demonstrate a concept for molecular imaging which bypasses the need for conventional imaging agents by perturbing the endogenous multimodal contrast provided by the vasculature. Variants of the calcitonin gene-related peptide artificially activate vasodilation pathways in rat brain and induce contrast changes that are readily measured by optical and magnetic resonance imaging. CGRP-based agents induce effects at nanomolar concentrations in deep tissue and can be engineered into switchable analyte-dependent forms and genetically encoded reporters suitable for molecular imaging or cell tracking. Such artificially engineered physiological changes, therefore, provide a highly versatile means for sensitive analysis of molecular events in living organisms.