Category Archives: light

Light-based computation made better with silver

It’s pretty amazing to imagine a future where computers run on light but according to a May 16, 2017 news item on ScienceDaily the idea is not beyond the realms of possibility,

Tomorrow’s computers will run on light, and gold nanoparticle chains show much promise as light conductors. Now Ludwig-Maximilians-Universitaet (LMU) in Munich scientists have demonstrated how tiny spots of silver could markedly reduce energy consumption in light-based computation.

Today’s computers are faster and smaller than ever before. The latest generation of transistors will have structural features with dimensions of only 10 nanometers. If computers are to become even faster and at the same time more energy efficient at these minuscule scales, they will probably need to process information using light particles instead of electrons. This is referred to as “optical computing.”

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. Capture: Liedl/Hohmann (NIM)

A March 15, 2017 LMU press release (also one EurekAlert), which originated the news item, describes a current use of light in telecommunications technology and this latest research breakthrough (the discrepancy in dates is likely due to when the paper was made available online versus in print),

Fiber-optic networks already use light to transport data over long distances at high speed and with minimum loss. The diameters of the thinnest cables, however, are in the micrometer range, as the light waves — with a wavelength of around one micrometer — must be able to oscillate unhindered. In order to process data on a micro- or even nanochip, an entirely new system is therefore required.

One possibility would be to conduct light signals via so-called plasmon oscillations. This involves a light particle (photon) exciting the electron cloud of a gold nanoparticle so that it starts oscillating. These waves then travel along a chain of nanoparticles at approximately 10% of the speed of light. This approach achieves two goals: nanometer-scale dimensions and enormous speed. What remains, however, is the energy consumption. In a chain composed purely of gold, this would be almost as high as in conventional transistors, due to the considerable heat development in the gold particles.

A tiny spot of silver

Tim Liedl, Professor of Physics at LMU and PI at the cluster of excellence Nanosystems Initiative Munich (NIM), together with colleagues from Ohio University, has now published an article in the journal Nature Physics, which describes how silver nanoparticles can significantly reduce the energy consumption. The physicists built a sort of miniature test track with a length of around 100 nanometers, composed of three nanoparticles: one gold nanoparticle at each end, with a silver nanoparticle right in the middle.

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. To make the silver particle’s plasmon oscillate, more excitation energy is required than for gold. Therefore, the energy just flows “around” the silver particle. “Transport is mediated via the coupling of the electromagnetic fields around the so-called hot spots which are created between each of the two gold particles and the silver particle,” explains Tim Liedl. “This allows the energy to be transported with almost no loss, and on a femtosecond time scale.”

Textbook quantum model

The decisive precondition for the experiments was the fact that Tim Liedl and his colleagues are experts in the exquisitely exact placement of nanostructures. This is done by the DNA origami method, which allows different crystalline nanoparticles to be placed at precisely defined nanodistances from each other. Similar experiments had previously been conducted using conventional lithography techniques. However, these do not provide the required spatial precision, in particular where different types of metals are involved.

In parallel, the physicists simulated the experimental set-up on the computer – and had their results confirmed. In addition to classical electrodynamic simulations, Alexander Govorov, Professor of Physics at Ohio University, Athens, USA, was able to establish a simple quantum-mechanical model: “In this model, the classical and the quantum-mechanical pictures match very well, which makes it a potential example for the textbooks.”

Here’s a link to and c citation for the paper,

Hotspot-mediated non-dissipative and ultrafast plasmon passage by Eva-Maria Roller, Lucas V. Besteiro, Claudia Pupp, Larousse Khosravi Khorashad, Alexander O. Govorov, & Tim Liedl. Nature Physics (2017) doi:10.1038/nphys4120 Published online 15 May 2017

This paper is behind a paywall.

Generating power from polluted air

I have no idea how viable this concept might be but it is certainly appealing, From a May 8, 2017 news item on Nanowerk (Note: A link has been removed),

Researchers from the University of Antwerp and KU Leuven (University of Leuven), Belgium, have succeeded in developing a process that purifies air and, at the same time, generates power. The device must only be exposed to light in order to function (ChemSusChem, “Harvesting Hydrogen Gas from Air Pollutants with an Unbiased Gas Phase Photoelectrochemical Cell”).

Caption: The new device must only be exposed to light in order to purify air and generate power. Credit: UAntwerpen and KU Leuven

A May 8, 2017 University of Leuven press release (also on EurekAlert), which originated the news item, describes this nifty research in slightly more detail,

“We use a small device with two rooms separated by a membrane,” explains Professor Sammy Verbruggen (UAntwerp/KU Leuven). “Air is purified on one side, while on the other side hydrogen gas is produced from a part of the degradation products. This hydrogen gas can be stored and used later as fuel, as is already being done in some hydrogen buses, for example.”

In this way, the researchers respond to two major social needs: clean air and alternative energy production. The heart of the solution lies at the membrane level, where the researchers use specific nanomaterials. “These catalysts are capable of producing hydrogen gas and breaking down air pollution,” explains Professor Verbruggen. “In the past, these cells were mostly used to extract hydrogen from water. We have now discovered that this is also possible, and even more efficient, with polluted air.”

It seems to be a complex process, but it is not: the device must only be exposed to light. The researchers’ goal is to be able to use sunlight, as the processes underlying the technology are similar to those found in solar panels. The difference here is that electricity is not generated directly, but rather that air is purified while the generated power is stored as hydrogen gas.

“We are currently working on a scale of only a few square centimetres. At a later stage, we would like to scale up our technology to make the process industrially applicable. We are also working on improving our materials so we can use sunlight more efficiently to trigger the reactions. “

Here’s a link to and a citation for the paper,

Harvesting Hydrogen Gas from Air Pollutants with an Unbiased Gas Phase Photoelectrochemical Cell. by  Prof. Dr. Sammy W. Verbruggen, Myrthe Van Hal1, Tom Bosserez, Dr. Jan Rongé, Dr. Birger Hauchecorne, Prof. Dr. Johan A. Martens, and Prof. Dr. Silvia Lenaerts. ChemSusChem Volume 10, Issue 7, pages 1413–1418, April 10, 2017 DOI: 10.1002/cssc.201601806 Version of Record online: 6 MAR 2017

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Magic nano ink

Colour changes © Nature Communications 2017 / MPI [Max Planck Institute] for Intelligent Systems

A March 1, 2017 news item on Nanowerk helps to explain the image seen above (Note: A link has been removed),

Plasmonic printing produces resolutions several times greater than conventional printing methods. In plasmonic printing, colours are formed on the surfaces of tiny metallic particles when light excites their electrons to oscillate. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart have now shown how the colours of such metallic particles can be altered with hydrogen (Nature Communications, “Dynamic plasmonic colour display”).

The technique could open the way for animating ultra-high-resolution images and for developing extremely sharp displays. At the same time, it provides new approaches for encrypting information and detecting counterfeits.

A March 1, 2017 Max Planck Institute press release, which originated the news item, provides more  history and more detail about the research,

Glass artisans in medieval times exploited the effect long before it was even known. They coloured the magnificent windows of gothic cathedrals with nanoparticles of gold, which glowed red in the light. It was not until the middle of the 20th century that the underlying physical phenomenon was given a name: plasmons. These collective oscillations of free electrons are stimulated by the absorption of incident electromagnetic radiation. The smaller the metallic particles, the shorter the wavelength of the absorbed radiation. In some cases, the resonance frequency, i.e., the absorption maximum, falls within the visible light spectrum. The unabsorbed part of the spectrum is then scattered or reflected, creating an impression of colour. The metallic particles, which usually appear silvery, copper-coloured or golden, then take on entirely new colours.

A resolution of 100,000 dots per inch

Researchers are also taking advantage of the effect to develop plasmonic printing, in which tailor-made square metal particles are arranged in specific patterns on a substrate. The edge length of the particles is in the order of less than 100 nanometres (100 billionths of a metre). This allows a resolution of 100,000 dots per inch – several times greater than what today’s printers and displays can achieve.

For metallic particles measuring several 100 nanometres across, the resonance frequency of the plasmons lies within the visible light spectrum. When white light falls on such particles, they appear in a specific colour, for example red or blue. The colour of the metal in question is determined by the size of the particles and their distance from each other. These adjustment parameters therefore serve the same purpose in plasmonic printing as the palette of colours in painting.

The trick with the chemical reaction

The Smart Nanoplasmonics Research Group at the Max Planck Institute for Intelligent Systems in Stuttgart also makes use of this colour variability. They are currently working on making dynamic plasmonic printing. They have now presented an approach that allows them to alter the colours of the pixels predictably – even after an image has been printed. “The trick is to use magnesium. It can undergo a reversible chemical reaction in which the metallic character of the element is lost,” explains Laura Na Liu, who leads the Stuttgart research group. “Magnesium can absorb up to 7.6% of hydrogen by weight to form magnesium hydride, or MgH2”, Liu continues. The researchers coat the magnesium with palladium, which acts as a catalyst in the reaction.

During the continuous transition of metallic magnesium into non-metallic MgH2, the colour of some of the pixels changes several times. The colour change and the speed of the rate at which it proceeds follow a clear pattern. This is determined both by the size of and the distance between the individual magnesium particles as well as by the amount of hydrogen present.

In the case of total hydrogen saturation, the colour disappears completely, and the pixels reflect all the white light that falls on them. This is because the magnesium is no longer present in metallic form but only as MgH2. Hence, there are also no free metal electrons that can be made to oscillate.

Minerva’s vanishing act

The scientists demonstrated the effect of such dynamic colour behaviour on a plasmonic print of Minerva, the Roman goddess of wisdom, which also bore the logo of the Max Planck Society. They chose the size of their magnesium particles so that Minerva’s hair first appeared reddish, the head covering yellow, the feather crest red and the laurel wreath and outline of her face blue. They then washed the micro-print with hydrogen. A time-lapse film shows how the individual colours change. Yellow turns red, red turns blue, and blue turns white. After a few minutes all the colours disappear, revealing a white surface instead of Minerva.

The scientists also showed that this process is reversible by replacing the hydrogen stream with a stream of oxygen. The oxygen reacts with the hydrogen in the magnesium hydride to form water, so that the magnesium particles become metallic again. The pixels then change back in reverse order, and in the end Minerva appears in her original colours.

In a similar manner the researchers first made the micro image of a famous Van Gogh painting disappear and then reappear. They also produced complex animations that give the impression of fireworks.

The principle of a new encryption technique

Laura Na Liu can imagine using this principle in a new encryption technology. To demonstrate this, the group formed various letters with magnesium pixels. The addition of hydrogen then caused some letters to disappear over time, like the image of Minerva. “As for the rest of the letters, a thin oxide layer formed on the magnesium particles after exposing the sample in air for a short time before palladium deposition,” Liu explains. This layer is impermeable to hydrogen. The magnesium lying under the oxide layer therefore remains metallic − and visible − because light is able to excite the plasmons in the magnesium.

In this way it is possible to conceal a message, for example by mixing real and nonsensical information. Only the intended recipient is able to make the nonsensical information disappear and filter out the real message. For example, after decoding the message “Hartford” with hydrogen, only the words “art or” would remain visible. To make it more difficult to crack such encrypted messages, the group is currently working on a process that would require a precisely adjusted hydrogen concentration for deciphering.

Liu believes that the technology could also be used some day in the fight against counterfeiting. “For example, plasmonic security features could be printed on banknotes or pharmaceutical packs, which could later be checked or read only under specific conditions unknown to counterfeiters.”

It doesn’t necessarily have to be hydrogen

Laura Na Liu knows that the use of hydrogen makes some applications difficult and impractical for everyday use such as in mobile displays. “We see our work as a starting shot for a new principle: the use of chemical reactions for dynamic printing,” the Stuttgart physicist says. It is certainly conceivable that the research will soon lead to the discovery of chemical reactions for colour changes other than the phase transition between magnesium and magnesium dihydride, for example, reactions that require no gaseous reactants.

Here’s a link to and a citation for the paper,

Dynamic plasmonic colour display by Xiaoyang Duan, Simon Kamin, & Na Liu. Nature Communications 8, Article number: 14606 (2017) doi:10.1038/ncomms14606 Published online: 24 February 2017

This paper is open access.

Making lead look like gold (so to speak)

Apparently you can make lead ‘look’ like gold if you can get it to reflect light in the same way. From a Feb. 28, 2017 news item on Nanowerk (Note: A link has been removed),

Since the Middle Ages, alchemists have sought to transmute elements, the most famous example being the long quest to turn lead into gold. Transmutation has been realized in modern times, but on a minute scale using a massive particle accelerator.

Now, theorists at Princeton University have proposed a different approach to this ancient ambition — just make one material behave like another. A computational theory published Feb. 24 [2017] in the journal Physical Review Letters (“How to Make Distinct Dynamical Systems Appear Spectrally Identical”) demonstrates that any two systems can be made to look alike, even if just for the smallest fraction of a second.

In this context, for two objects to “look” like each other, they need to reflect light in the same way. The Princeton researchers’ method involves using light to make non-permanent changes to a substance’s molecules so that they mimic the reflective properties of another substance’s molecules. This ability could have implications for optical computing, a type of computing in which electrons are replaced by photons that could greatly enhance processing power but has proven extremely difficult to engineer. It also could be applied to molecular detection and experiments in which expensive samples could be replaced by cheaper alternatives.

A Feb. 28, 2017 Princeton University news release (also on EurekAlert) by Tien Nguyen, which originated the news item, expands on the theme (Note: Links have been removed),

“It was a big shock for us that such a general statement as ‘any two objects can be made to look alike’ could be made,” said co-author Denys Bondar, an associate research scholar in the laboratory of co-author Herschel Rabitz, Princeton’s Charles Phelps Smyth ’16 *17 Professor of Chemistry.

The Princeton researchers posited that they could control the light that bounces off a molecule or any substance by controlling the light shone on it, which would allow them to alter how it looks. This type of manipulation requires a powerful light source such as an ultrafast laser and would last for only a femtosecond, or one quadrillionth of a second. Unlike normal light sources, this ultrafast laser pulse is strong enough to interact with molecules and distort their electron cloud while not actually changing their identity.

“The light emitted by a molecule depends on the shape of its electron cloud, which can be sculptured by modern lasers,” Bondar said. Using advanced computational theory, the research team developed a method called “spectral dynamic mimicry” that allowed them to calculate the laser pulse shape, which includes timing and wavelength, to produce any desired spectral output. In other words, making any two systems look alike.

Conversely, this spectral control could also be used to make two systems look as different from one another as possible. This differentiation, the researchers suggested, could prove valuable for applications of molecular detections such as identifying toxic versus safe chemicals.

Shaul Mukamel, a chemistry professor at the University of California-Irvine, said that the Princeton research is a step forward in an important and active research field called coherent control, in which light can be manipulated to control behavior at the molecular level. Mukamel, who has collaborated with the Rabitz lab but was not involved in the current work, said that the Rabitz group has had a prominent role in this field for decades, advancing technology such as quantum computing and using light to drive artificial chemical reactivity.

“It’s a very general and nice application of coherent control,” Mukamel said. “It demonstrates that you can, by shaping the optical paths, bring the molecules to do things that you want beforehand — it could potentially be very significant.”

Since the Middle Ages, alchemists have sought to transmute elements, the most famous example being the long quest to turn lead into gold. Now, theorists at Princeton University have proposed a different approach to this ancient ambition — just make one material behave like another, even if just for the smallest fraction of a second. The researchers are, left to right, Renan Cabrera, an associate research scholar in chemistry; Herschel Rabitz, Princeton’s Charles Phelps Smyth ’16 *17 Professor of Chemistry; associate research scholar in chemistry Denys Bondar; and graduate student Andre Campos. (Photo by C. Todd Reichart, Department of Chemistry)

Here’s a link to and a citation for the paper,

How to Make Distinct Dynamical Systems Appear Spectrally Identical by
Andre G. Campos, Denys I. Bondar, Renan Cabrera, and Herschel A. Rabitz.
Phys. Rev. Lett. 118, 083201 (Vol. 118, Iss. 8) DOI:https://doi.org/10.1103/PhysRevLett.118.083201 Published 24 February 2017

© 2017 American Physical Society

This paper is behind a paywall.

Bidirectional prosthetic-brain communication with light?

The possibility of not only being able to make a prosthetic that allows a tetraplegic to grab a coffee but to feel that coffee  cup with their ‘hand’ is one step closer to reality according to a Feb. 22, 2017 news item on ScienceDaily,

Since the early seventies, scientists have been developing brain-machine interfaces; the main application being the use of neural prosthesis in paralyzed patients or amputees. A prosthetic limb directly controlled by brain activity can partially recover the lost motor function. This is achieved by decoding neuronal activity recorded with electrodes and translating it into robotic movements. Such systems however have limited precision due to the absence of sensory feedback from the artificial limb. Neuroscientists at the University of Geneva (UNIGE), Switzerland, asked whether it was possible to transmit this missing sensation back to the brain by stimulating neural activity in the cortex. They discovered that not only was it possible to create an artificial sensation of neuroprosthetic movements, but that the underlying learning process occurs very rapidly. These findings, published in the scientific journal Neuron, were obtained by resorting to modern imaging and optical stimulation tools, offering an innovative alternative to the classical electrode approach.

A Feb. 22, 2017 Université de Genève press release on EurekAlert, which originated the news item, provides more detail,

Motor function is at the heart of all behavior and allows us to interact with the world. Therefore, replacing a lost limb with a robotic prosthesis is the subject of much research, yet successful outcomes are rare. Why is that? Until this moment, brain-machine interfaces are operated by relying largely on visual perception: the robotic arm is controlled by looking at it. The direct flow of information between the brain and the machine remains thus unidirectional. However, movement perception is not only based on vision but mostly on proprioception, the sensation of where the limb is located in space. “We have therefore asked whether it was possible to establish a bidirectional communication in a brain-machine interface: to simultaneously read out neural activity, translate it into prosthetic movement and reinject sensory feedback of this movement back in the brain”, explains Daniel Huber, professor in the Department of Basic Neurosciences of the Faculty of Medicine at UNIGE.

Providing artificial sensations of prosthetic movements

In contrast to invasive approaches using electrodes, Daniel Huber’s team specializes in optical techniques for imaging and stimulating brain activity. Using a method called two-photon microscopy, they routinely measure the activity of hundreds of neurons with single cell resolution. “We wanted to test whether mice could learn to control a neural prosthesis by relying uniquely on an artificial sensory feedback signal”, explains Mario Prsa, researcher at UNIGE and the first author of the study. “We imaged neural activity in the motor cortex. When the mouse activated a specific neuron, the one chosen for neuroprosthetic control, we simultaneously applied stimulation proportional to this activity to the sensory cortex using blue light”. Indeed, neurons of the sensory cortex were rendered photosensitive to this light, allowing them to be activated by a series of optical flashes and thus integrate the artificial sensory feedback signal. The mouse was rewarded upon every above-threshold activation, and 20 minutes later, once the association learned, the rodent was able to more frequently generate the correct neuronal activity.

This means that the artificial sensation was not only perceived, but that it was successfully integrated as a feedback of the prosthetic movement. In this manner, the brain-machine interface functions bidirectionally. The Geneva researchers think that the reason why this fabricated sensation is so rapidly assimilated is because it most likely taps into very basic brain functions. Feeling the position of our limbs occurs automatically, without much thought and probably reflects fundamental neural circuit mechanisms. This type of bidirectional interface might allow in the future more precisely displacing robotic arms, feeling touched objects or perceiving the necessary force to grasp them.

At present, the neuroscientists at UNIGE are examining how to produce a more efficient sensory feedback. They are currently capable of doing it for a single movement, but is it also possible to provide multiple feedback channels in parallel? This research sets the groundwork for developing a new generation of more precise, bidirectional neural prostheses.

Towards better understanding the neural mechanisms of neuroprosthetic control

By resorting to modern imaging tools, hundreds of neurons in the surrounding area could also be observed as the mouse learned the neuroprosthetic task. “We know that millions of neural connections exist. However, we discovered that the animal activated only the one neuron chosen for controlling the prosthetic action, and did not recruit any of the neighbouring neurons”, adds Daniel Huber. “This is a very interesting finding since it reveals that the brain can home in on and specifically control the activity of just one single neuron”. Researchers can potentially exploit this knowledge to not only develop more stable and precise decoding techniques, but also gain a better understanding of most basic neural circuit functions. It remains to be discovered what mechanisms are involved in routing signals to the uniquely activated neuron.

Caption: A novel optical brain-machine interface allows bidirectional communication with the brain. While a robotic arm is controlled by neuronal activity recorded with optical imaging (red laser), the position of the arm is fed back to the brain via optical microstimulation (blue laser). Credit: © Daniel Huber, UNIGE

Here’s a link to and a citation for the paper,

Rapid Integration of Artificial Sensory Feedback during Operant Conditioning of Motor Cortex Neurons by Mario Prsa, Gregorio L. Galiñanes, Daniel Huber. Neuron Volume 93, Issue 4, p929–939.e6, 22 February 2017 DOI: http://dx.doi.org/10.1016/j.neuron.2017.01.023 Open access funded by European Research Council

This paper is open access.

A plasmonic nanolaser operating at visible light frequencies using ‘dark lattice’ modes

Finnish scientists have created lasers made of nanoparticles according to a Jan. 3, 2017 news item on ScienceDaily,

Researchers at Aalto University, Finland are the first to develop a plasmonic nanolaser that operates at visible light frequencies and uses so-called dark lattice modes.

The laser works at length scales 1000 times smaller than the thickness of a human hair. The lifetimes of light captured in such small dimensions are so short that the light wave has time to wiggle up and down only a few tens or hundreds of times. The results open new prospects for on-chip coherent light sources, such as lasers, that are extremely small and ultrafast.

The laser operation in this work is based on silver nanoparticles arranged in a periodic array.

A Jan. 3, 2017 Aalto University press release (also on EurekAlert), which originated the news item, describes the work in more detail,

 In contrast to conventional lasers, where the feedback of the lasing signal is provided by ordinary mirrors, this nanolaser utilizes radiative coupling between silver nanoparticles. These 100-nanometer-sized particles act as tiny antennas. To produce high intensity laser light, the interparticle distance was matched with the lasing wavelength so that all particles of the array radiate in unison. Organic fluorescent molecules were used to provide the input energy (the gain) that is needed for lasing.

Light from the dark

A major challenge in achieving lasing this way was that light may not exist long enough in such small dimensions to be helpful. The researchers found a smart way around this potential problem: they produced lasing in dark modes.

“A dark mode can be intuitively understood by considering regular antennas: A single antenna, when driven by a current, radiates strongly, whereas two antennas — if driven by opposite currents and positioned very close to each other — radiate very little,” explains Academy Professor Päivi Törmä.

“A dark mode in a nanoparticle array induces similar opposite-phase currents in each nanoparticle, but now with visible light frequencies”, she continues.

“Dark modes are attractive for applications where low power consumption is needed. But without any tricks, dark mode lasing would be quite useless because the light is essentially trapped at the nanoparticle array and cannot leave”, adds staff scientist Tommi Hakala.

“But by utilizing the small size of the array, we found an escape route for the light. Towards the edges of the array, the nanoparticles start to behave more and more like regular antennas that radiate to the outer world”, tells Ph.D. student Heikki Rekola.

The research team used the nanofabrication facilities and cleanrooms of the national OtaNano research infrastructure.

The researchers have produced a video elucidating their research,

A revelatory soundtrack by Kevin MacLeod has been added to this video.

Finally, here’s a link to and a citation for the paper,

Lasing in dark and bright modes of a finite-sized plasmonic lattice by T. K. Hakala, H. T. Rekola, A. I. Väkeväinen, J.-P. Martikainen, M. Nečada, A. J. Moilanen & P. Törmä. Nature Communications  8, Article number: 13687 doi:10.1038/ncomms13687 Published 03 January 2017

This is an open access paper.

A biocompatible (implantable) micromachine (microrobot)

I appreciate the detail and information in this well written Jan. 4, 2017 Columbia University news release (h/t Jan. 4, 2016 Nanowerk; Note: Links have been removed),

A team of researchers led by Biomedical Engineering Professor Sam Sia has developed a way to manufacture microscale-sized machines from biomaterials that can safely be implanted in the body. Working with hydrogels, which are biocompatible materials that engineers have been studying for decades, Sia has invented a new technique that stacks the soft material in layers to make devices that have three-dimensional, freely moving parts. The study, published online January 4, 2017, in Science Robotics, demonstrates a fast manufacturing method Sia calls “implantable microelectromechanical systems” (iMEMS).

By exploiting the unique mechanical properties of hydrogels, the researchers developed a “locking mechanism” for precise actuation and movement of freely moving parts, which can provide functions such as valves, manifolds, rotors, pumps, and drug delivery. 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. They then tested the “payload” delivery in a bone cancer model and found that the 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, 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 Sia, also a member of the Data Science Institute. “We’re really excited about this because we’ve been able to connect the world of biomaterials with that of complex, elaborate medical devices. Our platform has a large number of potential applications, including the drug delivery system demonstrated in our paper which is linked to providing tailored drug doses for precision medicine.”

I particularly like this bit about hydrogels being a challenge to work with and the difficulties of integrating both rigid and soft materials,

Most current implantable microdevices have static components rather than moving parts and, because they require batteries or other toxic electronics, have limited biocompatibility. Sia’s team spent more than eight years working on how to solve this problem. “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.”

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.

Sia’s iMEMS technique addresses several fundamental considerations 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 were able to trigger the iMEMS device to release additional payloads over days to weeks after implantation. They were also able to achieve 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 FDA-approved for human use as contrast agents.)

In collaboration with Francis Lee, an orthopedic surgeon at Columbia University Medical Center at the time of the study, the team tested the drug delivery system on mice with bone cancer. The iMEMS system delivered chemotherapy adjacent to the cancer, and limited tumor growth while showing less toxicity than chemotherapy administered throughout the body.

“These microscale components can be used for microelectromechanical systems, for larger devices ranging from drug delivery to catheters to cardiac pacemakers, and soft robotics,” notes Sia. “People are already making replacement tissues and now 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 in developing soft miniaturized robots that can safely interact with humans and other living systems.”

Here’s a link to and a citation for the paper,

Additive manufacturing of hydrogel-based materials for next-generation implantable medical devices by Sau Yin Chin, Yukkee Cheung Poh, Anne-Céline Kohler, Jocelyn T. Compton, Lauren L. Hsu, Kathryn M. Lau, Sohyun Kim, Benjamin W. Lee, Francis Y. Lee, and Samuel K. Sia. Science Robotics  04 Jan 2017: Vol. 2, Issue 2, DOI: 10.1126/scirobotics.aah6451

This paper appears to be open access.

The researchers have provided a video demonstrating their work (you may want to read the caption below before watching),

Magnetic actuation of the Geneva drive device. A magnet is placed about 1cm below and without contact with the device. The rotating magnet results in the rotational movement of the smaller driving gear. With each full rotation of this driving gear, the larger driven gear is engaged and rotates by 60º, exposing the next reservoir to the aperture on the top layer of the device.

—Video courtesy of Sau Yin Chin/Columbia Engineering

You can hear some background conversation but it doesn’t seem to have been included for informational purposes.

Stretchy optical materials for implants that could pulse light

An Oct. 17, 2016 Massachusetts Institute of Technology (MIT) news release (also on EurekAlert) by Emily Chu describes research that could lead to long-lasting implants offering preventive health strategies,

Researchers from MIT and Harvard Medical School have developed a biocompatible and highly stretchable optical fiber made from hydrogel — an elastic, rubbery material composed mostly of water. The fiber, which is as bendable as a rope of licorice, may one day be implanted in the body to deliver therapeutic pulses of light or light up at the first sign of disease. [emphasis mine]

The researchers say the fiber may serve as a long-lasting implant that would bend and twist with the body without breaking down. The team has published its results online in the journal Advanced Materials.

Using light to activate cells, and particularly neurons in the brain, is a highly active field known as optogenetics, in which researchers deliver short pulses of light to targeted tissues using needle-like fibers, through which they shine light from an LED source.

“But the brain is like a bowl of Jell-O, whereas these fibers are like glass — very rigid, which can possibly damage brain tissues,” says Xuanhe Zhao, the Robert N. Noyce Career Development Associate Professor in MIT’s Department of Mechanical Engineering. “If these fibers could match the flexibility and softness of the brain, they could provide long-term more effective stimulation and therapy.”

Getting to the core of it

Zhao’s group at MIT, including graduate students Xinyue Liu and Hyunwoo Yuk, specializes in tuning the mechanical properties of hydrogels. The researchers have devised multiple recipes for making tough yet pliable hydrogels out of various biopolymers. The team has also come up with ways to bond hydrogels with various surfaces such as metallic sensors and LEDs, to create stretchable electronics.

The researchers only thought to explore hydrogel’s use in optical fibers after conversations with the bio-optics group at Harvard Medical School, led by Associate Professor Seok-Hyun (Andy) Yun. Yun’s group had previously fabricated an optical fiber from hydrogel material that successfully transmitted light through the fiber. However, the material broke apart when bent or slightly stretched. Zhao’s hydrogels, in contrast, could stretch and bend like taffy. The two groups joined efforts and looked for ways to incorporate Zhao’s hydrogel into Yun’s optical fiber design.

Yun’s design consists of a core material encased in an outer cladding. To transmit the maximum amount of light through the core of the fiber, the core and the cladding should be made of materials with very different refractive indices, or degrees to which they can bend light.

“If these two things are too similar, whatever light source flows through the fiber will just fade away,” Yuk explains. “In optical fibers, people want to have a much higher refractive index in the core, versus cladding, so that when light goes through the core, it bounces off the interface of the cladding and stays within the core.”

Happily, they found that Zhao’s hydrogel material was highly transparent and possessed a refractive index that was ideal as a core material. But when they tried to coat the hydrogel with a cladding polymer solution, the two materials tended to peel apart when the fiber was stretched or bent.

To bond the two materials together, the researchers added conjugation chemicals to the cladding solution, which, when coated over the hydrogel core, generated chemical links between the outer surfaces of both materials.

“It clicks together the carboxyl groups in the cladding, and the amine groups in the core material, like molecular-level glue,” Yuk says.

Sensing strain

The researchers tested the optical fibers’ ability to propagate light by shining a laser through fibers of various lengths. Each fiber transmitted light without significant attenuation, or fading. They also found that fibers could be stretched over seven times their original length without breaking.

Now that they had developed a highly flexible and robust optical fiber, made from a hydrogel material that was also biocompatible, the researchers began to play with the fiber’s optical properties, to see if they could design a fiber that could sense when and where it was being stretched.

They first loaded a fiber with red, green, and blue organic dyes, placed at specific spots along the fiber’s length. Next, they shone a laser through the fiber and stretched, for instance, the red region. They measured the spectrum of light that made it all the way through the fiber, and noted the intensity of the red light. They reasoned that this intensity relates directly to the amount of light absorbed by the red dye, as a result of that region being stretched.

In other words, by measuring the amount of light at the far end of the fiber, the researchers can quantitatively determine where and by how much a fiber was stretched.

“When you stretch a certain portion of the fiber, the dimensions of that part of the fiber changes, along with the amount of light that region absorbs and scatters, so in this way, the fiber can serve as a sensor of strain,” Liu explains.

“This is like a multistrain sensor through a single fiber,” Yuk adds. “So it can be an implantable or wearable strain gauge.”

The researchers imagine that such stretchable, strain-sensing optical fibers could be implanted or fitted along the length of a patient’s arm or leg, to monitor for signs of improving mobility.

Zhao envisions the fibers may also serve as sensors, lighting up in response to signs of disease.

“We may be able to use optical fibers for long-term diagnostics, to optically monitor tumors or inflammation,” he says. “The applications can be impactful.”

Here’s a link to and a citation for the paper,

Highly Stretchable, Strain Sensing Hydrogel Optical Fibers by Jingjing Guo, Xinyue Liu, Nan Jiang, Ali K. Yetisen, Hyunwoo Yuk, Changxi Yang, Ali Khademhosseini, Xuanhe Zhao, and Seok-Hyun Yun. Advanced Materials DOI: 10.1002/adma.201603160 Version of Record online: 7 OCT 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

New form of light could lead to circuits that run on photons instead of electrons

If circuits are running on photons instead of electrons, does that mean there will be no more electricity and electronics?  Apparently, the answer is not exactly. First, an Aug. 5, 2016 news item on ScienceDaily makes the announcement about photons and circuits,

New research suggests that it is possible to create a new form of light by binding light to a single electron, combining the properties of both.

According to the scientists behind the study, from Imperial College London, the coupled light and electron would have properties that could lead to circuits that work with packages of light — photons — instead of electrons.

It would also allow researchers to study quantum physical phenomena, which govern particles smaller than atoms, on a visible scale.

An Aug. 5, 2016 Imperial College of London (ICL) press release, which originated the news item, describes the research further (Note: A link has been removed),

In normal materials, light interacts with a whole host of electrons present on the surface and within the material. But by using theoretical physics to model the behaviour of light and a recently-discovered class of materials known as topological insulators, Imperial researchers have found that it could interact with just one electron on the surface.

This would create a coupling that merges some of the properties of the light and the electron. Normally, light travels in a straight line, but when bound to the electron it would instead follow its path, tracing the surface of the material.

Improved electronics

In the study, published today in Nature Communications, Dr Vincenzo Giannini and colleagues modelled this interaction around a nanoparticle – a small sphere below 0.00000001 metres in diameter – made of a topological insulator.

Their models showed that as well as the light taking the property of the electron and circulating the particle, the electron would also take on some of the properties of the light. [emphasis mine]

Normally, as electrons are travelling along materials, such as electrical circuits, they will stop when faced with a defect. However, Dr Giannini’s team discovered that even if there were imperfections in the surface of the nanoparticle, the electron would still be able to travel onwards with the aid of the light.

If this could be adapted into photonic circuits, they would be more robust and less vulnerable to disruption and physical imperfections.

Quantum experiments

Dr Giannini said: “The results of this research will have a huge impact on the way we conceive light. Topological insulators were only discovered in the last decade, but are already providing us with new phenomena to study and new ways to explore important concepts in physics.”

Dr Giannini added that it should be possible to observe the phenomena he has modelled in experiments using current technology, and the team is working with experimental physicists to make this a reality.

He believes that the process that leads to the creation of this new form of light could be scaled up so that the phenomena could observed much more easily.

Currently, quantum phenomena can only be seen when looking at very small objects or objects that have been super-cooled, but this could allow scientists to study these kinds of behaviour at room temperature.

An electron that takes on the properties of light? I find that fascinating.

Artistic image of light trapped on the surface of a nanoparticle topological insulator. Credit: Vincenzo Giannini

Artistic image of light trapped on the surface of a nanoparticle topological insulator. Credit: Vincenzo Giannini

For those who’d like more information, here’s a link to and a citation for the paper,

Single-electron induced surface plasmons on a topological nanoparticle by G. Siroki, D.K.K. Lee, P. D. Haynes,V. Giannini. Nature Communications 7, Article number: 12375  doi:10.1038/ncomms12375 Published 05 August 2016

This paper is open access.

Hologram with nanostructures could improve fraud protection

This research on holograms comes from Harvard University according to a May 13, 2016 news item on ScienceDaily,

Holograms are a ubiquitous part of our lives. They are in our wallets — protecting credit cards, cash and driver’s licenses from fraud — in grocery store scanners and biomedical devices.

Even though holographic technology has been around for decades, researchers still struggle to make compact holograms more efficient, complex and secure.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have programmed polarization into compact holograms. These holograms use nanostructures that are sensitive to polarization (the direction in which light vibrates) to produce different images depending on the polarization of incident light. This advancement, which works across the spectrum of light, improves anti-fraud holograms as well as those used in entertainment displays.

A May 13, 2016 Harvard University press release (also on EurekAlert) by Leah Burrows, which originated the news item, provides more detail,

“The novelty in this research is that by using nanotechnology, we’ve made holograms that are highly efficient, meaning that very little light is lost to create the image,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering and senior author of the paper. “By using incident polarized light, you can see far a crisper image and can store and retrieve more images. Polarization adds another dimension to holograms that can be used to protect against counterfeiting and in applications like displays.”

Harvard’s Office of Technology Development has filed patents on this and related technologies and is actively pursuing commercial opportunities.

Holograms, like digital photographs, capture a field of light around an object and encode it on a chip. However, photographs only record the intensity of light while holograms also capture the phase of light, which is why holograms appear three-dimensional.

“Our holograms work like any other but the image produced depends on the polarization state of the illuminating light, providing an extra degree of freedom in design for versatile applications,” said Mohammadreza Khorasaninejad, postdoctoral fellow in the Capasso Lab and first author of the paper.

There are several states of polarization. In linearly polarized light the direction of vibration remains constant while in circularly polarized light it rotates clockwise or counterclockwise. The direction of rotation is the chirality.

The team built silicon nanostructured patterns on a glass substrate, which act as superpixels. Each superpixel responds to a certain polarization state of the incident light. Even more information can be encoded in the hologram by designing and arranging the nanofins to respond differently to the chirality of the polarized incident light.

“Being able to encode chirality can have important applications in information security such as anti-counterfeiting,” said Antonio Ambrosio, a research scientist in the Capasso Lab and co-first author. “For example, chiral holograms can be made to display a sequence of certain images only when illuminated with light of specific polarization not known to the forger.”

“By using different nanofin designs in the future, one could store and retrieve far more images by employing light with many states of polarization,” said Capasso.

Because this system is compact, it has application in portable projectors, 3D movies and wearable optics.

“Modern polarization imaging systems require cascading several optical components such as beam splitters, polarizers and wave plates,” said Ambrosio. “Our metasurface can distinguish between incident polarization using a single layer dielectric surface.”

“We have also incorporated in some of the holograms a lens function that has allowed us to produce images at large angles,” said Khorasaninejad. “This functionality combined with the small footprint and lightweight, has significant potential for wearable optics applications.”

Here’s a link to and a citation for the paper,

Broadband and chiral binary dielectric meta-holograms by Mohammadreza Khorasaninejad, Antonio Ambrosio, Pritpal Kanhaiya, and Federico Capasso. Science Advances  13 May 2016: Vol. 2, no. 5, e1501258 DOI: 10.1126/sciadv.1501258

This paper is open access.