Walking DNA nanorobot could deliver a drug to a precise location in your body

DNA nanorobot cargo carrier (artist’s impression) (credit: Ella Maru Studio)

Caltech scientists have developed a “cargo sorting” DNA nanorobot programmed to autonomously “walk” around a surface, pick up certain molecules, and drop them off in designated locations.

The research is described in a paper in the Friday, September 15, 2017 issue of Science.

The major advance in this study is “their methodology for designing simple DNA devices that work in parallel to solve nontrivial tasks,” notes Duke University computer scientist John H. Reif in an article in the same issue of Science.

Such tasks could include synthesizing a drug in a molecular factory or delivering a drug only when a specific signal is present in bloodstreams, say the researchers. “So far, the development of DNA robots has been limited to simple functions,” the researchers note.

Walking nanobots that work in parallel

Conceptual illustration of two DNA nanorobots collectively performing a cargo-sorting task on a DNA origami surface: transporting fluorescent molecules with different colors from initially random locations to ordered destinations. (credit: Demin Liu)

The DNA nanorobot, intended as a proof of concept, has a “leg” with two “feet” for walking, and an “arm” and “hand” for picking up cargo. It also has a segment that can recognize a specific drop-off point and signal to the hand to release its cargo. Each of these building blocks are made of just a few nucleotides (molecules that form DNA) within a single strand of DNA.*

As the robot encounters cargo molecules tethered to pegs, it grabs them with its “hand” components and carries them around (with a 6-nm step size) until it detects the signal of the drop-off point.

Multiple DNA nanorobots independently execute three operations in parallel: [1] cargo pickup, [2] random movement to adjacent stepping stones, and [3] cargo drop-off at ordered locations. (credit: C. Bickel/Science)

In experiments, the nanorobots successfully sorted six randomly scattered molecules into their correct places in 24 hours. The process is slow, but adding more robots to the surface shortened the time it took to complete the task. The very simple robot design utilizes very little chemical energy, according to the researchers.**

“The same system design can be generalized to work with dozens of types of cargos at any arbitrary initial location on the surface,” says lead author Anupama Thubagere. “One could also have multiple robots performing diverse sorting tasks in parallel,” [programmed] like macroscopic robots.”

Future applications

“We don’t develop DNA robots for any specific applications. Our lab focuses on discovering the engineering principles that enable the development of general-purpose DNA robots,” explains Lulu Qian, assistant professor of bioengineering.

“However, it is my hope that other researchers could use these principles for exciting applications, such as synthesizing a therapeutic chemical from its constituent parts in an artificial molecular factory, or sorting molecular components in trash for recycling. Just like electromechanical robots are sent off to faraway places, like Mars, we would like to send molecular robots to minuscule places where humans can’t go, such as the bloodstream.”

Funding was provided by Caltech Summer Undergraduate Research Fellowships, the National Science Foundation, and the Burroughs Wellcome Fund.

* The key to designing DNA machines is the fact that DNA has unique chemical and physical properties that are known and programmable. A single strand of DNA is made up of four different molecules called nucleotides—abbreviated A, G, C, and T—and arranged in a string called a sequence. These nucleotides bond in specific pairs: A with T, and G with C. When a single strand encounters a “reverse complementary strand” — for example, CGATT meets AATCG —the two strands zip together in the classic double-helix shape.

** Using these chemical and physical principles, researchers can also design “playgrounds,” such as molecular pegboards, to test them on, according to the researchers. In the current work, the DNA robot moves around on a 58-nanometer-by-58-nanometer pegboard on which the pegs are made of single strands of DNA complementary to the robot’s leg and foot. The robot binds to a peg with its leg and one of its feet — the other foot floats freely. When random molecular fluctuations cause this free foot to encounter a nearby peg, it pulls the robot to the new peg and its other foot is freed. This process continues with the robot moving in a random direction at each step.

Abstract of A cargo-sorting DNA robot

Two critical challenges in the design and synthesis of molecular robots are modularity and
algorithm simplicity.We demonstrate three modular building blocks for a DNA robot that
performs cargo sorting at themolecular level. A simple algorithm encoding recognition between
cargos and their destinations allows for a simple robot design: a single-stranded DNA with
one leg and two foot domains for walking, and one arm and one hand domain for picking up and
dropping off cargos.The robot explores a two-dimensional testing ground on the surface of
DNA origami, picks up multiple cargos of two types that are initially at unordered locations, and
delivers them to specified destinations until all molecules are sorted into two distinct piles.
The robot is designed to perform a random walk without any energy supply. Exploiting this
feature, a single robot can repeatedly sort multiple cargos. Localization on DNA origami allows
for distinct cargo-sorting tasks to take place simultaneously in one test tube or for multiple
robots to collectively perform the same task.

Radical new vertically integrated 3D chip design combines computing and data storage

Four vertical layers in new 3D nanosystem chip. Top (fourth layer): sensors and more than one million carbon-nanotube field-effect transistor (CNFET) logic inverters; third layer, on-chip non-volatile RRAM (1 Mbit memory); second layer, CNFET logic with classification accelerator (to identify sensor inputs); first (bottom) layer, silicon FET logic. (credit: Max M. Shulaker et al./Nature)

A radical new 3D chip that combines computation and data storage in vertically stacked layers — allowing for processing and storing massive amounts of data at high speed in future transformative nanosystems — has been designed by researchers at Stanford University and MIT.

The new 3D-chip design* replaces silicon with carbon nanotubes (sheets of 2-D graphene formed into nanocylinders) and integrates resistive random-access memory (RRAM) cells.

Carbon-nanotube field-effect transistors (CNFETs) are an emerging transistor technology that can scale beyond the limits of silicon MOSFETs (conventional chips), and promise an order-of-magnitude improvement in energy-efficient computation. However, experimental demonstrations of CNFETs so far have been small-scale and limited to integrating only tens or hundreds of devices (see earlier 2015 Stanford research, “Skyscraper-style carbon-nanotube chip design…”).

The researchers integrated more than 1 million RRAM cells and 2 million carbon-nanotube field-effect transistors in the chip, making it the most complex nanoelectronic system ever made with emerging nanotechnologies, according to the researchers. RRAM is an emerging memory technology that promises high-capacity, non-volatile data storage, with improved speed, energy efficiency, and density, compared to dynamic random-access memory (DRAM).

Instead of requiring separate components, the RRAM cells and carbon nanotubes are built vertically over one another, creating a dense new 3D computer architecture** with interleaving layers of logic and memory. By using ultradense through-chip vias (electrical interconnecting wires passing between layers), the high delay with conventional wiring between computer components is eliminated.

The new 3D nanosystem can capture massive amounts of data every second, store it directly on-chip, perform in situ processing of the captured data, and produce “highly processed” information. “Such complex nanoelectronic systems will be essential for future high-performance, highly energy-efficient electronic systems,” the researchers say.

How to combine computation and storage

Illustration of separate CPU (bottom) and RAM memory (top) in current computer architecture (images credit: iStock)

The new chip design aims to replace current chip designs, which separate computing and data storage, resulting in limited-speed connections.

Separate 2D chips have been required because “building conventional silicon transistors involves extremely high temperatures of over 1,000 degrees Celsius,” explains lead author Max Shulaker, an assistant professor of electrical engineering and computer science at MIT and lead author of a paper published July 5, 2017 in the journal Nature. “If you then build a second layer of silicon circuits on top, that high temperature will damage the bottom layer of circuits.”

Instead, carbon nanotube circuits and RRAM memory can be fabricated at much lower temperatures: below 200 C. “This means they can be built up in layers without harming the circuits beneath,” says Shulaker.

Overcoming communication and computing bottlenecks

As applications analyze increasingly massive volumes of data, the limited rate at which data can be moved between different chips is creating a critical communication “bottleneck.” And with limited real estate on increasingly miniaturized chips, there is not enough room to place chips side-by-side.

At the same time, embedded intelligence in areas ranging from autonomous driving to personalized medicine is now generating huge amounts of data, but silicon transistors are no longer improving at the historic rate that they have for decades.

Instead, three-dimensional integration is the most promising approach to continue the technology-scaling path set forth by Moore’s law, allowing an increasing number of devices to be integrated per unit volume, according to Jan Rabaey, a professor of electrical engineering and computer science at the University of California at Berkeley, who was not involved in the research.

Three-dimensional integration “leads to a fundamentally different perspective on computing architectures, enabling an intimate interweaving of memory and logic,” he says. “These structures may be particularly suited for alternative learning-based computational paradigms such as brain-inspired systems and deep neural nets, and the approach presented by the authors is definitely a great first step in that direction.”

The new 3D design provides several benefits for future computing systems, including:

  • Logic circuits made from carbon nanotubes can be an order of magnitude more energy-efficient compared to today’s logic made from silicon.
  • RRAM memory is denser, faster, and more energy-efficient compared to conventional DRAM (dynamic random-access memory) devices.
  • The dense through-chip vias (wires) can enable vertical connectivity that is 1,000 times more dense than conventional packaging and chip-stacking solutions allow, which greatly improves the data communication bandwidth between vertically stacked functional layers. For example, each sensor in the top layer can connect directly to its respective underlying memory cell with an inter-layer via. This enables the sensors to write their data in parallel directly into memory and at high speed.
  • The design is compatible in both fabrication and design with today’s CMOS silicon infrastructure.

Shulaker next plans to work with Massachusetts-based semiconductor company Analog Devices to develop new versions of the system.

This work was funded by the Defense Advanced Research Projects Agency, the National Science Foundation, Semiconductor Research Corporation, STARnet SONIC, and member companies of the Stanford SystemX Alliance.

* As a working-prototype demonstration of the potential of the technology, the researchers took advantage of the ability of carbon nanotubes to also act as sensors. On the top layer of the chip, they placed more than 1 million carbon nanotube-based sensors, which they used to detect and classify ambient gases for detecting signs of disease by sensing particular compounds in a patient’s breath, says Shulaker. By layering sensing, data storage, and computing, the chip was able to measure each of the sensors in parallel, and then write directly into its memory, generating huge bandwidth in just one device, according to Shulaker. The top layer could be replaced with additional computation or data storage subsystems, or with other forms of input/output, he explains.

** Previous R&D in 3D chip technologies and their limitations are covered here, noting that “in general, 3D integration is a broad term that includes such technologies as 3D wafer-level packaging (3DWLP); 2.5D and 3D interposer-based integration; 3D stacked ICs (3D-SICs), monolithic 3D ICs; 3D heterogeneous integration; and 3D systems integration.” The new Stanford-MIT nanosystem design significantly expands this definition.

Abstract of Three-dimensional integration of nanotechnologies for computing and data storage on a single chip

The computing demands of future data-intensive applications will greatly exceed the capabilities of current electronics, and are unlikely to be met by isolated improvements in transistors, data storage technologies or integrated circuit architectures alone. Instead, transformative nanosystems, which use new nanotechnologies to simultaneously realize improved devices and new integrated circuit architectures, are required. Here we present a prototype of such a transformative nanosystem. It consists of more than one million resistive random-access memory cells and more than two million carbon-nanotube field-effect transistors—promising new nanotechnologies for use in energy-efficient digital logic circuits and for dense data storage—fabricated on vertically stacked layers in a single chip. Unlike conventional integrated circuit architectures, the layered fabrication realizes a three-dimensional integrated circuit architecture with fine-grained and dense vertical connectivity between layers of computing, data storage, and input and output (in this instance, sensing). As a result, our nanosystem can capture massive amounts of data every second, store it directly on-chip, perform in situ processing of the captured data, and produce ‘highly processed’ information. As a working prototype, our nanosystem senses and classifies ambient gases. Furthermore, because the layers are fabricated on top of silicon logic circuitry, our nanosystem is compatible with existing infrastructure for silicon-based technologies. Such complex nano-electronic systems will be essential for future high-performance and highly energy-efficient electronic systems.

Carbon nanotubes found safe for reconnecting damaged neurons

(credit: Polina Shuvaeva/iStock)

Multiwall carbon nanotubes (MWCNTs) could safely help repair damaged connections between neurons by serving as supporting scaffolds for growth or as connections between neurons.

That’s the conclusion of an in-vitro (lab) open-access study with cultured neurons (taken from the hippcampus of neonatal rats) by a multi-disciplinary team of scientists in Italy and Spain, published in the journal Nanomedicine: Nanotechnology, Biology, and Medicine.

A multi-walled carbon nanotube (credit: Eric Wieser/CC)

The study addressed whether MWCNTs that are interfaced to neurons affect synaptic transmission by modifying the lipid (fatty) cholesterol structure in artificial neural membranes.

Significantly, they found that MWCNTs:

  • Facilitate the full growth of neurons and the formation of new synapses. “This growth, however, is not indiscriminate and unlimited since, as we proved, after a few weeks, a physiological balance is attained.”
  • Do not interfere with the composition of lipids (cholesterol in particular), which make up the cellular membrane in neurons.
  • Do not interfere in the transmission of signals through synapses.

The researchers also noted that they recently reported (in an open access paper) low tissue reaction when multiwall carbon nanotubes were implanted in vivo (in live animals) to reconnect damaged spinal neurons.

The researchers say they proved that carbon nanotubes “perform excellently in terms of duration, adaptability and mechanical compatibility with tissue” and that “now we know that their interaction with biological material, too, is efficient. Based on this evidence, we are already studying an in vivo application, and preliminary results appear to be quite promising in terms of recovery of lost neurological functions.”

The research team comprised scientists from SISSA (International School for Advanced Studies), the University of Trieste, ELETTRA Sincrotrone, and two Spanish institutions, Basque Foundation for Science and CIC BiomaGUNE.

Abstract of Sculpting neurotransmission during synaptic development by 2D nanostructured interfaces

Carbon nanotube-based biomaterials critically contribute to the design of many prosthetic devices, with a particular impact in the development of bioelectronics components for novel neural interfaces. These nanomaterials combine excellent physical and chemical properties with peculiar nanostructured topography, thought to be crucial to their integration with neural tissue as long-term implants. The junction between carbon nanotubes and neural tissue can be particularly worthy of scientific attention and has been reported to significantly impact synapse construction in cultured neuronal networks. In this framework, the interaction of 2D carbon nanotube platforms with biological membranes is of paramount importance. Here we study carbon nanotube ability to interfere with lipid membrane structure and dynamics in cultured hippocampal neurons. While excluding that carbon nanotubes alter the homeostasis of neuronal membrane lipids, in particular cholesterol, we document in aged cultures an unprecedented functional integration between carbon nanotubes and the physiological maturation of the synaptic circuits.

Crystal ‘domain walls’ may lead to tinier electronic devices

Abstract art? No, nanoscale crystal sheets with moveable conductive “domain walls” that can modify a circuit’s electronic properties (credit: Queen’s University Belfast)

Queen’s University Belfast physicists have discovered a radical new way to modify the conductivity (ease of electron flow) of electronic circuits — reducing the size of future devices.

The two latest KurzweilAI articles on graphene cited faster/lower-power performance and device-compatibility features. This new research takes another approach: Altering the properties of a crystal to eliminate the need for multiple circuits in devices.

Reconfigurable nanocircuitry

To do that, the scientists used “ferroelectric copper-chlorine boracite” crystal sheets, which are almost as thin as graphene. The researchers discovered that squeezing the crystal sheets with a sharp needle at a precise location causes a jigsaw-puzzle-like pattern of “domains walls” to develop around the contact point.

Then, using external applied electric fields, these writable, erasable domain walls can be repeatedly moved around in the crystal to create a variety of new electronic properties. They can appear, disappear, or move around within the crystal, all without permanently altering the crystal itself.

Eliminating the need for multiple circuits may reduce the size of future computers and other devices, according to the researchers.

The team’s findings have been published in an open-access paper in Nature Communications.

Abstract of Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite

Ferroelectric domain walls constitute a completely new class of sheet-like functional material. Moreover, since domain walls are generally writable, erasable and mobile, they could be useful in functionally agile devices: for example, creating and moving conducting walls could make or break electrical connections in new forms of reconfigurable nanocircuitry. However, significant challenges exist: site-specific injection and annihilation of planar walls, which show robust conductivity, has not been easy to achieve. Here, we report the observation, mechanical writing and controlled movement of charged conducting domain walls in the improper-ferroelectric Cu3B7O13Cl. Walls are straight, tens of microns long and exist as a consequence of elastic compatibility conditions between specific domain pairs. We show that site-specific injection of conducting walls of up to hundreds of microns in length can be achieved through locally applied point-stress and, once created, that they can be moved and repositioned using applied electric fields.

New chemical method could revolutionize graphene use in electronics

Adding a molecular structure containing carbon, chromium, and oxygen atoms retains graphene’s superior conductive properties. The metal atoms (silver, in this experiment) to be bonded are then added to the oxygen atoms on top. (credit: Songwei Che et al./Nano Letters)

University of Illinois at Chicago scientists have solved a fundamental problem that has held back the use of wonder material graphene in a wide variety of electronics applications.

When graphene is bonded (attached) to metal atoms (such as molybdenum) in devices such as solar cells, graphene’s superior conduction properties degrade.

The solution: Instead of adding molecules directly to the individual carbon atoms of graphene, the new method first adds a sort of buffer (consisting of chromium, carbon, and oxygen atoms) to the graphene, and then adds the metal atoms to this buffer material instead. That enables the graphene to retain its unique properties of electrical conduction.

In an experiment, the researchers successfully added silver nanoparticles to graphene with this method. That increased the material’s ability to boost the efficiency of graphene-based solar cells by 11 fold, said Vikas Berry, associate professor and department head of chemical engineering and senior author of a paper on the research, published in Nano Letters.

Researchers at Indian Institute of Technology and Clemson University were also involved in the study. The research was funded by the National Science Foundation.

Abstract of Retained Carrier-Mobility and Enhanced Plasmonic-Photovoltaics of Graphene via ring-centered η6 Functionalization and Nanointerfacing

Binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp2 hybridized carbons to maintain its carrier-mobility, has remained a challenge. The conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via “carbon-centered” covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp2to tetrahedral sp3. This disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties. Here, we show large-area, vapor-phase, “ring-centered” hexahapto (η6) functionalization of graphene to create nucleation-sites for silver nanoparticles (AgNPs) without disrupting its sp2 character. This is achieved by the grafting of chromium tricarbonyl [Cr(CO)3] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η6-graphene)Cr(CO)3 complex. This nondestructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 K); with AgNPs attached on graphene/n-Si solar cells, we report an ∼11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).

Graphene-based computer would be 1,000 times faster than silicon-based, use 100th the power

How a graphene-based transistor would work. A graphene nanoribbon (GNR) is created by unzipping (opening up) a portion of a carbon nanotube (CNT) (the flat area, shown with pink arrows above it). The GRN switching is controlled by two surrounding parallel CNTs. The magnitudes and relative directions of the control current, ICTRL (blue arrows) in the CNTs determine the rotation direction of the magnetic fields, B (green). The magnetic fields then control the GNR magnetization (based on the recent discovery of negative magnetoresistance), which causes the GNR to switch from resistive (no current) to conductive, resulting in current flow, IGNR (pink arrows) — in other words, causing the GNR to act as a transistor gate. The magnitude of the current flow through the GNR functions as the binary gate output — with binary 1 representing the current flow of the conductive state and binary 0 representing no current (the resistive state). (credit: Joseph S. Friedman et al./Nature Communications)

A future graphene-based transistor using spintronics could lead to tinier computers that are a thousand times faster and use a hundredth of the power of silicon-based computers.

The radical transistor concept, created by a team of researchers at Northwestern University, The University of Texas at Dallas, University of Illinois at Urbana-Champaign, and University of Central Florida, is explained this month in an open-access paper in the journal Nature Communications.

Transistors act as on and off switches. A series of transistors in different arrangements act as logic gates, allowing microprocessors to solve complex arithmetic and logic problems. But the speed of computer microprocessors that rely on silicon transistors has been relatively stagnant since around 2005, with clock speeds mostly in the 3 to 4 gigahertz range.

Clock speeds approaching the terahertz range

The researchers discovered that by applying a magnetic field to a graphene ribbon (created by unzipping a carbon nanotube), they could change the resistance of current flowing through the ribbon. The magnetic field — controlled by increasing or decreasing the current through adjacent carbon nanotubes — increased or decreased the flow of current.

A cascading series of graphene transistor-based logic circuits could produce a massive jump, with clock speeds approaching the terahertz range — a thousand times faster.* They would also be smaller and substantially more efficient, allowing device-makers to shrink technology and squeeze in more functionality, according to Ryan M. Gelfand, an assistant professor in The College of Optics & Photonics at the University of Central Florida.

The researchers hope to inspire the fabrication of these cascaded logic circuits to stimulate a future transformative generation of energy-efficient computing.

* Unlike other spintronic logic proposals, these new logic gates can be cascaded directly through the carbon materials without requiring intermediate circuits and amplification between gates. That would result in compact circuits with reduced area that are far more efficient than with CMOS switching, which is limited by charge transfer and accumulation from RLC (resistance-inductance-capacitance) interconnect delays.

Abstract of Cascaded spintronic logic with low-dimensional carbon

Remarkable breakthroughs have established the functionality of graphene and carbon nanotube transistors as replacements to silicon in conventional computing structures, and numerous spintronic logic gates have been presented. However, an efficient cascaded logic structure that exploits electron spin has not yet been demonstrated. In this work, we introduce and analyse a cascaded spintronic computing system composed solely of low-dimensional carbon materials. We propose a spintronic switch based on the recent discovery of negative magnetoresistance in graphene nanoribbons, and demonstrate its feasibility through tight-binding calculations of the band structure. Covalently connected carbon nanotubes create magnetic fields through graphene nanoribbons, cascading logic gates through incoherent spintronic switching. The exceptional material properties of carbon materials permit Terahertz operation and two orders of magnitude decrease in power-delay product compared to cutting-edge microprocessors. We hope to inspire the fabrication of these cascaded logic circuits to stimulate a transformative generation of energy-efficient computing.

New 3D printing method may allow for fast, low-cost, more-flexible medical implants for millions

UF Soft Matter | Silicone is 3D-printed into the micro-organogel support material. The printing nozzle follows a predefined trajectory, depositing liquid silicone in its wake. The liquid silicone is supported by the micro-organogel material during this printing process.

University of Florida (UF) researchers have developed a method for 3D printing soft-silicone medical implants that are stronger, quicker, less expensive, more flexible, and more comfortable than the implants currently available. That should be good news for the millions of people every year who need medical devices implanted.

Model 3D-printed silicone trachea implant (credit: University of Florida)

Currently, such devices — such as ports for draining bodily fluids (cerebral spinal fluid in hydrocephalus, for example), implantable bands, balloons, soft catheters, slings and meshes — are mass produced and made through molding processes. To create customized parts for individual patients with molding would be very expensive and could take days or weeks for each job.

The 3D printing method cuts that time to hours, potentially saving lives.

The ability to easily replace silicone implants at low cost is especially important for children, where “implants may need to be replaced frequently as they grow up,” Thomas E. Angelini, an associate professor of mechanical engineering  of the UF Department of Mechanical and Aerospace Engineering, explained to KurzweilAI. Angelini is senior author of a paper published May 10, 2017 in the open-access journal Science Advances.

The research could also pave the way for new therapeutic devices that encapsulate and control the release of drugs or small molecules for guiding tissue regeneration or assisting diseased organs, such as the pancreas or prostate, according to lead author Christopher O’Bryan, a UF mechanical and aerospace engineering doctoral student.

UF Soft Matter | Water is pumped from one reservoir to another using a 3D-printed silicone valve. The silicone valve contains two encapsulated ball valves that allow water to be pumped through the valve by squeezing the lower chamber. The silicone valve demonstrates the ability of the UF 3D-printing method to create multiple encapsulated components in a single part — something that cannot be done with a traditional 3D-printing approach.

Abstract of Self-assembled micro-organogels for 3D printing silicone structures

The widespread prevalence of commercial products made from microgels illustrates the immense practical value of harnessing the jamming transition; there are countless ways to use soft, solid materials that fluidize and become solid again with small variations in applied stress. The traditional routes of microgel synthesis produce materials that predominantly swell in aqueous solvents or, less often, in aggressive organic solvents, constraining ways that these exceptionally useful materials can be used. For example, aqueous microgels have been used as the foundation of three-dimensional (3D) bioprinting applications, yet the incompatibility of available microgels with nonpolar liquids, such as oils, limits their use in 3D printing with oil-based materials, such as silicone. We present a method to make micro-organogels swollen in mineral oil, using block copolymer self-assembly. The rheological properties of this micro-organogel material can be tuned, leveraging the jamming transition to facilitate its use in 3D printing of silicone structures. We find that the minimum printed feature size can be controlled by the yield stress of the micro-organogel medium, enabling the fabrication of numerous complex silicone structures, including branched perfusable networks and functional fluid pumps.

Robotic system can 3-D print basic structure of an entire building

Architectural-scale dome section case study for 3-D printing system (top view). For initial tests, the system fabricated the foam-insulation framework used to form a finished concrete structure. As a proof of concept, the researchers used a prototype to build the basic structure of the walls of a 50-foot-diameter, 12-foot-high dome — a project that was completed in less than 14 hours of “printing” time. (credit: Steven Keating, Julian Leland, Levi Cai, and Neri Oxman/Mediated Matter Group)

MIT researchers have designed a “Digital Construction Platform” system that can 3-D print the basic structure of an entire building. It could enable faster, cheaper, more adaptable building construction — replacing traditional fabrication technologies that are dangerous, slow, and energy-intensive in the annual $8.5 trillion construction industry.

The Digital Construction Platform system consists of a tracked vehicle that carries a large, industrial robotic arm, which has a smaller, precision-motion robotic arm (orange) at its end. This highly controllable arm can be used to direct any conventional (or unconventional) construction nozzle, such as those used for pouring concrete or spraying insulation material. The nozzles can be adapted to vary the density of the material being poured, and even to mix different materials as it goes along. The system is equipped with a scoop that could be used to both prepare the building surface and acquire local materials, such as dirt for a rammed-earth building, for the construction itself. The whole system could be operated electrically, even powered by solar panels, as shown here. The system can also create complex shapes and overhangs, which the team demonstrated by including a wide, built-in bench in their prototype dome. (credit: Steven J. Keating et al./Science Robotics)

Described in an open-access paper in the journal Science Robotics, this free-moving system is intended to be self-sufficient and can construct an object of almost any size. It could enable the design and construction of new kinds of buildings that would not be feasible with traditional building methods.

A building could be completely customized to the needs of a particular site and the desires of its maker. Even the internal structure could be modified in new ways — different materials could be incorporated as the process goes along, and material density could be varied to provide optimum combinations of strength, insulation, or other properties.

Rendering showing use of the Digital Construction Platform in an urban environment, including robotic chain welding fabrication — a building as an organism, computationally grown, additively manufactured, and possibly biologically augmented. In the future, the supporting pillars of such a building could be placed in optimal locations based on ground-penetrating radar analysis of the site, and walls could have varying thickness depending on their orientation. For example, a building could have thicker, more insulated walls on its north side in cold climates, or walls that taper from bottom to top as their load-bearing requirements decrease, or curves that help the structure withstand winds. (credit: Steven J. Keating et al./Science Robotics)

The researchers showed that the system can be easily adapted to existing building sites and equipment, and that it will fit existing building codes without requiring whole new evaluations. Such systems could be deployed to remote regions, for example in the developing world, or to areas for disaster relief after a major storm or earthquake, to provide durable shelter rapidly.

Keating says the team’s analysis shows that such construction methods could produce a structure faster and less expensively than present methods can, and would also be much safer by reducing hands-on work*. In addition, because shapes and thicknesses can be optimized for what is needed structurally, rather than having to match what’s available in premade lumber and other materials, the total amount of material needed could be reduced.

For initial tests, the system fabricated a foam-insulation framework. In this construction method, polyurethane foam molds are filled with concrete, similar to traditional commercial insulated-concrete formwork techniques. Any needed wiring and plumbing can be inserted into the mold before the concrete is poured, providing a finished wall structure all at once. It can even incorporate data about the site collected during the process, using built-in sensors for temperature, light, and other parameters to make adjustments to the structure as it is built. (credit: Steven J. Keating et al./Science Robotics)

The ultimate vision is “in the future, to have something totally autonomous, that you could send to the moon or Mars or Antarctica, and it would just go out and make these buildings for years,” says Keating, who led the development of the system as his doctoral thesis work. Meanwhile, “with this process, we can replace one of the key parts of making a building, right now,” he says.

Automated ice structure fabrication in polar environment with power sourced through rollable photovoltaic panels and materials gathered locally. (credit: Steven J. Keating et al./Science Robotics)

Fabrication with local sand to create fractal structures for future immersion in the ocean to support coral reef regrowth. Power sourced via deployable rollable photovoltaics. (credit: Steven J. Keating et al./Science Robotics)

* The International Labour Organization estimated in 2005 that more than 50,000 people die globally in the construction industry per year, accounting for 17% of workplace accident fatalities.

Abstract of Toward site-specific and self-sufficient robotic fabrication on architectural scales

Contemporary construction techniques are slow, labor-intensive, dangerous, expensive, and constrained to primarily rectilinear forms, often resulting in homogenous structures built using materials sourced from centralized factories. To begin to address these issues, we present the Digital Construction Platform (DCP), an automated construction system capable of customized on-site fabrication of architectural-scale structures using real-time environmental data for process control. The system consists of a compound arm system composed of hydraulic and electric robotic arms carried on a tracked mobile platform. An additive manufacturing technique for constructing insulated formwork with gradient properties from dynamic mixing was developed and implemented with the DCP. As a case study, a 14.6-m-diameter, 3.7-m-tall open dome formwork structure was successfully additively manufactured on site with a fabrication time under 13.5 hours. The DCP system was characterized and evaluated in comparison with traditional construction techniques and existing large-scale digital construction research projects. Benefits in safety, quality, customization, speed, cost, and functionality were identified and reported upon. Early exploratory steps toward self-sufficiency—including photovoltaic charging and the sourcing and use of local materials—are discussed along with proposed future applications for autonomous construction.

New artificial photosynthesis process converts CO2 in air to fuel

Professor Fernando Uribe-Romo and his team of students created a way to use LED light and a porous synthetic metal-organic frameworks (MOF) material to break down carbon dioxide into fuel. (credit: Bernard Wilchusky/UCF)

A University of Central Florida (UCF) chemistry professor has invented a revolutionary way to remove carbon dioxide (CO2) from air by triggering artificial photosynthesis in a synthetic material — breaking down carbon dioxide while also producing fuel for energy.

UCF Assistant Professor Fernando Uribe-Romo and his students used a synthetic material called a metal–organic framework (MOF), which converts carbon dioxide into harmless organic materials — similar to how plants convert CO2 and sunlight into food.

Scientists have been pursuing this goal for years, but the challenge is finding an economical way for visible light to trigger the chemical transformation. Ultraviolet rays have enough energy to enable the reaction in common materials, but UVs make up only about 4% of the light Earth receives from the Sun. For the lower-energy visible range, there are only a few materials that work, such as platinum, rhenium and iridium, but these are scarce and expensive.

New material converts CO2 to fuel

The solution was to combine cost-effective titanium with a highly porous metal–organic framework (MOF) material for light harvesting. (MOFs are used in the MIT-UC Berkeley system for condensing water out of air, also using only sunlight, as described recently on KurzweilAI.) The light-harvesting molecules, called N-alkyl-2-aminoterephthalates, can be designed to absorb specific colors of light when incorporated in the MOF — in this case, the color blue.

CO2 removal process. Blue light combined with a metal–organic framework (MOF) material causes CO2 to convert to formate, a fuel. (credit: adapted from illustration by Matthew W. Logan et al./ Journal of Materials Chemistry A)

In an experiment, the research team assembled a blue LED photoreactor — a glowing blue cylinder that looks like a tanning bed, using strips of LED lights inside the chamber of the cylinder to mimic the sun’s blue wavelength — and fed in CO2. The CO2 was found to convert into two modified forms of carbon — formate and formamides (two kinds of solar fuel) — and in the process, cleaning the air.

Uribe-Romo plans to continue to fine-tune the approach to create greater amounts of modified CO2 so it is more efficient and to see if other wavelengths of visible light may also trigger the reaction, with adjustments to the MOF material. If the process works efficiently, it could be a significant way to help treat greenhouse gases, while also creating a clean way to produce energy, says Uribe-Romo.

Rooftop shingles to clean air and power homes

“The idea would be to set up stations that capture large amounts of CO2, like next to a power plant. The gas would be sucked into the station, go through the process and recycle the greenhouse gases while producing energy that would be put back into the power plant.”

He also speculates that someday, homeowners could purchase rooftop shingles made of the MOF material, which would clean the air in their neighborhood while producing energy that could be used to power their homes.

The research findings are published in the Journal of Materials Chemistry A. Researchers at Florida State University also helped interpret the results of the experiments.

Abstract of Systematic Variation of the Optical Bandgap in Titanium Based Isoreticular Metal-Organic Frameworks for Photocatalytic Reduction of CO2 under Blue Light

A series of metal-organic frameworks isoreticular to MIL-125-NH2 were prepared, where the 2-amino-terephthalate organic links feature N-alkyl groups of increasing chain length (from methyl to heptyl) and varying connectivity (primary and secondary). The prepared materials display reduced optical bandgaps correlated to the inductive donor ability of the alkyl substituent as well as high photocatalytic activity towards the reduction of carbon dioxide under blue illumination operating over 120 h. Secondary N-alkyl substitution (isopropyl, cyclopentyl and cyclohexyl) exhibit larger apparent quantum yields than the primary N-alkyl analogs directly related to their longer lived excited-state lifetime. In particular, MIL-125-NHCyp (Cyp = cyclopentyl) exhibits a small bandgap (Eg = 2.30 eV), a long-lived excited-state (τ = 68.8 ns) and the larger apparent quantum yield (Φapp = 1.80%) compared to the parent MIL-125-NH2 (Eg = 2.56 eV, Φapp = 0.31%, τ = 12.8 ns), making it a promising candidate for the next generation of photocatalysts for solar fuel production based on earth-abundant elements.

The first 2D microprocessor — based on a layer of just 3 atoms

Overview of the entire chip. AC = Accumulator, internal buffer; PC = Program Counter, points at the next instruction to be executed; IR = Instruction Register, used to buffer data- and instruction-bits received from the external memory; CU = Control Unit, orchestrates the other units according to the instruction to be executed; OR = Output Register, memory used to buffer output-data; ALU = Arithmetic Logic Unit, does the actual calculations. (credit: TU Wien)

Researchers at Vienna University of Technology (known as TU Wien) in Vienna, Austria, have developed the world’s first two-dimensional microprocessor — the most complex 2D circuitry so far. Microprocessors based on atomically thin 2D materials promise to one day replace traditional microprocessors as well as open up new applications in flexible electronics.

Consisting of 115 transistors, the microprocessor can run, simple user-defined programs stored in an external memory, perform logical operations, and communicate with peripheral devices. The microprocessor is based on molybdenum disulphide (MoS2), a three-atoms-thick 2D semiconductor transistor layer consisting of molybdenum and sulphur atoms, with a surface area of around 0.6 square millimeters.

Schematic drawing of an inverter (“NOT” logic) circuit (top) and an individual MoS2 transistor (bottom) (credit: Stefan Wachter et al./Nature Communications)

For demonstration purposes, the microprocessor is currently a 1-bit design, but it’s scalable to a multi-bit design using industrial fabrication methods, says Thomas Mueller, PhD., team leader and senior author of an open-access paper on the research published in Nature Communications.*

New sensors and flexible displays

Two-dimensional materials are flexible, making future 2D microprocessors and other integrated circuits ideal for uses such as medical sensors and flexible displays. They promise to extend computing to the atomic level, as silicon reaches its physical limits.

However, to date, it has only been possible to produce individual 2D digital components using a few transistors. The first 2D MoS2 transistor with a working 1-nanometer (nm) gate was created in October 2016 by a team led by Lawrence Berkeley National Laboratory (Berkeley Lab) scientists, as KurzweilAI reported.

Mueller said much more powerful and complex circuits with thousands or even millions of transistors will be required for this technology to have practical applications. Reproducibility continues to be one of the biggest challenges currently being faced within this field of research, along with the yield in the production of the transistors used, he explained.

* “We also gave careful consideration to the dimensions of the individual transistors,” explains Mueller. “The exact relationships between the transistor geometries within a basic circuit component are a critical factor in being able to create and cascade more complex units. … the major challenge that we faced during device fabrication is yield. Although the yield for subunits was high (for example, ∼80% of ALUs were fully functional), the sheer complexity of the full system, together with the non-fault tolerant design, resulted in an overall yield of only a few per cent of fully functional devices. Imperfections of the MoS2 film, mainly caused by the transfer from the growth to the target substrate, were identified as main source for device failure. However, as no metal catalyst is required for the synthesis of TMD films, direct growth on the target substrate is a promising route to improve yield.

Abstract of A microprocessor based on a two-dimensional semiconductor

The advent of microcomputers in the 1970s has dramatically changed our society. Since then, microprocessors have been made almost exclusively from silicon, but the ever-increasing demand for higher integration density and speed, lower power consumption and better integrability with everyday goods has prompted the search for alternatives. Germanium and III–V compound semiconductors are being considered promising candidates for future high-performance processor generations and chips based on thin-film plastic technology or carbon nanotubes could allow for embedding electronic intelligence into arbitrary objects for the Internet-of-Things. Here, we present a 1-bit implementation of a microprocessor using a two-dimensional semiconductor—molybdenum disulfide. The device can execute user-defined programs stored in an external memory, perform logical operations and communicate with its periphery. Our 1-bit design is readily scalable to multi-bit data. The device consists of 115 transistors and constitutes the most complex circuitry so far made from a two-dimensional material.