Graduate students Siyuan Xing and Jia Jiang developed a new textile microfluidic platform using hydrophilic (water-attracting) threads stitched into a highly water-repellent fabric. They were able to create patterns of threads that suck droplets of water from one side of the fabric, propel them along the threads and expel them from the other side.

“We intentionally did not use any fancy microfabrication techniques so it is compatible with the textile manufacturing process and very easy to scale up,” said Xing, lead graduate student on the project.

It’s not just that the threads conduct water through capillary action. The water-repellent properties of the surrounding fabric also help drive water down the channels. Unlike conventional fabrics, the water-pumping effect keeps working even when the water-conducting fibers are completely saturated, because of the sustaining pressure gradient generated by the surface tension of droplets.

The rest of the fabric stays completely dry and breathable. By adjusting the pattern of water-conducting fibers and how they are stitched on each side of the fabric, the researchers can control where sweat is collected and where it drains away on the outside.

Workout enthusiasts, athletes and clothing manufacturers are all interested in fabrics that remove sweat and let the skin breathe. Cotton fibers, for example, wick away sweat — but during heavy exercise, cotton can get soaked, making it clingy and uncomfortable.

A paper describing the research was published recently in the journal Lab on a Chip. The work was funded in part by the National Science Foundation.

Reprinted from University of California Davis (UCD).

“Similar to the chloroplasts in green plants that carry out photosynthesis, our artificial photosynthetic system is composed of two semiconductor light absorbers, an interfacial layer for charge transport, and spatially separated co-catalysts,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division, who led this research. “To facilitate solar water- splitting in our system, we synthesized tree-like nanowire heterostructures, consisting of silicon trunks and titanium oxide branches. Visually, arrays of these nanostructures very much resemble an artificial forest.”

Yang, who also holds appointments with the University of California Berkeley’s Chemistry Department and Department of Materials Science and Engineering, is the corresponding author of a paper describing this research in the journal NANO Letters. The paper is titled “A Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting.” Co-authors are Chong Liu, Jinyao Tang, Hao Ming Chen and Bin Liu.

Solar technologies are the ideal solutions for carbon-neutral renewable energy — there’s enough energy in one hour’s worth of global sunlight to meet all human needs for a year. Artificial photosynthesis, in which solar energy is directly converted into chemical fuels, is regarded as one of the most promising of solar technologies. A major challenge for artificial photosynthesis is to produce hydrogen cheaply enough to compete with fossil fuels. Meeting this challenge requires an integrated system that can efficiently absorb sunlight and produce charge-carriers to drive separate water reduction and oxidation half-reactions.

“In natural photosynthesis the energy of absorbed sunlight produces energized charge-carriers that execute chemical reactions in separate regions of the chloroplast,” Yang says. “We’ve integrated our nanowire nanoscale heterostructure into a functional system that mimics the integration in chloroplasts and provides a conceptual blueprint for better solar-to-fuel conversion efficiencies in the future.”

When sunlight is absorbed by pigment molecules in a chloroplast, an energized electron is generated that moves from molecule to molecule through a transport chain until ultimately it drives the conversion of carbon dioxide into carbohydrate sugars. This electron transport chain is called a “Z-scheme” because the pattern of movement resembles the letter Z on its side. Yang and his colleagues also use a Z-scheme in their system only they deploy two Earth abundant and stable semiconductors — silicon and titanium oxide — loaded with co-catalysts and with an ohmic contact inserted between them. Silicon was used for the hydrogen-generating photocathode and titanium oxide for the oxygen-generating photoanode. The tree-like architecture was used to maximize the system’s performance. Like trees in a real forest, the dense arrays of artificial nanowire trees suppress sunlight reflection and provide more surface area for fuel producing reactions.

“Upon illumination photo-excited electron−hole pairs are generated in silicon and titanium oxide, which absorb different regions of the solar spectrum,” Yang says. “The photo-generated electrons in the silicon nanowires migrate to the surface and reduce protons to generate hydrogen while the photo-generated holes in the titanium oxide nanowires oxidize water to evolve oxygen molecules. The majority charge carriers from both semiconductors recombine at the ohmic contact, completing the relay of the Z-scheme, similar to that of natural photosynthesis.”

Under simulated sunlight, this integrated nanowire-based artificial photosynthesis system achieved a 0.12-percent solar-to-fuel conversion efficiency. Although comparable to some natural photosynthetic conversion efficiencies, this rate will have to be substantially improved for commercial use. However, the modular design of this system allows for newly discovered individual components to be readily incorporated to improve its performance. For example, Yang notes that the photocurrent output from the system’s silicon cathodes and titanium oxide anodes do not match, and that the lower photocurrent output from the anodes is limiting the system’s overall performance.

“We have some good ideas to develop stable photoanodes with better performance than titanium oxide,” Yang says. “We’re confident that we will be able to replace titanium oxide anodes in the near future and push the energy conversion efficiency up into single digit percentages.”

This research was supported by the DOE Office of Science.

Reprinted from DOE/Lawrence Berkeley National Laboratory.

With the hand of nature trained on a beaker of chemical fluid, the most delicate flower structures have been formed in a Harvard laboratory — and not at the scale of inches, but microns.

These minuscule sculptures, curved and delicate, don’t resemble the cubic or jagged forms normally associated with crystals, though that’s what they are. Rather, fields of carnations and marigolds seem to bloom from the surface of a submerged glass slide, assembling themselves a molecule at a time.

By simply manipulating chemical gradients in a beaker of fluid, Wim L. Noorduin, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS) and lead author of a paper appearing on the cover of the May 17 issue of Science, has found that he can control the growth behavior of these crystals to create precisely tailored structures.

“For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature. This work helps to demonstrate what’s possible just through environmental, chemical changes,” says Noorduin.

The precipitation of the crystals depends on a reaction of compounds that are diffusing through a liquid solution. The crystals grow toward or away from certain chemical gradients as the pH of the reaction shifts back and forth. The conditions of the reaction dictate whether the structure resembles broad, radiating leaves, a thin stem, or a rosette of petals.

It is not unusual for chemical gradients to influence growth in nature; for example, delicately curved marine shells form from calcium carbonate under water, and gradients of signaling molecules in a human embryo help set up the plan for the body. Similarly, Harvard biologist Howard Berg has shown that bacteria living in colonies can sense and react to plumes of chemicals from one another, which causes them to grow, as a colony, into intricate geometric patterns.

Replicating this type of effect in the laboratory was a matter of identifying a suitable chemical reaction and testing, again and again, how variables like the pH, temperature, and exposure to air might affect the nanoscale structures.

The project fits right in with the work of Joanna Aizenberg, an expert in biologically inspired materials science, biomineralization, and self-assembly, and principal investigator for this research.

Aizenberg is the Amy Smith Berylson Professor of Materials Science at Harvard SEAS, Professor of Chemistry and Chemical Biology in the Harvard Department of Chemistry and Chemical Biology, and a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard.

Her recent work has included the invention of an extremely slippery material, inspired by the pitcher plant, and the discovery of how bacteria use their flagella to cling to the surfaces of medical implants.

“Our approach is to study biological systems, to think what they can do that we can’t, and then to use these approaches to optimize existing technologies or create new ones,” says Aizenberg. “Our vision really is to build as organisms do.”

To create the flower structures, Noorduin and his colleagues dissolve barium chloride (a salt) and sodium silicate (also known as waterglass) into a beaker of water. Carbon dioxide from air naturally dissolves in the water, setting off a reaction which precipitates barium carbonate crystals. As a byproduct, it also lowers the pH of the solution immediately surrounding the crystals, which then triggers a reaction with the dissolved waterglass. This second reaction adds a layer of silica to the growing structures, uses up the acid from the solution, and allows the formation of barium carbonate crystals to continue.

“You can really collaborate with the self-assembly process,” says Noorduin. “The precipitation happens spontaneously, but if you want to change something then you can just manipulate the conditions of the reaction and sculpt the forms while they’re growing.”

Increasing the concentration of carbon dioxide, for instance, helps to create ‘broad-leafed’ structures. Reversing the pH gradient at the right moment can create curved, ruffled structures.

Noorduin and his colleagues have grown the crystals on glass slides and metal blades; they’ve even grown a field of flowers in front of President Lincoln’s seat on a one-cent coin.

“When you look through the electron microscope, it really feels a bit like you’re diving in the ocean, seeing huge fields of coral and sponges,” describes Noorduin. “Sometimes I forget to take images because it’s so nice to explore.”

In addition to her roles at Harvard SEAS, the Department of Chemistry and Chemical Biology, and the Wyss Institute, Joanna Aizenberg is Director of the Kavli Institute for Bionano Science and Technology at Harvard and Director of the Science Program at the Radcliffe Institute for Advanced Study.

Coauthors included Alison Grinthal, a research scientist at Harvard SEAS, and L. Mahadevan, who is the Lola England de Valpine Professor of Applied Mathematics at SEAS, Professor of Organismic and Evolutionary Biology and of Physics, and a Core Faculty Member at the Wyss Institute.

The project was supported by National Science Foundation grants to the Harvard Materials Research Science and Engineering Center (DMR-0820484) and the Harvard Center for Nanoscale Systems (ECS-0335765); and by the Netherlands Organization for Scientific Research.

Reprinted from Harvard School of Engineering and Applied Sciences.

Zhenan Bao, a professor of chemical engineering at Stanford, has developed a heart monitor thinner than a dollar bill and no wider than a postage stamp. The flexible skin-like monitor, worn under an adhesive bandage on the wrist, is sensitive enough to help doctors detect stiff arteries and cardiovascular problems.

The devices could one day be used to continuously track heart health and provide doctors a safer method of measuring a key vital sign for newborn and other high-risk surgery patients.

“The pulse is related to the condition of the artery and the condition of the heart,” said Bao, whose lab develops artificial skin-like materials. “The better the sensor, the better doctors can catch problems before they develop.”

Your pulse

To find your pulse, press your index and middle finger into the underside of your opposite wrist. You should feel the steady rhythm of your heart as it pumps blood through your veins.

Each beat you feel is actually made up of two distinct peaks, even though you can’t tell them apart with just your fingers. The first, larger peak is from your heart pumping out blood. Shortly after a heartbeat, your lower body sends a reflecting wave back to your artery system, creating a smaller second peak.

The relative sizes of these two peaks can be used by medical experts to measure your heart’s health.

“You can use the ratio of the two peaks to determine the stiffness of the artery, for example,” said Gregor Schwartz, a post-doctoral fellow and a physicist for the project. “If there is a change in the heart’s condition, the wave pattern will change. Fortunately, when I tested this on myself, my heart looked fine.”

To make the heart monitor both sensitive and small, Bao’s team uses a thin middle layer of rubber covered with tiny pyramid bumps. Each mold-made pyramid is only a few microns across — smaller than a human red blood cell.

When pressure is put on the device, the pyramids deform slightly, changing the size of the gap between the two halves of the device. This change in separation causes a measurable change in the electromagnetic field and the current flow in the device.

The more pressure placed on the monitor, the more the pyramids deform and the larger the change in the electromagnetic field. Using many of these sensors on a prosthetic limb could act like an electronic skin, creating an artificial sense of touch.

When the sensor is placed on someone’s wrist using an adhesive bandage, the sensor can measure that person’s pulse wave as it reverberates through the body.

The device is so sensitive that it can detect more than just the two peaks of a pulse wave. When engineers looked at the wave drawn by their device, they noticed small bumps in the tail of the pulse wave invisible to conventional sensors. Bao said she believes these fluctuations could potentially be used for more detailed diagnostics in the future.

Blood pressure and babies

Doctors already use similar, albeit much bulkier, sensors to keep track of a patient’s heart health during surgery or when taking a new medication. But in the future Bao’s device could help keep track of another vital sign.

“In theory, this kind of sensor can be used to measure blood pressure,” said Schwartz. “Once you have it calibrated, you can use the signal of your pulse to calculate your blood pressure.”

This non-invasive method of monitoring heart health could replace devices inserted directly into an artery, called intravascular catheters. These catheters create a high risk of infection, making them impractical for newborns and high-risk patients. Thus, an external monitor like Bao’s could provide doctors a safer way to gather information about the heart, especially during infant surgeries.

Bao’s team is working with other Stanford researchers to make the device completely wireless. Using wireless communication, doctors could receive a patient’s minute-by-minute heart status via cell phone, all thanks to a device as thick as a human hair.

“For some patients with a potential heart disease, wearing a bandage would allow them to constantly measure their heart’s condition,” Bao said. “This could be done without interfering with their daily life at all, since it really just requires wearing a small bandage.”

The team published its work in the May 12 edition of Nature Communications. The team’s research is supported by funding from the National Science Foundation and the Air Force Office of Scientific Research.

The idea of an underwater pumped hydroelectric power plant may sound like Jules Verne fiction, but then it was hatched by a German engineer who has spent much of his professional life working in aerospace technology.

“Imagine opening a hatch in a submarine under water. The water will flow into the submarine with enormous force. It is precisely this energy potential we want to utilize,” explains Rainer Schramm, inventor and founder of the company Subhydro AS to Gemini.no. “Many people have launched the idea of storing energy by exploiting the pressure at the seabed, but we are the first in the world to apply a specific patent-pending technology to make this possible,” he adds. He has joined forces with SINTEF in order to realize the concept.

Turbine converts energy

“SINTEF has experts in the fields of energy generation, materials technology and not least offshore and deep-water technology, which means we have all the expertise we need in one place,” says the German inventor. To use the water pressure at the sea bed in practice, the mechanical energy is converted by a reversible pump turbine, as in a normal pumped storage hydroelectric plant. “A pumped storage power plant is a hydroelectric plant which can be “charged” up again by pumping the water back to the upper reservoir once it has passed through a turbine. This type of power plant is used as a “battery,” when connected to the power grid,” the inventor explains. In this pumped storage power plant turbine will be connected to a tank on the seabed at a depth of 400-800 metres. The turbine is fitted with a valve, and when this is opened, water flows in and starts turning the turbine. The turbine drives a generator to produce electricity. One can connect as many tanks as one wishes. In other words, it is the number of water tanks that decides how long the plant can generate electricity, before the energy storage capacity is exhausted.

High degree of storage efficiency

“When the water tanks are full, the water must be removed from the tanks,” Schramm explains. This is achieved by running the turbine in reverse, so that it functions as a pump. The process consumes energy from the power grid, just as when one charges an ordinary battery. Although a bit more energy is used to empty the water tanks than can be recovered from flooding them, the degree of efficiency of this type of power plant is just as high as that of a conventional, onshore plant. According to Schramm, calculations indicate an electric storage efficiency of approximately 80 per cent round-trip.

Another advantage of the system is that equipment can be scaled according to users’ requirements, both as regards the turbine size and the number of water tanks. A plant of normal size will produce roughly 300 megawatts for a period of 7-8 hours. This is enough energy to supply just over 200,000 British households with electricity for the same time.

“We envisage that this type of storage plant will function well in conjunction with, for example, wind farms. At strong wind conditions, excess electricity is sent subsea to pump water out of the storage tanks. In periods with little wind, energy can be obtained from this underwater plant instead. The same applies to solar generation: the pumped storage power station can contribute to constant electricity production at night time when there is no sunshine to run a solar power plant,” says Rainer Schramm.

The deeper the better In addition to the number of tanks, the sea depth also determines the effectiveness of the plant: the deeper the equipment is located, the greater is the pressure difference between the sea surface and the seabed, and the more energy is stored in a single tank. “This is part of the reason why we want to try out the technology in Norway,” says Rainer Schramm. In his native country Germany the sea is too shallow for the system to be profitable, but there are many parts of the world where great water depths are located close inshore, such as the marine areas around Italy, Portugal and Spain, as well as North and South America.

Advanced concrete technology

One of the challenges faced by the SINTEF research scientists is to develop a type of concrete which can be used to cast the water tanks which are placed on the seabed. Tor Arne Martius-Hammer at SINTEF Building and Infrastructure is an expert on strong, light concrete types.

“The challenge is to find the optimal balance between strength and cost. If we achieve the goal of creating a concrete which will withstand at least 5 times as high loading as ordinary concrete, we can reduce the wall thickness by 75 per cent. This is a critical factor. We need to reach production and installation costs which make storage of energy economical in relation to the price of electrical energy,” Martius-Hammer explains.

One of the solutions SINTEF will work on is reinforcing the concrete with thin steel fibres instead of the normal steel rebar. This will result in a significant simplification of the production process. Concrete is in existence at present which can be used, but our job is to develop a cheaper alternative,” says Martius-Hammer.

Reprinted from SINTEF, via AlphaGalileo.