Tag Archives: Wei Gao

Smart contact lenses harvest energy from tears

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After posting about a bioenergy harvesting battery for implants such as pacemakers and deep brain stimulators (see my May 17, 2024 posting), it seems like a good time to highlight another such device, in this case, contact lenses.

From an April 1, 2024 article by Julianne Pepitone for IEEE (Institute for Electrical and Electronics Engineers) Spectrum,

The potential use cases for smart contacts are compelling and varied. Pop a lens on your eye and monitor health metrics like glucose levels; receive targeted drug delivery for ocular diseases; experience augmented reality and read news updates with displays of information literally in your face.

But the eye is quite a challenge for electronics design: With one of the highest nerve densities of any human tissue, the cornea is 300 to 600 times as sensitive as our skin. Researchers have developed small, flexible chips, but power sources have proved more difficult, as big batteries and wires clearly won’t do here. Existing applications offer less-than-ideal solutions like overnight induction charging and other designs that rely on some type of external battery.

Now, a team from the University of Utah says they’ve developed a better solution: an all-in-one hybrid energy-generation unit specifically designed for eye-based tech.

In a paper published in the journal Small on 13 March [2024], the researchers describe how they built the device, combining a flexible silicon solar cell with a new device that converts tears to energy. The system can reliably supply enough electricity to operate smart contacts and other ocular devices.This is a major improvement over wireless power transfer from separate batteries, says Erfan Pourshaban, who worked on the system while a doctoral student at University of Utah.

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Researchers tested a contact-lens power system on a fake eye. ERFAN POURSHABAN [downloaded from https://spectrum.ieee.org/power-smart-contact-lenses]

Here’s an excerpt from the explanation for how this system works, from the April 1, 2024 article,

To create the power pack, Pourshaban and his colleagues fabricated custom pieces. The first step was miniaturized, flexible silicon solar cells that can capture light from the sun as well as from artificial sources like lamps. The team connected eight tiny (1.5 by 1.5 by 0.1 millimeters) rigid crystalline cells and encapsulated them in a polymer to make a flexible photovoltaic system.

The second half is an eye-blinking-activated system that functions like a metal-air battery. The wearer’s natural tears—more specifically the electrolytes within them—serve as a biofuel to generate power.

…

The harvesting occurs literally in the blink of an eye: When the eye is completely open, the harvester is off. Then when the eye starts to blink, the tear electrolytes meet the magnesium anode, causing an oxidation reaction and the generation of electrons. …

Applications for the technology were also discussed, from the April 1, 2024 article,

“The reliable power output from this device can fuel a broad spectrum of applications, including wearable biosensors and electrically responsive drug-delivery systems, directly within the eye’s environment,” Gao adds.[Wei Gao, a biosensors expert and assistant professor of medical engineering at Caltech, who was not involved in the research.

…

Pourshaban agrees, adding that there are obvious consumer applications, such as lenses that display to a runner the heart rate, pace, and calorie burn during a workout. Retailers could glean valuable insights from tracking how a shopper scans shelves and selects items. [emphases mine] Commercialization potential is significant and varied, he says.

However, Pourshaban is perhaps most excited about potential applications in monitoring eye health, from prosaic conditions like presbyopia—age-related farsightedness, which can begin in the mid-40s—to more insidious diseases including glaucoma.

…

If you have the time, Pepitone’s April 1, 2024 article is an engaging and accessible read.

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

Power Scavenging Microsystem for Smart Contact Lenses by Erfan Pourshaban, Mohit U. Karkhanis, Adwait Deshpande, Aishwaryadev Banerjee, Md Rabiul Hasan, Amirali Nikeghbal, Chayanjit Ghosh, Hanseup Kim, Carlos H. Mastrangelo. Small DOI: https://doi.org/10.1002/smll.202401068 First published: 13 March 2024

This paper is open access.

Embroidery as a low-cost solution for making wearable electronics?

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A November 22, 2022 news item on Nanowerk explores embroidery as a means for affixing wearable electronics to textiles,

Embroidering power-generating yarns onto fabric allowed researchers to embed a self-powered, numerical touch-pad and movement sensors into clothing. The technique offers a low-cost, scalable potential method for making wearable devices.

“Our technique uses embroidery, which is pretty simple – you can stitch our yarns directly on the fabric,” said the study’s lead author Rong Yin, assistant professor of textile engineering, chemistry and science at North Carolina State University. “During fabric production, you don’t need to consider anything about the wearable devices. You can integrate the power-generating yarns after the clothing item has been made.”

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Caption: Yu Chen, graduate student at NC State, demonstrates embroidery techniques. Courtesy: North Caroline State University

A North Carolina State University November 22, 2022 news release (also on EurekAlert), which originated the news item, describes the research in more detail,

In the study published in Nano Energy, researchers tested multiple designs for power-generating yarns. To make them durable enough to withstand the tension and bending of the embroidery stitching process, they ultimately used five commercially available copper wires, which had a thin polyurethane coating, together. Then, they stitched them onto cotton fabric with another material called PTFE.

“This is a low-cost method for making wearable electronics using commercially available products,” Yin said. “The electrical properties of our prototypes were comparable to other designs that relied on the same power generation mechanism.”

The researchers relied on a method of generating electricity called the “triboelectric effect,” which involves harnessing electrons exchanged by two different materials, like static electricity. They found the PTFE fabric had the best performance in terms of voltage and current when in contact with the polyurethane-coated copper wires, as compared to other types of fabric that they tested, including cotton and silk. They also tested coating the embroidery samples in plasma to increase the effect.

In our design, you have two layers – one is your conductive, polyurethane-coated copper wires, and the other is PTFE, and they have a gap between them,” Yin said. “When the two non-conductive materials come into contact with each other, one material will lose some electrons, and some will get some electrons. When you link them together, there will be a current.”

Researchers tested their yarns as motion sensors by embroidering them with the PTFE fabric on denim. They placed the embroidery patches on the palm, under the arm, at the elbow and at the knee to track electrical signals generated as a person moves. They also attached fabric with their embroidery on the insole of a shoe to test its use as a pedometer, finding their electrical signals varied depending on whether the person was walking, running or jumping.

Lastly, they tested their yarns in a textile-based numeric keypad on the arm, which they made by embroidering numbers on a piece of cotton fabric, and attaching them to a piece of PTFE fabric. Depending on the number that the person pushed on the keypad, they saw different electrical signals generated for each number.

“You can embroider our yarns onto clothes, and when you move, it generates an electrical signal, and those signals can be used as a sensor,” Yin said. “When we put the embroidery in a shoe, if you are running, it generates a higher voltage than if you were just walking. When we stitched numbers onto fabric, and press them, it generates a different voltage for each number. It could be used as an interface.”

Since textile products will inevitably be washed, they tested the durability of their embroidery design in a series of washing and rubbing tests. After hand washing and rinsing the embroidery with detergent, and drying it in an oven, they found no difference or a slight increase in voltage. For the prototype coated in plasma, they found weakened but still superior performance compared with the original sample. After an abrasion test, they found that there was no significant change in electrical output performance of their designs after 10,000 rubbing cycles.

In future work, they plan to integrate their sensors with other devices to add more functions.

“The next step is to integrate these sensors into a wearable system,” Yin said.

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

Flexible, durable, and washable triboelectric yarn and embroidery for self-powered sensing and human-machine interaction by Yu Chen, Erdong Chen, Zihao Wang, Yali Ling, Rosie Fisher, Mengjiao Li, Jacob Hart, Weilei Mu, Wei Gao, Xiaoming Tao, Bao Yang and Rong Yin. Nano Energy Volume 104, Part A, 15 December 2022, 107929 DOI: 10.1016/j.nanoen.2022.107929 Available online: 27 October 2022 Version of Record: 4 November 2022.

This paper is behind a paywall.

The inside scoop on beetle exoskeletons

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In the past I’ve covered work on the Namib beetle and its bumps which allow it to access condensation from the air in one of the hottest places on earth and work on jewel beetles and how their structural colo(u)r is derived. Now, there’s research into a beetle’s body armor from the University of Nebraska-Lincoln according to a Feb. 22, 2017 news item on ScienceDaily,

Beetles wear a body armor that should weigh them down — think medieval knights and turtles. In fact, those hard shells protecting delicate wings are surprisingly light, allowing even flight.

Better understanding the structure and properties of beetle exoskeletons could help scientists engineer lighter, stronger materials. Such materials could, for example, reduce gas-guzzling drag in vehicles and airplanes and reduce the weight of armor, lightening the load for the 21st-century knight.

But revealing exoskeleton architecture at the nanoscale has proven difficult. Nebraska’s Ruiguo Yang, assistant professor of mechanical and materials engineering, and his colleagues found a way to analyze the fibrous nanostructure. …

A Feb. 22, 2017 University of Nebraska-Lincoln news release by Gillian Klucas (also on EurekAlert), which originated the news item, describes skeletons and the work in more detail,

The lightweight exoskeleton is composed of chitin fibers just around 20 nanometers in diameter (a human hair measures approximately 75,000 nanometers in diameter) and packed and piled into layers that twist in a spiral, like a spiral staircase. The small diameter and helical twisting, known as Bouligand, make the structure difficult to analyze.

Yang and his team developed a method of slicing down the spiral to reveal a surface of cross-sections of fibers at different orientations. From that viewpoint, the researchers were able to analyze the fibers’ mechanical properties with the aid of an atomic force microscope. This type of microscope applies a tiny force to a test sample, deforms the sample and monitors the sample’s response. Combining the experimental procedure and theoretical analysis, the researchers were able to reveal the nanoscale architecture of the exoskeleton and the material properties of the nanofibers.

Yang holds a piece of the atomic force microscope used to measure the beetle's surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

Craig Chandler | University Communication

Yang holds a piece of the atomic force microscope used to measure the beetle’s surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

They made their discoveries in the common figeater beetle, Cotinis mutabilis, a metallic green native of the western United States. But the technique can be used on other beetles and hard-shelled creatures and might also extend to artificial materials with fibrous structures, Yang said.

Comparing beetles with differing demands on their exoskeletons, such as defending against predators or environmental damage, could lead to evolutionary insights as well as a better understanding of the relationship between structural features and their properties.

Yang’s co-authors are Alireza Zaheri and Horacio Espinosa of Northwestern University; Wei Gao of the University of Texas at San Antonio; and Cheryl Hayashi of the University of California, Riverside.

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

Exoskeletons: AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties by Ruiguo Yang, Alireza Zaheri,Wei Gao, Charely Hayashi, Horacio D. Espinosa. Adv. Funct. Mater. vol. 27 (6) 2017 DOI: 10.1002/adfm.201770031 First published: 8 February 2017

This paper is behind a paywall.

Nanomechanics for deciphering beetle exoskeletons

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Beetles carry remarkably light yet strong armor in the form of their exoskeletons and a research team at Northwestern University (US) is looking to those beetle exoskeletons for inspiration according to a Jan. 11, 2017 news item on ScienceDaily,

What can a beetle tell us about good design principles? Quite a lot, actually.

Many insects and crustaceans possess hard, armor-like exoskeletons that, in theory, should weigh the creatures down. But, instead, the exoskeletons are surprisingly light — even allowing the armor-wearing insects, like the beetle, to fly.

Northwestern Engineering’s Horacio D. Espinosa and his group are working to understand the underlying design principles and mechanical properties that result in structures with these unique, ideal properties. This work could ultimately uncover information that could guide the design and manufacturing of new and improved artificial materials by emulating these time-tested natural patterns, a process known as bio-mimicry.

Supported by the Air Force Office of Scientific Research’s Multidisciplinary University Research Initiative (MURI), the research was featured on the cover of Advanced Functional Materials. Postdoctoral fellows Ruiguo Yang and Wei Gao and graduate student Alireza Zaheri, all members of Espinosa’s laboratory, were co-first authors of the paper. Cheryl Hayashi, professor of biology at the University of California, Riverside, was also a co-author.

A Jan. 11, 2017 Northwestern University news release, which originated the news item, expands on the theme,

Though there are more than a million species of beetles, the team is first studying the exoskeleton of the Cotinis mutabilis, a field crop pest beetle native to the western United States. Like all insects and crustaceans, its exoskeleton is composed of twisted plywood structures, known as Bouligand structures, which help protect against predators. Fibers in this Bouligand structure are bundles of chitin polymer chains wrapped with proteins. In this chain structure, each fiber has a higher density along the length than along the transverse.

“It is very challenging to characterize the properties of such fibers given that they are directionally dependent and have a small diameter of just 20 nanometers,” said Espinosa, the James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at Northwestern’s McCormick School of Engineering. “We had to develop a novel characterization method by taking advantage of the spatial distribution of fibers in the Bouligand structure.”

To meet this challenge, Espinosa and his team employed a creative way to identify the geometry and material properties of the fibers that comprise the exoskeleton. They cut the Bouligand structure along a plane, resulting in a surface composed of closely packed cross-sections of fibers with different orientations. They were then able to analyze the mechanics of the fibers.

“With more than a million species, which greatly vary from each other in taxomic relatedness, size, and ecology, the beetle is the largest group of insects,” Hayashi said. “What makes this research exciting is that the methods applied to the Cotinis mutabilis beetle exoskeleton can be extended to other beetle species.”

By correlating the mechanical properties with the exoskeleton geometries from diverse beetle species, Espinosa and his team plan to gain insight into natural selection and better understand structure-function-properties relationships.

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

AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties by Ruiguo Yang, Alireza Zaheri, Wei Gao, Cheryl Hayashi, and Horacio D. Espinosa. Advanced Functional Materials DOI: 10.1002/adfm.201603993 Version of Record online: 27 DEC 2016

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

This paper is behind a paywall.

Synthetic microfish (nanoengineered and 3D printed) to inspire ‘smart’ microbots

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An August 26, 2015 news item on Nanowerk features some microfish (they look like sharks to me) fabricated in University of California at San Diego (UCSD) laboratories,

Nanoengineers at the University of California, San Diego used an innovative 3D printing technology they developed to manufacture multipurpose fish-shaped microrobots — called microfish — that swim around efficiently in liquids, are chemically powered by hydrogen peroxide and magnetically controlled. These proof-of-concept synthetic microfish will inspire a new generation of “smart” microrobots that have diverse capabilities such as detoxification, sensing and directed drug delivery, researchers said.

3D-printed microfish contain functional nanoparticles that enable them to be self-propelled, chemically powered and magnetically steered. The microfish are also capable of removing and sensing toxins. Image credit: J. Warner, UC San Diego Jacobs School of Engineering.

3D-printed microfish contain functional nanoparticles that enable them to be self-propelled, chemically powered and magnetically steered. The microfish are also capable of removing and sensing toxins. Image credit: J. Warner, UC San Diego Jacobs School of Engineering.

An August 25, 2015 UCSD news release (also on EurekAlert) by Liezel Labios, which originated the news item, provides more detail,

The technique used to fabricate the microfish provides numerous improvements over other methods traditionally employed to create microrobots with various locomotion mechanisms, such as microjet engines, microdrillers and microrockets. Most of these microrobots are incapable of performing more sophisticated tasks because they feature simple designs — such as spherical or cylindrical structures — and are made of homogeneous inorganic materials. In this new study, researchers demonstrated a simple way to create more complex microrobots.

…

By combining Chen’s 3D printing technology with Wang’s expertise in microrobots, the team was able to custom-build microfish that can do more than simply swim around when placed in a solution containing hydrogen peroxide. Nanoengineers were able to easily add functional nanoparticles into certain parts of the microfish bodies. They installed platinum nanoparticles in the tails, which react with hydrogen peroxide to propel the microfish forward, and magnetic iron oxide nanoparticles in the heads, which allowed them to be steered with magnets.

Here’s an illustration of the platinum and iron oxide microfish,

Schematic illustration of the process of functionalizing the microfish. Platinum nanoparticles are first loaded into the tail of the fish for propulsion via reaction with hydrogen peroxide. Next, iron oxide nanoparticles are loaded into the head of the fish for magnetic control. Image credit: W. Zhu and J. Li, UC San Diego Jacobs School of Engineering.

Schematic illustration of the process of functionalizing the microfish. Platinum nanoparticles are first loaded into the tail of the fish for propulsion via reaction with hydrogen peroxide. Next, iron oxide nanoparticles are loaded into the head of the fish for magnetic control. Image credit: W. Zhu and J. Li, UC San Diego Jacobs School of Engineering.

Back to the news release,

“We have developed an entirely new method to engineer nature-inspired microscopic swimmers that have complex geometric structures and are smaller than the width of a human hair. With this method, we can easily integrate different functions inside these tiny robotic swimmers for a broad spectrum of applications,” said the co-first author Wei Zhu, a nanoengineering Ph.D. student in Chen’s research group at the Jacobs School of Engineering at UC San Diego.

As a proof-of-concept demonstration, the researchers incorporated toxin-neutralizing nanoparticles throughout the bodies of the microfish. Specifically, the researchers mixed in polydiacetylene (PDA) nanoparticles, which capture harmful pore-forming toxins such as the ones found in bee venom. The researchers noted that the powerful swimming of the microfish in solution greatly enhanced their ability to clean up toxins. When the PDA nanoparticles bind with toxin molecules, they become fluorescent and emit red-colored light. The team was able to monitor the detoxification ability of the microfish by the intensity of their red glow.

“The neat thing about this experiment is that it shows how the microfish can doubly serve as detoxification systems and as toxin sensors,” said Zhu.

“Another exciting possibility we could explore is to encapsulate medicines inside the microfish and use them for directed drug delivery,” said Jinxing Li, the other co-first author of the study and a nanoengineering Ph.D. student in Wang’s research group.

For anyone curious about the new 3D printing technique, the news release provides more information about that too,

The new microfish fabrication method is based on a rapid, high-resolution 3D printing technology called microscale continuous optical printing (μCOP), which was developed in Chen’s lab. Some of the benefits of the μCOP technology are speed, scalability, precision and flexibility. Within seconds, the researchers can print an array containing hundreds of microfish, each measuring 120 microns long and 30 microns thick. This process also does not require the use of harsh chemicals. Because the μCOP technology is digitized, the researchers could easily experiment with different designs for their microfish, including shark and manta ray shapes. [emphasis mine] “With our 3D printing technology, we are not limited to just fish shapes. We can rapidly build microrobots inspired by other biological organisms such as birds,” said Zhu.

The key component of the μCOP technology is a digital micromirror array device (DMD) chip, which contains approximately two million micromirrors. Each micromirror is individually controlled to project UV light in the desired pattern (in this case, a fish shape) onto a photosensitive material, which solidifies upon exposure to UV light. The microfish are built using a photosensitive material and are constructed one layer at a time, allowing each set of functional nanoparticles to be “printed” into specific parts of the fish bodies.

“This method has made it easier for us to test different designs for these microrobots and to test different nanoparticles to insert new functional elements into these tiny structures. It’s my personal hope to further this research to eventually develop surgical microrobots that operate safer and with more precision,” said Li.

Nice to see I can recognize a shark shape when I see one. Getting back to the research, yet again, here’s a link to and a citation for the paper.

3D-Printed Artificial Microfish by Wei Zhu, Jinxing Li, Yew J. Leong, Isaac Rozen, Xin Qu, Renfeng Dong, Zhiguang Wu, Wei Gao, Peter H. Chung, Joseph Wang, and Shaochen Chen. Advanced Materials Volume 27, Issue 30, pages 4411–4417, August 12, 2015 DOI: 10.1002/adma.201501372 Article first published online: 29 JUN 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Paint your own battery

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Reserchers at Pulickel Ajayan’s laboratory at Rice University have developed a paintable battery (here’s the video),

The June 28, 2012 Rice University news release offers more details about how the paintable battery was achieved,

Lead author [research paper appeared in Nature’s online, open-access journal Scientific Reports] Neelam Singh, a Rice graduate student, and her team spent painstaking hours formulating, mixing and testing paints for each of the five layered components – two current collectors, a cathode, an anode and a polymer separator in the middle.

The materials were airbrushed onto ceramic bathroom tiles, flexible polymers, glass, stainless steel and even a beer stein to see how well they would bond with each substrate.

In the first experiment, nine bathroom tile-based batteries were connected in parallel. One was topped with a solar cell that converted power from a white laboratory light. When fully charged by both the solar panel and house current, the batteries alone powered a set of light-emitting diodes that spelled out “RICE” for six hours; the batteries provided a steady 2.4 volts.

The researchers reported that the hand-painted batteries were remarkably consistent in their capacities, within plus or minus 10 percent of the target. They were also put through 60 charge-discharge cycles with only a very small drop in capacity, Singh said.

You can also find the details and more images at the June 28, 2012 news item on physorg.com,

Each layer is an optimized stew. The first, the positive current collector, is a mixture of purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second is the cathode, which contains lithium cobalt oxide, carbon and ultrafine graphite (UFG) powder in a binder solution. The third is the polymer separator paint of Kynar Flex resin, PMMA and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium titanium oxide and UFG in a binder, and the final layer is the negative current collector, a commercially available conductive copper paint, diluted with ethanol.

“The hardest part was achieving mechanical stability, and the separator played a critical role,” Singh said. “We found that the nanotube and the cathode layers were sticking very well, but if the separator was not mechanically stable, they would peel off the substrate. Adding PMMA gave the right adhesion to the separator.” Once painted, the tiles and other items were infused with the electrolyte and then heat-sealed and charged.

Singh said the batteries were easily charged with a small solar cell. She foresees the possibility of integrating paintable batteries with recently reported paintable solar cells to create an energy-harvesting combination that would be hard to beat. As good as the hand-painted batteries are, she said, scaling up with modern methods will improve them by leaps and bounds. “Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.

Ajayan’s lab must be a very exciting place to work given the research that has been published in 2012 so far (my Serendipity and coaxial cables post; my Nanosponges clean up spilled oil and release the oil for future use post; my Good heat, bad heat, and cooling oils post).

And to give credit to everyone: co-authors of the paper are graduate students Charudatta Galande and Akshay Mathkar, alumna Wei Gao, now a postdoctoral researcher at Los Alamos National Laboratory, and research scientist Arava Leela Mohana Reddy, all of Rice; Rice Quantum Institute intern Andrea Miranda; and Alexandru Vlad, a former research associate at Rice, now a postdoctoral researcher at the Université Catholique de Louvain, Belgium.