Batteries have always been a barrier in the evolution and adoption in soft, wearable devices. You wouldn't want the chemicals inside batteries to leak out onto your skin and ideally there wouldn't be a big risk of them bursting into flames either. Stanford engineers have developed a new kind of solid polymer battery that can stretch without breaking and doesn't contain liquid or gel that might seep out and ignite. From Stanford Engineering:

"Until now we haven't had a power source that could stretch and bend the way our bodies do, so that we can design electronics that people can comfortably wear," said chemical engineer Zhenan Bao, who teamed up with materials scientist Yi Cui to develop the device they describe in the Nov. 26 edition of Nature Communications....

The prototype is thumbnail-sized and stores roughly half as much energy, ounce for ounce, as a comparably sized conventional battery. Graduate student David Mackanic said the team is working to increase the stretchable battery's energy density, build larger versions of the device and run future experiments to demonstrate its performance outside the lab. One potential application for such a device would be to power stretchable sensors designed to stick to the skin to monitor heart rate and other vital signs as part of the BodyNet wearable technology being developed in Bao's lab.

More: Decoupling of mechanical properties and ionic conductivity in supramolecular lithium ion conductors (Nature Communications) Read the rest

The US Air Force Research Laboratory (AFRL) has developed a new form of liquid metal with very strange conductive properties. Usually, when a flexible, conductive material is stressed or stretched, its electrical conductivity drops and resistance increases when it's stress or stretched. Just the opposite, Air Force's novel "Polymerized Liquid Metal Networks... can be strained up to 700%, autonomously respond to that strain to keep the resistance between those two states virtually the same, and still return to their original state." The researchers published their results in the scientific journal Advanced Materials. From the Air Force:

It is all due to the self-organized nanostructure within the material that performs these responses automatically.

“This response to stretching is the exact opposite of what you would expect,” said Dr. Christopher Tabor, AFRL lead research scientist on the project. “Typically a material will increase in resistance as it is stretched simply because the current has to pass through more material. Experimenting with these liquid metal systems and seeing the opposite response was completely unexpected and frankly unbelievable until we understood what was going on.”

Wires maintaining their properties under these different kinds of mechanical conditions have many applications, such as next-generation wearable electronics. For instance, the material could be integrated into a long-sleeve garment and used for transferring power through the shirt and across the body in a way that bending an elbow or rotating a shoulder won’t change the power transferred.

A favorite kitchen chemistry (and physics) experiment of kids (and adults), Ooblek is the weird result of mixing cornstarch with water. Now, MIT engineers have developed a mathematical model that can predict and simulate how the non-Newtonian fluid switches between liquid and solid depending on the pressure applied to it. From MIT News:

Aside from predicting what the stuff might do in the hands of toddlers, the new model can be useful in predicting how oobleck and other solutions of ultrafine particles might behave for military and industrial applications. Could an oobleck-like substance fill highway potholes and temporarily harden as a car drives over it? Or perhaps the slurry could pad the lining of bulletproof vests, morphing briefly into an added shield against sudden impacts. With the team’s new oobleck model, designers and engineers can start to explore such possibilities.

“It’s a simple material to make — you go to the grocery store, buy cornstarch, then turn on your faucet,” says Ken Kamrin, associate professor of mechanical engineering at MIT. “But it turns out the rules that govern how this material flows are very nuanced...”

Kamrin’s primary work focuses on characterizing the flow of granular material such as sand. Over the years, he’s developed a mathematical model that accurately predicts the flow of dry grains under a number of different conditions and environments. When (grad student Aaron) Baumgarten joined the group, the researchers started work on a model to describe how saturated wet sand moves. It was around this time that Kamrin and Baumgarten saw a scientific talk on oobleck.

Snail slime -- called an epiphragm -- is an incredibly strong yet reversible adhesive. Now, University of Pennsylvania scientists have developed a new kind of glue that employs the same mechanism as the epiphragm. The new material dries like superglue but once wet, it loses its adhesion. For years, scientists have explored adhesions inspired by nature but none have been demonstrated to have the same amount of strength and reversibility. For example, the researchers report that their new adhesive "is 89 times stronger than gecko adhesion." From the University of Pennsylvania:

The breakthrough came one day when Gaoxiang Wu was working on another project that involved a hydrogel made of a polymer called polyhydroxyethylmethacrylate (PHEMA) and noticed its unusual adhesive properties. PHEMA is rubbery when wet but rigid when dry, a quality that makes it useful for contact lenses but also, as Yang's team discovered, for adhesives.

When PHEMA is wet, it conforms to all of the small grooves on a surface, from a tree trunk's distinct ridges to the invisible microporosity of a seemingly smooth wall. This conformal contact is what allows PHEMA to stick to a surface.

To demonstrate just how durable their PHEMA adhesive is, one of Yang's lab members and co-first author, Jason Christopher Jolly, volunteered to suspend himself from a harness held up only by a postage-stamp-sized patch of their adhesive; the material easily held the weight of an entire human body. Based on the lab tests, the team determined that, although PHEMA may not be the strongest adhesive in existence, it is currently the strongest known candidate available for reversible adhesion.

A new paper in Nature describes the US-Army-funded research of U Penn materials scientists to create a new generation of 3D printed "smart objects" whose geometry and materials enable them to interact with their environments without having to use embedded computers, sensors or actuators. Read the rest

This short documentary on the creative process behind Iris van Herpen's Spring/Summer 2017 line is really cool. So many possibilities! Read the rest

MIT Media Lab researchers developed software to design and 3D print hair-like structures in bulk. Eventually, the 3D-printed hair could be used as sensors, actuators modeled on the cilia in our own lungs, and even Velcro-like adhesives for robots and other devices.

Their innovation was actually on the software side of the 3D-printing process. From MIT News:

Instead of using conventional computer-aided design (CAD) software to draw thousands of individual hairs on a computer — a step that would take hours to compute — the team built a new software platform, called “Cilllia,” that lets users define the angle, thickness, density, and height of thousands of hairs, in just a few minutes.

Using the new software, the researchers designed arrays of hair-like structures with a resolution of 50 microns — about the width of a human hair. Playing with various dimensions, they designed and then printed arrays ranging from coarse bristles to fine fur, onto flat and also curved surfaces, using a conventional 3-D printer...

To demonstrate adhesion, the team printed arrays that act as Velcro-like bristle pads. Depending on the angle of the bristles, the pads can stick to each other with varying forces. For sensing, the researchers printed a small furry rabbit figure, equipped with LED lights that light up when a person strokes the rabbit in certain directions. And to see whether 3-D-printed hair can help actuate, or move objects, the team fabricated a weight-sorting table made from panels of printed hair with specified angles and heights.

The brilliant popular engineering Sustainable Materials - with Both Eyes Open: Future Buildings, Vehicles, Products and Equipment - Made Efficiently and Made with Less New Material has just been released in the USA. I reviewed this book last November, when it came out in the UK. Here's a brief excerpt from then:

We review a lot of popular science books around here, but Sustainable Materials (like Sustainable Energy) is a popular engineering text, a rare and wonderful kind of book. Sustainable Materials is an engineer's audit of the materials that our world is made of, the processes by which those materials are extracted, refined, used, recycled and disposed of, and the theoretical and practical efficiencies that we could, as a society, realize.

Allwood and Cullen write about engineering with the elegance of the best pop-science writers -- say, James Gleick or Rebecca Skloot -- but while science is never far from their work, their focus is on engineering. They render lucid and comprehensible the processes and calculations needed to make things and improve things, touching on chemistry, physics, materials science, economics and logistics without slowing down or losing the reader.

The authors quickly demonstrate that any effort to improve the sustainability of our materials usage must focus on steel and aluminum, first because of the prominence of these materials in our construction and fabrication, and second because they are characteristic microcosms of our other material usage, and what works for them will be generalizable to other materials.

From there, the book progresses to a fascinating primer on the processes associated with these metals, from ore to finished product and back through recycling, and the history of efficiency gains in these processes, and the theoretical limits on efficiency at each stage.

Julian Allwood and Jonathan Cullen's Sustainable Materials - with Both Eyes Open: Future Buildings, Vehicles, Products and Equipment - Made Efficiently and Made with Less New Material is a companion volume to Sustainable Energy Without the Hot Air, one of the best books on science, technology and the environment I've ever read.

We review a lot of popular science books around here, but Sustainable Materials (like Sustainable Energy) is a popular engineering text, a rare and wonderful kind of book. Sustainable Materials is an engineer's audit of the materials that our world is made of, the processes by which those materials are extracted, refined, used, recycled and disposed of, and the theoretical and practical efficiencies that we could, as a society, realize.

Allwood and Cullen write about engineering with the elegance of the best pop-science writers -- say, James Gleick or Rebecca Skloot -- but while science is never far from their work, their focus is on engineering. They render lucid and comprehensible the processes and calculations needed to make things and improve things, touching on chemistry, physics, materials science, economics and logistics without slowing down or losing the reader.

The authors quickly demonstrate that any effort to improve the sustainability of our materials usage must focus on steel and aluminum, first because of the prominence of these materials in our construction and fabrication, and second because they are characteristic microcosms of our other material usage, and what works for them will be generalizable to other materials.

From there, the book progresses to a fascinating primer on the processes associated with these metals, from ore to finished product and back through recycling, and the history of efficiency gains in these processes, and the theoretical limits on efficiency at each stage. Read the rest