If you’ve ever worn soft contact lenses, you may know that they dry out and harden if they are not stored in a solution. This pervasive issue of hydrogel materials occurs when the solvent leaks or evaporates, affecting their mechanical properties. In this week’s post, polymer scientists develop super-soft dry elastomers (very elastic or rubbery polymers) that surpass the softness and elasticity of hydrogels, all without getting their hands wet.
In these unprecedented and fluid times, conferences and symposia have gone virtual as STEM collectively settles into a new normal. Many large meetings, like the formerly “in-person only” American Physical Society (APS) and American Chemical Society (ACS) national meetings, have been cancelled or transitioned to virtual-only participation this year. The 2021 Spring APS meeting will go virtual as well. I love big in-person meetings and have shied away from virtual alternatives thinking they would not provide the same feeling of community with my fellow scientists. However, the isolation of quarantine and the desire to get comfortable with the “new normal” motivated me to step out of my comfort zone and into the world of virtual science meetings this summer. So, when the opportunity to attend the 2020 Virtual Polymer Physics Symposium (VPPS) arose in July, I jumped at the chance to participate.
The entirety of our genetic information is encoded in our DNA. In our cells, it wraps together with proteins to form a flexible fiber about 2 metres long known as chromatin. Despite its length, each cell in our body keeps a copy of our chromatin in its nucleus, which is only about 10 microns across. For scale, if the nucleus was the size of a basketball, its chromatin would be about 90 miles long. How can it all fit in there? To make matters worse, the cell needs chromatin to be easily accessible for reading and copying, so it can’t be all tangled up. It’s not surprising then that scientists have been puzzled as to how this packing problem can be reliably solved in every cell. The solution is to pack the chromatin in a specific way, and research suggests that this may be in the form of a “fractal globule”.
I was ready. I was so ready. I had all my chargers and AV adapters. My presentation was backed up on a USB drive. I had every talk I wanted to go to on my calendar. I had sent emails to professors I wanted to meet and network with. I reached out to friends I only see in March in a different city every year. It was 10 pm on Saturday, February 29. My flight to Denver was leaving at 6 am in the morning. Then the email arrived —
Our bodies are made up of cells that can sense and respond to their dynamic environment. As an example, pancreatic beta cells chemically sense increased blood sugar concentrations and respond by producing insulin. Scientists have found that cells can also mechanically sense their environment; “mechanosensing” determines whether a cell should grow or die. Cancer is characterized by uncontrolled cellular growth, where cells often contain mutations that inhibit the natural mechanisms of cell death. Because mechanosensing is one such mechanism, scientists have hypothesized that cancer cells keep growing because they lack the ability to probe their environments. In this week’s paper, published in Nature Materials, an international research team led by Bo Yang and Michael Sheetz from the National University of Singapore investigated that hypothesis by combining tools from soft matter physics and biology.
Recently, Nicholas Charles and researchers from Harvard published a study that used simulations of elastic fibers to probe their response to stretching and rotation applied simultaneously. The results shed light on how DNA, proteins, and other fibrous materials respond to forces and get their intricate shapes.
Standing in the center of a crowded bus on your way to class, you might think: “why don’t these people just move? It’s hot and I can’t breathe!” Male penguins huddling to keep their eggs warm in the Antarctic winter have the opposite problem – no penguin wants to be at the cold edge of the huddle. A penguin in the huddle wants to stay in the warm center, since the outside temperature can reach -45 oC. However, penguins on the edge of the huddle are trying to push through the crowd to reach the center. Through the independent motion of each penguin, the huddle stays tight enough for the center to remain warm but loose enough to keep moving.
Conventional robots typically move by moving rigid pieces relative to one another — think of a robotic hand where rigid bars rotate at joints. In other words, conventional robots have a small number of “degrees of freedom” — the angle of bending of the joint of a robot hand would be one degree of freedom, for example. Soft robots, on the other hand, have many degrees of freedom: they can bend and deform into lots of different configurations. )Because of this, they often display continuum-like behaviour, similar to what is seen in the movement of natural organisms such as worms and octopuses. These robots offer great promise in many fields, from soft instruments for minimally invasive surgery to shape changing airfoils for increased flight control. One of the particularly difficult challenges in soft robotics is to design systems that are flat at rest but can rapidly transform to an arbitrary three dimensional shape when activated. Recently, Emmanuel Siéfert and co-workers developed baromorphs— thin, flexible sheets which can be air inflated (“pneumatically activated”) into a pre-programmed target shape.
A granular material, such as sand, coffee beans, or balls in ball pit, is a collection of particles that interact with each other and dissipate energy. These materials can act like solids, flow like liquids, or suddenly transition between the two phases – for example, in a landslide, the soil stops holding its shape and flows. The Granular and Particulate Networks Workshop, PARNET19, brought together the physicists, engineers, and mathematicians who study these materials in a series of lectures and discussions.
Physicists like to ignore things. In some cases, we may neglect gravity or assume that the temperature is zero degrees Kelvin — colder than any known substance in the universe. And friction is almost comically absent in most models, despite the fact that a world without it would be utterly uninhabitable (this is nicely illustrated in cartoon form here: https://xkcd.com/669/).