The living silly putty, episode 2: the spreading!

Douezan et al PNAS 2011

In episode one of this series, I presented a research paper by Stéphane Douezan and his colleagues in which they studied a ball of cells (called a cellular aggregate) sitting on a flat surface. After introducing the concept of cellular aggregate wetting by comparing it to the classical system of a drop of water, today I present the main part of the paper which looks at the dynamics of spreading of the cellular aggregate. I strongly suggest that the reader reads the first post before reading this one.

Rebuilding hard matter with soft matter

The skeleton is the backbone of the body, both literally and figuratively. Healthy bones protect soft organs from injury and enable the body to move. Starting from childhood, staying active and following a healthy diet helps the body maintain healthy bones. However, as people age, their bones can start to weaken. There are often no early symptoms to weakening bones, and as a result the first indication of a problem may be a painful break once the weakening has already significantly progressed.

Kepler’s New Year’s Gift — On the Six-Cornered Snowflake

Some things never change. In winter 1610, Johannes Kepler was stressing out about holiday gifts -- in particular, one for his friend and benefactor, the rather grandly-named Johannes Matthaeus Wacker von Wackenfels. Kepler, at the time employed as Imperial Mathematician at the court of Holy Roman Emperor Rudolph II, records his musings on the problem in the opening pages of his now-famous discourse, The Six-Cornered Snowflake.

Drop deformation in miniature channels under electric field

Microfluidics is the science and technology of manipulating small volumes of fluids in channels with dimensions as small as the size of human hair. You can think of a microfluidic system as a plumbing network composed of miniature pipes. Microfluidics has the potential to advance revolutionize biology, chemistry, and medical diagnostics by allowing many operations such as mixing of fluids, and synthesis of materials, as well as lab analyses to be miniaturized and integrated into a single device. Such a device is typically only a few cm² in size and is called a lab-on-chip platform. Electric fields are often used in lab-on-chip systems to control droplet generation, sorting, merging, and mixing. Today's paper study the interaction between electric field and droplets

The living silly putty

Have you ever noticed how drops of water have different shapes on a clean piece of glass and in a frying pan? The frying pan surface is coated with a hydrophobic ("water-repellant") molecule so it does not stick to food, which typically contains a lot of water. As a result, a drop of water will take on a roughly spherical shape to reduce as much as possible its area of contact with the frying pan. If a surface has an even more hydrophobic coating than a frying pan, the drop can even reach a perfectly spherical shape (this is called ultrahydrophobicity).

Dripping, Buckling and Collapsing of a Droplet

The scale bar is 20 micron.

Cell membrane is evolved to be flexible rather than rigid. This fluid 2D sheet plays a key role in cells's survival, be it tailoring the nutrition trafficking or rendering a mechanical toughness. In recent decades, however, artificial membranes have been developed with enhanced mechanical properties. Of such systems are particle-stabilized emulsions and in this post we will look into characterizing mechanical strength of such emulsion.

When espresso evaporates: the physics of coffee rings

I’ve spilled a lot of coffee over the years. Usually not a whole cup, just a drop or two while pouring. And when it’s just a drop, it’s easy to justify waiting to clean it up. When the drop dries on the table, it forms a stain with a ring (Figure 1), giving it the look of a deliberately outlined splotch of brown in a contemporary art piece (In this context, the phrase “coffee ring” refers to this small-scale, spontaneously formed circular stain rather than the imprint left on a table from the bottom of a wet coffee cup). But the appearance of these stains is simply a result of the physics happening inside the drop. Coffee is made of tiny granules of ground up coffee beans suspended in water, so the ring must mean that these granules migrate to the edge of the droplet when it dries. Why do the granules travel as they dry? Today’s paper by Robert D. Deegan, Olgica Bakajin, Todd F. Dupont, Greb Huber, Sidney R. Nagel and Thomas A. Witten provides evidence that coffee rings arise due to capillary flow--  the flow of liquid due to intermolecular forces within the liquid and between the liquid and its surrounding surfaces.

Termite Climate Control

Termites are among nature’s most spectacular builders, constructing mounds that can reach heights of several meters. Relative to the size of their bodies, these structures are considerably larger than the tallest skyscrapers constructed by humans [1]. Surprisingly, in many termite species, individual termites don’t spend much time in these mounds. Instead, they live in an underground network of tunnels and chambers that can be home to millions of individual insects. But, if not to live in them, why do termites build such intricate and gigantic above-ground structures [2]?

Brick-by-brick to Build Tiny Capsules

In past two decades, several approaches have been developed and optimized to encapsulate a wide variety of materials, from food to cosmetics and the more demanding realm of therapeutic reagents. Inspired by biological cells, the first attempts were to use either natural or synthetic lipid molecules to form encapsulation vessels, i.e., liposomes. Then, with the increasing awareness of controlled release of cargo, especially for therapeutic purposes, advanced materials such as polymers were developed to form carrying vessels. Despite the enormous progress in encapsulation technologies, however, these methods can be limited in their applicability regarding encapsulation efficacy, permeability, mechanical strength, and for biological applications, compatibility.