Discovery of Liquid Crystals in Short DNA

Ever since its discovery, scientists have known that the DNA molecule is present in every life form. It carries the genetic information of all living organisms and many viruses. Today, however, we will strip DNA of its genetic importance and look at it from a different perspective. We will discuss why DNA attracts attention even outside of the biological context: What is the connection between DNA and liquid crystals? What are end-to-end stacking interactions and why are they important? If you want to get answers on these questions (and many more), keep reading.

Knotty DNA

Try taking out your earphones from your pocket and, in all probability, you’ll find knots and entanglements between the ends. As it turns out, this knotting effect is not limited to macroscopic objects, but occurs on the nanoscale as well. A DNA molecule that carries the genetic information of a living organism is actually a long string-like polymer, so you can imagine that it would also get tangled up just like the cords of your earphones. In today’s paper, Calin Plesa and his colleagues at TU Delft are able to observe and measure these knots in DNA strands and uncover behaviour which has not been observed before.

Soft nanoparticles: when polymers meet soap

For more than four decades, scientists have been investigating the properties of small objects dispersed in solutions. Some of these objects - produced in laboratories - are the so called soft nanoparticles. The name soft comes from the fact that these particles are partly solid and partly liquid. One of the scientists’ aims is to design nanoparticles that will be used as carriers of medical compounds (like drugs, DNA segments, and enzymes). The nanoparticles’ role will be to protect this cargo from partial degradation through the human body until reaching the specific target cells where the nanoparticles’ structure will break up and the useful compounds will be released. This technology will allow for disease treatments using smaller amounts of drugs, which will mean fewer side effects for the patients.

How swimming bacteria spin fluid

In today’s study, Dunkel and his colleagues investigate how bacteria can make flow patterns that look turbulent -  chaotic and full of vortices - even though bacteria are tiny and slow.  The bacteria push the fluid around as they swim and create vortices, spinning regions in the fluid. The 5 μm long bacteria create vortices with diameters of 80 μm by swimming at the speed of 30 μm/s!

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.