Tag Archives: Indian Institute of Technology (IIT)

Droplets take the stairs

Stair climbing is not an activity usually associated with water droplets but that’s how the activity is described in a July 11, 2017 American Institute of Physics news release (titled: Even Droplets Sometimes Take the Stairs; h/t July 11, 2017 news item on Nanowerk) about research  addressing ‘wettability’,

Sometimes, liquid drops don’t drop. Instead, they climb. Using computer simulations, researchers have now shown how to induce droplets to climb stairs all by themselves.

This stair-climbing behavior could be useful in everything from water treatment and new lab-on-a-chip microfluidic devices, to biochemical processing and medical diagnostic tools. The researchers, from the Indian Institute of Technology in Roorkee, India, and York University in Toronto, describe their findings this week in the journal Physics of Fluids, from AIP Publishing.

To get the droplets to climb, this new research reveals you need a staircase whose surface adheres to each droplet more readily with each step. A surface on which a droplet sticks easily has what’s called a high wettability, causing the droplet to spread out and flatten. On a low-wettability surface, however, the droplet would stay more spherical, like raindrops beading up on a waterproof jacket.

The researchers have previously used a gradient of increasing wettability to coax droplets to move across a flat surface and even to go up a slope. A water droplet, for example, is more attracted to a hydrophilic surface with its greater wettability, so an incline featuring an increasing hydrophilic surface as it rises can “pull” a droplet uphill.

Real surfaces are never perfectly smooth, however; at small-enough scales, a surface eventually appears rough. A slope at these scales is actually a microscopic staircase. “Most surfaces are textured, and mobility of a droplet over such surfaces require climbing stairs,” said Arup Kumar Das of IIT Roorkee.

To explore how a droplet could climb steps — and thus if this technique can work on more real-world surface applications — the researchers simulated the physics of microliter-sized droplets on staircases with a wettability gradient.

These droplets are wider than the length of each step, so their leading side is on a higher step with a more wettable surface, than the trailing side. The front part of the droplet thus spreads more, forming a smaller, flatter angle with the surface.

The difference in angles between the front and back of the climbing droplets causes the liquid inside the droplet to circulate. When the leading edge of the droplet reaches the next step, the circulation drives the droplet forward, spilling over onto the next higher step, and the process repeats itself.

Whether the droplet has enough force to overcome gravity depends on the size of the droplet, the steepness of the steps and the differences in wettability. In general, a bigger droplet is better at climbing stairs, and for steeper steps, there needs to be a higher wettability gradient.

The researchers are now working on experiments to confirm the simulation results.

Many other methods to control droplets rely on external forces such as temperature variations, and electric and magnetic fields. But, Das explained, those methods are often challenging and complex. The new study shows that passive approaches like wettability could be more efficient. “Passive means [we] can manipulate a droplet to even climb stairs sustainably without using an external force,” he said. 

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

Proposition of stair climb of a drop using chemical wettability gradient by Prabh P. S. Seerha, Parmod Kumar, Arup K. Das, and Sushanta K. Mitra. Physics of Fluids 29, 072103 (2017); doi: http://dx.doi.org/10.1063/1.4985213 Volume 29, Issue 7

This paper is behind a paywall.

Nanomedicine and the immune system

Interest in how the body reacts to nanoparticle drug delivery materials seems to be gaining momentum (see my Sept. 9, 2016 post about how the liver prevents nanoparticles from reaching cancer cells and my April 27, 2016 post about the discovery that fewer than 1% of nanoparticle-based drugs reach their destination). Now, we can add this research to the list according to an Oct. 4, 2016 news item on phys.org,

Katie Whitehead, assistant professor of chemical engineering at Carnegie Mellon University, has focused her research efforts on two clear objectives: treating and preventing disease. Her clinical-minded approach to laboratory research has recently led her to join forces with immunologists at the Indian Institute of Technology (IIT) in Bombay on a project that will explore how the immune system reacts to nanoparticle drug delivery materials.

“At its face, it may seem like an obvious goal. You would want a drug delivery system that doesn’t provoke an immune response,” says Whitehead. “However, the immune response to drug delivery vehicles is an understudied area because it’s complicated and expensive—but it deserves more attention.”

An Oct. 4, 2016 Carnegie Mellon University news release, which originated the news item, describes the research in more detail (Note: A link has been removed),

If the immune system reacts to a drug delivery system, the body mistakenly identifies the material as an invading pathogen and goes into a heightened state of alert. This response can trigger inflammation throughout the body and lead to a host of issues. According to Nature, about 25 percent of all Phase II and III clinical trials fail, not because the drug did not treat the disease, but because of safety concerns.

Creating a drug delivery system that effectively treats disease at the same time as avoiding immune response are two separate aims in drug delivery research. But for Whitehead, “My argument has always been that both pieces of the puzzle are equally important. If a system causes an immune response, then it’s a nonstarter. It may yield great results in treating disease in the lab, but it won’t ever reach a patient.”

Unfortunately, very little is understood about how the chemical molecules that make up nanoparticles ultimately affect our body’s immune response. “This research, however, is going to fill a critical gap in our knowledge base that will allow us to create nanoparticle systems that effectively deliver drugs without provoking our body’s natural defense mechanisms,” explains Whitehead. “Such knowledge will give us a head start in moving our delivery systems into clinical settings.”

Whitehead’s lab creates a number of nanoparticle drug delivery systems for diseases ranging from inflammatory bowel disease to Mantle cell lymphoma. She is tackling the challenge of immune response head-on with the help of a four-year, $500,000 grant from the Wadhwani Foundation for her work with IIT Bombay. She’ll specifically study how the chemical structure of the drug delivery nanoparticles affects the immune system.

Here’s a video of Katie Whitehead discussing her work in a simplified fashion,