Physicists developed self-propelled droplets that can act as programmable micro-carriers

June 07, 2018

"Using droplets as micro carriers in biomedicine, for example, is a goal that has been pursued already for some time", says Ralf Seemann, Professor of Experimental Physics at the University of Saarland. However, these droplets could only move passively through the body, for example via the bloodstream. For their current study on active "micro-swimmers", the physicists from Saarbrücken experimented with a model system that developed from single phase emulsion droplets into so-called Janus droplets: They found that they can actively move and also act as a "smart" carrier for transporting and depositing a cargo.

Janus droplets consist of two different parts: a leading water-rich droplet and a trailing ethanol- and surfactant-rich droplet. The cause of the special abilities of the Janus droplets lies in their formation: they go through a total of three developmental stages, in which different interactions with the environment occur. The researchers were able to use these development steps for "programming" the droplets as active carriers.

"Starting point are homogeneous droplets, which are produced from a water-ethanol mixture. These droplets swim in an oil phase in which a surfactant is dissolved," explains Jean-Baptiste Fleury, who is a group leader at the department. In the first development phase, ethanol exits the droplet and dissolves in the surrounding oil phase. This results in different tensions on the surface of the droplets, which cause the so-called Marangoni flow on the surface as well as in the droplet. "With the Marangoni effect, liquids migrate from a region of low surface tension to a region of high surface tension" explains Martin Brinkmann, who is also part of the research team, the physical principle. "During the first stage, the Marangoni flow pushes the particle forward - an active movement caused by the continual loss of ethanol into the oil phase." At the same time, surfactants from the oil phase migrate into the drop; because they want to surround themselves preferentially with the ethanol contained therein. Finally, water and ethanol segregate and small droplets of ethanol-surfactant mixture form in the drop, which quickly merge and, due to the flow within the droplet accumulate at the rear end. At the end of stage two, a characteristic Janus drop has formed. In the following third stage, the surfactants on the surface of the water-rich drop are still "sucked off" by the rear, ethanol-rich drop, and the surface tension at the rear part of the surface is increased. This gradient causes the liquid on the surface of the front drop to flow into the direction of the higher surface tension and thus sets the entire Janus drop in motion. "In the course of their formation, the Janus droplets exhibit specific driving mechanisms; moreover, they result in different flow fields in the respective stages", says Dr. Brinkmann.

The researchers from Saarbrücken have precisely explored the motion of these Janus droplets. "We can observe how they move in the experimental cell during their development, which lasts about ten to fifteen minutes, and how they interact differently with obstacles, depending on their evolution stage," explains Dr. Fleury. The length of the individual stages of development can be controlled by the initial ethanol concentration in the droplet and its size. In order to test their abilities as carriers, the droplets in the experiment were also loaded with DNA molecules as cargo, which accumulate in the ethanol-rich phase. "Our carrier can selectively walk along obstacles of a specific geometry and surface condition and also deliver its cargo in a targeted manner," says Prof. Seemann, summing up the results of his work group. Thus, the study describes a first but simple example of a programmable active carrier capable of performing spatially and temporally controlled cargo delivery.
-end-


Saarland University

Related Ethanol Articles from Brightsurf:

Spraying ethanol to nanofiber masks makes them reusable
A joint research team from POSTECH and Japan's Shinshu University evaluates the filtration efficiency of nanofiber and melt-blown filters when cleaned with ethanol.

Anaerobically disinfect soil to increase phosphorus using diluted ethanol
Anaerobic disinfection of soil is an effective method to kill unwanted bacteria, parasites and weeds without using chemical pesticides.

Fractionation processes can improve profitability of ethanol production
The US is the world's largest producer of bioethanol as renewable liquid fuel, with more than 200 commercial plants processing over 16 billion gallons per year.

Ethanol fuels large-scale expansion of Brazil's farming land
A University of Queensland-led study has revealed that future demand for ethanol biofuel could potentially expand sugarcane farming land in Brazil by 5 million hectares by 2030.

Measuring ethanol's deadly twin
ETH Zurich researchers have developed an inexpensive, handheld measuring device that can distinguish between methanol and potable alcohol.

Modified enzyme can increase second-generation ethanol production
Using a protein produced by a fungus that lives in the Amazon, Brazilian researchers developed a molecule capable of increasing glucose release from biomass for fermentation.

Scientists develop a chemocatalytic approach for one-pot reaction of cellulosic ethanol
Scientists at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences have developed a chemocatalytic approach to convert cellulose into ethanol in a one-pot process by using a multifunctional Mo/Pt/WOx catalyst.

New core-shell catalyst for ethanol fuel cells
Scientists at Brookhaven Lab and the University of Arkansas have developed a highly efficient catalyst for extracting electrical energy from ethanol, an easy-to-store liquid fuel that can be generated from renewable resources.

Yeast makes ethanol to prevent metabolic overload
Why do some yeast cells produce ethanol? Scientists have wondered about this apparent waste of resources for decades.

Corncob ethanol may help cut China's greenhouse gas emissions
A new Biofuels, Bioproducts and Biorefining study has found that using ethanol from corncobs for energy production may help reduce greenhouse gas emissions in China, if used instead of starch-based ethanol.

Read More: Ethanol News and Ethanol Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.