June 27, 2014
Janus Capsules Easily And Affordably Produced For First Time
Alan McStravick for redOrbit.com - Your Universe online
Representing both beginnings and endings, the Roman god Janus is signified by a figure that is a double-faced head, each looking in opposite directions. This myth of duality caused ancient Romans to worship at the altar of Janus when seeds were planted and later when it was time to harvest. As the god of gates and doors, Janus was also revered as a sign of transition between primitive life and civilization, country living and city dwelling, peace and war, and the growing-up of young people. This long and storied history makes appropriate the summoning of Janus for a new discovery first reported on redOrbit last month.
Comprised of bubbles made up of two micro- or nanoparticle shells composed of different properties, Janus capsules have, for some time, attracted the attention of researchers. This is because it is believed they will be an excellent transport model for pharmaceuticals. The team that made this breakthrough is a group of scientists from Norwegian and French research institutions and the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw.
Current production of the spheres had been possible but was both cost and time prohibitive. It involved the sticking together of two drops of different substances. Once merged, the newly combined drop would need to undergo a fast fixation by quick cooling it or by initiating polymerisation of the combined materials. Current real world use of these spheres, as an example, are made up of white and black halves that are used for image generation in electrophoretic displays like that of an e-book reading device.
"Janus capsules differ from Janus spheres: the former are hollow structures, and their partially permeable shell is made of colloidal particles. How to make such a 'two-faced bubble' using micro- and nanoparticles? Many researchers reflect on the problem. We proposed a really not complicated solution", says Dr Zbigniew Rozynek (IPC PAS), who experimentally studied Janus capsules during his postdoctoral training at Norwegian University of Science and Technology in Trondheim.
While experimenting with this novel approach, the international team of researchers produced Janus capsules with drops of a single millimeter. Those drops were coated with two different substances, either in structure itself or color. Due to what is known as the action of capillary forces, the introduced particles were durably kept on the surfaces of both drops, being almost uniformly distributed across the surface.
At this point, the researchers introduced an external electric field which induced microflows into the interior and exterior of the two oil-based droplets. This microflow action carried the surface particles to the 'equator' of both of the droplets. During this stage of the experiment, the scientists were able to control the colloidal particles by simply shaking the drops in a slowly alternating electric field. This 'packing' of the particles is a very important step, as it is done to determine the number and size of pores of the future capsule, and consequently the capsule permeability.
“It's like the famous James Bond martini: it was always to be shaken, not stirred,” mused Dr. Rozynek.
Other processes that force the micro- and nanoparticles into a loose ribbon shape are performed before another current is introduced that re-expands the particles across the surface and compels the two opposite poles of the spheres to move closer to one another forming more of an oblong structure.
With this novel and less cost prohibitive approach to forming the Janus capsule, items like microobjects, nanoparticles and molecules, which must be protected against the environment because of their sensitivity or reactivity, have now been enabled to be encapsulated. Janus capsules will be of particular interest to the pharmaceutical industry, as well as finding use in the dye and food industry. Additionally, the team contends Janus capsules will attract the attentions of the materials engineering and medical fields for their potential to aid in innovative developments.
Image 2 (below): These are typical capsules (mainly Janus capsules) obtained with the method described in the press release of the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw. Credit: adopted from Nat. Commun. 5, 3945 (2014)