Swell and shrink at the touch of a button

Application as an active ingredient transporter

Rahimzadeh and Stock discovered reversible shrinkage by ultrasound several years ago. In “Advanced Science”, together with TU physics professor Regine von Klitzing and the working group of Mario Kupnik, professor in the Department of Electrical Engineering and Information Technology, they now present another interesting aspect.

“PNIPAM is amphiphilic, i.e. it loves both water and fat,” explains Rahimzadeh. In an oil-water mixture, the beads therefore migrate to the interface between the two liquids and thus reduce the interfacial tension. As a result, oil and water mix better. In their current study, the researchers found that ultrasound not only causes the beads to shrink, but also accelerates their adhesion to the oil-water interface. Both effects together significantly reduce the interfacial tension. This should be of interest for many industrial processes, as substances such as water and oil could be mixed with PNIPAM beads via ultrasound. In addition, the microgel can not only store and release water at the touch of a button, but also catalytically or pharmaceutically active substances.

According to Rahimzadeh, the use of the microgel beads as drug transporters in medicine is particularly promising: “Under the influence of ultrasound, they could release their cargo specifically at cell membranes and other interfaces in our body.” It will still be some time before they can be used in practice, however, as extensive safety tests and regulatory approval procedures are required for such purposes. In any case, Rahimzadeh and Stock's researchers are not primarily interested in new drug delivery systems. Instead, they want to understand in detail how ultrasound waves interact with soft particles. In doing so, they are tapping into an area that is still largely unexplored.