The impact of ultrasound on Janus capsules at gel-liquid interface

Abstract

Ultrasound-responsive Janus capsules gain increasing recognition in the scientific world due to the wide spectrum of their potential applications. Spherical structures with the heterogeneous shells composed of two kinds of fused polymeric microparticles can be particularly useful when the cargo should be released in a strictly controlled manner. Distinct physical properties of individual hemispheres have a significant impact on the course of the payload release process. In this paper we deal with the problem of the influence of high-frequency and low intensity ultrasound on the behaviour of Janus capsules placed at the gel-liquid interface. Such a boundary between two phases can simulate the natural barriers occurring for example in biological systems. We show that 1 MHz acoustic waves are able to liberate the content from Janus capsule and push the freed liquid cargo through the interface so that it penetrates into the gel medium. We demonstrate that the size of the Janus capsule and, above all, its orientation at the interface in relation to the direction of acoustic wave propagation, are the key factors determining the progress of payload release and its transfer to the gel medium. Shell region that is mechanically weaker tends to break faster, which defines the initial path of payload release. Presented results contribute to a better understanding of physical phenomena occurring during the interaction of ultrasound with particle capsules. They can also become a source of inspiration not only for further experimental research, but also for theoretical analysis.