Droplet manipulation in liquid flow using of magnetic micromotors for drug delivery and microfluidic systems

The task of droplet manipulation is of great practical importance in such areas as biochemistry, drug delivery and microfluidic systems. Here we demonstrate a method for controlling the movement of droplets in an oil-in-water emulsion flow using magnetic nanoparticles (MNPs). A distinctive feature of this method is that the MNPs are not dispersed within droplets but in the continuous phase of the emulsion. Due to this, after the droplet manipulation procedure is completed, the MNPs can be easily removed from the emulsion without destroying the droplets. This method represents an innovative alternative to the previously known methods. The MNPs can be used to change the speed and direction of droplet movement in a liquid flow. If the magnetic field gradient is directed against the liquid flow, and the flow velocity is less than a certain critical value, then with help of a magnetic field it is possible to move droplets against the liquid flow. The ability to control the movement of droplets in a flow largely depends on the surface wettability of the MNPs. Hydrophobic MNPs are adsorbed on the surface of droplets and move with them in a magnetic field. If the magnetic field gradient is directed along the liquid flow, this leads to an increase in the droplet speed. In the case of using hydrophilic MNPs, the influence of the magnetic field on the droplet speed in the flow turns out to be ambiguous. These results can provide a basis for the development of magnetic droplet-based drug delivery systems. [Display omitted]