Manipulation of ferrofluid marbles and droplets using repulsive force in magnetic digital microfluidics

Magnetic actuation of marbles and droplets has found to have broad applications in magnetic digital microfluidics with promising engineering and biomedical applications like biochemistry, microfluidic systems, targeted drug delivery, and tissue engineering. This study investigates a novel method of manipulating ferrofluid marbles (FM) and droplets utilizing a pair of Helmholtz coils and different configurations of permanent magnets. The concept of employing magnetic repulsive force is introduced for the manipulation of marbles and droplets and is experimentally investigated. In this study, for the first time, we utilize the repulsive magnetic force instead of the conventional magnetic attraction force to achieve better control over the marbles and droplets manipulation. To this aim, at first, the dynamic behavior of an FM in response to magnetic repulsive force is experimentally evaluated. Afterward, a theoretical model is suggested to predict the dynamic behavior of the FM which shows good agreement with the experimental data for different cases. Results show that by increasing the volume of the FM and the current of Helmholtz coils and decreasing the initial distance between the FM and permanent magnets, the average and maximum velocity of the FM increase. Furthermore, different arrangements of the experimental setup are implemented to show the capability of the proposed system in the simultaneous shape deformation and manipulation of the ferrofluid droplets.