Magnetic Droplet Merging by Hybrid Magnetic Fields

Wireless and programmable manipulation of droplets is a challenge. We addressed this challenge by a combination of magnetic fluids and hybrid magnetic fields. We investigated the remote, wireless and programmable manipulation of ferrofluid droplets in a capillary microfluidic platform by a combination of uniform and non-uniform magnetic fields. The time-dependent motion of droplets under the influence of magnetic field was studied. Actuation and inter-droplet spacing of the droplets could be controlled by tuning the magnetic field strength. The influence of viscosity on the inter-droplet spacing was investigated. The time-dependent merging of (a) ferrofluid-ferrofluid and (b) ferrofluid-rhodamine droplets was demonstrated. Simulation and experimental results are in good agreement. The present work can be used for magnetically controlled, remote, wireless and programmable droplet actuation and merging relevant to biomedical assay, cell manipulation, tissue culture, drug efficacy, and synthesis of magnet-polymer composite particles.