Droplet on soft shuttle: a new concept for manipulation of droplets on open-top microfluidic systems
Creators: name: RUVALCABA CARDENAS, Ana Daysi
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400305
subject: Biomedical instrumentation
classificationCode: 400908
subject: Microelectronics
classificationCode: 401705
subject: Microelectromechanical systems (MEMS)

description: Open-top microfluidic systems offer several advantages compared to their widely used channel-based counterparts. These include simple fabrication procedures that do not rely on microfabrication facilities, simple operational procedures due to the elimination of pumps, tubes, interfaces, leakage, bubble formation and clogging as well as direct sample manipulation using external stimuli due to the elimination of channel walls. In particular, open-top microfluidic systems benefit droplet-based assays. The droplets can be considered as soft, small chambers capable of storage, handling, mixing, and reacting of liquid samples, which can be easily placed onto or removed from the substrate.<br><br> 
This research aims to further expand the utility of open-top droplet-based microfluidic systems by introducing versatile yet simple techniques and strategies. <br><br>
As the first contribution, the PhD candidate introduced the novel concept of a soft shuttle for transportation, manipulation, and diffusion studies of small liquid droplets using electrowetting on the dielectric mechanism. This method enabled manipulation of droplets several times smaller than the electrode size, and importantly, minimized evaporation, contamination, and exposure of the sample to high voltages. Various modes of droplet loading, transporting, and unloading were explored. Several deep learning image processing techniques were tailored to detect, classify, and track individual droplets. Furthermore, they were used to analyze the complex dynamics of the shuttle and droplet. Changing the water concentration of the soft shuttle allowed for modulation of the diffusion kinetics of liquid samples into the shuttle. This novel approach can advance the field of droplet-based open microfluidics and can be potentially useful for diverse applications in biotechnology, diagnostics, or analytical chemistry.<br><br>
As the second contribution, the PhD candidate explored the magnetic actuation of soft shuttles for open-top microfluidic applications. The system composed of two immiscible liquids, including glycerol as the soft shuttle and a suspension of iron powder in sucrose solution as the magnetic drop. Permanent magnets assembled on 3D printed motorized actuators were used for the actuation of the magnetic drop, enabling the glycerol shuttle to be propelled along customized linear, circular, and sinusoidal paths. The dynamics of the hybrid shuttle-magnetic drop system was governed by the magnetic force, the friction at the interface of the shuttle and substrate, and the surface tension at the interface of the shuttle and magnetic drop. Increasing the magnetic force could lead to the localized deformation of the shuttle and eventually, the full extraction of the magnetic drop. The versatility of the system was demonstrated through the propelling of the shuttle across a rough surface patterned with microfabricated barriers as well as taking advantage of the optical properties of the shuttle for the magnification and translation of microscale characters patterned on a planar surface. The integration of the system with current electrowetting actuation mechanisms enables the highly controlled motion of the magnetic drop on the surface of a moving shuttle. The simplicity, versatility, and controllability of the system provide opportunities for various fluid manipulation, sample preparation, and analysis for a range of chemical, biochemical and biological applications