Efficient Simulation of Droplet Merging in Channel-Based Microfluidic Devices

Channel-based microfluidic devices, often in the form of so-called Lab-on-a-Chip (LoC), have a broad range of applications in domains such as biology, chemistry, medicine, etc. Many of these applications rely on merging of droplets, e.g., in order to trigger some kind of reaction inside the droplets. However, the design process of LoCs is, in general, still in its infancy and mostly relies on simplifications, assumptions, as well as the expertise of the designer-making this process rather error-prone and frequently resulting in a 'trial-and-error' approach. Simulation tools can help in this regard. While Computational Fluid Dynamics (CFD) tools can simulate the merging of droplets, their complex setup and computational efforts limit their applicability to rather small components and do not allow simulations of larger microfluidic devices. Instead, considerations on the so-called one-dimensional model (1D model) offer a more abstract and, hence, computationally much faster simulation. However, currently there are no simulators based on the 1D model available that support the merging of droplets-severely restricting the applicability of such simulators. In this work, we address this problem by proposing a concept for droplet merging based on the 1D-model and implementing these ideas on top of an already existing 1D-simulator. The resulting simulator (which is made publicly available as part of the Munich Microfluidics Toolkit (MMFT)) eventually allows for the efficient simulation of channel-based microfluidic devices where droplet merging is an essential part.