Title : Inlet spacing optimization for sorting of drops in microfluidic networks
Abstract :
Droplet microfluidics involves the generation and manipulation of drops in channels of size less than a millimeter. Droplet microfluidic networks find applications in sorting, synchronization, merging, and sequencing of drops, Boolean computation using drops, and so on. A microfluidic network consists of several interconnected microchannels. When the drops suspended in a continuous phase fluid are sent to the network, they inte ract with each other. The drops take discrete decisions while moving from one branch to another. A well-known network model, along with a decision rule, helps simulate the movement of drops in the network. However, there is no closed-form expression for the position of drops in the network.
We identified that inlet spacing or the entry times of drops in the network could significantly affect the interactions between the drops and result in different outlet patterns. In this work, we chose the functionality to be sorted and investigated if the inlet spacing could be designed to sort drops. We have attempted the problem of sorting of two types of drops; type-A or type-B. We identified inlet spacings that resulted in all type- A drops leaving through one outlet and all type-B drops leaving through another outlet of the network. The spacing design problem was initially solved using genetic algorithms (GA) for four drops. GA successfully identified the inlet spacings for all the sequences in which drops could enter the network. However, due to the inherent nature of these techniques, one cannot comment on the existence of a solution for the general case of n drops in a given network. We developed another approach, a mathematical programming technique, that involves educated, systematic and sequential enumeration of all the possible events. From a sequence of enumerated events, the conditions that ensure the occurrence of events were generated. The feasibility of these conditions ensures sorting. This approach answers the question of the existence of a solution. Besides, it identifies a range of inlet spacings that results in sorting. The details of both approaches and important results will be discussed in the talk.