8. Generating Droplet Sequences

The passive droplet routing mechanism allows to route a payload droplet (containing the biological sample) through different paths of a microfluidic network and, by this, allows for executing different experiments on a single device. But in order to establish a routing for the payload, a dedicated orchestration of droplet injections has to be realized. In fact, whenever a payload is supposed to take a non-default successor at any bifurcation in the network, it has to be made sure that another droplet (called header droplet) arrives before and flows through the default successor in order to “block it”. Especially for application-specific architectures, generating the corresponding droplet sequences and injection times is not obvious. To address this problem, this chapter first proposes an abstraction of the flow behavior in the form of a discrete model. Based on this discrete model, the generation for the desired droplet sequence can now be formulated as a combinatorial problem and, hence, allows to use automatic methods for solving it. Based on that, this chapter eventually describes corresponding methods for the generation of droplet sequences realizing the desired experiments.