Chapter 6
Passive Droplet Routing
The methods presented in Part II address tasks for designing droplet microfluidic
networks in general. This part additionally considers a dedicated droplet routing
mechanism for these microfluidic networks, which is called passive droplet routing.
Passive droplet routing, as briefly reviewed in Chap. 1, allows to control the path
which a droplet flows through a microfluidic network. Instead of using valves,
switches, or any other active components, passive droplet routing only exploits
the hydrodynamic effect that a droplet always enters the channel with the highest
instantaneous volumetric flow rate [30, 37, 67].
This physical effect is used to route a droplet along a path which is not solely
composed of default successors at bifurcations. Whenever a droplet should take
a non-default successor at a bifurcation, a so-called header droplet (which does
not contain any biological information and is only used to navigate payloads) is
injected so that it arrives at the bifurcation right before the droplet which should
enter the non-default successor. By this, the droplet containing the sample, the socalled payload droplet, can be routed along a desired path through the microfluidic
network, which, eventually, realizes the experiment.
Exploiting this routing mechanism allows to design entirely passive microfluidic
networks, which have been introduced as Networked Labs-on-Chips (NLoCs, [23])
and Hydrodynamic Controlled Microfluidic Networks (HCNs, [24]). NLoCs/HCNs
support the execution of multiple different experiments on the same device and,
hence, increase the device’s flexibility, effectiveness, as well as reusability.
Despite these promises, passive droplet routing requires dedicated design methods, which are proposed in this part of the book. More precisely,
• Chapter 7 presents a method for designing application-specific architectures and
• Chapter 8 presents methods for generating droplet sequences, which eventually
realize the desired droplet routings.
These dedicated methods plus the methods proposed in Part II can eventually be
composed to an integrated design process, which supports the designer in the task
© Springer Nature Switzerland AG 2020
A. Grimmer, R. Wille, Designing Droplet Microfluidic Networks,
https://doi.org/10.1007/978-3-030-20713-7_6
79
Passive Droplet Routing
The methods presented in Part II address tasks for designing droplet microfluidic
networks in general. This part additionally considers a dedicated droplet routing
mechanism for these microfluidic networks, which is called passive droplet routing.
Passive droplet routing, as briefly reviewed in Chap. 1, allows to control the path
which a droplet flows through a microfluidic network. Instead of using valves,
switches, or any other active components, passive droplet routing only exploits
the hydrodynamic effect that a droplet always enters the channel with the highest
instantaneous volumetric flow rate [30, 37, 67].
This physical effect is used to route a droplet along a path which is not solely
composed of default successors at bifurcations. Whenever a droplet should take
a non-default successor at a bifurcation, a so-called header droplet (which does
not contain any biological information and is only used to navigate payloads) is
injected so that it arrives at the bifurcation right before the droplet which should
enter the non-default successor. By this, the droplet containing the sample, the socalled payload droplet, can be routed along a desired path through the microfluidic
network, which, eventually, realizes the experiment.
Exploiting this routing mechanism allows to design entirely passive microfluidic
networks, which have been introduced as Networked Labs-on-Chips (NLoCs, [23])
and Hydrodynamic Controlled Microfluidic Networks (HCNs, [24]). NLoCs/HCNs
support the execution of multiple different experiments on the same device and,
hence, increase the device’s flexibility, effectiveness, as well as reusability.
Despite these promises, passive droplet routing requires dedicated design methods, which are proposed in this part of the book. More precisely,
• Chapter 7 presents a method for designing application-specific architectures and
• Chapter 8 presents methods for generating droplet sequences, which eventually
realize the desired droplet routings.
These dedicated methods plus the methods proposed in Part II can eventually be
composed to an integrated design process, which supports the designer in the task
© Springer Nature Switzerland AG 2020
A. Grimmer, R. Wille, Designing Droplet Microfluidic Networks,
https://doi.org/10.1007/978-3-030-20713-7_6
79