A key bottleneck in bioprocess development is that state-of-the-art tools used for screening of cells and optimization of cultivation conditions do not represent the conditions enforced at industrial scale. At industrial scale, cell growth is strictly controlled (“fed-batch”) to optimize the metabolites produced by the cells. In contrast, cell growth is uncontrolled (“batch”) in microwells commonly used for bioprocess development due to the difficulty to continuously supply minute amounts of nutrients to the cells in these wells over the course of the cultivation experiment. This work addresses this bottleneck through the development of a droplet-based fed-batch nanobioreactor. A key challenge addressed in this work is the implementation of the required non-steady droplet operations on chip to establish a semi-continuous nutrient supply, while keeping the chip and its operation as simple as possible. The ability to study micro-organisms under nutrient-controlled fed-batch conditions is demonstrated using the yeast Cyberlindnera (Pichia) jadinii, with the cell growth rate controlled through the glucose concentration. Given the relative ease of operation and the potential to extend its features, the presented nanobioreactor provides a solid platform technology for further development and use in the field of bioprocess development and beyond.

We report the development of a droplet-based microfluidic device, which enables long term culturing of microorganisms inside water in oil microdroplets under semi-continuous conditions. Firstly, a microdroplet containing yeast cells is trapped on chip. After an initial incubation phase, this cell laden droplet is coalesced with smaller nutrient droplets to enable cultivation and time-lapsing under semi-continuous conditions. We demonstrate a proof-of-principle study on a sequential batch experiment, which lays a sound foundation for screening of microorganisms under semi-continuous conditions.