Programmable Droplets Udayan Umapathi, Patrick Shin, Sam Gen Chin, Dimitris Koutentakis, Carolynn E Will, Will Walker (MIT Design Lab), Rui Qing (CBA), Noah Jakimo (CBA), Joseph M Jacobson (CBA), Hiroshi Ishii

Programmable Droplets
The process of electrically moving liquid has existed since the 1875 experiments of physicist Gabriel Lippmann. Since then, significant work has been done using electrowetting for paper-like displays. A larger interest in the technique has been in the automation of biology—popularly known as digital microfluidics. We have been developing a digital microfluidic lab-on-a-chip based on the principles of electrowetting on dielectric (EWOD). EWOD allows for the precise control of motion, merging, and stirring of biological samples programmatically. Our focus is on developing a robust EWOD microfluidic chip able to manipulate large numbers of samples, in parallel and without cross contamination.
To that end, we have created a large 2D grid array on inexpensive manufactured printed circuit boards (PCBs) with direct addressability on each electrode and significantly reduced droplet pinning. Direct addressability at large scales provides a method for users to customize the microfluidic chip, allowing multiple experiments to run in parallel.
This work also includes development of various surface coatings for the microfluidic chip that inherently prevent a droplet from leaving behind a trail—thus avoiding cross-contamination.
Highlights of Programmable Droplets system
Our work has allowed us to manipulate a range of biological materials on the same surface, and the large surface area can be leveraged for large-scale experiments simultaneously. We have developed a new surface coating with almost no droplet pinning, allowing for low actuation voltages (<100V). This work differs from prior art in several other distinct ways:
Fabrication process and electronics: We have optimized the PCB fabrication process to reduce droplet pinning—that is, droplets leave behind smaller amounts of residue than in other systems, and droplets move reliably across the surface at lower actuation voltages (<100V). The lower actuation voltages of this system allow for manipulation of range of biological materials including cell samples within droplets without damage to the cells. We use the same type of chip used in touchscreens to sense the location of droplets on every electrode. This sensing functionality allows for quick error correction in droplet motion, and can measure the concentration of cells in a droplet reactor.
Surface coating: A primary technical challenge in the development of the Programmable Droplets system was the surface coating for the chip. We developed a surface that prevents protein and/or cell droplets from leaving a trail behind as they move on the chip. This means that a library of biological materials can be manipulated on the same surface without cross-contamination.
Our ultimate goal: scale this technology toward massive parallelization of programmable droplet manipulation. This will enable faster drug discovery and detection of diseases.
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