Rapid parallel generation of a fluorescently barcoded drop library from a microtiter plate using the plate-interfacing parallel encapsulation (PIPE) chip.

In drop-based microfluidics, an aqueous sample is partitioned into drops using individual pump sources that drive water and oil into a drop-making device. Parallelization of drop-making devices is necessary to achieve high-throughput screening of multiple experimental conditions, especially in time-sensitive studies. Here, we present the plate-interfacing parallel encapsulation (PIPE) chip, a microfluidic chip designed to generate 50 to 90 µm diameter drops of up to 96 different conditions in parallel by interfacing individual drop makers with a standard 384-well microtiter plate. The PIPE chip is used to generate two types of optically barcoded drop libraries consisting of two-color fluorescent particle combinations: a library of 24 microbead barcodes and a library of 192 quantum dot barcodes. Barcoded combinations in the drop libraries are rapidly measured within a microfluidic device using fluorescence detection and distinct barcoded populations in the fluorescence drop data are identified using DBSCAN data clustering. Signal analysis reveals that particle size defines the source of dominant noise present in the fluorescence intensity distributions of the barcoded drop populations, arising from Poisson loading for microbeads and shot noise for quantum dots. A barcoded population from a drop library is isolated using fluorescence-activated drop sorting, enabling downstream analysis of drop contents. The PIPE chip can improve multiplexed high-throughput assays by enabling simultaneous encapsulation of barcoded samples stored in a microtiter plate and reducing sample preparation time.

Coupling fluid flow to hydrogel fluidic devices with reversible "pop-it" connections.

Hydrogels are soft, water-based polymer gels that are increasingly used to fabricate free-standing fluidic devices for tissue and biological engineering applications. For many of these applications, pressurized liquid must be driven through the hydrogel device. To couple pressurized liquid to a hydrogel device, a common approach is to insert tubing into a hole in the gel; however, this usually results in leakage and expulsion of the tubing, and other options for coupling pressurized liquid to hydrogels remain limited. Here, we describe a simple coupling approach where microfluidic tubing is inserted into a plastic, 3D-printed bulb-shaped connector, which "pops" into a 3D-printed socket in the gel. By systematically varying the dimensions of the connector relative to those of the socket entrance, we find an optimal head-socket ratio that provides maximum resistance to leakage and expulsion. The resulting connection can withstand liquid pressures on the order of several kilopascals, three orders of magnitude greater than traditional, connector-free approaches. We also show that two-sided connectors can be used to link multiple hydrogels to one another to build complex, reconfigurable hydrogel systems from modular components. We demonstrate the potential usefulness of these connectors by established long-term nutrient flow through a 3D-printed hydrogel device containing bacteria. The simple coupling approach outlined here will enable a variety of applications in hydrogel fluidics.