(638b) Multifunctional Screening of Active Microswimmers Enabled By Dynamic Self-Assembly on an Open-Surface Microgel Array

Image-based screening of in vivo small animal models has been critical for system-level investigation to understand many fundamental biological questions, such as gene functions, neurodevelopment, and aging. However, performing whole-animal screening is challenging due to the difficulty to handle and isolate the small, active animals in a high-throughput manner. In addition, it is necessary for small animal handling techniques to provide precise control of microenvironments that stimulate individual samples in order to screen for animals’ responses.

In the last decade, various microfluidic techniques have been developed to meet these needs. Taking one of the most-studied multicellular organism, Caenorhabditis elegans, as an example, different closed-channel microfluidic systems are designed and coupled with automated microscopy, to isolate large numbers of C. elegans in microchannels for high-resolution imaging or in microchambers for animal behavior analysis. Comprehensive forward genetic screening by image-based deep phenotyping and large-scale drug screening are hence made possible. Despite these already impactful applications, however, the adaptation of these microfluidic technologies into general biology laboratories and biotechnology industries are slow. It is mainly because most biology labs are not readily equipped with necessary engineering expertise, including: (i) special cleanroom environment and skills to fabricate microfluidic devices; (ii) sophisticate off-chip controllers and user expertise to operate these microfluidic systems and to achieve automation. Furthermore, a microfluidic device is usually designed only for one screening function, such as mutant sorting based on high-resolution imaging of immobilized animals or freely moving behavior analysis in response to chemical stimuli. Prototyping new microfluidic designs is cumbersome, time consuming and can be expensive. Therefore, a simple screening platform is needed to allow for isolation of active small animals without the need of complicated operating controllers, and to enable multifunctional screening applications without the need of additional device designs.

To address this issue, we present an open-surface platform for rapid isolation and multifunctional screening of active microswimmers, using C. elegans as a model. The open-surface device consists of an array of hydrophilic PEG-based microgel pads surrounded by a less hydrophilic plastic surface made of structured Kapton tape. Our device can be easily prototyped using common and readily available materials and fabricated outside a cleanroom. The heterogeneous microgel array enables a novel equipment-free method to rapidly isolate a large number (>100) of active microswimmers on the open surface in 30 seconds by a dynamic self-assembly mechanism. General users with no previous engineering expertise can master the operation within minutes.

The unique open-accessibility of our device allows for individual interrogation of microswimmers and enables various screening functions. We demonstrate its versatile utility by three fundamental image-based screening applications. First, we show that the microgel pad can be used to immobilize active microswimmers by controlled release of anesthetic agents. Consequently, we can achieve high-resolution phenotypical screening of sub-cellular features, such as in vivo synapse development with standard fluorescent confocal microscopy. This sets the foundation for most image-based screenings. Second, taking advantage of the open-surface accessibility, we develop an equipment-free on-demand mutant selection workflow. We validate the workflow by performing selective recovery of rare mutant animals within a mixed population based on their fluorescent phenotypes. This workflow can benefit rapid selection of animals in large-scale studies, such as identifying and enriching rare mutagenized populations through forward genetic screening. Third, we demonstrate a multiplexed chemical screening assay through analysis of individual-animal behavioral response. This is performed by individually modifying the chemical microenvironment of each microgel pad with a panel of different concentrations of an anthelmintic drug and screening the heterogeneous paralysis dynamic of isolated C. elegans. This function provides a straightforward approach to conduct multiplexed screening assays, which could be instrumental for biomedical applications from elucidating fundamental neuronal mechanism to evaluating drug efficacy. Because of its simplicity and versatility, we envision this platform can be easily adapted in general life science laboratories, and potentially tailored for other model biological systems with simple modifications.