UCLA

Cells act as the building blocks upon which the intricate machinery of life operates. Whether we examine mammalian cells, bacterial cells, or any other type, they serve as the fundamental units that orchestrate the myriad processes within organisms. Within these cells, proteins and nucleic acids emerge as the workhorses, driving essential functions and defining physiological states.

However, when it comes to measuring cells and their products, we face a significant challenge. Common vessels for screening and measuring cells and their products include well plates and at the industrial scale – bioreactors. These vessels are much larger than the individual cells or molecules of interest, and thus the measurements can (1) mask heterogeneity of samples and (2) allow for only a few readouts per sample due to volume required per measurement.

In order to compartmentalize cells or biomarkers, several approaches have been developed that leverage microfluidics. Microchambers use microfabrication techniques to create uniform structures where samples can be added in a batch process. While this allows for thousands of parallel reactions, it is limited by complicated processing steps or use of specialized equipment with high capital cost. Microdroplets are another approach, where droplet microfluidics is used to continually generate uniform water in oil emulsions. The challenges here include inability to add/remove reagents, Poisson loading of cells and/or immunoassay beads, as well as coupling with specialized equipment for emulsion readout.

In our lab, we have developed many different lab-on-a-particle approaches to combat these obstacles in compartmentalization. These are hydrogel microparticles, typically PEG-based with various functionalization. Their compartmentalization arises from the presence of a cavity in the structure where the cells or biofluids are loaded for assays. Particles give us the best of both worlds – they provide a solid substrate for multiple reagent addition/wash steps, but also are individually suspended to allow compatibility with standard lab equipment, such as flow cytometers and microscopes.

These particles are fabricated using various microfluidic lithography approaches, resulting in diverse particle types of varying complexity and materials tailored for different applications. In general, particle geometries are templated by the precursor solutions and then polymerized by UV light. The resulting particles can be used for droplet generation, tissue scaffolding, diagnostic tests, and cellular assays. In this thesis, I will discuss two types of hydrogel microparticles engineered for very different applications. For the first, I continued innovation on a method developed in our lab, called coaxial flow lithography, to fabricate amphiphilic particles with concentric hydrophobic and hydrophilic layers to spontaneously generate droplets, expanding the diagnostic applications of the platform. For the second, I developed a new method by adapting our lab’s nanovial (bowl-shaped microparticles) technology that allows measurement of a cell’s gene expression and secretions simultaneously, allowing us to discover new cell subpopulations.

These works exemplify how compartmentalization through microparticles democratizes existing lab workflows and fosters revolutionary research. Microparticles can be conveniently distributed as reagents, making them easily accessible to labs worldwide, empowering researchers with cutting-edge tools to advance scientific understanding.