PicoShells: Hollow Hydrogel Microparticles for High-Throughput Screening of Clonal Libraries.

Microfluidics enables the creation of monodisperse, micron-scale aqueous droplets, or other compartments. These droplets serve as picolitre-volume reaction chambers which can be utilized for various chemical assays or reactions. Here we describe the use of a microfluidic droplet generator to encapsulate single cells within hollow hydrogel microparticles called PicoShells. The PicoShell fabrication utilizes a mild pH-based crosslinking modality of an aqueous two-phase prepolymer system, avoiding the cell death and unwanted genomic modifications that accompany more typical, ultraviolet light crosslinking techniques. The cells are grown inside of these PicoShells into monoclonal colonies in any number of environments, including scaled production environments using commercially relevant incubation methods. Colonies can be phenotypically analyzed and/or sorted using standard, high-throughput laboratory techniques, namely, fluorescence-activated cell sorting (FACS). Cell viability is maintained throughout particle fabrication and analysis, and cells exhibiting a desired phenotype can be selected and released for re-culturing and downstream analysis. Large-scale cytometry runs are of particular use when measuring the protein expression of heterogeneous cells in response to environmental stimuli, notably to identify targets early in the drug discovery process. The sorted cells can also be encapsulated multiple times to direct the evolution of a cell line to a desired phenotype.

Enabling Clonal Analyses of Yeast in Outer Space by Encapsulation and Desiccation in Hollow Microparticles.

Studying microbes at the single-cell level in space can accelerate human space exploration both via the development of novel biotechnologies and via the understanding of cellular responses to space stressors and countermeasures. High-throughput technologies for screening natural and engineered cell populations can reveal cellular heterogeneity and identify high-performance cells. Here, we present a method to desiccate and preserve microbes in nanoliter-scale compartments, termed PicoShells, which are microparticles with a hollow inner cavity. In PicoShells, single cells are confined in an inner aqueous core by a porous hydrogel shell, allowing the diffusion of nutrients, wastes, and assay reagents for uninhibited cell growth and flexible assay protocols. Desiccated PicoShells offer analysis capabilities for single-cell derived colonies with a simple, low resource workflow, requiring only the addition of water to rehydrate hundreds of thousands of PicoShells and the single microbes encapsulated inside. Our desiccation method results in the recovery of desiccated microparticle morphology and porosity after a multi-week storage period and rehydration, with particle diameter and porosity metrics changing by less than 18% and 7%, respectively, compared to fresh microparticles. We also recorded the high viability of Saccharomyces cerevisiae yeast desiccated and rehydrated inside PicoShells, with only a 14% decrease in viability compared to non-desiccated yeast over 8.5 weeks, although we observed an 85% decrease in initial growth potential over the same duration. We show a proof-of-concept for a growth rate-based analysis of single-cell derived colonies in rehydrated PicoShells, where we identified 11% of the population that grows at an accelerated rate. Desiccated PicoShells thus provide a robust method for cell preservation before and during launch, promising a simple single-cell analysis method for studying heterogeneity in microbial populations in space.

High-throughput selection of cells based on accumulated growth and division using PicoShell particles.

Production of high-energy lipids by microalgae may provide a sustainable energy source that can help tackle climate change. However, microalgae engineered to produce more lipids usually grow slowly, leading to reduced overall yields. Unfortunately, culture vessels used to select cells based on growth while maintaining high biomass production, such as well plates, water-in-oil droplet emulsions, and nanowell arrays, do not provide production-relevant environments that cells experience in scaled-up cultures (e.g., bioreactors or outdoor cultivation farms). As a result, strains that are developed in the laboratory may not exhibit the same beneficial phenotypic behavior when transferred to industrial production. Here, we introduce PicoShells, picoliter-scale porous hydrogel compartments, that enable >100,000 individual cells to be compartmentalized, cultured in production-relevant environments, and selected based on growth and bioproduct accumulation traits using standard flow cytometers. PicoShells consist of a hollow inner cavity where cells are encapsulated and a porous outer shell that allows for continuous solution exchange with the external environment. PicoShells allow for cell growth directly in culture environments, such as shaking flasks and bioreactors. We experimentally demonstrate that Chlorella sp., Saccharomyces cerevisiae, and Chinese hamster ovary cells, used for bioproduction, grow to significantly larger colony sizes in PicoShells than in water-in-oil droplet emulsions (P < 0.05). We also demonstrate that PicoShells containing faster dividing and growing Chlorella clonal colonies can be selected using a fluorescence-activated cell sorter and regrown. Using the PicoShell process, we select a Chlorella population that accumulates chlorophyll 8% faster than does an unselected population after a single selection cycle.

Rapid Detection and Inhibition of SARS-CoV-2-Spike Mutation-Mediated Microthrombosis.

Activation of endothelial cells following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is thought to be the primary driver for the increasingly recognized thrombotic complications in coronavirus disease 2019 patients, potentially due to the SARS-CoV-2 Spike protein binding to the human angiotensin-converting enzyme 2 (hACE2). Vaccination therapies use the same Spike sequence or protein to boost host immune response as a protective mechanism against SARS-CoV-2 infection. As a result, cases of thrombotic events are reported following vaccination. Although vaccines are generally considered safe, due to genetic heterogeneity, age, or the presence of comorbidities in the population worldwide, the prediction of severe adverse outcome in patients remains a challenge. To elucidate Spike proteins underlying patient-specific-vascular thrombosis, the human microcirculation environment is recapitulated using a novel microfluidic platform coated with human endothelial cells and exposed to patient specific whole blood. Here, the blood coagulation effect is tested after exposure to Spike protein in nanoparticles and Spike variant D614G in viral vectors and the results are corroborated using live SARS-CoV-2. Of note, two potential strategies are also examined to reduce blood clot formation, by using nanoliposome-hACE2 and anti-Interleukin (IL) 6 antibodies.