Elucidating the effects of microbubble pinch-off dynamics on mammalian cell viability.

In the biotechnology industry, ensuring the health and viability of mammalian cells, especially Chinese Hamster Ovary (CHO) cells, plays a significant role in the successful production of therapeutic agents. These cells are typically cultivated in aerated bioreactors, where they encounter fluid stressors from rapidly deforming bubbles. These stressors can disrupt essential biological processes and potentially lead to cell death. However, the impact of these transient, elevated stressors on cell viability remains elusive. In this study, we first employ /cgqamicrofluidics to expose CHO cells near to bubbles undergoing pinch-off, subsequently collecting and assaying the cells to quantify the reduction in viability. Observing a significant impact, we set out to understand this phenomenon. We leverage computational fluid dynamics and numerical particle tracking to map the stressor field history surrounding a rapidly deforming bubble. Separately, we expose CHO cells to a known stressor level in a flow constriction device, collecting and assaying the cells to quantify the reduction in viability. By integrating the numerical data and results from the flow constriction device experiments, we develop a predictive model for cell viability reduction. We validate this model by comparing its predictions to the earlier microfluidic results, observing good agreement. Our findings provide critical insights into the relationship between bubble-induced fluid stressors and mammalian cell viability, with implications for bioreactor design and cell culture protocol optimization in the biotechnology sector.

Detection of SARS-CoV-2 Antibodies in Immunoglobulin Products.

BACKGROUND: For patients with primary antibody deficiency, the first line of therapy is replacement with immunoglobulin (Ig) products. Prior to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, Ig products did not contain antibodies with specificity for this virus, and there have been limited data on the antibodies present in the Ig products in current use. OBJECTIVE: To quantitatively examine SARS-CoV-2 antibodies in current Ig products. METHODS: We examined 142 unique lots of 11 different Ig products intended for intravenous and/or subcutaneous delivery for IgG-binding activities against recombinant SARS-CoV-2 receptor binding domain, spike, and nucleocapsid proteins by enzyme-linked immunosorbent assays. In addition, to assess functionality, 48 of these unique lots were assessed for their ability to inhibit the variants SARS-CoV-2 Ancestral, Alpha, Beta, Delta, and Omicron spike binding to angiotensin-converting enzyme 2 (ACE2). RESULTS: Significantly increased antibody values were observed for products manufactured after the year 2020 (expiration dates 2023-2024), as compared with Ig products before 2020 (prepandemic). Sixty percent and 85% of the Ig products with expiration dates of 2023 and 2024 were positive for antibody to SARS-CoV-2 proteins, respectively. The area under the curve values were significantly higher in products with later expiration dates. Later dates of expiration were also strongly correlated with inhibition of ACE2-binding activity; however, a decline in inhibition activity was observed with later variants. CONCLUSIONS: Overall, more recent Ig products (expiration dates 2023-2025) contained significantly higher binding and inhibition activities against SARS-CoV-2 proteins, compared with earlier, or prepandemic products. Normal donor SARS-CoV-2 antibodies are capable of inhibiting ACE2-binding activities and may provide a therapeutic benefit for patients who do not make a robust vaccine response.

Enrichment of Scavenged Particles in Jet Drops Determined by Bubble Size and Particle Position.

When small bubbles rupture in a contaminated water source, the resulting liquid jet breaks up into droplets that can aerosolize solid particulates such as bacteria, viruses, and microplastics. Particles collected on the bubble surface have the potential to become highly concentrated in the jet drops, dramatically increasing their impact. It has been assumed that only particles small enough to fit within a thin microlayer surrounding the bubble can be transported into its influential top jet drop. Yet here, we demonstrate that not only can larger particles be transported into this jet drop, but also that these particles can exceed previous enrichment measurements. Through experiments and simulations, we identify the prerupture location of the liquid that develops into the top jet drop and model how interfacial rearrangement combines with the bubble size, particle size, and the angular distribution of particles on the bubble surface to set the particle enrichment.

Microscale heterogeneous pore occupancy with variable background resistance.

Fluid flow through porous media often involves the spontaneous displacement of one immiscible fluid by another. On the level of adjacent channels, a pore doublet model can estimate the relative flow rates in the two channels and the final fluid occupancy of the pair. Pore doublet models nominally capture the dominant roles of capillarity and viscosity, by describing the flow using hydraulic circuit theory. However, this approach neglects the more complex fluid flow in the region where the immiscible fluids meet, and therefore the applicability of this model for low aspect-ratio pores commonly seen in natural media is questionable. We show that for large channel aspect ratios, the numerical results replicate the traditional pore doublet models; however, as the aspect ratio approaches unity, the accuracy of these models break down. We quantify the effect of complex flow on the final fluid occupancy, which we link to the excess energy dissipation rate from the flow near the immiscible interface. Our results indicate that a minimal 1D pore doublet model may be sufficient to model global dynamics, including the fraction of residual oil that remains trapped in a reservoir, where the pore diameter and length are comparable.

Aerosol agitation: Quantifying the hydrodynamic stressors on particulates encapsulated in small droplets.

Lower respiratory tract infections originate from multiple aerosol sources, varying from droplets erupting from bursting bubbles in a toilet or those produced by human speech. A key component of the aerosol-based infection pathway-from source to potential host-is the survival of the pathogen during aerosolization. Due to their finite-time instability, pinch-off processes occurring during aerosolization have the potential to rapidly accelerate the fluid into focused regions of these droplets, stress objects therein, and if powerful enough, disrupt biological life. However, the extent that a pathogen will be exposed to damaging hydrodynamic stressors during the aerosolization process is unknown. Here we compute the probability that particulates will be exposed to a hydrodynamic stressor during the generation of droplets that range in size from one to 100 microns. For example, particulates in water droplets less than 5 µm have a 50% chance of being subjected to an energy dissipation rate in excess of 1011 W/m3, hydrodynamic stresses in excess of 104 Pa, and strain rates in excess of 107 s-1, values known to damage certain biological cells. Using a combination of numerical simulations and self-similar dynamics, we show how the exposure within a droplet can be generally predicted from its size, surface tension, and density, even across different aerosolization mechanisms. Collectively, these results introduce aerosol agitation as a potential factor in pathogen transmission and implicate the pinch-off singularity flow as setting the distribution of hydrodynamic stressors experienced within the droplet.

Quantifying the potential for bursting bubbles to damage suspended cells.

Bubbles that rise to the surface of a cell suspension can damage cells when they pop. This phenomenon is particularly problematic in the biotechnology industry, as production scale bioreactors require continuous injection of oxygen bubbles to maintain cell growth. Previous studies have linked cell damage to high energy dissipation rates (EDR) and have predicted that for small bubbles the EDR could exceed values that would kill many cells used in bioreactors, including Chinese Hamster Ovary (CHO) cells. However, it's unclear how many cells would be damaged by a particular bursting bubble, or more precisely how much volume around the bubble experiences these large energy dissipation rates. Here we quantify these volumes using numerical simulations and demonstrate that even though the volume exceeding a particular EDR increases with bubble size, on a volume-to-volume basis smaller bubbles have a more significant impact. We validate our model with high-speed experiments and present our results in a non-dimensionalized framework, enabling predictions for a variety of liquids and bubble sizes. The results are not restricted to bubbles in bioreactors and may be relevant to a variety of applications ranging from fermentation processes to characterizing the stress levels experienced by microorganisms within the sea surface microlayer.

Periodic jetting and monodisperse jet drops from oblique gas injection.

When air is blown in a straw or tube near an air-liquid interface, typically one of two behaviors is observed: a dimple in the liquid's surface, or a frenzy of sputtering bubbles, waves, and spray. Here we report and characterize an intermediate regime that can develop when a confined air jet enters the interface at an angle. This regime is oscillatory with a distinct characteristic frequency and can develop periodic angled jets that can break up into monodisperse aerosols. The underlying mechanisms responsible for this highly periodic regime are not well understood. Here we flow a continuous stream of gas through a tube near a liquid surface, observing both optically and acoustically the deformation of the liquid-air interface as various parameters are systematically adjusted. We show that the Kelvin-Helmholtz instability is responsible for the inception of waves within a cavity formed by the gas. Inertia, gravity, and capillary forces both shape the cavity and govern the frequency and amplitude of these gas-induced cavity waves. The flapping cavity focuses the waves into a series of periodic jets that can break up into droplets following the Rayleigh-Plateau instability. We present scaling arguments to rationalize the fundamental frequencies driving this system, as well as the conditions that bound the periodic regime. These frequencies and conditions compare well with our experimental results.