Real-time monitoring of cell migration, phagocytosis and cell surface receptor dynamics using a novel, live-cell opto-microfluidic technique

Acousto-optofluidic 3D single cell imaging of macrophage phagocytosis of Pseudomonas Aeruginosa

Understanding how immune cells such as monocytes or macrophages within our blood and tissue engulf and destroy foreign organisms is important for developing new therapies. The process undertaken by these cells, called phagocytosis, has yet to be observed in real-time at the single cell level. Microfluidic-based imaging platforms offer a wide range of tools for precise fluid control and biomolecule manipulation that makes regulating long term experiments and data collection possible. With the compatibility between acoustofluidics and light-sheet fluorescent microscopy (LSFM) previously demonstrated, here an acousto-optfluidic device with on-chip fluid flow direction control was developed. The standing surface acoustic waves (SSAWs) were used to trap, load and safeguard individual cells within a highly controllable fluid loop, created via the triggering of on-chip PDMS valves, to demonstrate multiple rounds of live single cell imaging. The valves allowed for the direction of the fluid flow to be changed (between forward and reverse operation) without altering the inlet flow rate, an important factor for performing reproducible and comparable imaging of samples over time. With this high-resolution imaging system, volumetric reconstructions of phagocytosed bacteria within macrophages could be resolved over a total of 9 rounds of imaging: totalling 19 reconstructed images of the cell membrane with visible intracellular bacteria.

Exploring Cell Migration Mechanisms in Cancer: From Wound Healing Assays to Cellular Automata Models

PURPOSE

Cell migration is a critical driver of metastatic tumor spread, contributing significantly to cancer-related mortality. Yet, our understanding of the underlying mechanisms remains incomplete.

METHODS

In this study, a wound healing assay was employed to investigate cancer cell migratory behavior, with the aim of utilizing migration as a biomarker for invasiveness. To gain a comprehensive understanding of this complex system, we developed a computational model based on cellular automata (CA) and rigorously calibrated and validated it using in vitro data, including both tumoral and non-tumoral cell lines. Harnessing this CA-based framework, extensive numerical experiments were conducted and supported by local and global sensitivity analyses in order to identify the key biological parameters governing this process.

RESULTS

Our analyses led to the formulation of a power law equation derived from just a few input parameters that accurately describes the governing mechanism of wound healing. This groundbreaking research provides a powerful tool for the pharmaceutical industry. In fact, this approach proves invaluable for the discovery of novel compounds aimed at disrupting cell migration, assessing the efficacy of prospective drugs designed to impede cancer invasion, and evaluating the immune system's responses.

A microfluidic-based analysis of 3D macrophage migration after stimulation by Mycobacterium, Salmonella and Escherichia

Macrophages play an essential role in the process of recognition and containment of microbial infections. These immune cells are recruited to infectious sites to reach and phagocytose pathogens. Specifically, in this article, bacteria from the genus Mycobacterium, Salmonella and Escherichia, were selected to study the directional macrophage movement towards different bacterial fractions. We recreated a three-dimensional environment in a microfluidic device, using a collagen-based hydrogel that simulates the mechanical microarchitecture associated to the Extra Cellular Matrix (ECM). First, we showed that macrophage migration is affected by the collagen concentration of their environment, migrating greater distances at higher velocities with decreasing collagen concentrations. To recreate the infectious microenvironment, macrophages were exposed to lateral gradients of bacterial fractions obtained from the intracellular pathogens M. tuberculosis and S. typhimurium. Our results showed that macrophages migrated directionally, and in a concentration-dependent manner, towards the sites where bacterial fractions are located, suggesting the presence of attractants molecules in all the samples. We confirmed that purified M. tuberculosis antigens, as ESAT-6 and CFP-10, stimulated macrophage recruitment in our device. Finally, we also observed that macrophages migrate towards fractions from non-pathogenic bacteria, such as M. smegmatis and Escherichia coli. In conclusion, our microfluidic device is a useful tool which opens new perspectives to study the recognition of specific antigens by innate immune cells.

A near-infrared plasma membrane-specific AIE probe for fluorescence lifetime imaging of phagocytosis

Phagocytosis is a biological process that plays a key role in host defense and tissue homeostasis. Efficient approaches for realtime imaging of phagocytosis are highly desired but limited. Herein, an AIE-active near-infrared fluorescent probe, named TBTCP, was developed for fluorescence lifetime imaging of phagocytosis. TBTCP could selectively label the cell plasma membrane with fast staining, wash-free process, high signal-to-background ratio, and excellent photostability. Cellular membrane statuses under different osmolarities as well as macrophage phagocytosis of bacteria or large silica particles in early stages could be reported by the fluorescence lifetime changes of TBTCP. Compared with current fluorescence imaging methods, which target the bioenvironmental changes in the late phagocytosis stage, this approach detects the changes in the cell membrane, thus giving a faster response to phagocytosis. This article provides a functional tool to report the phagocytic dynamics of macrophages which may greatly contribute to the studies of phagocytic function-related diseases.

Patterns of bacterial motility in microfluidics-confining environments

Understanding the motility behavior of bacteria in confining microenvironments, in which they search for available physical space and move in response to stimuli, is important for environmental, food industry, and biomedical applications. We studied the motility of five bacterial species with various sizes and flagellar architectures (Vibrio natriegens, Magnetococcus marinus, Pseudomonas putida, Vibrio fischeri, and Escherichia coli) in microfluidic environments presenting various levels of confinement and geometrical complexity, in the absence of external flow and concentration gradients. When the confinement is moderate, such as in quasi-open spaces with only one limiting wall, and in wide channels, the motility behavior of bacteria with complex flagellar architectures approximately follows the hydrodynamics-based predictions developed for simple monotrichous bacteria. Specifically, V. natriegens and V. fischeri moved parallel to the wall and P. putida and E. coli presented a stable movement parallel to the wall but with incidental wall escape events, while M. marinus exhibited frequent flipping between wall accumulator and wall escaper regimes. Conversely, in tighter confining environments, the motility is governed by the steric interactions between bacteria and the surrounding walls. In mesoscale regions, where the impacts of hydrodynamics and steric interactions overlap, these mechanisms can either push bacteria in the same directions in linear channels, leading to smooth bacterial movement, or they could be oppositional (e.g., in mesoscale-sized meandered channels), leading to chaotic movement and subsequent bacterial trapping. The study provides a methodological template for the design of microfluidic devices for single-cell genomic screening, bacterial entrapment for diagnostics, or biocomputation.

Heart-on-a-Chip: An Investigation of the Influence of Static and Perfusion Conditions on Cardiac (H9C2) Cell Proliferation, Morphology, and Alignment

Lab-on-a-chip systems are increasingly used as tools for cultures and investigation of cardiac cells. In this article, we present how the geometry of microsystems and microenvironmental conditions (static and perfusion) influence the proliferation, morphology, and alignment of cardiac cells (rat cardiomyoblasts-H9C2). Additionally, studies of cell growth after incubation with verapamil hydrochloride were performed. For this purpose, poly(dimethylsiloxane) (PDMS)/glass microfluidic systems with three different geometries of microchambers (a circular chamber, a longitudinal channel, and three parallel microchannels separated by two rows of micropillars) were prepared. It was found that static conditions did not enhance the growth of H9C2 cells in the microsystems. On the contrary, perfusion conditions had an influence on division, morphology, and the arrangement of the cells. The highest number of cells, their parallel orientation, and their elongated morphology were obtained in the longitudinal microchannel. It showed that this kind of microsystem can be used to understand processes in heart tissue in detail and to test newly developed compounds applied in the treatment of cardiac diseases.