Profile analysis of C. elegans rheotaxis behavior using a microfluidic device

Microfluidic Platforms for Real-Time In Situ Monitoring of Biomarkers for Cellular Processes

Cellular processes are mechanisms carried out at the cellular level that are aimed at guaranteeing the stability of the organism they comprise. The investigation of cellular processes is key to understanding cell fate, understanding pathogenic mechanisms, and developing new therapeutic technologies. Microfluidic platforms are thought to be the most powerful tools among all methodologies for investigating cellular processes because they can integrate almost all types of the existing intracellular and extracellular biomarker-sensing methods and observation approaches for cell behavior, combined with precisely controlled cell culture, manipulation, stimulation, and analysis. Most importantly, microfluidic platforms can realize real-time in situ detection of secreted proteins, exosomes, and other biomarkers produced during cell physiological processes, thereby providing the possibility to draw the whole picture for a cellular process. Owing to their advantages of high throughput, low sample consumption, and precise cell control, microfluidic platforms with real-time in situ monitoring characteristics are widely being used in cell analysis, disease diagnosis, pharmaceutical research, and biological production. This review focuses on the basic concepts, recent progress, and application prospects of microfluidic platforms for real-time in situ monitoring of biomarkers in cellular processes.

Microfluidic-Assisted Caenorhabditis elegans Sorting: Current Status and Future Prospects

Caenorhabditis elegans (C. elegans) has been a popular model organism for several decades since its first discovery of the huge research potential for modeling human diseases and genetics. Sorting is an important means of providing stage- or age-synchronized worm populations for many worm-based bioassays. However, conventional manual techniques for C. elegans sorting are tedious and inefficient, and commercial complex object parametric analyzer and sorter is too expensive and bulky for most laboratories. Recently, the development of lab-on-a-chip (microfluidics) technology has greatly facilitated C. elegans studies where large numbers of synchronized worm populations are required and advances of new designs, mechanisms, and automation algorithms. Most previous reviews have focused on the development of microfluidic devices but lacked the summaries and discussion of the biological research demands of C. elegans, and are hard to read for worm researchers. We aim to comprehensively review the up-to-date microfluidic-assisted C. elegans sorting developments from several angles to suit different background researchers, i.e., biologists and engineers. First, we highlighted the microfluidic C. elegans sorting devices' advantages and limitations compared to the conventional commercialized worm sorting tools. Second, to benefit the engineers, we reviewed the current devices from the perspectives of active or passive sorting, sorting strategies, target populations, and sorting criteria. Third, to benefit the biologists, we reviewed the contributions of sorting to biological research. We expect, by providing this comprehensive review, that each researcher from this multidisciplinary community can effectively find the needed information and, in turn, facilitate future research.

Collective Behaviors of Active Matter Learning from Natural Taxes Across Scales

Taxis orientation is common in microorganisms, and it provides feasible strategies to operate active colloids as small-scale robots. Collective taxes involve numerous units that collectively perform taxis motion, whereby the collective cooperation between individuals enables the group to perform efficiently, adaptively, and robustly. Hence, analyzing and designing collectives is crucial for developing and advancing microswarm toward practical or clinical applications. In this review, natural taxis behaviors are categorized and synthetic microrobotic collectives are discussed as bio-inspired realizations, aiming at closing the gap between taxis strategies of living creatures and those of functional active microswarms. As collective behaviors emerge within a group, the global taxis to external stimuli guides the group to conduct overall tasks, whereas the local taxis between individuals induces synchronization and global patterns. By encoding the local orientations and programming the global stimuli, various paradigms can be introduced for coordinating and controlling such collective microrobots, from the viewpoints of fundamental science and practical applications. Therefore, by discussing the key points and difficulties associated with collective taxes of different paradigms, this review potentially offers insights into mimicking natural collective behaviors and constructing intelligent microrobotic systems for on-demand control and preassigned tasks.

Crosstalk between neurons and glia through G-protein coupled receptors: Insights from Caenorhabditis elegans

The past decades have witnessed a dogmatic shift from glia as supporting cells in the nervous system to their active roles in neurocentric functions. Neurons and glia communicate and show bidirectional responses through tripartite synapses. Studies across species indicate that neurotransmitters released by neurons are perceived by glial receptors, which allow for gliotransmitter release. These gliotransmitters can result in activation of neurons via neuronal GPCR receptors. However, studies of these molecular interactions are in their infancy. Caenorhabditis elegans has a conserved neuron-glia architectural repertoire with molecular and functional resemblance to mammals. Further, glia in C. elegans can be manipulated through ablation and mutations allowing for deciphering of glial dependent processes in vivo at single glial resolutions. Here, we will review recent findings from vertebrate and invertebrate organisms with a focus on how C. elegans can be used to advance our understanding of neuron-glia interactions through GPCRs.

Whole-organism phenotypic screening methods used in early-phase anthelmintic drug discovery

Diseases caused by parasitic helminths (worms) represent a major global health burden in both humans and animals. As vaccines against helminths have yet to achieve a prominent role in worm control, anthelmintics are the primary tool to limit production losses and disease due to helminth infections in both human and veterinary medicine. However, the excessive and often uncontrolled use of these drugs has led to widespread anthelmintic resistance in these worms - particularly of animals - to almost all commercially available anthelmintics, severely compromising control. Thus, there is a major demand for the discovery and development of new classes of anthelmintics. A key component of the discovery process is screening libraries of compounds for anthelmintic activity. Given the need for, and major interest by the pharmaceutical industry in, novel anthelmintics, we considered it both timely and appropriate to re-examine screening methods used for anthelmintic discovery. Thus, we reviewed current literature (1977-2021) on whole-worm phenotypic screening assays developed and used in academic laboratories, with a particular focus on those employed to discover nematocides. This review reveals that at least 50 distinct phenotypic assays with low-, medium- or high-throughput capacity were developed over this period, with more recently developed methods being quantitative, semi-automated and higher throughput. The main features assessed or measured in these assays include worm motility, growth/development, morphological changes, viability/lethality, pharyngeal pumping, egg hatching, larval migration, CO₂- or ATP-production and/or enzyme activity. Recent progress in assay development has led to the routine application of practical, cost-effective, medium- to high-throughput whole-worm screening assays in academic or public-private partnership (PPP) contexts, and major potential for novel high-content, high-throughput platforms in the near future. Complementing this progress are major advances in the molecular data sciences, computational biology and informatics, which are likely to further enable and accelerate anthelmintic drug discovery and development.

Microfluidic electric parallel egg-laying assay and application to in-vivo toxicity screening of microplastics using C. elegans

Environmental pollutants like microplastics are posing health concerns on aquatic animals and the ecosystem. Microplastic toxicity studies using Caenorhabditis elegans (C. elegans) as a model are evolving but methodologically hindered from obtaining statistically strong data sets, detecting toxicity effects based on microplastics uptake, and correlating physiological and behavioural effects at an individual-worm level. In this paper, we report a novel microfluidic electric egg-laying assay for phenotypical assessment of multiple worms in parallel. The effects of glucose and polystyrene microplastics at two concentrations on the worms' electric egg-laying, length, diameter, and length contraction during exposure to electric signal were studied. The device contained eight parallel worm-dwelling microchannels called electric traps, with equivalent electrical fields, in which the worms were electrically stimulated for egg deposition and fluorescently imaged for assessment of neuronal and microplastic uptake expression. A new bidirectional stimulation technique was developed, and the device design was optimized to achieve a testing efficiency of 91.25%. Exposure of worms to 100 mM glucose resulted in a significant reduction in their egg-laying and size. The effects of 1 μm polystyrene microparticles at concentrations of 100 and 1000 mg/L on the electric egg-laying behaviour, size, and neurodegeneration of N2 and NW1229 (expressing GFP pan-neuronally) worms were also studied. Of the two concentrations, 1000 mg/L caused severe egg-laying deficiency and growth retardation as well as neurodegeneration. Additionally, using single-worm level phenotyping, we noticed intra-population variability in microplastics uptake and correlation with the above physiological and behavioural phenotypes, which was hidden in the population-averaged results. Taken together, these results suggest the appropriateness of our microfluidic assay for toxicological studies and for assessing the phenotypical heterogeneity in response to microplastics.

A low-cost microfluidic platform coupled with light emitting diode for optogenetic analysis of neuronal response in C. elegans

Optogenetic method is widely used for dissecting the neuronal function and connectivity in a specific neural circuit, which can help understanding how the animal process information and generate behavior. The nematode C. elegans has a simple but complete nervous system, making it an attractive model to study the dynamics signals of neural circuits. However, in vivo analysis on neural circuits usually rely on the complex and expensive optical equipment to allow optogenetic stimulating the neuron while recording its activities in such a freely moving animal. Hence, in this paper we reported a portable optofluidic platform that works based on optical fiber illumination and functional imaging for worm optogenetic manipulation. A light beam from LED laser pen crossing the 3D-printed optical fiber channel is used to activate the neurons specific-expressed with light sensitive proteins ChR-2. The imaging light path is perpendicular to the stimulation light, which allows activating neuron precisely and measuring cellular signals simultaneously. By using such an easy-to-assemble device, optical stimulation of the specific neurons and detection of dynamic calcium responses of other neurons could be proceeded simultaneously. Thus, the developed microfluidic platform puts forward a simple, rapid and low-cost strategy for further neural circuits studies.

Straightforward neuron micropatterning and neuronal network construction on cell-repellent polydimethylsiloxane using microfluidics-guided functionalized Pluronic modification

Neuronal cell microengineering involving micropatterning and polydimethylsiloxane (PDMS) microfluidics enables promising advances in microscale neuron control. However, a facile methodology for the precise and effective manipulation of neurons on a cell-repellent PDMS substrate remains challenging. Herein, a simple and straightforward strategy for neuronal cell patterning and neuronal network construction on PDMS based on microfluidics-assisted modification of functionalized Pluronic is described. The cell patterning process simply involves a one-step microfluidic modification and routine in vitro culture. It is demonstrated that multiple types of neuronal cell arrangements with various spatial profiles can be conveniently produced using this patterning tool. The precise control of neuronal cells with high patterning fidelity up to single cell resolution, as well as high adhesion and differentiation, is achieved too. Furthermore, neuronal network construction using the respective cell population and single cell patterning prove to be applicable. This achievement provides a convenient and feasible methodology for engineering neuronal cells on PDMS substrates, which will be useful for applications in many neuron-related microscale analytical research fields, including cell engineering, neurobiology, neuropharmacology, and neuronal sensing.

Comprehensive Evaluation of Stable Neuronal Cell Adhesion and Culture on One-Step Modified Polydimethylsiloxane Using Functionalized Pluronic

Polydimethylsiloxane (PDMS) is a popular and property-advantageous material for developing biomedical microsystems and advancing cell microengineering. The requirement of constructing a robust cell-adhesive PDMS interface drives the exploration of simple, straightforward, and applicable surface modification methods. Here, a comprehensive evaluation of highly stable neuronal cell adhesion and culture on the PDMS surface modified in one step using functionalized Pluronic is presented. According to multiple comparative tests, this modification is sufficiently verified to enable more significant cell adhesion and spreading in both quantity and stability, higher neuronal differentiation and viability/growth, more complete formation of the neuronal network, and stabler neuronal cell culture than the common coating tools on the PDMS substrate. The comparable and even superior cellular effects of this modification on PDMS to the standard coating of polystyrene for in vitro neurological research are demonstrated. Long-term microfluidic neuron culture with stable adhesion and high differentiation on the modified PDMS interface is accomplished, too. The achievement provides a detailed experimental demonstration of this simple and effective modification for strengthening neuronal cell culture on the PDMS substrate, which is useful for potential applications in the fields of neurobiology, neuron microengineering, and brain-on-a-chip.

An integrated microfluidics for assessing the anti-aging effect of caffeic acid phenethylester in Caenorhabditis elegans

Aging is a fundamental and fascinating process. Anti-aging research tried to find the mysteries about the human lifespan. To investigate the longevity-extending role of caffeic acid phenethylester (CAPE) and reveal the possible regulation mechanism, the long-term cultivation under well-defined environments, real-time monitoring, and live imaging is highly desired. In this paper, a well-designed microfluidic device was proposed to analyze the anti-aging effect of CAPE in Caenorhabditis elegans. With the combined use of multiple functional units, including micro-pillar, worm responder, a branching network of distribution channels, and microchambers, the longitudinal measurements of the exact number of worms throughout the whole lifespans is possible. Meanwhile, the brief cooling function of temperature-controllable system can achieve temporary and repeated immobilization of nematodes for fluorescence imaging. Our research data showed that CAPE can increase the survival of worms under normal and stress condition, including heat stress and paraquat-induced oxidative stress. The further studies revealed the anti-aging mechanism of CAPE. This proposed strategy and device would be a useful platform to facilitate future anti-aging studies and the finding of new lead compounds.