Microfluidic Platform for the Study of Caenorhabditis elegans

Worm-Based Diagnosis Combining Microfluidics toward Early Cancer Screening

Early cancer diagnosis increases therapy efficiency and saves huge medical costs. Traditional blood-based cancer markers and endoscopy procedures demonstrate limited capability in the diagnosis. Reliable, non-invasive, and cost-effective methods are in high demand across the world. Worm-based diagnosis, utilizing the chemosensory neuronal system of C. elegans, emerges as a non-invasive approach for early cancer diagnosis with high sensitivity. It facilitates effectiveness in large-scale cancer screening for the foreseeable future. Here, we review the progress of a unique route of early cancer diagnosis based on the chemosensory neuronal system of C. elegans. We first introduce the basic procedures of the chemotaxis assay of C. elegans: synchronization, behavior assay, immobilization, and counting. Then, we review the progress of each procedure and the various cancer types for which this method has achieved early diagnosis. For each procedure, we list examples of microfluidics technologies that have improved the automation, throughput, and efficiency of each step or module. Finally, we envision that microfluidics technologies combined with the chemotaxis assay of C. elegans can lead to an automated, cost-effective, non-invasive early cancer screening technology, with the development of more mature microfluidic modules as well as systematic integration of functional modules.

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.

Microfluidic chips: recent advances, critical strategies in design, applications and future perspectives

Microfluidic chip technology is an emerging tool in the field of biomedical application. Microfluidic chip includes a set of groves or microchannels that are engraved on different materials (glass, silicon, or polymers such as polydimethylsiloxane or PDMS, polymethylmethacrylate or PMMA). The microchannels forming the microfluidic chip are interconnected with each other for desired results. This organization of microchannels trapped into the microfluidic chip is associated with the outside by inputs and outputs penetrating through the chip, as an interface between the macro- and miniature world. With the help of a pump and a chip, microfluidic chip helps to determine the behavioral change of the microfluids. Inside the chip, there are microfluidic channels that permit the processing of the fluid, for example, blending and physicochemical responses. Microfluidic chip has numerous points of interest including lesser time and reagent utilization and alongside this, it can execute numerous activities simultaneously. The miniatured size of the chip fastens the reaction as the surface area increases. It is utilized in different biomedical applications such as food safety sensing, peptide analysis, tissue engineering, medical diagnosis, DNA purification, PCR activity, pregnancy, and glucose estimation. In the present study, the design of various microfluidic chips has been discussed along with their biomedical applications.

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.

Studying Parkinson’s disease using Caenorhabditis elegans models in microfluidic devices

Parkinson’s disease (PD) is a progressive neurological disorder associated with the loss of dopaminergic neurons (DNs) in the substantia nigra and the widespread accumulation of α-synuclein (α-syn) protein, leading to motor impairments and eventual cognitive dysfunction. In-vitro cell cultures and in-vivo animal models have provided the opportunity to investigate the PD pathological hallmarks and identify different therapeutic compounds. However, PD pathogenesis and causes are still not well understood, and effective inhibitory drugs for PD are yet to be discovered. Biologically simple but pathologically relevant disease models and advanced screening technologies are needed to reveal the mechanisms underpinning protein aggregation and PD progression. For instance, Caenorhabditis elegans (C. elegans) offers many advantages for fundamental PD neurobehavioral studies including a simple, well-mapped, and accessible neuronal system, genetic homology to humans, body transparency and amenability to genetic manipulation. Several transgenic worm strains that exhibit multiple PD-related phenotypes have been developed to perform neuronal and behavioral assays and drug screening. However, in conventional worm-based assays, the commonly used techniques are equipment-intensive, slow and low in throughput. Over the past two decades, microfluidics technology has contributed significantly to automation and control of C. elegans assays. In this review, we focus on C. elegans PD models and the recent advancements in microfluidic platforms used for manipulation, handling and neurobehavioral screening of these models. Moreover, we highlight the potential of C. elegans to elucidate the in-vivo mechanisms of neuron-to-neuron protein transfer that may underlie spreading Lewy pathology in PD, and its suitability for in-vitro studies. Given the advantages of C. elegans and microfluidics technology, their integration has the potential to facilitate the investigation of disease pathology and discovery of potential chemical leads for PD.

Microfluidic Devices Developed for and Inspired by Thermotaxis and Chemotaxis

Taxis has been reported in many cells and microorganisms, due to their tendency to migrate toward favorable physical situations and avoid damage and death. Thermotaxis and chemotaxis are two of the major types of taxis that naturally occur on a daily basis. Understanding the details of the thermo- and chemotactic behavioral response of cells and microorganisms is necessary to reveal the body function, diagnosing diseases and developing therapeutic treatments. Considering the length-scale and range of effectiveness of these phenomena, advances in microfluidics have facilitated taxis experiments and enhanced the precision of controlling and capturing microscale samples. Microfabrication of fluidic chips could bridge the gap between in vitro and in situ biological assays, specifically in taxis experiments. Numerous efforts have been made to develop, fabricate and implement novel microchips to conduct taxis experiments and increase the accuracy of the results. The concepts originated from thermo- and chemotaxis, inspired novel ideas applicable to microfluidics as well, more specifically, thermocapillarity and chemocapillarity (or solutocapillarity) for the manipulation of single- and multi-phase fluid flows in microscale and fluidic control elements such as valves, pumps, mixers, traps, etc. This paper starts with a brief biological overview of the concept of thermo- and chemotaxis followed by the most recent developments in microchips used for thermo- and chemotaxis experiments. The last section of this review focuses on the microfluidic devices inspired by the concept of thermo- and chemotaxis. Various microfluidic devices that have either been used for, or inspired by thermo- and chemotaxis are reviewed categorically.

On-chip microfluidic biocommunication assay for studying male-induced demise in C. elegans hermaphrodites

Like other animals, C. elegans nematodes have the ability to socially interact and to communicate through exchange and sensing of small soluble signaling compounds that help them cope with complex environmental conditions. For the time being, worm biocommunication assays are being performed mainly on agar plates; however, microfluidic assays may provide significant advantages compared to traditional methods, such as control of signaling molecule concentrations and gradients or confinement of distinct worm populations in different microcompartments. Here, we propose a microfluidic device for studying signaling via diffusive secreted compounds between two specific C. elegans populations over prolonged durations. In particular, we designed a microfluidic assay to investigate the biological process of male-induced demise, i.e. lifespan shortening and accelerated age-related phenotype alterations, in C. elegans hermaphrodites in the presence of a physically separated male population. For this purpose, male and hermaphrodite worm populations were confined in adjacent microchambers on the chip, whereas molecules secreted by males could be exchanged between both populations by periodically activating the controlled fluidic transfer of μl-volume aliquots of male-conditioned medium. For male-conditioned hermaphrodites, we observed a reduction of 4 days in mean lifespan compared to the non-conditioned on-chip culture. We also observed an enhanced muscle decline, as expressed by a faster decrease in the thrashing frequency and the appearance of vacuolar-like structures indicative of accelerated aging. The chip was placed in an incubator at 20 °C for accurate control of the lifespan assay conditions. An on-demand bacteria feeding protocol was applied, and the worms were observed during long-term on-chip culture over the whole worm lifespan.

A hybrid microfluidic device for on-demand orientation and multidirectional imaging of C. elegans organs and neurons

C. elegans is a well-known model organism in biology and neuroscience with a simple cellular (959 cells) and nervous (302 neurons) system and a relatively homologous (40%) genome to humans. Lateral and longitudinal manipulation of C. elegans to a favorable orientation is important in many applications such as neural and cellular imaging, laser ablation, microinjection, and electrophysiology. In this paper, we describe a micro-electro-fluidic device for on-demand manipulation of C. elegans and demonstrate its application in imaging of organs and neurons that cannot be visualized efficiently under natural orientation. To achieve this, we have used the electrotaxis technique to longitudinally orient the worm in a microchannel and then insert it into an orientation and imaging channel in which we integrated a rotatable glass capillary for orientation of the worm in any desired direction. The success rates of longitudinal and lateral orientations were 76% and 100%, respectively. We have demonstrated the application of our device in optical and fluorescent imaging of vulva, uterine-vulval cell (uv1), vulB1\2 (adult vulval toroid cells), and ventral nerve cord of wild-type and mutant worms. In comparison to existing methods, the developed technique is capable of orienting the worm at any desired angle and maintaining the orientation while providing access to the worm for potential post-manipulation assays. This versatile tool can be potentially used in various applications such as neurobehavioral imaging, neuronal ablation, microinjection, and electrophysiology.

Acoustofluidic Rotational Manipulation of Cells and Organisms Using Oscillating Solid Structures

A polydimethylsiloxane microchannel featuring sidewall sharp-edge structures and bare channels, and a piezoelement transducer is attached to a thin glass slide. When an external acoustic field is applied to the microchannel, the oscillation of the sharp-edge structures and the thin glass slide generate acoustic streaming flows which in turn rotate single cells and C. elegans in-plane and out-of-plane.

Microfluidic Devices for Behavioral Analysis, Microscopy, and Neuronal Imaging in Caenorhabditis elegans

Microfluidic devices offer several advantages for C. elegans research, particularly for presenting precise physical and chemical environments, immobilizing animals during imaging, quantifying behavior, and automating screens. However, challenges to their widespread adoption in the field include increased complexity over conventional methods, operational problems (such as clogging, leaks, and bubbles), difficulty in obtaining or fabricating devices, and the need to characterize biological results obtained from new assay formats. Here we describe the preparation and operation of simple, reusable microfluidic devices for quantifying behavioral responses to chemical patterns, and single-use devices to arrange animals for time-lapse microscopy and to measure neuronal activity. We focus on details that eliminate or reduce the frustrations commonly experienced by new users of microfluidic devices.

Quantitative analysis of Caenorhabditis elegans chemotaxis using a microfluidic device

Caenorhabditis elegans, one of the widely studied model organisms, sense external chemical cues and perform relative chemotaxis behaviors through its simple chemosensory neuronal system. To study the mechanism underlying chemosensory behavior, a rapid and reliable method for quantitatively analyzing the worms' behaviors is essential. In this work, we demonstrated a microfluidic approach for investigating chemotaxis responses of worms to chemical gradients. The flow-based microfluidic chip was consisted of circular tree-like microchannels, which was able to generate eight flow streams containing stepwise chemical concentrations without the difference in flow velocity. Worms' upstream swimming into microchannels with various concentrations was monitored for quantitative analysis of the chemotaxis behavior. By using this microfluidic chip, the attractive and repellent responses of C. elegans to NaCl were successfully quantified within several minutes. The results demonstrated the wild type-like repellent responses and severely impaired attractive responses in grk-2 mutant animals with defects in calcium influx. In addition, the chemotaxis analysis of the third stage larvae revealed that its gustatory response was different from that in the adult stage. Thus, our microfluidic method provided a useful platform for studying the chemosensory behaviors of C. elegans and screening of chemosensation-related chemical drugs.

Vertical sidewall electrodes monolithically integrated into 3D glass microfluidic chips using water-assisted femtosecond-laser fabrication for in situ control of electrotaxis

Novel sidewall metal patterning with high flexibility enables facile integration of vertical electrodes in microchannels for in situ control of electrotaxis.

Microfluidic platform integrated with worm-counting setup for assessing manganese toxicity

We reported a new microfluidic system integrated with worm responders for evaluating the environmental manganese toxicity. The micro device consists of worm loading units, worm observing chambers, and a radial concentration gradient generator (CGG). Eight T-shape worm loading units of the micro device were used to load the exact number of worms into the corresponding eight chambers with the assistance of worm responders and doorsills. The worm responder, as a key component, was employed for performing automated worm-counting assay through electric impedance sensing. This label-free and non-invasive worm-counting technique was applied to the microsystem for the first time. In addition, the disk-shaped CGG can generate a range of stepwise concentrations of the appointed chemical automatically and simultaneously. Due to the scalable architecture of radial CGG, it has the potential to increase the throughput of the assay. Dopaminergic (DAergic) neurotoxicity of manganese on C. elegans was quantitatively assessed via the observation of green fluorescence protein-tagged DAergic neurons of the strain BZ555 on-chip. In addition, oxidative stress triggered by manganese was evaluated by the quantitative fluorescence intensity of the strain CL2166. By scoring the survival ratio and stroke frequency of worms, we characterized the dose- and time-dependent mobility defects of the manganese-exposed worms. Furthermore, we applied the microsystem to investigate the effect of natural antioxidants to protect manganese-induced toxicity.

From cradle to grave: high-throughput studies of aging in model organisms

Aging-the progressive decline of biological functions-is a universal fact of life. Decades of intense research in unicellular and metazoan model organisms have highlighted that aging manifests at all levels of biological organization - from the decline of individual cells, to tissue and organism degeneration. To better understand the aging process, we must first aim to integrate quantitative biological understanding on the systems and cellular levels. A second key challenge is to then understand the many heterogeneous outcomes that may result in aging cells, and to connect cellular aging to organism-wide degeneration. Addressing these challenges requires the development of high-throughput aging and longevity assays. In this review, we highlight the emergence of high-throughput aging approaches in the most commonly used model organisms. We conclude with a discussion of the critical questions that can be addressed with these new methods.

A microfluidic-enabled mechanical microcompressor for the immobilization of live single- and multi-cellular specimens

A microcompressor is a precision mechanical device that flattens and immobilizes living cells and small organisms for optical microscopy, allowing enhanced visualization of sub-cellular structures and organelles. We have developed an easily fabricated device, which can be equipped with microfluidics, permitting the addition of media or chemicals during observation. This device can be used on both upright and inverted microscopes. The apparatus permits micrometer precision flattening for nondestructive immobilization of specimens as small as a bacterium, while also accommodating larger specimens, such as Caenorhabditis elegans, for long-term observations. The compressor mount is removable and allows easy specimen addition and recovery for later observation. Several customized specimen beds can be incorporated into the base. To demonstrate the capabilities of the device, we have imaged numerous cellular events in several protozoan species, in yeast cells, and in Drosophila melanogaster embryos. We have been able to document previously unreported events, and also perform photobleaching experiments, in conjugating Tetrahymena thermophila.

Mainstreaming Caenorhabditis elegans in experimental evolution

Experimental evolution provides a powerful manipulative tool for probing evolutionary process and mechanism. As this approach to hypothesis testing has taken purchase in biology, so too has the number of experimental systems that use it, each with its own unique strengths and weaknesses. The depth of biological knowledge about Caenorhabditis nematodes, combined with their laboratory tractability, positions them well for exploiting experimental evolution in animal systems to understand deep questions in evolution and ecology, as well as in molecular genetics and systems biology. To date, Caenorhabditis elegans and related species have proved themselves in experimental evolution studies of the process of mutation, host-pathogen coevolution, mating system evolution and life-history theory. Yet these organisms are not broadly recognized for their utility for evolution experiments and remain underexploited. Here, we outline this experimental evolution work undertaken so far in Caenorhabditis, detail simple methodological tricks that can be exploited and identify research areas that are ripe for future discovery.

Microbeam irradiation of C. elegans nematode in microfluidic channels

To perform high-throughput studies on the biological effects of ionizing radiation in vivo, we have implemented a microfluidic tool for microbeam irradiation of Caenorhabditis elegans. The device allows the immobilization of worms with minimal stress for a rapid and controlled microbeam irradiation of multiple samples in parallel. Adapted from an established design, our microfluidic clamp consists of 16 tapered channels with 10-μm-thin bottoms to ensure charged particle traversal. Worms are introduced into the microfluidic device through liquid flow between an inlet and an outlet, and the size of each microchannel guarantees that young adult worms are immobilized within minutes without the use of anesthesia. After site-specific irradiation with the microbeam, the worms can be released by reversing the flow direction in the clamp and collected for analysis of biological endpoints such as repair of radiation-induced DNA damage. For such studies, minimal sample manipulation and reduced use of drugs such as anesthetics that might interfere with normal physiological processes are preferable. By using our microfluidic device that allows simultaneous immobilization and imaging for irradiation of several whole living samples on a single clamp, here we show that 4.5-MeV proton microbeam irradiation induced DNA damage in wild-type C. elegans, as assessed by the formation of Rad51 foci that are essential for homologous repair of radiation-induced DNA damage.

Microfluidic device for the selective chemical stimulation of neurons and characterization of peptide release with mass spectrometry

Neuropeptides are synthesized in and released from neurons and are involved in a wide range of physiological processes, including temperature homeostasis, learning, memory, and disease. When working with sparse neuronal networks, the ability to collect and characterize small sample volumes is important as neurons often release only a small proportion of their mass-limited content. Microfluidic systems are well suited for the study of neuropeptides. They offer the ability to control and manipulate the extracellular environment and small sample volumes, thereby reducing the dilution of peptides following release. We present an approach for the culture and stimulation of a neuronal network within a microfluidic device, subsequent collection of the released peptides, and their detection via mass spectrometry. The system employs microvalve-controlled stimulation channels to selectively stimulate a low-density neuronal culture, allowing us to determine the temporal onset of peptide release. Released peptides from the well-characterized, peptidergic bag cell neurons of Aplysia californica were collected and their temporal pattern of release was characterized with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We show a robust difference in the timing of release for chemical solutions containing elevated K(+) (7 ± 3 min), when compared to insulin (19 ± 7 min) (p < 0.000 01).

Microfluidic technologies for accelerating the clinical translation of nanoparticles

Using nanoparticles for therapy and imaging holds tremendous promise for the treatment of major diseases such as cancer. However, their translation into the clinic has been slow because it remains difficult to produce nanoparticles that are consistent 'batch-to-batch', and in sufficient quantities for clinical research. Moreover, platforms for rapid screening of nanoparticles are still lacking. Recent microfluidic technologies can tackle some of these issues, and offer a way to accelerate the clinical translation of nanoparticles. In this Progress Article, we highlight the advances in microfluidic systems that can synthesize libraries of nanoparticles in a well-controlled, reproducible and high-throughput manner. We also discuss the use of microfluidics for rapidly evaluating nanoparticles in vitro under microenvironments that mimic the in vivo conditions. Furthermore, we highlight some systems that can manipulate small organisms, which could be used for evaluating the in vivo toxicity of nanoparticles or for drug screening. We conclude with a critical assessment of the near- and long-term impact of microfluidics in the field of nanomedicine.