A student team in a University of Michigan biomedical engineering design course constructs a microfluidic bioreactor for studies of zebrafish development

A fluidic platform for mobility evaluation of zebrafish with gene deficiency

Introduction

Zebrafish is a suitable animal model for molecular genetic tests and drug discovery due to its characteristics including optical transparency, genetic manipulability, genetic similarity to humans, and cost-effectiveness. Mobility of the zebrafish reflects pathological conditions leading to brain disorders, disrupted motor functions, and sensitivity to environmental challenges. However, it remains technologically challenging to quantitively assess zebrafish's mobility in a flowing environment and simultaneously monitor cellular behavior in vivo.

Methods

We herein developed a facile fluidic device using mechanical vibration to controllably generate various flow patterns in a droplet housing single zebrafish, which mimics its dynamically flowing habitats.

Results

We observe that in the four recirculating flow patterns, there are two equilibrium stagnation positions for zebrafish constrained in the droplet, i.e., the “source” with the outward flow and the “sink” with the inward flow. Wild-type zebrafish, whose mobility remains intact, tend to swim against the flow and fight to stay at the source point. A slight deviation from streamline leads to an increased torque pushing the zebrafish further away, whereas zebrafish with motor neuron dysfunction caused by lipin-1 deficiency are forced to stay in the “sink,” where both their head and tail align with the flow direction. Deviation angle from the source point can, therefore, be used to quantify the mobility of zebrafish under flowing environmental conditions. Moreover, in a droplet of comparable size, single zebrafish can be effectively restrained for high-resolution imaging.

Conclusion

Using the proposed methodology, zebrafish mobility reflecting pathological symptoms can be quantitively investigated and directly linked to cellular behavior in vivo.

"Learning on a chip:" Microfluidics for formal and informal science education

Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.

Microfluidic devices for embryonic and larval zebrafish studies

Zebrafish or Danio rerio is an established model organism for studying the genetic, neuronal and behavioral bases of diseases and for toxicology and drug screening. The embryonic and larval stages of zebrafish have been used extensively in fundamental and applied research due to advantages offered such as body transparency, small size, low cost of cultivation and high genetic homology with humans. However, the manual experimental methods used for handling and investigating this organism are limited due to their low throughput, labor intensiveness and inaccuracy in delivering external stimuli to the zebrafish while quantifying various neuronal and behavioral responses. Microfluidic and lab-on-a-chip devices have emerged as ideal technologies to overcome these challenges. In this review paper, the current microfluidic approaches for investigation of behavior and neurobiology of zebrafish at embryonic and larval stages will be reviewed. Our focus will be to provide an overview of the microfluidic methods used to manipulate (deliver and orient), immobilize and expose or inject zebrafish embryos or larvae, followed by quantification of their responses in terms of neuron activities and movement. We will also provide our opinion in terms of the direction that the field of zebrafish microfluidics is heading toward in the area of biomedical engineering.

Microstructured Devices for Optimized Microinjection and Imaging of Zebrafish Larvae

Zebrafish have emerged as a powerful model of various human diseases and a useful tool for an increasing range of experimental studies, spanning fundamental developmental biology through to large-scale genetic and chemical screens. However, many experiments, especially those related to infection and xenograft models, rely on microinjection and imaging of embryos and larvae, which are laborious techniques that require skill and expertise. To improve the precision and throughput of current microinjection techniques, we developed a series of microstructured devices to orient and stabilize zebrafish embryos at 2 days post fertilization (dpf) in ventral, dorsal, or lateral orientation prior to the procedure. To aid in the imaging of embryos, we also designed a simple device with channels that orient 4 zebrafish laterally in parallel against a glass cover slip. Together, the tools that we present here demonstrate the effectiveness of photolithographic approaches to generate useful devices for the optimization of zebrafish techniques.

The role of jab1, a putative downstream effector of the neurotrophic cytokine macrophage migration inhibitory factor (MIF) in zebrafish inner ear hair cell development

Macrophage migration inhibitory factor (MIF) is a neurotrophic cytokine essential for inner ear hair cell (HC) development and statoacoustic ganglion (SAG) neurite outgrowth, and SAG survival in mouse, chick and zebrafish. Another neurotrophic cytokine, Monocyte chemoattractant protein 1 (MCP1) is known to synergize with MIF; but MCP1 alone is insufficient to support mouse/chick SAG neurite outgrowth or neuronal survival. Because of the relatively short time over which the zebrafish inner ear develops (~30hpf), the living zebrafish embryo is an ideal system to examine mif and mcp1 cytokine pathways and interactions. We used a novel technique: direct delivery of antisense oligonucleotide morpholinos (MOs) into the embryonic zebrafish otocyst to discover downstream effectors of mif as well as to clarify the relationship between mif and mcp1 in inner ear development. MOs for mif, mcp1 and the presumptive mif and mcp1 effector, c-Jun activation domain-binding protein-1 (jab1), were injected and then electroporated into the zebrafish otocyst 25-48hours post fertilization (hpf). We found that although mif is important at early stages (before 30hpf) for auditory macular HC development, jab1 is more critical for vestibular macular HC development before 30hpf. After 30hpf, mcp1 becomes important for HC development in both maculae.

Microstructured Surface Arrays for Injection of Zebrafish Larvae

Microinjection of zebrafish larvae is an essential technique for delivery of treatments, dyes, microbes, and xenotransplantation into various tissues. Although a number of casts are available to orient embryos at the single-cell stage, no device has been specifically designed to position hatching-stage larvae for microinjection of different tissues. In this study, we present a reusable silicone device consisting of arrayed microstructures, designed to immobilize 2 days postfertilization larvae in lateral, ventral, and dorsal orientations, while providing maximal access to target sites for microinjection. Injection of rhodamine dextran was used to demonstrate the utility of this device for precise microinjection of multiple anatomical targets.

Fish-on-a-chip: microfluidics for zebrafish research

High-efficiency zebrafish (embryo) handling platforms are crucially needed to facilitate the deciphering of the increasingly expanding vertebrate-organism model values. However, the manipulation platforms for zebrafish are scarce and rely mainly on the conventional "static" microtiter plates or glass slides with rigid gel, which limits the dynamic, three-dimensional (3D), tissue/organ-oriented information acquisition from the intact larva with normal developmental dynamics. In addition, these routine platforms are not amenable to high-throughput handling of such swimming multicellular biological entities at the single-organism level and incapable of precisely controlling the growth microenvironment by delivering stimuli in a well-defined spatiotemporal fashion. Recently, microfluidics has been developed to address these technical challenges via tailor-engineered microscale structures or structured arrays, which integrate with or interface to functional components (e.g. imaging systems), allowing quantitative readouts of small objects (zebrafish larvae and embryos) under normal physiological conditions. Here, we critically review the recent progress on zebrafish manipulation, imaging and phenotype readouts of external stimuli using these microfluidic tools and discuss the challenges that confront these promising "fish-on-a-chip" technologies. We also provide an outlook on future potential trends in this field by combining with bionanoprobes and biosensors.

Comparative toxicity of lead (Pb(2+)), copper (Cu(2+)), and mixtures of lead and copper to zebrafish embryos on a microfluidic chip

Investigations were conducted to determine acute effects of Pb(2+) and Cu(2+) presented individually and collectively on zebrafish embryos. Aquatic safety testing requires a cheap, fast, and highly efficient platform for real-time evaluation of single and mixture of metal toxicity. In this study, we have developed a microfluidic system for phenotype-based evaluation of toxic effects of Pb(2+) and Cu(2+) using zebrafish (Danio rerio) embryos. The microfluidic chip is composed of a disc-shaped concentration gradient generator and 24 culture chambers, which can generate one blank solution, seven mixture concentrations, and eight single concentrations for each metal solution, thus enabling the assessment of zebrafish embryos. To test the accuracy of this new chip platform, we have examined the toxicity and teratogenicity of Pb(2+) and Cu(2+) on embryos. The individual and combined impact of Pb(2+) and Cu(2+) on zebrafish embryonic development was quantitatively assessed by recording a series of physiological indicators, such as spontaneous motion at 22 hours post fertilization (hpf), mortality at 24 hpf, heartbeat and body length at 96 hpf, etc. It was found that Pb(2+) or Cu(2+) could induce deformity and cardiovascular toxicity in zebrafish embryos and the mixture could induce more severe toxicity. This chip is a multiplexed testing apparatus that allows for the examination of toxicity and teratogenicity for substances and it also can be used as a potentially cost-effective and rapid aquatic safety assessment tool.

Fishing on chips: up-and-coming technological advances in analysis of zebrafish and Xenopus embryos

Biotests performed on small vertebrate model organisms provide significant investigative advantages as compared with bioassays that employ cell lines, isolated primary cells, or tissue samples. The main advantage offered by whole-organism approaches is that the effects under study occur in the context of intact physiological milieu, with all its intercellular and multisystem interactions. The gap between the high-throughput cell-based in vitro assays and low-throughput, disproportionally expensive and ethically controversial mammal in vivo tests can be closed by small model organisms such as zebrafish or Xenopus. The optical transparency of their tissues, the ease of genetic manipulation and straightforward husbandry, explain the growing popularity of these model organisms. Nevertheless, despite the potential for miniaturization, automation and subsequent increase in throughput of experimental setups, the manipulation, dispensing and analysis of living fish and frog embryos remain labor-intensive. Recently, a new generation of miniaturized chip-based devices have been developed for zebrafish and Xenopus embryo on-chip culture and experimentation. In this work, we review the critical developments in the field of Lab-on-a-Chip devices designed to alleviate the limits of traditional platforms for studies on zebrafish and clawed frog embryo and larvae. © 2014 International Society for Advancement of Cytometry.

Zebrafish on a chip: a novel platform for real-time monitoring of drug-induced developmental toxicity

Pharmaceutical safety testing requires a cheap, fast and highly efficient platform for real-time evaluation of drug toxicity and secondary effects. In this study, we have developed a microfluidic system for phenotype-based evaluation of toxic and teratogenic effects of drugs using zebrafish (Danio rerio) embryos and larvae as the model organism. The microfluidic chip is composed of two independent functional units, enabling the assessment of zebrafish embryos and larvae. Each unit consists of a fluidic concentration gradient generator and a row of seven culture chambers to accommodate zebrafish. To test the accuracy of this new chip platform, we examined the toxicity and teratogenicity of an anti-asthmatic agent-aminophylline (Apl) on 210 embryos and 210 larvae (10 individuals per chamber). The effect of Apl on zebrafish embryonic development was quantitatively assessed by recording a series of physiological indicators such as heart rate, survival rate, body length and hatch rate. Most importantly, a new index called clonic convulsion rate, combined with mortality was used to evaluate the toxicities of Apl on zebrafish larvae. We found that Apl can induce deformity and cardiovascular toxicity in both zebrafish embryos and larvae. This microdevice is a multiplexed testing apparatus that allows for the examination of indexes beyond toxicity and teratogenicity at the sub-organ and cellular levels and provides a potentially cost-effective and rapid pharmaceutical safety assessment tool.

Microfluidic tools for developmental studies of small model organisms--nematodes, fruit flies, and zebrafish

Studying the genetics of development with small model organisms such as the zebrafish (Danio Rerio), the fruit fly (Drosophila melanogaster), and the soil-dwelling nematode (Caenorhabditis elegans), provide unique opportunities for understanding related processes and diseases in humans. These model organisms also have potential for use in drug discovery and toxicity-screening applications. There have been sweeping developments in microfabrication and microfluidic technologies for manipulating and imaging small objects, including small model organisms, which allow high-throughput quantitative biological studies. Here, we review recent progress in microfluidic tools able to manipulate small organisms and project future directions and applications of these techniques and technologies.

Fish and Chips: a microfluidic perfusion platform for monitoring zebrafish development

We have developed a multi-channel microfluidic perfusion platform for culturing zebrafish embryos and capturing live images of various tissues and organs inside the embryo. The Fish and Chips was micro-fabricated in silicon and glass for reproducibility and accuracy of the microfluidic structure. The microfluidic platform consists of three parts: a microfluidic gradient generator, a row of eight fish tanks, in which the fish embryos are individually placed, and eight output channels. The fluidic gradient generator supports dose-dependent drug and chemical studies. A unique perfusion system ensures a uniform and constant flow of media to the fish tank while the wastes are efficiently removed. The fish tanks restrict the embryo movements, except rotationally, for live imaging of internal tissues and organs. The embryos showed developmental abnormalities under the influence of the drug valproic acid (VPA).

Zebrafish embryos and larvae: a new generation of disease models and drug screens

Technological innovation has helped the zebrafish embryo gain ground as a disease model and an assay system for drug screening. Here, we review the use of zebrafish embryos and early larvae in applied biomedical research, using selected cases. We look at the use of zebrafish embryos as disease models, taking fetal alcohol syndrome and tuberculosis as examples. We discuss advances in imaging, in culture techniques (including microfluidics), and in drug delivery (including new techniques for the robotic injection of compounds into the egg). The use of zebrafish embryos in early stages of drug safety-screening is discussed. So too are the new behavioral assays that are being adapted from rodent research for use in zebrafish embryos, and which may become relevant in validating the effects of neuroactive compounds such as anxiolytics and antidepressants. Readouts, such as morphological screening and cardiac function, are examined. There are several drawbacks in the zebrafish model. One is its very rapid development, which means that screening with zebrafish is analogous to "screening on a run-away train." Therefore, we argue that zebrafish embryos need to be precisely staged when used in acute assays, so as to ensure a consistent window of developmental exposure. We believe that zebrafish embryo screens can be used in the pre-regulatory phases of drug development, although more validation studies are needed to overcome industry scepticism. Finally, the zebrafish poses no challenge to the position of rodent models: it is complementary to them, especially in early stages of drug research.

An integrated microfluidic array system for evaluating toxicity and teratogenicity of drugs on embryonic zebrafish developmental dynamics

Seeking potential toxic and side effects for clinically available drugs is considerably beneficial in pharmaceutical safety evaluation. In this article, the authors developed an integrated microfluidic array system for phenotype-based evaluation of toxic and teratogenic potentials of clinical drugs by using zebrafish (Danio rerio) embryos as organism models. The microfluidic chip consists of a concentration gradient generator from upstream and an array of open embryonic culture structures by offering continuous stimulation in gradients and providing guiding, cultivation and exposure to the embryos, respectively. The open culture reservoirs are amenable to long-term embryonic culturing. Gradient test substances were delivered in a continuous or a developmental stage-specific manner, to induce embryos to generate dynamic developmental toxicity and teratogenicity. Developmental toxicity of doxorubicin on zebrafish eggs were quantitatively assessed via heart rate, and teratological effects were characterized by pericardial impairment, tail fin, notochord, and SV-BA distance ∕body length. By scoring the teratogenic severity, we precisely evaluated the time- and dose-dependent damage on the chemical-exposed embryos. The simple and easily operated method presented herein demonstrates that zebrafish embryo-based pharmaceutic assessment could be performed using microfluidic systems and holds a great potential in high-throughput screening for new compounds at single animal resolution.

Zebrafish embryo development in a microfluidic flow-through system

The zebrafish embryo is a small, cheap, whole-animal model which may replace rodents in some areas of research. Unfortunately, zebrafish embryos are commonly cultured in microtitre plates using cell-culture protocols with static buffer replacement. Such protocols are highly invasive, consume large quantities of reagents and do not readily permit high-quality imaging. Zebrafish and rodent embryos have previously been cultured in static microfluidic drops, and zebrafish embryos have also been raised in a prototype polydimethylsiloxane setup in a Petri dish. Other than this, no animal embryo has ever been shown to undergo embryonic development in a microfluidic flow-through system. We have developed and prototyped a specialized lab-on-a-chip made from bonded layers of borosilicate glass. We find that zebrafish embryos can develop in the chip for 5 days, with continuous buffer flow at pressures of 0.005-0.04 MPa. Phenotypic effects were seen, but these were scored subjectively as 'minor'. Survival rates of 100% could be reached with buffer flows of 2 µL per well per min. High-quality imaging was possible. An acute ethanol exposure test in the chip replicated the same assay performed in microtitre plates. More than 100 embryos could be cultured in an area, excluding infrastructure, smaller than a credit card. We discuss how biochip technology, coupled with zebrafish larvae, could allow biological research to be conducted in massive, parallel experiments, at high speed and low cost.