Microfluidics and numerical simulation as methods for standardization of zebrafish sperm cell activation

Parental (F0) exposure to Cadmium and Ketoprofen induces developmental deformities in offspring (F1): A transgenerational toxicity assessment in zebrafish model

In the aquatic environment, the primary pollutants of heavy metals and pharmaceuticals always occur in coexisting forms, and the research about combined impacts remains unclear, especially transgenerational effects. Cadmium (Cd) is a heavy metal that can damage the endocrine reproduction systems and cause thyroid dysfunction in fish. Meanwhile, ketoprofen (KPF) is a nonsteroidal anti-inflammatory drug (NSAID) that can cause neurobehavioral damage and physiological impairment. However, to our knowledge, the combined exposure of Cd and KPF in transgenerational studies has not been reported. In this investigation, sexually mature zebrafish were subjected to isolated exposure and combined exposure to Cd (10 μg/L) and KPF (10 and 100 μg/L) at environmentally relevant concentrations for 42 days. In this background, breeding capacity, chemical accumulation rate in gonads, and tissue morphologies are investigated in parental fish. This is followed by examining the malformation rate, inflammation rate, and gene transcription in the F1 offspring. Our results indicate that combined exposure of Cd and KPF to the parental fish could increase the chemical accumulation rate and tissue damage in the gonads of fish and significantly reduce the breeding ability. Furthermore, these negative impacts were transmitted to its produced F1 embryos, reflected by hatching rate, body deformities, and thyroid axis-related gene transcription. These findings provide further insights into the harm posed by Cd in the presence of KPF to the aquatic ecosystems.

Opportunities involving microfluidics and 3D culture systems to the in vitro embryo production

Traditional methods of gamete handling, fertilization, and embryo culture often face limitations in efficiency, consistency, and the ability to closely mimic in vivo conditions. This review explores the opportunities presented by microfluidic and 3D culture systems in overcoming these challenges and enhancing in vitro embryo production. We discuss the basic principles of microfluidics, emphasizing their inherent advantages such as precise control of fluid flow, reduced reagent consumption, and high-throughput capabilities. Furthermore, we delve into microfluidic devices designed for gamete manipulation, in vitro fertilization, and embryo culture, highlighting innovations such as droplet-based microfluidics and on-chip monitoring. Next, we explore the integration of 3D culture systems, including the use of biomimetic scaffolds and organ-on-a-chip platforms, with a particular focus on the oviduct-on-a-chip. Finally, we discuss the potential of these advanced systems to improve embryo production outcomes and advance our understanding of early embryo development. By leveraging the unique capabilities of microfluidics and 3D culture systems, we foresee significant advancements in the efficiency, effectiveness, and clinical success of in vitro embryo production.

Investigating and Modelling an Engineered Millifluidic In Vitro Oocyte Maturation System Reproducing the Physiological Ovary Environment in the Sheep Model

In conventional assisted reproductive technologies (ARTs), oocytes are in vitro cultured in static conditions. Instead, dynamic systems could better mimic the physiological in vivo environment. In this study, a millifluidic in vitro oocyte maturation (mIVM) system, in a transparent bioreactor integrated with 3D printed supports, was investigated and modeled thanks to computational fluid dynamic (CFD) and oxygen convection-reaction-diffusion (CRD) models. Cumulus-oocyte complexes (COCs) from slaughtered lambs were cultured for 24 h under static (controls) or dynamic IVM in absence (native) or presence of 3D-printed devices with different shapes and assembly modes, with/without alginate filling. Nuclear chromatin configuration, mitochondria distribution patterns, and activity of in vitro matured oocytes were assessed. The native dynamic mIVM significantly reduced the maturation rate compared to the static group (p < 0.001) and metaphase II (MII) oocytes showed impaired mitochondria distribution (p < 0.05) and activity (p < 0.001). When COCs were included in a combination of concave+ring support, particularly with alginate filling, oocyte maturation and mitochondria pattern were preserved, and bioenergetic/oxidative status was improved (p < 0.05) compared to controls. Results were supported by computational models demonstrating that, in mIVM in biocompatible inserts, COCs were protected from shear stresses while ensuring physiological oxygen diffusion replicating the one occurring in vivo from capillaries.

Computer simulation of submicron fluid flows in microfluidic chips and their applications in food analysis

In recent years, countries around the world have maintained a zero-tolerance attitude toward safety problems in the food industry. In order to ensure human health, a fast, sensitive, and high-throughput analysis of food contaminants is necessary to ensure safe food products on the market. Microfluidics, as a high-efficiency and sensitive detection technology, has many advantages in the detection of food contaminants, including foodborne pathogens, pesticides, heavy metal ions, toxic substances, and so forth, especially in conjunction with a variety of submicron fluid driving methods, making food detection and analysis more efficient and accurate. This review introduces the principle of submicron fluid driving modes and discusses the driving simulation of submicron fluid in microfluidic chips. In addition, the latest developments in the application of simulation in food analysis from 2006 to 2020 are discussed, and the computer simulation of submicron fluid flow in microfluidic chips and its application and development trend in food analysis are also highlighted. The review indicates that microfluidic technology, using numerical simulation as an auxiliary tool, combined with traditional methods has greatly improved the detection and analysis of food products. In addition, microfluidics combined with a variety of control methods embodies the ability of specific, multifunctional, and sensitive detection and analysis of food products. The development of high-sensitivity, high-throughput, portable, integrated microfluidic chips will enable the technology to be applied in practice.

Exploiting Microfluidics for Extracellular Vesicle Isolation and Characterization: Potential Use for Standardized Embryo Quality Assessment

Recent decades have seen a growing interest in the study of extracellular vesicles (EVs), driven by their role in cellular communication, and potential as biomarkers of health and disease. Although it is known that embryos secrete EVs, studies on the importance of embryonic EVs are still very limited. This limitation is due mainly to small sample volumes, with low EV concentrations available for analysis, and to laborious, costly and time-consuming procedures for isolating and evaluating EVs. In this respect, microfluidics technologies represent a promising avenue for optimizing the isolation and characterization of embryonic EVs. Despite significant improvements in microfluidics for EV isolation and characterization, the use of EVs as markers of embryo quality has been held back by two key challenges: (1) the lack of specific biomarkers of embryo quality, and (2) the limited number of studies evaluating the content of embryonic EVs across embryos with varying developmental competence. Our core aim in this review is to identify the critical challenges of EV isolation and to provide seeds for future studies to implement the profiling of embryonic EVs as a diagnostic test for embryo selection. We first summarize the conventional methods for isolating EVs and contrast these with the most promising microfluidics methods. We then discuss current knowledge of embryonic EVs and their potential role as biomarkers of embryo quality. Finally, we identify key ways in which microfluidics technologies could allow researchers to overcome the challenges of embryonic EV isolation and be used as a fast, user-friendly tool for non-invasive embryo selection.

Parental Transfer of Microcystin-LR-Induced Innate Immune Dysfunction of Zebrafish: A Cross-Generational Study

Transgenerational effects of microcystin-LR (MC-LR) released by cyanobacterial blooms have become a hot topic. In the present study, adult zebrafish pairs were exposed to 0, 0.4, 2, and 10 μg/L MC-LR for 60 days and the embryos (F1 generation) were hatched without or with continued MC-LR exposures at the same concentrations until 5 days postfertilization (dpf). The results showed the existence of MC-LR both in F0 gonads and in F1 embryos and indicated that MC-LR could be transferred directly from the F0 adult fish to F1 offspring. The adverse effects on sex hormone levels, sexual development, and fecundity in F0 generation along with abnormal development in F1 offspring were observed. Furthermore, downregulation of antioxidant genes (cat, mn-sod, gpx1a) and upregulation of innate immune-related genes (tlr4a, myd88, tnfα, il1β) as well as increased proinflammation cytokine contents (TNF-α, IL-1β, IL-6) were noticed in F1 offspring without/with continued MC-LR exposures. In addition, significant differences between the two F1 embryo treatments demonstrated that continuous MC-LR exposure could result in a higher degree of inflammatory response compared to those without MC-LR exposure. Our findings revealed that MC-LR could exert cross-generational effects of immunotoxicity by inhibiting the antioxidant system and activating an inflammatory response.

Microfluidic retention of progressively motile zebrafish sperms

Genetic manipulation of zebrafish results in thousands of mutant strains and to efficiently preserve them for future use, zebrafish sperms have been cryopreserved in various cryopreservation centers. However, cryopreservation protocols are known to alter genetic entities. Therefore, there is an urgent need for an efficient method that can select morphologically superior and progressively motile zebrafish sperms after their activation for in vitro fertilization success. However, unlike those of other mammalian species, fish sperms do not take any physical or chemical cues to travel towards the egg. Their inertness towards any external cues makes the control of their orientation in a microfluidic environment difficult. In this aspect, a new microfluidic concept was demonstrated where PDMS baffles were inserted in the sidewalls to form microscale confinement creating a flow stagnation zone towards sperm retention. Two distinct microfluidic device designs were selected to evidence the improvement in sperm retention through the unique hydrodynamic feature provided by the microchannel design. Under similar flow conditions, 44% improvement was noticed for the device with a modified baffle design in terms of sperm retrieving efficiency. It was further noticed that with a flow tuning of 0.7 μL min^-1, 80% of the total sperms swimming into the retention zones was retained within a specific time window. The present work further explains the significance of the hydrodynamic dependency of zebrafish sperm kinematics that paves the way for highly efficient spermatozoan manipulation.

Workshop report: Cryopreservation of aquatic biomedical models

The genetic resources of aquatic biomedical model organisms are the products of millions of years of evolution, decades of scientific development, and hundreds of millions of dollars of research funding investment. Genetic resources (e.g., specific alleles, transgenes, or combinations) of each model organism can be considered a form of scientific wealth that can be accumulated and exchanged, typically in the form of live animals or germplasm. Large-scale maintenance of live aquatic organisms that carry these genetic resources is inefficient, costly, and risky. In situ maintenance may be substantially enhanced and backed up by combining cryopreserved germplasm repositories and genetic information systems with live animal culture. Unfortunately, cryopreservation has not advanced much beyond the status of an exploratory research for most aquatic species, lacks widespread application, and methods for successful cryopreservation remain poorly defined. For most aquatic species biological materials other than sperm or somatic cells are not comprehensively banked to represent and preserve a broad range of genetic diversity for each species. Therefore, new approaches and standardization are needed for repository-level application to ensure reproducible recovery of cryopreserved materials. Additionally, development of new technologies is needed to address preservation of novel biological materials, such as eggs and embryos of aquatic species. To address these goals, the Office of Research Infrastructure Programs (ORIP) of the National Institutes of Health (NIH) hosted the Cryopreservation of Aquatic Biomedical Models Workshop on January 7 to 8, 2017, in conjunction with the 8th Aquatic Animal Models of Human Disease Conference in Birmingham, Alabama. The goals of the workshop were to assess the status of germplasm cryopreservation in various biomedical aquatic models and allow representatives of the scientific community to develop and prioritize a consensus of specific actionable recommendations that will move the field of cryopreservation of aquatic resources forward. This workshop included sessions devoted to new approaches for cryopreservation of aquatic species, discussion of current efforts and approaches in preservation of aquatic model germplasm, consideration of needs for standardization of methods to support reproducibility, and enhancement of repository development by establishment of scalable high-throughput technologies. The following three broad recommendations were forwarded from workshop attendees: 1: Establish a comprehensive, centralized unit ("hub") to programmatically develop training for and documentation of cryopreservation methods for aquatic model systems. This would include development of species-specific protocols and approaches, outreach programs, community development and standardization, freezing services and training of the next generation of experts in aquatic cryopreservation. 2: Provide mechanisms to support innovative technical advancements that will increase the reliability, reproducibility, simplicity, throughput, and efficiency of the cryopreservation process, including vitrification and pipelines for sperm, oocytes, eggs, embryos, larvae, stem cells, and somatic cells of all aquatic species. This recommendation encompasses basic cryopreservation knowledge and engineering technology, such as microfluidics and automated processing technologies. 3: Implement mechanisms that allow the various aquatic model stock centers to increase their planning, personnel, ability to secure genetic resources and to promote interaction within an integrated, comprehensive repository network for aquatic model species repositories.

A microfluidic device for motility and osmolality analysis of zebrafish sperm

A microfluidic chip is described that facilitates research and quality control analysis of zebrafish sperm which, due to its miniscule (i.e., 2-5 μl) sample volume and short duration of motility (i.e., <1 min), present a challenge for traditional manual assessment methods. A micromixer molded in polydimethylsiloxane (PDMS) bonded to a glass substrate was used to activate sperm samples by mixing with water, initiated by the user depressing a transfer pipette connected to the chip. Sample flow in the microfluidic viewing chamber was able to be halted within 1 s, allowing for rapid analysis of the sample using established computer-assisted sperm analysis (CASA) methods. Zebrafish sperm cell activation was consistent with manual hand mixing and yielded higher values of motility at earlier time points, as well as more subtle time-dependent trends in motility, than those processed by hand. Sperm activation curves, which indicate sample quality by evaluating percentage and duration of motility at various solution osmolalities, were generated with on-chip microfabricated gold floor electrodes interrogated by impedance spectroscopy. The magnitude of admittance was linearly proportional to osmolality and was not affected by the presence of sperm cells in the vicinity of the electrodes. This device represents a pivotal step in streamlining methods for consistent, rapid assessment of sperm quality for aquatic species. The capability to rapidly activate sperm and consistently measure motility with CASA using the microfluidic device described herein will help improve the reproducibility of studies on sperm and assist development of germplasm repositories.

Addressing Reproducibility in Cryopreservation, and Considerations Necessary for Commercialization and Community Development in Support of Genetic Resources of Aquatic Species

For the past six decades a repeated cycle of developing new cryopreservation protocols or simply reinventing them to counteract a lack of reproducibility has led to hundreds of published studies that have offered little to the establishment of a genetic resources community for aquatic species. This has hampered repository development and inhibited industrial application. Most protocols were developed without standardized approaches, leading to irreproducible studies and questionable or meaningless comparisons. Thus cryopreservation of germplasm in aquatic species would greatly benefit from strategies to facilitate reproducibility. Our objectives were to: (1) identify major sources of irreproducibility across research, small-scale, repository, and commercial-scale development levels, (2) provide recommendations to address reproducibility challenges, and (3) offer suggestions on how researchers can directly influence commercial development and application of cryopreservation research. Sources of irreproducibility include lack of standardized procedural approaches, lack of standardized terminology, and lack of reporting guidelines. To address these challenges, we propose implementation of standard operating procedures (SOP), support of stock centers and internet content for development of training programs, and strengthening of the role of scientific journals and reviewers in reducing the frequency of irreproducible outcomes. Reproducibility is the foundation for quality management programs and product reliability, and therefore standardization is necessary to assure efficient transition to commercial-scale application and repository development. Progress can only be possible through community-based approaches focused on coalescence and consensus of disparate groups involved in aquatic species cryopreservation and management of genetic resources.

Fish Sperm Assessment Using Software and Cooling Devices

For gamete quality evaluation, there are innovative, rapid, and quantitative techniques that can provide useful data for aquaculture. Computerized systems for sperm analysis were developed to measure several parameters and one of the most commonly measured is the sperm motility. Initially, this computer technology was designed for mammalian species, although it can also be used for fish sperm analysis. Fish have specific features that can affect sperm assessment such as a short motility time after activation and, in some cases, adaptation to lower temperatures. Thus, it is necessary to modify both software and hardware components to make motility analysis more efficient for fish sperm analysis. For mammalian sperm, the heating plate is used to maintain optimal temperatures of spermatozoa. However, for some fish species, it is advantageous to use a lower temperature to prolong the duration of motility, since the sperm remain active for less than 2 min. Therefore, cooling devices are necessary to refrigerate samples at constant temperature over the time of analysis, including on the optical microscope. This protocol describes the analysis of fish sperm motility using software for sperm analysis and new cooling devices to optimize the results.

Exposure to tris(1,3-dichloro-2-propyl) phosphate for Two generations decreases fecundity of zebrafish at environmentally relevant concentrations

Previous studies reported that exposure to environmentally relevant concentrations of TDCIPP significantly decreased the number of cumulative eggs in zebrafish, but effects on the quantity of eggs and sperms remained unknown. Therefore, in this study, effects of TDCIPP on yolk diameter, surface morphology of eggs, sperm density and total motility were evaluated. First generation (F0) zebrafish larvae (Danio rerio) were exposed to 0, 50, 500 or 5000 ng/L tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) from 14 days post fertilization (dpf) to 120 dpf. The F0 generation of zebrafish were paired and F1 generation of embryos were collected and continuously exposed to the same concentrations of TDCIPP until 150 dpf. TDCIPP bioconcentration in the whole body as well as effects on survival and fecundity were evaluated in F1 generation. Exposure to TDCIPP resulted in an accumulation of the chemical and decreased survival of F1 generation of zebrafish. TDCIPP decreased cumulative production and changed surface morphology of eggs in females. In males, TDCIPP decreased total motility of sperm but did not affect sperm density. These effects on quality of egg and sperm might be responsible for the decreased hatching rates observed in cross mating experiments. Furthermore, TDCIPP exposure resulted in down-regulated gene expression related to gonadal development and maturation of germ cells in females or/and males, and the down-regulation was correlated to decreased fecundity. Taken together, the results suggested that exposure to TDCIPP could decrease the quantity of eggs and sperms by down-regulating the expression of genes related to gonadal development and maturation of germ cells in zebrafish.

Sperm activation through orbital and self-axis revolutions using an artificial cilia embedded serpentine microfluidic platform

The zebrafish sperm activation profoundly depends upon the homogeneous mixing of the sperm cells with its diluent in a quick succession as it alters the cell's extracellular medium and initiates their motility. Manual stirring, the traditional method for zebrafish sperm activation is tedious, time-consuming, and has a poor outcome. In this aspect, an artificial cilia embedded serpentine microfluidic is designed through which hydrodynamic factors of the microfluidic environment can be precisely regulated to harness uniform mixing, hence ensuring a superior sperm activation. To quantify the sperm motility, computer assisted sperm analysis software (CASA) was used whereas to quantify the generated flow field, micro particle image velocimetry (μPIV) was used. With this proposed microfluidic, 74.4% of the zebrafish sperm were activated which is 20% higher than its currently existing manual measurements. The μPIV analysis demonstrates that the curvature of the microchannel induces an orbital rotation to the flow field along the length of the microchannel together with the artificial cilia actuation which instigates a local rotation to the flow field of the artificial cilia location. The collective rotation in the whole flow field induce vorticity that promotes the change in temporal dynamics of the sperm cells towards their activation.

Microfluidics for cryopreservation

Cryopreservation has utility in clinical and scientific research but implementation is highly complex and includes labor-intensive cell-specific protocols for the addition/removal of cryoprotective agents and freeze-thaw cycles. Microfluidic platforms can revolutionize cryopreservation by providing new tools to manipulate and screen cells at micro/nano scales, which are presently difficult or impossible with conventional bulk approaches. This review describes applications of microfluidic tools in cell manipulation, cryoprotective agent exposure, programmed freezing/thawing, vitrification, and in situ assessment in cryopreservation, and discusses achievements and challenges, providing perspectives for future development.

Improved bovine embryo production in an oviduct-on-a-chip system: prevention of poly-spermic fertilization and parthenogenic activation

The oviduct provides the natural micro-environment for gamete interaction, fertilization and early embryo development in mammals, such as the cow. In conventional culture systems, bovine oviduct epithelial cells (BOEC) undergo a rapid loss of essential differentiated cell properties; we aimed to develop a more physiological in vitro oviduct culture system capable of supporting fertilization. U-shaped chambers were produced using stereo-lithography and mounted with polycarbonate membranes, which were used as culture inserts for primary BOECs. Cells were grown to confluence and cultured at an air-liquid interface for 4 to 6 weeks and subsequently either fixed for immune staining, incubated with sperm cells for live-cell imaging, or used in an oocyte penetration study. Confluent BOEC cultures maintained polarization and differentiation status for at least 6 weeks. When sperm and oocytes were introduced into the system, the BOECs supported oocyte penetration in the absence of artificial sperm capacitation factors while also preventing polyspermy and parthenogenic activation, both of which occur in classical in vitro fertilization systems. Moreover, this "oviduct-on-a-chip" allowed live imaging of sperm-oviduct epithelium binding and release. Taken together, we describe for the first time the use of 3D-printing as a step further on bio-mimicking the oviduct, with polarized and differentiated BOECs in a tubular shape that can be perfused or manipulated, which is suitable for live imaging and supports in vitro fertilization.

Designing 3-Dimensional In Vitro Oviduct Culture Systems to Study Mammalian Fertilization and Embryo Production

The oviduct was long considered a largely passive conduit for gametes and embryos. However, an increasing number of studies into oviduct physiology have demonstrated that it specifically and significantly influences gamete interaction, fertilization and early embryo development. While oviduct epithelial cell (OEC) function has been examined during maintenance in conventional tissue culture dishes, cells seeded into these two-dimensional (2-D) conditions suffer a rapid loss of differentiated OEC characteristics, such as ciliation and secretory activity. Recently, three-dimensional (3-D) cell culture systems have been developed that make use of cell inserts to create basolateral and apical medium compartments with a confluent epithelial cell layer at the interface. Using such 3-D culture systems, OECs can be triggered to redevelop typical differentiated cell properties and levels of tissue organization can be developed that are not possible in a 2-D culture. 3-D culture systems can be further refined using new micro-engineering techniques (including microfluidics and 3-D printing) which can be used to produce ‘organs-on-chips’, i.e. live 3-D cultures that bio-mimic the oviduct. In this review, concepts for designing bio-mimic 3-D oviduct cultures are presented. The increased possibilities and concomitant challenges when trying to more closely investigate oviduct physiology, gamete activation, fertilization and embryo production are discussed.

Three-dimensional printing with polylactic acid (PLA) thermoplastic offers new opportunities for cryobiology

Development of devices through design, prototyping, testing, and fabrication is especially necessary for enhancement of research and eventual application in cryobiology. The advent of 3-dimensional printing offers unique opportunities for this process, given that the materials involved are suitable for use in cryogenic temperatures. We report herein that 3-D printing with polylactic acid (PLA) thermoplastic is ideally suited for cryobiology device development. Devices that are designed and standardized in open-source fashion can be electronically distributed and created locally on increasingly affordable 3-D printers, and can accelerate cryobiology findings and improve reproducibility of results.