Microfluidic method reduces osmotic stress injury to oocytes during cryoprotectant addition and removal processes in porcine oocytes

A compact, high-throughput semi-automated embryo vitrification system based on hydrogel

RESEARCH QUESTION

What is the efficiency and efficacy of the novel Biorocks semi-automated vitrification system, which is based on a hydrogel?

DESIGN

This comparative experimental laboratory study used mouse model and human day 6 blastocysts. Mouse oocytes and embryos were quality assessed post-vitrification.

RESULTS

The Biorocks system successfully automated the solution exchanges during the vitrification process, achieving a significantly improved throughput of up to 36 embryos/oocytes per hour. Using hydrogel for cryoprotective agent delivery, 12 vessels could be processed simultaneously, fitting comfortably within an assisted reproductive technology (ART) workstation. In tests involving the cryopreservation of oocytes and embryos, the system yielded outcomes equivalent to the manual Cryotop method. For example, the survival rate for mouse oocytes was 98% with the Biorocks vitrification system (n = 46) and 95% for the manual Cryotop method (n = 39), of which 46% and 41%, respectively, progressed to blastocysts on day 5 after IVF. CC-grade day 6 human blastocysts processed with the Biorocks system (n = 39) were associated with a 92% 2 h re-expansion rate, equivalent to the 90% with Cryotop (n = 30). The cooling/warming rates achieved by the Biorocks system were 31,900°C/minute and 24,700°C/minute, respectively. Oocyte quality was comparable or better post-vitrification for Biorocks than Cryotop.

CONCLUSIONS

The Biorocks semi-automated vitrification system offers enhanced throughput without compromising the survival and developmental potential of oocytes and embryos. This innovative system may help to increase the efficiency and standardization of vitrification in ART clinics. Further investigations are needed to confirm its efficacy in a broader clinical context.

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.

New Cryoprotectant Loading Method for Cell Droplet Vitrification with Continuous Evaporation

Droplet-based vitrification is considered to be a promising cryopreservation method, which achieves high cell viability through high cooling rates and low concentrations of cryoprotective agents (CPAs). However, the droplet vitrification cryopreservation process needs in-depth research, such as the balance of the CPA concentration and the cooling rate, the CPA loading process, and the droplet encapsulation method. Here, we developed a chip with a high cooling rate for vitrification droplet encapsulation and provided a new method for continuous loading of low-concentration CPA droplets by evaporation. The results showed that the CPA droplet volume decreased exponentially with the evaporation time, and the larger the initial droplet size, the longer the evaporation time to achieve the critical vitrification concentration. There was no significant difference in the viability of MSCs, NHEK, and A549 cells between the evaporation loading vitrification method and the traditional slow freezing method, but the former was easier to operate and can balance the cooling rate and concentration by controlling the evaporation time. Moreover, a theoretical model was proposed to predict the CPA concentration inside the microdroplets dependent on the evaporation time. The current work provides a potential method to load low-concentration CPAs for cell vitrification preservation, which is more beneficial for cell therapy and other regenerative medicine applications.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Development of an Open Microfluidic Platform for Oocyte One-Stop Vitrification with Cryotop Method

Oocyte vitrification technology is widely used for assisted reproduction and fertility preservation, which requires precise washing sequences and timings of cryoprotectant agents (CPAs) treatment to relieve the osmotic shock to cells. The gold standard Cryotop method is extensively used in oocyte vitrification and is currently the most commonly used method in reproductive centers. However, the Cryotop method requires precise and complex manual manipulation by an embryologist, whose proficiency directly determines the effect of vitrification. Therefore, in this study, an automatic microfluidic system consisting of a novel open microfluidic chip and a set of automatic devices was established as a standardized operating protocol to facilitate the conventional manual Cryotop method and minimize the osmotic shock applied to the oocyte. The proposed open microfluidic system could smoothly change the CPA concentration around the oocyte during vitrification pretreatment, and transferred the treated oocyte to the Cryotop with a tiny droplet. The system better conformed to the operating habits of embryologists, whereas the integration of commercialized Cryotop facilitates the subsequent freezing and thawing processes. With standardized operating procedures, our system provides consistent treatment effects for each operation, leading to comparable survival rate, mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) level of oocytes to the manual Cryotop operations. The vitrification platform is the first reported microfluidic system integrating the function of cells transfer from the processing chip, which avoids the risk of cell loss or damage in a manual operation and ensures the sufficient cooling rate during liquid nitrogen (LN2) freezing. Our study demonstrates significant potential of the automatic microfluidic approach to serve as a facile and universal solution for the vitrification of various precious cells.

Thermally conductive graphene-based nanofluids, a novel class of cryosolutions for mouse blastocysts vitrification

Limited heating and cooling rates have long been recognized as bottlenecks in improving embryo cryopreservation. As a result, efforts to achieve higher heat transfer rates gave rise to milestones like open cryodevices and minimal media loading. A crucial but commonly ignored variable is heat conduction by cryosolutions. The low heat conductivity of the aqueous media surrounding embryos slows down cooling and heating rates of the embryo, imposing the risk of preventable damages. In this study, we introduce a novel thermally conductive cryosolution based on graphene oxide nanoparticles and test its performance against conventional sucrose-based solutions for vitrification of mouse blastocysts. Replacing sucrose with graphene oxide brought about similar re-expansion, hatching, and implantation rates of post-vitrification embryos while also preventing an array of cellular and molecular stresses. Our results showed significantly reduced oxidative stress, characterized by control-level expression of Sod1 and significant downregulation of Sod2 transcription when graphene oxide was used instead of sucrose. This molecular response was in agreement with the reduced level of reactive oxygen species produced in vitrified/warmed embryos using graphene-based solutions. The downstream impacts of this stress reduction manifested in significant downregulation of two major pro-apoptotic genes, Bax and Trp53, down to the same level as fresh embryos. Interestingly, embryos maintained their spherical shape during dehydration in graphene-based solutions and did not "collapse" when shrinking, like in sucrose-based solutions. These results provide new insights into the benefits of thermally conductive cryosolutions and showcase the potential of graphene oxide as a cryoprotectant in embryo vitrification.

The Future of IVF: The New Normal in Human Reproduction

Increased demand for in vitro fertilization (IVF) due to socio-demographic trends, and supply facilitated by new technologies, converged to transform the way a substantial proportion of humans reproduce. The purpose of this article is to describe the societal and demographic trends driving increased worldwide demand for IVF, as well as to provide an overview of emerging technologies that promise to greatly expand IVF utilization and lower its cost.

Challenges and Considerations during In Vitro Production of Porcine Embryos

Genetically modified pigs have become valuable tools for generating advances in animal agriculture and human medicine. Importantly, in vitro production and manipulation of embryos is an essential step in the process of creating porcine models. As the in vitro environment is still suboptimal, it is imperative to examine the porcine embryo culture system from several angles to identify methods for improvement. Understanding metabolic characteristics of porcine embryos and considering comparisons with other mammalian species is useful for optimizing culture media formulations. Furthermore, stressors arising from the environment and maternal or paternal factors must be taken into consideration to produce healthy embryos in vitro. In this review, we progress stepwise through in vitro oocyte maturation, fertilization, and embryo culture in pigs to assess the status of current culture systems and address points where improvements can be made.

Toward embryo cryopreservation-on-a-chip: A standalone microfluidic platform for gradual loading of cryoprotectants to minimize cryoinjuries

Embryo vitrification is a fundamental practice in assisted reproduction and fertility preservation. A key step of this process is replacing the internal water with cryoprotectants (CPAs) by transferring embryos from an isotonic to a hypertonic solution of CPAs. However, this applies an abrupt osmotic shock to embryos, resulting in molecular damages that have long been a source of concern. In this study, we introduce a standalone microfluidic system to automate the manual process and minimize the osmotic shock applied to embryos. This device provides the same final CPA concentrations as the manual method but with a gradual increase over time instead of sudden increases. Our system allows the introduction of the dehydrating non-permeating CPA, sucrose, from the onset of CPA-water exchange, which in turn reduced the required time of CPA loading for successful vitrification without compromising its outcomes. We compared the efficacy of our device and the conventional manual procedure by studying vitrified-warmed mouse blastocysts based on their re-expansion and hatching rates and transcription pattern of selected genes involved in endoplasmic reticulum stress, oxidative stress, heat shock, and apoptosis. While both groups of embryos showed comparable re-expansion and hatching rates, on-chip loading reduced the detrimental gene expression of cryopreservation. The device developed here allowed us to automate the CPA loading process and push the boundaries of cryopreservation by minimizing its osmotic stress, shortening the overall process, and reducing its molecular footprint.

Understanding and Assisting Reproduction in Wildlife Species Using Microfluidics

Conservation breeding and assisted reproductive technologies (ARTs) are invaluable tools to save wild animal species that are on the brink of extinction. Microfluidic devices recently developed for human or domestic animal reproductive medicine could significantly help to increase knowledge about fertility and contribute to the success of ART in wildlife. Some of these microfluidic tools could be applied to wild species, but dedicated efforts will be necessary to meet specific needs in animal conservation; for example, they need to be cost-effective, applicable to multiple species, and field-friendly. Microfluidics represents only one powerful technology in a complex toolbox and must be integrated with other approaches to be impactful in managing wildlife reproduction.

Follicular extracellular vesicles enhance meiotic resumption of domestic cat vitrified oocytes

Extracellular vesicles (EVs) contain multiple factors that regulate cell and tissue function. However, understanding of their influence on gametes, including communication with the oocyte, remains limited. In the present study, we characterized the proteome of domestic cat (Felis catus) follicular fluid EVs (ffEV). To determine the influence of follicular fluid EVs on gamete cryosurvival and the ability to undergo in vitro maturation, cat oocytes were vitrified using the Cryotop method in the presence or absence of ffEV. Vitrified oocytes were thawed with or without ffEVs, assessed for survival, in vitro cultured for 26 hours and then evaluated for viability and meiotic status. Cat ffEVs had an average size of 129.3 ± 61.7 nm (mean ± SD) and characteristic doughnut shaped circular vesicles in transmission electron microscopy. Proteomic analyses of the ffEVs identified a total of 674 protein groups out of 1,974 proteins, which were classified as being involved in regulation of oxidative phosphorylation, extracellular matrix formation, oocyte meiosis, cholesterol metabolism, glycolysis/gluconeogenesis, and MAPK, PI3K-AKT, HIPPO and calcium signaling pathways. Furthermore, several chaperone proteins associated with the responses to osmotic and thermal stresses were also identified. There were no differences in the oocyte survival among fresh and vitrified oocyte; however, the addition of ffEVs to vitrification and/or thawing media enhanced the ability of frozen-thawed oocytes to resume meiosis. In summary, this study is the first to characterize protein content of cat ffEVs and their potential roles in sustaining meiotic competence of cryopreserved oocytes.

From Extremely Water-Repellent Coatings to Passive Icing Protection—Principles, Limitations and Innovative Application Aspects

The severe environmental conditions in winter seasons and/or cold climate regions cause many inconveniences in our routine daily-life, related to blocked road infrastructure, interrupted overhead telecommunication, internet and high-voltage power lines or cancelled flights due to excessive ice and snow accumulation. With the tremendous and nature-inspired development of physical, chemical and engineering sciences in the last few decades, novel strategies for passively combating the atmospheric and condensation icing have been put forward. The primary objective of this review is to reveal comprehensively the major physical mechanisms regulating the ice accretion on solid surfaces and summarize the most important scientific breakthroughs in the field of functional icephobic coatings. Following this framework, the present article introduces the most relevant concepts used to understand the incipiency of ice nuclei at solid surfaces and the pathways of water freezing, considers the criteria that a given material has to meet in order to be labelled as icephobic and clarifies the modus operandi of superhydrophobic (extremely water-repellent) coatings for passive icing protection. Finally, the limitations of existing superhydrophobic/icephobic materials, various possibilities for their unconventional practical applicability in cryobiology and some novel hybrid anti-icing systems are discussed in detail.