Live sperm trap microarray for high throughput imaging and analysis

Microfluidic sperm trap array for single-cell flagellar analysis with unrestricted 2D flagellar movement

Sperm capture techniques that immobilize sperm to halt their motility are essential for the long-term analysis of individual sperm. These techniques are beneficial in assisted reproductive technologies such as intracytoplasmic sperm injection (ICSI) by allowing selective screening of sperm. However, there is a notable lack of high-throughput and non-destructive sperm capture methods that allow the flagellum to beat freely, which is crucial for accurately reflecting the behavior of unfettered, freely swimming sperm. To bridge this gap, we introduce a novel microfluidic device specifically engineered to capture sperm without restricting flagellar motion. The design utilizes sperm's innate boundary-following behavior in both 3D and 2D environments to direct them into a capture zone. Once captured, the sperm head is restrained while the flagellum remains free to exhibit natural beating patterns. Utilizing this device, we explore the effects of hyperactivating agents, temperature, and their combined influence on the dynamics of bovine sperm flagella. The unrestricted flagellar motion offered by our device yields two prominent advantages: it mirrors the flagellar behavior of free-swimming sperm, ensuring research findings are consistent with natural sperm activity, and it prevents imaging overlap between the flagellum and the capture structures, simplifying the automation of flagellar tracking and analysis. This technological advancement facilitates the collection of waveform parameters along the entire flagellum, addressing inconsistencies that have arisen in previous research due to differing measurement sites, and enabling precise extraction of sperm behavioral properties.

Microfluidics as an emerging paradigm for assisted reproductive technology: A sperm separation perspective

Millions of people are subject to infertility worldwide and one in every six people, regardless of gender, experiences infertility at some period in their life, according to the World Health Organization. Assisted reproductive technologies are defined as a set of procedures that can address the infertility issue among couples, culminating in the alleviation of the condition. However, the costly conventional procedures of assisted reproduction and the inherent vagaries of the processes involved represent a setback for its successful implementation. Microfluidics, an emerging tool for processing low-volume samples, have recently started to play a role in infertility diagnosis and treatment. Given its host of benefits, including manipulating cells at the microscale, repeatability, automation, and superior biocompatibility, microfluidics have been adopted for various procedures in assisted reproduction, ranging from sperm sorting and analysis to more advanced processes such as IVF-on-a-chip. In this review, we try to adopt a more holistic approach and cover different uses of microfluidics for a variety of applications, specifically aimed at sperm separation and analysis. We present various sperm separation microfluidic techniques, categorized as natural and non-natural methods. A few of the recent developments in on-chip fertilization are also discussed.

Microfluidic platform for omics analysis on single cells with diverse morphology and size: A review

BACKGROUND

Microfluidic techniques have emerged as powerful tools in single-cell research, facilitating the exploration of omics information from individual cells. Cell morphology is crucial for gene expression and physiological processes. However, there is currently a lack of integrated analysis of morphology and single-cell omics information. A critical challenge remains: what platform technologies are the best option to decode omics data of cells that are complex in morphology and size?

RESULTS

This review highlights achievements in microfluidic-based single-cell omics and isolation of cells based on morphology, along with other cell sorting methods based on physical characteristics. Various microfluidic platforms for single-cell isolation are systematically presented, showcasing their diversity and adaptability. The discussion focuses on microfluidic devices tailored to the distinct single-cell isolation requirements in plants and animals, emphasizing the significance of considering cell morphology and cell size in optimizing single-cell omics strategies. Simultaneously, it explores the application of microfluidic single-cell sorting technologies to single-cell sequencing, aiming to effectively integrate information about cell shape and size.

SIGNIFICANCE AND NOVELTY

The novelty lies in presenting a comprehensive overview of recent accomplishments in microfluidic-based single-cell omics, emphasizing the integration of different microfluidic platforms and their implications for cell morphology-based isolation. By underscoring the pivotal role of the specialized morphology of different cells in single-cell research, this review provides robust support for delving deeper into the exploration of single-cell omics data.

Microfluidic chip as a promising evaluation method in assisted reproduction: A systematic review

The aim of assisted reproductive technology (ART) is to select the high-quality sperm, oocytes, and embryos, and finally achieve a successful pregnancy. However, functional evaluation is hindered by intra- and inter-operator variability. Microfluidic chips emerge as the one of the most powerful tools to analyze biological samples for reduced size, precise control, and flexible extension. Herein, a systematic search was conducted in PubMed, Scopus, Web of Science, ScienceDirect, and IEEE Xplore databases until March 2023. We displayed and prospected all detection strategies based on microfluidics in the ART field. After full-text screening, 71 studies were identified as eligible for inclusion. The percentages of human and mouse studies equaled with 31.5%. The prominent country in terms of publication number was the USA (n = 13). Polydimethylsiloxane (n = 49) and soft lithography (n = 28) were the most commonly used material and fabrication method, respectively. All articles were classified into three types: sperm (n = 38), oocytes (n = 20), and embryos (n = 13). The assessment contents included motility, counting, mechanics, permeability, impedance, secretion, oxygen consumption, and metabolism. Collectively, the microfluidic chip technology facilitates more efficient, accurate, and objective evaluation in ART. It can even be combined with artificial intelligence to assist the daily activities of embryologists. More well-designed clinical studies and affordable integrated microfluidic chips are needed to validate the safety, efficacy, and reproducibility. Trial registration: The protocol was registered in the Open Science Frame REGISTRIES (identification: osf.io/6rv4a).

Lab-on-chip (LoC) application for quality sperm selection: An undelivered promise?

Quality sperm selection is essential to ensure the effectiveness of assisted reproductive techniques (ART). However, the methods employed for sperm selection in ART often yield suboptimal outcomes, contributing to lower success rates. In recent years, microfluidic devices have emerged as a promising avenue for investigating the natural swimming behavior of spermatozoa and developing innovative approaches for quality sperm selection. Despite their potential, the commercial translation of microfluidic-based technologies has remained limited. This comprehensive review aims to critically evaluate the inherent potential of lab-on-chip technology in unraveling sophisticated mechanisms encompassing rheotaxis, thermotaxis, and chemotaxis. By reviewing the current state-of-the-art associated with microfluidic engineering and the swimming of spermatozoa, the goal is to shed light on the multifaceted factors that have impeded the broader commercialization of these cutting-edge technologies and recommend a commercial that can surmount the prevailing constraints. Furthermore, this scholarly exploration seeks to enlighten and actively engage reproductive clinicians in the profound potential and implications of microfluidic methodologies within the context of human infertility.

Improving outcomes of assisted reproductive technologies using artificial intelligence for sperm selection

Within the field of assisted reproductive technology, artificial intelligence has become an attractive tool for potentially improving success rates. Recently, artificial intelligence-based tools for sperm evaluation and selection during intracytoplasmic sperm injection (ICSI) have been explored, mainly to improve fertilization outcomes and decrease variability within ICSI procedures. Although significant advances have been achieved in developing algorithms that track and rank single sperm in real-time during ICSI, the clinical benefits these might have in improving pregnancy rates from a single assisted reproductive technology cycle remain to be established.

Design of a gradient-rheotaxis microfluidic chip for sorting of high-quality Sperm with progressive motility

Assisted reproductive technology (ART) is an important invention for the treatment of human infertility, and the isolation of high-quality sperm with progressive motility is one of the most critical steps that eventually affect the fertilization rate. Conventional sperm separation approaches include the swim-up method and density gradient centrifugation. However, the quality of isolated sperm obtained from both approaches can still be improved by improving sorted sperm motility, minimizing the DNA fragmentation rate, and removing abnormal phenotypes. Here, we report a Progressive Sperm Sorting Chip (PSSC) for high-quality sperm isolation. Based on the rheotaxis behavior of sperm, a gradient flow field is created in the chip for progressive sperm sorting. Clinical experiment results for 10 volunteers showed that greater than 90% of isolated sperm exhibit high motility (> 25 μm/s), high linearity (0.8), and a very low DNA fragmentation rate (< 5%). In addition, the whole process is label and chemical free. These features aid in gentle sperm sorting to obtain healthy sperm. This device uniquely enables the selection of high-quality sperm with progressive motility and might be clinically applied for infertility treatment in the near future.

Motility Assessment of Ram Spermatozoa

For successful fertilisation to occur, spermatozoa need to successfully migrate through the female reproductive tract and penetrate the oocyte. Predictably, poor sperm motility has been associated with low rates of fertilisation in many mammalian species, including the ram. As such, motility is one of the most important parameters used for in vitro evaluation of ram sperm quality and function. This review aims to outline the mechanical and energetic processes which underpin sperm motility, describe changes in motility which occur as a result of differences in sperm structure and the surrounding microenvironment, and assess the effectiveness of the various methods used to assess sperm motility in rams. Methods of subjective motility estimation are convenient, inexpensive methods widely used in the livestock industries, however, the subjective nature of these methods can make them unreliable. Computer-assisted sperm analysis (CASA) technology accurately and objectively measures sperm motility via two-dimensional tracing of sperm head motion, making it a popular method for sperm quality assurance in domesticated animal production laboratories. Newly developed methods of motility assessment including flagellar tracing, three-dimensional sperm tracing, in vivo motility assessment, and molecular assays which quantify motility-associated biomarkers, enable analysis of a new range of sperm motion parameters with the potential to reveal new mechanistic insights and improve ram semen assessment. Experimental application of these technologies is required to fully understand their potential to improve semen quality assessment and prediction of reproductive success in ovine artificial breeding programs.

A robot-assisted acoustofluidic end effector

Liquid manipulation is the foundation of most laboratory processes. For macroscale liquid handling, both do-it-yourself and commercial robotic systems are available; however, for microscale, reagents are expensive and sample preparation is difficult. Over the last decade, lab-on-a-chip (LOC) systems have come to serve for microscale liquid manipulation; however, lacking automation and multi-functionality. Despite their potential synergies, each has grown separately and no suitable interface yet exists to link macro-level robotics with micro-level LOC or microfluidic devices. Here, we present a robot-assisted acoustofluidic end effector (RAEE) system, comprising a robotic arm and an acoustofluidic end effector, that combines robotics and microfluidic functionalities. We further carried out fluid pumping, particle and zebrafish embryo trapping, and mobile mixing of complex viscous liquids. Finally, we pre-programmed the RAEE to perform automated mixing of viscous liquids in well plates, illustrating its versatility for the automatic execution of chemical processes.

Lab on a chip devices for fertility: from proof-of-concept to clinical impact

Microfluidics offers tremendous opportunities to understand the underlying biology of fertilization at the single-cell level and improve infertility management, however, its true clinical impact is yet to be realized. Lab-on-a-chip devices have generally failed to diffuse into clinical practice due to issues associated with their translation or their practicality and performance in clinical settings. In this perspective, I reflect on how the full potential of microfluidic technologies for fertility can be realized by considering regulatory and manufacturing considerations at the development stage and by redefining our developmental goals to directly target the ultimate clinical needs. I also challenge the common rationale around developing technologies for infertility treatment based on reducing cost and complexity in operation as the ultimate outcome is invaluable, human life.

Rheotaxis quality index: a new parameter that reveals male mammalian in vivo fertility and low sperm DNA fragmentation

The female reproductive tract simultaneously guides and selects high-quality sperm using rheotaxis in mammalian species. Sperm quality, however, is traditionally evaluated only by their movement velocities and concentration using computer-assisted sperm analysis (CASA), which ignores sperm rheotaxis. Here, by mimicking the female reproductive tracts' dimensions and hydrodynamic features, a new method is introduced to quantify sperm rheotaxis ability for evaluating semen quality. The combination of our RHEOtaxis quaLity indEX (RHEOLEX) and motile sperm concentration is able to predict sperm fertility levels in artificial insemination at various shear rates within 5 minutes. This means that RHEOLEX could be a biomarker for determining male in vivo fertility, unlike conventional semen quality parameters which fail to provide statistically significant predictions. In addition, a high RHEOLEX is associated with a low DNA fragmentation index (DFI), showing that this new parameter is able to identify low-DFI samples. Not only does this work highlight the importance of rheotaxis in determining male in vivo fertility, but it also provides a solid benchmark for developing fast microfluidic devices for male fertility prediction as well as DFI. Last, the data imply that the female reproductive tract might use rheotaxis to keep sperm with fragmented DNA from reaching the fertilization site.

Machine learning for sperm selection

Infertility rates and the number of couples seeking fertility care have increased worldwide over the past few decades. Over 2.5 million cycles of assisted reproductive technologies are being performed globally every year, but the success rate has remained at ~33%. Machine learning, an automated method of data analysis based on patterns and inference, is increasingly being deployed within the health-care sector to improve diagnostics and therapeutics. This technique is already aiding embryo selection in some fertility clinics, and has also been applied in research laboratories to improve sperm analysis and selection. Tremendous opportunities exist for machine learning to advance male fertility treatments. The fundamental challenge of sperm selection - selecting the most promising candidate from 10⁸ gametes - presents a challenge that is uniquely well-suited to the high-throughput capabilities of machine learning algorithms paired with modern data processing capabilities.

Rapid sperm capture: high-throughput flagellar waveform analysis

STUDY QUESTION

Can flagellar analyses be scaled up to provide automated tracking of motile sperm, and does knowledge of the flagellar waveform provide new insight not provided by routine head tracking?

SUMMARY ANSWER

High-throughput flagellar waveform tracking and analysis enable measurement of experimentally intractable quantities such as energy dissipation, disturbance of the surrounding medium and viscous stresses, which are not possible by tracking the sperm head alone.

WHAT IS KNOWN ALREADY

The clinical gold standard for sperm motility analysis comprises a manual analysis by a trained professional, with existing automated sperm diagnostics [computer-aided sperm analysis (CASA)] relying on tracking the sperm head and extrapolating measures. It is not currently possible with either of these approaches to track the sperm flagellar waveform for large numbers of cells in order to unlock the potential wealth of information enclosed within.

STUDY DESIGN, SIZE, DURATION

The software tool in this manuscript has been developed to enable high-throughput, repeatable, accurate and verifiable analysis of the sperm flagellar beat.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Using the software tool [Flagellar Analysis and Sperm Tracking (FAST)] described in this manuscript, we have analysed 176 experimental microscopy videos and have tracked the head and flagellum of 205 progressive cells in diluted semen (DSM), 119 progressive cells in a high-viscosity medium (HVM) and 42 stuck cells in a low-viscosity medium. Unscreened donors were recruited at Birmingham Women's and Children's NHS Foundation Trust after giving informed consent.

MAIN RESULTS AND THE ROLE OF CHANCE

We describe fully automated tracking and analysis of flagellar movement for large cell numbers. The analysis is demonstrated on freely motile cells in low- and high-viscosity fluids and validated on published data of tethered cells undergoing pharmacological hyperactivation. Direct analysis of the flagellar beat reveals that the CASA measure 'beat cross frequency' does not measure beat frequency; attempting to fit a straight line between the two measures gives ${\mathrm{R}}^2$ values of 0.042 and 0.00054 for cells in DSM and HVM, respectively. A new measurement, track centroid speed, is validated as an accurate differentiator of progressive motility. Coupled with fluid mechanics codes, waveform data enable extraction of experimentally intractable quantities such as energy dissipation, disturbance of the surrounding medium and viscous stresses. We provide a powerful and accessible research tool, enabling connection of the mechanical activity of the sperm to its motility and effect on its environment.

LARGE SCALE DATA

The FAST software package and all documentation can be downloaded from www.flagellarCapture.com.

LIMITATIONS, REASONS FOR CAUTION

The FAST software package has only been tested for use with negative phase contrast microscopy. Other imaging modalities, with bright cells on a dark background, have not been tested but may work. FAST is not designed to analyse raw semen; it is specifically for precise analysis of flagellar kinematics, as that is the promising area for computer use. Flagellar capture will always require that cells are at a dilution where their paths do not frequently cross.

WIDER IMPLICATIONS OF THE FINDINGS

Combining tracked flagella with mathematical modelling has the potential to reveal new mechanistic insight. By providing the capability as a free-to-use software package, we hope that this ability to accurately quantify the flagellar waveform in large populations of motile cells will enable an abundant array of diagnostic, toxicological and therapeutic possibilities, as well as creating new opportunities for assessing and treating male subfertility.

STUDY FUNDING/COMPETING INTEREST(S)

M.T.G., G.C., J.C.K-B. and D.J.S. gratefully acknowledge funding from the Engineering and Physical Sciences Research Council, Healthcare Technologies Challenge Award (Rapid Sperm Capture EP/N021096/1). J.C.K-B. is funded by a National Institute of Health Research (NIHR) and Health Education England, Senior Clinical Lectureship Grant: The role of the human sperm in healthy live birth (NIHRDH-HCS SCL-2014-05-001). This article presents independent research funded in part by the NIHR and Health Education England. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. The data for experimental set (2) were funded through a Wellcome Trust-University of Birmingham Value in People Fellowship Bridging Award (E.H.O.).The authors declare no competing interests.

Nanoadhesive layer to prevent protein absorption in a poly(dimethylsiloxane) microfluidic device

Poly(dimethylsiloxane) (PDMS) is widely used as a microfluidics platform material; however, it absorbs various molecules, perturbing specific chemical concentrations in microfluidic channels. We present a simple solution to prevent adsorption into a PDMS microfluidic device. We used a vapor-phase-deposited nanoadhesive layer to seal PDMS microfluidic channels. Absorption of fluorescent molecules into PDMS was efficiently prevented in the nanolayer-treated PDMS device. Importantly, when cultured in a nanolayer-treated PDMS device, yeast cells exhibited the expected concentration-dependent response to a mating pheromone, including mating-specific morphological and gene expression changes, while yeast cultured in an untreated PDMS device did not properly respond to the pheromone. Our method greatly expands microfluidic applications that require precise control of molecule concentrations.