Microfluidic single sperm entrapment and analysis

Microfluidic sperm sorting selects a subpopulation of high-quality sperm with a higher potential for fertilization

STUDY QUESTION

Is a microfluidic sperm sorter (MSS) able to select higher quality sperm compared to conventional methods?

SUMMARY ANSWER

The MSS selects sperm with improved parameters, lower DNA fragmentation, and higher fertilizing potential.

WHAT IS KNOWN ALREADY

To date, the few studies that have compared microfluidics sperm selection with conventional methods have used heterogeneous study population and have lacked molecular investigations.

STUDY DESIGN, SIZE, DURATION

The efficiency of a newly designed MSS in isolating high-quality sperm was compared to the density-gradient centrifugation (DGC) and swim-up (SU) methods, using 100 semen samples in two groups, during 2023-2024.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen specimens from 50 normozoospermic and 50 non-normozoospermic men were sorted using MSS, DGC, and SU methods to compare parameters related to the quality and fertilizing potential of sperm. The fertilizing potential of sperm was determined by measurement of phospholipase C zeta (PLCζ) and post-acrosomal sheath WW domain-binding protein (PAWP) expression using flow cytometry, and the chromatin dispersion test was used to assess sperm DNA damage.

MAIN RESULTS AND THE ROLE OF CHANCE

In both normozoospermic and non-normozoospermic groups, the MSS-selected sperm with the highest progressive motility, PLCζ positive expression and PLCζ and PAWP fluorescence intensity the lowest non-progressive motility, and minimal DNA fragmentation, compared to sperm selected by DGC and SU methods (P < 0.05).

LIMITATION, REASONS FOR CAUTION

The major limitations of our study were the low yield of sperm in the MSS chips and intentional exclusion of severe male factor infertility to yield a sufficient sperm count for molecular experiments; thus testing with severe oligozoospermic semen and samples with low count and motility is still required. In addition, due to ethical considerations, at present, it was impossible to use the sperm achieved from MSS in the clinic to assess the fertilization rate and further outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

Our research presents new evidence that microfluidic sperm sorting may result in the selection of high-quality sperm from raw semen. This novel technology might be a key to improving clinical outcomes of assisted reproduction in infertile patients.

STUDY FUNDING/COMPETING INTEREST(S)

The study is funded by the Iran University of Medical Sciences and no competing interest exists.

TRIAL REGISTRATION NUMBER

N/A.

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).

Advances in microfluidic technology for sperm screening and in vitro fertilization

About 18% of reproductive-age adults worldwide are affected by infertility. In vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are widely used assisted reproductive technologies (ARTs) aimed at improving clinical outcomes. Efficient and noninvasive selection and isolation of highly motile sperm with intact DNA are essential for the success of IVF and ICSI and can potentially impact the therapeutic efficacy and the health of the offspring. Compared to traditional methods, microfluidic technology offers significant advantages such as low sample consumption, high efficiency, minimal damage, high integration, similar microenvironment, and high automation, providing a new platform for ARTs. Here, we review the current situation of microfluidic technology in the field of sperm motility screening and evaluation and IVF research. First, we focus on the working principle, structural design, and screening results of sperm selection microfluidic platforms. We then highlight how the multiple steps of the IVF process can be facilitated and integrated into a microfluidic chip, including oocyte capture, sperm collection and isolation, sperm sorting, fertilization, and embryo culture. Ultimately, we summarize how microfluidics can complement and optimize current sperm sorting and IVF protocols, and challenges and possible solutions are discussed.

Sustainable animal production: exploring the benefits of sperm sexing technologies in addressing critical industry challenges

The sex of the animals is of paramount importance in many animal production systems. This is particularly evident in the production of milk or in breeding programs focused on the production of female animals. In some cases, slaughter or euthanasia of animals of the unwanted sex becomes the only solution, highlighting ethical and economic concerns. As global demand for food continues to rise, the importance of addressing these issues becomes more evident. Reproductive technologies, such as sperm sexing techniques, may hold the key to addressing both animal welfare and the sustainability of animal production. The use of semen enriched with sperm capable of producing offspring of the desired sex can serve as a valuable tool for producers to exert greater control over production outcomes, not only helping to mitigate welfare issues related to the unnecessary premature death of unwanted offspring but also providing a possible ally in the face of stricter animal welfare guidelines. In addition, sexed semen can also contribute to financial gains and reduce greenhouse gas emissions and food waste associated with the less profitable part of the herd. This paper explores the positive impacts that sperm sexing can have on animal welfare, economy, and environment. It also discusses currently available options and strategies for more successful implementation of sexed semen. Partnerships between companies and scientists will be essential to find innovative ways to adapt current production systems and develop sperm sexing technologies that apply to most livestock industries.

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.

Label-Free Microfluidic Impedance Cytometry for Acrosome Integrity Assessment of Boar Spermatozoa

Microfluidics and lab-on-chip technologies have been used in a wide range of biomedical applications. They are known as versatile, rapid, and low-cost alternatives for expensive equipment and time-intensive processing. The veterinary industry and human fertility clinics could greatly benefit from label-free and standardized methods for semen analysis. We developed a tool to determine the acrosome integrity of spermatozoa using microfluidic impedance cytometry. Spermatozoa from boars were treated with the calcium ionophore A23187 to induce acrosome reaction. The magnitude, phase and opacity of individual treated and non-treated (control) spermatozoa were analyzed and compared to conventional staining for acrosome integrity. The results show that the opacity at 19 MHz over 0.5 MHz is associated with acrosome integrity with a cut-off threshold at 0.86 (sensitivity 98%, specificity 97%). In short, we have demonstrated that acrosome integrity can be determined using opacity, illustrating that microfluidic impedance cytometers have the potential to become a versatile and efficient alternative in semen analysis and for fertility treatments in the veterinary industry and human fertility clinics.

A Review of the Impact of Microfluidics Technology on Sperm Selection Technique

Sperm sorting procedures depend on centrifugation processes. These processes produce oxidative stress and cell damage that are undesirable for in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) outcomes because they affect fertilization and implantation chances. The microfluidic sperm selection technique has shown promise in this area. It can create a platform for isolating and manipulating good-quality sperm cells using diverse triggers such as mechanical factors, chemical agents, and temperature gradients. Furthermore, microfluidic platforms can direct sperm cells for IVF or sperm sorting by utilizing an approach that is passive or active. In this review, we explain the use of microfluidics technologies for sorting and arranging sperm cells for different purposes. We also discuss the use of microfluidics technology in selecting and assessing sperm parameters and how it affects male infertility.

Application and Progress of Raman Spectroscopy in Male Reproductive System

Raman spectroscopy is a fast-developing, unmarked, non-invasive, non-destructive technique which allows for real-time scanning and sampling of biological samples in situ, reflecting the subtle biochemical composition alterations of tissues and cells through the variations of spectra. It has great potential to identify pathological tissue and provide intraoperative assistance in clinic. Raman spectroscopy has made many exciting achievements in the study of male reproductive system. In this review, we summarized literatures about the application and progress of Raman spectroscopy in male reproductive system from PubMed and Ovid databases, using MeSH terms associated to Raman spectroscopy, prostate, testis, seminal plasma and sperm. The existing challenges and development opportunities were also discussed and prospected.

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.

Recent Microfluidic Innovations for Sperm Sorting

Sperm selection is a clinical need for guided fertilization in men with low-quality semen. In this regard, microfluidics can provide an enabling platform for the precise manipulation and separation of high-quality sperm cells through applying various stimuli, including chemical agents, mechanical forces, and thermal gradients. In addition, microfluidic platforms can help to guide sperms and oocytes for controlled in vitro fertilization or sperm sorting using both passive and active methods. Herein, we present a detailed review of the use of various microfluidic methods for sorting and categorizing sperms for different applications. The advantages and disadvantages of each method are further discussed and future perspectives in the field are given.

Enrichment of bovine X-sperm using microfluidic dielectrophoretic chip: A proof-of- concept study

The microfluidic dielectrophoretic (MF-DEP) chip is a new, economical and readily-available technology that might be used to enrich X-sperm for increasing female offspring in dairy farms. In this study, we sought to develop an MF-DEP chip to enrich X bovine sperm. The MF-DEP chip was composed of an electrode attached to a glass slide and a microchannel made from polydimethylsiloxane. Sex-sorted sperm from flow cytometry were used to identify optimal electric field conditions while unsorted sperm were later tested for sorting efficiency. The results show that during dielectrophoresis some sperm attached to the electrode (called positive DEP; pDEP) whereas other moved away from the electrode (called negative DEP; nDEP). X and Y-sperm responded to dielectrophoresis differently depending on various factors such as buffers, voltages, and frequencies. We found that the condition 4 V 1 MHz significantly reduced (P < 0.05) the percentage of Y-sperm to nearly 30 and therefore enriched X-sperm. The sorting efficiency was dependent on buffer, bull, sorting cycle, flow rate, electrical voltage, and frequency. Notably, the best sorting buffer found in this experiment was the conducting buffer, but this buffer significantly reduced sperm viability and motility. Other sperm-friendly buffers, TRIS and mHTF, were also used, but could not enrich X-sperm. In conclusion, this is a proof of concept that the MF-DEP chip can be effectively used to enrich bovine X-sperm. However, more research must be performed particularly to find the best sorting buffer to effectively sex-sort sperm while providing high motility and sperm viability.

Fluorescent labelling of boar spermatozoa for quantitative studies on competitive sperm-oviduct binding

Invitro sperm-oviduct binding assays enable assessment of the capacity of spermatozoa to form a 'reservoir' in the oviduct. Competitive approaches, such as experimental set-ups that test multiple males or semen samples simultaneously on the same tissue explants, are desirable because they reduce the likelihood of bias when using material from different females. Therefore, we established a fluorescent labelling technique that allows tagging and storage of spermatozoa before competitive studies of sperm-oviduct binding invitro. Fluorescent markers were tested for reliability and compatibility with parameters of boar spermatozoa viability. The addition of seminal plasma after density gradient centrifugation was essential to counteract centrifugation stress during the labelling procedure. It was demonstrated that sperm tagged with MitoTracker Green FM or MitoTracker Red FM can be successfully used in competitive sperm-oviduct binding studies. The assay was sensitive enough to indicate subtle effects of semen storage temperature on the ability of the spermatozoa to contribute to the female sperm reservoir.

Microfluidic systems for hydrodynamic trapping of cells and clusters

Microfluidic devices have been widely applied to trapping and isolation of cells and clusters for controllable intercellular environments and high-throughput analysis, triggering numerous advances in disease diagnosis and single-cell analysis. Passive hydrodynamic cell trapping is one of the simple and effective methods that has been gaining attention in recent years. Our aim here is to review the existing passive microfluidic trapping approaches, including microposts, microfiltration, microwells, and trapping chambers, with emphasis on design principles and performance. We summarize the remarkable advances that hydrodynamic trapping methods offer, as well as the existing challenges and prospects for development. Finally, we hope that an improved understanding of hydrodynamic trapping approaches can lead to sophisticated and useful platforms to advance medical and biological research.

Male Infertility and the Future of In Vitro Fertilization

The male contribution to infertility has traditionally been overlooked, or at best oversimplified. In recent years efforts have been made to optimize diagnostic and therapeutic techniques to maximize fertility outcomes. A renewed focus on the male partner has resulted in an increased understanding of both genetic and epigenetic changes within the male germline. Furthermore, single-nucleotide polymorphisms, copy-number variants, DNA damage, sperm cryopreservation, obesity, and paternal age have recently been recognized as important factors that play a role in male fertility. Developing a deeper knowledge of these issues could potentially lead to improved success with assisted reproductive technology.

Separation of spermatozoa from erythrocytes using their tumbling mechanism in a pinch flow fractionation device

Men suffering from azoospermia can father a child, by extracting spermatozoa from a testicular biopsy sample. The main complication in this procedure is the presence of an abundance of erythrocytes. Currently, the isolation of the few spermatozoa from the sample is manually performed due to ineffectiveness of filtering methods, making it time consuming and labor intensive. The spermatozoa are smaller in both width and height than any other cell type found in the sample, with a very small difference compared with the erythrocyte for the smallest, making this not the feature to base the extraction on. However, the length of the spermatozoon is 5× larger than the diameter of an erythrocyte and can be utilized. Here we propose a microfluidic chip, in which the tumbling behavior of spermatozoa in pinched flow fractionation is utilized to separate them from the erythrocytes. We show that we can extract 95% of the spermatozoa from a sample containing 2.5% spermatozoa, while removing around 90% of the erythrocytes. By adjusting the flow rates, we are able to increase the collection efficiency while slightly sacrificing the purity, tuning the solution for the available sample in the clinic.

Accounting for the Moral Significance of Technology: Revisiting the Case of Non-Medical Sex Selection

This article explores the moral significance of technology, reviewing a microfluidic chip for sperm sorting and its use for non-medical sex selection. I explore how a specific material setting of this new iteration of pre-pregnancy sex selection technology-with a promised low cost, non-invasive nature and possibility to use at home-fosters new and exacerbates existing ethical concerns. I compare this new technology with the existing sex selection methods of sperm sorting and Prenatal Genetic Diagnosis. Current ethical and political debates on emerging technologies predominantly focus on the quantifiable risk-and-benefit logic that invites an unequivocal "either-or" decision on their future and misses the contextual ethical impact of technology. The article aims to deepen the discussion on sex selection and supplement it with the analysis of the new technology's ethical potential to alter human practices, perceptions and the evaluative concepts with which we approach it. I suggest that the technological mediation approach (Verbeek, 2005, 2011) can be useful to ethically contextualize technologies and highlight the value of such considerations for the informed deliberation regarding their use, design and governance.

Live sperm trap microarray for high throughput imaging and analysis

There is a growing appreciation and understanding of cell-to-cell variability in biological samples. However, research and clinical practice in male fertility has relied on population, or sample-based characteristics. Single-cell resolution is particularly important given the winner-takes-all nature of both natural and in vitro fertilization: it is the properties of a single cell, not the population, that are passed to the next generation. While there are a range of methods for single cell analysis, arraying a larger number of live sperm has not been possible due to the strong locomotion of the cells. Here we present a 103-trap microarray that traps, aligns and arrays individual live sperm. The method enables high-resolution imaging of the aligned cell head, the application of dye-based DNA and mitochondrial analyses, and the quantification of motility characteristics, such as tail beat. In testing, a 2400-post array trapped ∼400 sperm for individual analyses of tail beating frequency and amplitude, DNA integrity via acridine orange staining, and mitochondrial activity via staining. While literature results are mixed regarding a possible correlation between motility and DNA integrity of sperm at sample-level, results here find no statistical correlation between tail beat characteristics and DNA integrity at the cell-level. The trap array uniquely enables the high-throughput study of individual live sperm in semen samples - assessing the inherently single-cell selection process of fertilization, with single-cell resolution.

Sperm selection methods in the 21st century

Natural sperm selection in humans is a rigorous process resulting in the highest quality sperm reaching, and having an opportunity to fertilize, the oocyte. Relative to other mammalian species, the human ejaculate consists of a heterogeneous pool of sperm, varying in characteristics such as shape, size, and motility. Semen preparation in assisted reproductive technologies (ART) has long been performed using either a simple swim-up method or density gradients. Both methodologies provide highly motile sperm populations; however neither replicates the complex selection processes seen in nature. A number of methods have now been developed to mimic some of the natural selection processes that exist in the female reproductive tract. These methods attempt to select a better individual, or population of, spermatozoa when compared to classical methods of preparation. Of the approaches already tested, platforms based upon sperm membrane markers, such as hyaluronan or annexin V, have been used to either select or deselect sperm with varied success. One technology that utilizes the size, motility, and other characteristics of sperm to improve both semen analysis and sperm selection is microfluidics. Here, we sought to review the efficacy of both available and emerging techniques that aim to improve the quality of the sperm pool available for use in ART.

Microfluidic devices for the study of sperm migration

Microfluidics technology offers us an opportunity to model the biophysical and biochemical environments encountered by sperm moving through the female reproductive tract and, at the same time, to study sperm swimming dynamics at a quantitative level. In humans, coitus results in the deposition of sperm in the vagina at the entrance to the cervix. Consequently, sperm must swim or be drawn through the cervix, uterus, uterotubal junction and oviductal isthmus to reach the oocyte in the oviductal ampulla. Only a very small percentage of inseminated sperm reach the ampulla in the periovulatory period, indicating that strong selection pressures act on sperm during migration. A better understanding of how sperm interact with the female tract would inspire improvements in diagnosis of fertility problems and development of novel-assisted reproductive technologies that minimize damage to sperm and mimic natural selection pressures on sperm.

Recent advances in the use of microfluidic technologies for single cell analysis

The inherent heterogeneity in cell populations has become of great interest and importance as analytical techniques have improved over the past decades. With the advent of personalized medicine, understanding the impact of this heterogeneity has become an important challenge for the research community. Many different microfluidic approaches with varying levels of throughput and resolution exist to study single cell activity. In this review, we take a broad view of the recent microfluidic developments in single cell analysis based on microwell, microchamber, and droplet platforms. We cover physical, chemical, and molecular biology approaches for cellular and molecular analysis including newly emerging genome-wide analysis.

Non-Invasive Approaches to Epigenetic-Based Sperm Selection

Since sperm size and form do not necessarily provide information on internal sperm structures, novel sperm markers need to be found in order to conduct assisted reproductive therapies (ART) successfully. Currently, the priority of andrologists is not only to select those sperm able to fertilize the oocyte, but also a high quality of sperm that will guarantee a healthy embryo. Evidence of this shows us the importance of studying sperm intensively on genetic and epigenetic levels, because these could probably be the cause of a percentage of infertility diagnosed as idiopathic. Thus, more attention is being paid to posttranslational modifications as the key for better understanding of the fertilization process and its impact on embryo and offspring. Advances in the discovery of new sperm markers should go hand in hand with finding appropriate techniques for selecting the healthiest sperm, guaranteeing its non-invasiveness. To date, most sperm selection techniques can be harmful to sperm due to centrifugation or staining procedures. Some methods, such as microfluidic techniques, sperm nanopurifications, and Raman spectroscopy, have the potential to make selection gentle to sperm, tracking small abnormalities undetected by methods currently used. The fact that live cells could be analyzed without harmful effects creates the expectation of using them routinely in ART. In this review, we focus on the combination of sperm epigenetic status (modifications) as quality markers, with non-invasive sperm selection methods as novel approaches to improve ART outcomes.

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.

A Review of New Technologies that may Become Useful for in vitro Production of Boar Sperm

Making sperm cells outside the original testicular environment in a culture dish has been considered for a long time as impossible due to the very complicated process of spermatogenesis and sperm maturation, which altogether, encompasses a 2-month period. However, new approaches in complex three-dimensional co-cell cultures, micro-perfusion and micro-fluidics technologies, new knowledge in the functioning, culturing and differentiation of spermatogonial stem cells (SSC) and their precursor cells have revolutionized this field. Furthermore, the use of better molecular markers as well as stimulatory factors has led to successful in vitro culture of stem cells either derived from germ line stem cells, from induced pluripotent stem cells (iPSC) or from embryonic stem cells (ESC). These stem cells when placed into small seminiferous tubule fragments are able to become SSC. The SSC beyond self-renewal can also be induced into haploid sperm-like cells under in vitro conditions. In mouse, this in vitro produced sperm can be injected into a mature oocyte and allow post-fertilization development into an early embryo in vitro. After transferring such obtained embryos into the uterus of a recipient mouse, they can further develop into healthy offspring. Recently, a similar approach has been performed with combining selected cells from testicular cell suspensions followed by a complete in vitro culture of seminiferous cords producing sperm-like cells. However, most of the techniques developed are laborious, time-consuming and have low efficiency, placing questionable that it will become useful used for setting up an efficient in vitro sperm production system for the boar. The benefits and drawbacks as well as the likeliness of in vitro pig sperm production to become applied in assisted technologies for swine reproduction are critically discussed. In this contribution, also the process of sperm production in the testis and sperm maturation is reviewed.

Upward swimming of a sperm cell in shear flow

Mammalian sperm cells are required to swim over long distances, typically around 1000-fold their own length. They must orient themselves and maintain a swimming motion to reach the ovum, or egg cell. Although the mechanism of long-distance navigation is still unclear, one possible mechanism, rheotaxis, was reported recently. This work investigates the mechanism of the rheotaxis in detail by simulating the motions of a sperm cell in shear flow adjacent to a flat surface. A phase diagram was developed to show the sperm's swimming motion under different shear rates, and for varying flagellum waveform conditions. The results showed that, under shear flow, the sperm is able to hydrodynamically change its swimming direction, allowing it to swim upwards against the flow, which suggests that the upward swimming of sperm cells can be explained using fluid mechanics, and this can then be used to further understand physiology of sperm cell navigation.

Fourier transform infrared spectroscopic analysis of sperm chromatin structure and DNA stability

Sperm chromatin structure and condensation determine accessibility for damage, and hence success of fertilization and development. The aim of this study was to reveal characteristic spectral features coinciding with abnormal sperm chromatin packing (i.e., DNA-protein interactions) and decreased fertility, using Fourier transform infrared spectroscopy. Chromatin structure in spermatozoa obtained from different stallions was investigated. Furthermore, spermatozoa were exposed to oxidative stress, or treated with thiol-oxidizing and disulfide-reducing agents, to alter chromatin structure and packing. Spectroscopic studies were corroborated with flow cytometric analyses using the DNA-intercalating fluorescent dye acridine orange. Decreased fertility of individuals correlated with increased abnormal sperm morphology and decreased stability toward induced DNA damage. Treatment with the disulfide reducing agent dithiothreitol resulted in increased sperm chromatin decondensation and DNA accessibility, similar as found for less mature epididymal spermatozoa. In situ infrared spectroscopic analysis revealed that characteristic bands arising from the DNA backbone (ν1230, ν1086, ν1051 cm(-1) ) changed in response to induced oxidative damage, water removal, and decondensation. This coincided with changes in the amide-I region (intensity at ν1620 vs. ν1640 cm(-1) ) denoting concomitant changes in protein secondary structure. Reduction in protein disulfide bonds resulted in a decreased value of the asymmetric to symmetric phosphate band intensity (ν1230/ν1086 cm(-1) ), suggesting that this band ratio is sensitive for the degree of chromatin condensation. Moreover, when analyzing spermatozoa from different individuals, it was found that the asymmetric/symmetric phosphate band ratio negatively correlated with the percentage of morphologically abnormal spermatozoa.

Cellular Cargo Delivery: Toward Assisted Fertilization by Sperm-Carrying Micromotors

We present artificially motorized sperm cells-a novel type of hybrid micromotor, where customized microhelices serve as motors for transporting sperm cells with motion deficiencies to help them carry out their natural function. Our results indicate that metal-coated polymer microhelices are suitable for this task due to potent, controllable, and nonharmful 3D motion behavior. We manage to capture, transport, and release single immotile live sperm cells in fluidic channels that allow mimicking physiological conditions. Important steps toward fertilization are addressed by employing proper means of sperm selection and oocyte culturing. Despite the fact that there still remain some challenges on the way to achieve successful fertilization with artificially motorized sperms, we believe that the potential of this novel approach toward assisted reproduction can be already put into perspective with the present work.

Sperm selection in natural conception: what can we learn from Mother Nature to improve assisted reproduction outcomes?

BACKGROUND

In natural conception only a few sperm cells reach the ampulla or the site of fertilization. This population is a selected group of cells since only motile cells can pass through cervical mucus and gain initial entry into the female reproductive tract. In animals, some studies indicate that the sperm selected by the reproductive tract and recovered from the uterus and the oviducts have higher fertilization rates but this is not a universal finding. Some species show less discrimination in sperm selection and abnormal sperm do arrive at the oviduct. In contrast, assisted reproductive technologies (ART) utilize a more random sperm population. In this review we contrast the journey of the spermatozoon in vivo and in vitro and discuss this in the context of developing new sperm preparation and selection techniques for ART.

METHODS

A review of the literature examining characteristics of the spermatozoa selected in vivo is compared with recent developments in in vitro selection and preparation methods. Contrasts and similarities are presented.

RESULTS AND CONCLUSIONS

New technologies are being developed to aid in the diagnosis, preparation and selection of spermatozoa in ART. To date progress has been frustrating and these methods have provided variable benefits in improving outcomes after ART. It is more likely that examining the mechanisms enforced by nature will provide valuable information in regard to sperm selection and preparation techniques in vitro. Identifying the properties of those spermatozoa which do reach the oviduct will also be important for the development of more effective tests of semen quality. In this review we examine the value of sperm selection to see how much guidance for ART can be gleaned from the natural selection processes in vivo.

Microfluidic assessment of swimming media for motility-based sperm selection

Selection medium is important in sperm isolation for assisted reproductive technologies. Contrary to the naturally occurring human cervical mucus which has a high viscosity, most current practices for motility based sperm selection use a low viscosity medium. In this study, we used a microfluidic device to assess the effects of high viscosity media made with hyaluronic acid (HA) and methyl cellulose (MC) on bovine and human sperm motility and viability (sperm transferred directly from cryoprotectant). The microfluidic penetration test, viability, and motility were compared for sperm swimming in both HA and MC media with about 20cp viscosity (measured at 20 °C). Our resulted indicate that MC medium resulted in a significantly higher number of viable bovine sperm penetrating the medium as compared to HA. Furthermore, MC resulted in the selection of a sperm subpopulation with a 274% increase in sperm viability in comparison to the raw semen, while HA increased viability by only 133%. In addition to viability, bovine sperm motility parameters were significantly higher in the MC medium as compared with HA. Experiments with human sperm swimming in MC indicate that sperm swim slower and straighter at higher viscosities. In conclusion, the results indicate that in a micro-confined environment representative of the in vivo environment, MC is a preferred high viscosity medium to ensure the highest concentration of motile and viable sperm.