Microfluidic devices for the study of sperm migration

Qualified sperm selection based on the rheotaxis and thigmotaxis in a microfluidic system

Microfluidic systems with the ability to mimic the female reproductive tract (FRT) and sperm features have emerged as promising methods to separate sperm with higher quality for the assistant reproductive technology. Thereby, we designed and fabricated a microfluidic system based on FRT features with a focus on rheotaxis and thigmotaxis for passive sperm separation. In this regard, four various geometries (linear, square, zigzag, and sinusoidal) were designed, and the effect of rheotaxis and thigmotaxis were investigated. Although separated sperm in all microchannels were 100% motile, non-linear geometries were more effective than linear geometry in the term of separating the progressive sperm with high quality. In the presence of upstream flow, periodical changes in the slope of walls (in non-linear geometries) give rise to the periodical facing sperm with a high flow rate in the middle of microchannels, which was a reason for the high quality of separated sperm. However, because of sharp corners in the square and zigzag microchannels that create dead zones with a lack of upstream flow, which is noticeable via simulation results, these geometries have obstacles against sperm swimming toward the outlet, which was proved by image analysis. The sinusoidal geometry showed the highest enhancement level of the designed geometries compared to the linear geometry. Separated sperm exhibited 34.7% normal morphology, 100% motility, and 100% viability in the sinusoidal geometry. Therefore, the periodic change in the position of sperm from one wall to another wall can be a strategy for separating sperm with high quality.

Graphical abstract

In the present study, we used a microfluidic system for studying the combined effects of thigmotaxis and rheotaxis for sperm separation process to achieve the successful Assisted reproductive technology (ART). The designed PDMS-based microfluidic system had four various geometries, including linear, square, zigzag, and sinusoidal. The functionality of separated sperm was evaluated by sperm tracking (ImageJ), motility assay (CASA software), and morphology assay (Papanicolaou ultrafast staining). Probing various geometries revealed 100% motility. In non-linear geometries, sperm's periodic detachment from the walls gave rise to the periodic interaction with the high flow velocity in the center of the channel, resulting in the separation of high-quality sperm with progressive motility. The collected data proved the influence of thigmotaxis on the quality of separated sperm. Morphologically improvement in separated sperm from the sinusoidal geometry was significant than others, which means the sinusoidal structure would be the best candidate for the sperm separation process.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-023-00294-8.

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.

The influence of the female reproductive tract and sperm features on the design of microfluidic sperm-sorting devices

Although medical advancements have successfully helped a lot of couples with their infertility by assisted reproductive technologies (ART), sperm selection, a crucial stage in ART, has remained challenging. Therefore, we aimed to investigate novel sperm separation methods, specifically microfluidic systems, as they do sperm selection based on sperm and/or the female reproductive tract (FRT) features without inflicting any damage to the selected sperm during the process. In this review, after an exhaustive studying of FRT features, which can implement by microfluidics devices, the focus was centered on sperm selection and investigation devices. During this study, we tried not to only point to the deficiencies of these systems, but to put forth suggestions for their improvement as well.

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.

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.

Sperm selection in IVF: the long and winding road from bench to bedside

Spermatozoa wage battle to conquer fertilization but the traits needed to succeed remain elusive. The natural advantageous qualities that enable only a few selected sperm cells to reach the site of fertilization remain unknown. Although in vitro fertilization (IVF) facilitates the job of spermatozoa, a universally acceptable means of sperm selection is yet to be developed. No objective or reliable sperm quality indicators have been established and sperm selection is, to a great extent, based on subjective qualitative evaluation. The best method for sperm selection in IVF presents several challenges: intrinsic sperm qualities cannot be evaluated and the ideal endpoint for these studies is debatable. An ideal method for sperm selection in ART should be noninvasive and cost-effective, and allow the identification of high-quality spermatozoa and yield better outcomes in terms of pregnancy and live birth rates. This narrative review included 85 papers and focused on the new available methods and technologies that might shed some light on sperm selection in IVF. It discusses the available data on microfluidic devices, omics profiling, micronuclei studies, sperm plasma membrane markers, and other techniques, such as Magnetic Activated Cell Sorting (MACS), Raman micro-spectroscopy, and artificial intelligence systems. The new techniques herein reviewed offer fresh approaches to an old problem, for which a definite solution has yet to cross the bridge from bench to IVF clinics around the world, since clinical usefulness and application remain unproven.

A treatment approach for couples with disrupted sperm DNA integrity and recurrent ART failure

OBJECTIVE

To test a novel method to select spermatozoa with high chromatin integrity.

DESIGN

Specimens with high sperm chromatin fragmentation (SCF) were selected by density gradient selection (DGS) and microfluidic sperm sorting (MSS).

SETTING

Academic medical center.

PATIENT(S)

Ejaculates from consenting men were processed by DGS/MSS. Couples underwent ICSI cycles with spermatozoa processed by DGS/MSS. Clinical outcomes were evaluated after embryo transfer.

INTERVENTION(S)

SCF was measured by TUNEL. ICSI with spermatozoa selected by DGS and MSS was performed.

MAIN OUTCOME MEASURE(S)

Fertilization, embryo implantation, and pregnancy outcomes were compared between DGS and MSS.

RESULT(S)

A total of 23 men had an average SCF of 20.7 ± 10%. After DGS and MSS, the SCF was 12.5 ± 5% and 1.8 ± 1%, respectively. In couples who underwent ICSI, the average SCF was 28.8 ± 9%, which fell to 21.0 ± 9% after DGS and 1.3 ± 0.7% after MSS. Four couples underwent 11 ICSI cycles with DGS and achieved one (25%) pregnancy that resulted in pregnancy loss. In four subsequent ICSI cycles with MSS, an ongoing clinical pregnancy rate of 50% was achieved. Five additional couples underwent 12 cycles of ICSI with DGS. After preimplantation genetic testing for aneuploidy, 30.3% of the embryos were euploid. One pregnancy was achieved, resulting in pregnancy loss. With MSS, 31.5% of the embryos were euploid and 4 couples obtained a pregnancy. Finally, sixteen couples underwent 20 ICSI cycles solely with MSS at our center. Of these couples, 8 had failed 13 ICSI cycles with DGS elsewhere. These couples achieved an overall implantation of 34.5% (10/29) and a pregnancy rate of 58.8% (10/17).

CONCLUSION(S)

Microfluidic selection yielded spermatozoa with optimal genomic integrity and improved chances of obtaining a euploid conceptus.

Strictures of a microchannel impose fierce competition to select for highly motile sperm

Investigating sperm locomotion in the presence of external fluid flow and geometries simulating the female reproductive tract can lead to a better understanding of sperm motion during fertilization. Using a microfluidic device featuring a stricture that simulates the fluid mechanical properties of narrow junctions inside the female reproductive tract, we documented the gate-like role played by the stricture in preventing sperm with motilities below a certain threshold from advancing through the stricture to the other side (i.e., fertilization site). All the slower sperm accumulate below (i.e., in front of) the stricture and swim in a butterfly-shaped path between the channel walls, thus maintaining the potential for penetrating the stricture and ultimately advancing toward the fertilization site. Accumulation below the stricture occurs in a hierarchical manner so that dense concentrations of sperm with higher velocities remain closer to the stricture, with more sparsely distributed arrays of lower-velocity sperm lagging behind.

Novel distance-progesterone-combined selection approach improves human sperm quality

Background

Sperm selection is essential for the health of offspring conceived via assistive reproductive technology (ART). Various methods of sperm preparation for in vitro fertilization and intracytoplasmic sperm injection have been developed to acquire sperm with better quality and to avoid potential genetic disorders. However, current sperm processing and selection techniques bypass the natural selection that occurs during fertilization in vivo. The aim of this study was to present a novel distance-progesterone-combined selection approach with an original device based on the human female reproductive tract, and to report on its effectiveness based on sperm progressive motility, as well as chemotaxis.

Methods

A novel device with long distance channels which mimicked the female human reproductive system was designed and fabricated. This ready-to-be-used device was developed using a progesterone gradient and human tube fluid media. Sperm swam for 150 min in the device under conditions of 37 °C air temperature with 5% CO₂ after separation from seminal plasma via discontinuous Percoll gradient treatment. The selected sperm were assessed for normal morphology using Diff-Quik staining. A chromatin diffusion assay assessed sperm for DNA fragments and apoptosis was assessed using annexin V-fluorescein isothiocyanate/propidium iodide fluorescent staining.

Results

Our distance-progesterone-combined sperm selection method was successfully established. After sperm were selected, the percentage of sperm with normal morphology increased (before vs. after selection, 11.2 ± 1.3% vs. 40.3 ± 6.6%, P = 0.000), the percentage of sperm with DNA fragmentation decreased (before vs. after selection, 15.4 ± 4.0% vs. 6.8 ± 3.3%, P = 0.001), and the percentage of sperm with apoptosis did not change significantly.

Conclusions

Our newly-developed method is capable of successfully selecting sperm of high quality. The method will be benefit clinical ART practice as it can reduce sperm-related genetic risks.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1575-7) contains supplementary material, which is available to authorized users.

Separation of sperm cells from samples containing high concentrations of white blood cells using a spiral channel

Microfluidic technology has potential to separate sperm cells from unwanted debris while improving the effectiveness of assisted reproductive technologies (ART). Current clinical protocol limitations regarding the separation of sperm cells from other cells/cellular debris can lead to low sperm recovery when the sample contains a low concentration of mostly low motility sperm cells and a high concentration of unwanted cells/cellular debris, such as in semen samples from patients with pyospermia [high white blood cell (WBC) semen]. This study demonstrates label-free separation of sperm cells from such semen samples using inertial microfluidics. The approach does not require any externally applied forces except the movement of the fluid sample through the instrument. Using this approach, it was possible to recover not only any motile sperm, but also viable less-motile and non-motile sperm cells with high recovery rates. Our results demonstrate the ability of inertial microfluidics to significantly reduce WBC concentration by flow focusing of target WBCs within a spiral channel flow. The estimated sample process time was more rapid (∼5 min) and autonomous than the conventional method (gradient centrifuge sperm wash; ∼1 h). A mixture of sperm/WBC was injected as the device input and 83% of sperm cells and 93% of WBCs were collected separately from two distinct outlets. The results show promise for enhancing sperm samples through inertial flow processing of WBCs and sperm cells that can provide an advantage to ART procedures such as sample preparation for intrauterine insemination.

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.