Exhaustion of racing sperm in nature-mimicking microfluidic channels during sorting

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.

Microfluidics: The future of sperm selection in assisted reproduction

BACKGROUND

Obtaining functional sperm cells is the first step to treat infertility. With the ever-increasing trend in male infertility, clinicians require access to effective solutions that are able to single out the most viable spermatozoa, which would max out the chance for a successful pregnancy. The new generation techniques for sperm selection involve microfluidics, which offers laminar flow and low Reynolds number within the platforms can provide unprecedented opportunities for sperm selection. Previous studies showed that microfluidic platforms can provide a novel approach to this challenge and since then researchers across the globe have attacked this problem from multiple angles.

OBJECTIVE

In this review, we seek to provide a much-needed bridge between the technical and medical aspects of microfluidic sperm selection. Here, we provide an up-to-date list on microfluidic sperm selection procedures and its application in assisted reproductive technology laboratories.

SEARCH METHOD

A literature search was performed in Web of Science, PubMed, and Scopus to select papers reporting microfluidic sperm selection using the keywords: microfluidic sperm selection, self-motility, non-motile sperm selection, boundary following, rheotaxis, chemotaxis, and thermotaxis. Papers published before March 31, 2023 were selected.

OUTCOMES

Our results show that most studies have used motility-based properties for sperm selection. However, microfluidic platforms are ripe for making use of other properties such as chemotaxis and especially rheotaxis. We have identified that low throughput is one of the major hurdles to current microfluidic sperm selection chips, which can be solved via parallelization.

CONCLUSION

Future work needs to be performed on numerical simulation of the microfluidics chip prior to fabrication as well as relevant clinical assessment after the selection procedure. This would require a close collaboration and understanding among engineers, biologists, and medical professionals. It is interesting that in spite of two decades of microfluidics sperm selection, numerical simulation and clinical studies are lagging behind. It is expected that microfluidic sperm selection platforms will play a major role in the development of fully integrated start-to-finish assisted reproductive technology systems.

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.

Live motile sperm sorting device for enhanced sperm-fertilization competency: comparative analysis with density-gradient centrifugation and microfluidic sperm sorting

PURPOSE

A live motile sperm sorting device (LensHooke^® CA0) developed to prevent the deleterious effects of centrifugation was evaluated comparatively with conventional density-gradient centrifugation (DGC) and microfluidic-based device (Zymot) in sperm selection.

METHODS

Semen samples from 239 men were collected. CA0 under different incubation intervals (5, 10, 30, and 60 min) and temperatures (20, 25, and 37℃) was conducted. The sperm quality in CA0-, DGC-, and Zymot-processed samples was then comparatively evaluated. Semen parameters included concentration, motility, morphology, motion kinematics, DNA fragmentation index (DFI), and the rate of acrosome-reacted sperm (AR).

RESULTS

Total motility and motile sperm concentration increased in a time- and temperature-dependent manner and the total motility peaked for 30 min at 37℃. In paired analysis, CA0 showed significantly higher total motility (94.0%), progressive motility (90.8%), rapid progressive motility (83.6%), normal morphology (10.3%), and lower DFI (2.4%) and AR (4.7%) than the other two methods in normozoospermic samples (all p < 0.05). For non-normozoospermic samples, CA0 had significantly better results than the other two methods (total motility 89.2%, progressive motility 80.4%, rapid progressive motility 74.2%, normal morphology 8.5%, DFI 4.0%, and AR 4.0%; all p < 0.05).

CONCLUSION

CA0 yielded spermatozoa with enhanced sperm fertilization potentials; DFI was minimized in samples processed by CA0. CA0 was effective for both normal and abnormal semen samples due to its consistent selection efficiency.

A microfluidic method for passive trapping of sperms in microstructures

Sperm motility is a prerequisite for male fertility. Enhancing the concentration of motile sperms in assisted reproductive technologies - for human and animal reproduction - is typically achieved through aggressive methods such as centrifugation. Here, we propose a passive technique for the amplification of motile sperm concentration, with no externally imposed forces or flows. The technique is based on the disparity between probability rates, for motile cells, of entering and escaping from complex structures. The effectiveness of the technique is demonstrated in microfluidic experiments with microstructured devices, comparing the trapping power in different geometries. In these micro-traps, we observe an enhancement of cells' concentration close to 10, with a contrast between motile and non-motile cells increased by a similar factor. Simulations of suitable interacting model sperms in realistic geometries reproduce quantitatively the experimental results, extend the range of observations and highlight the components that are key to the optimal trap design.

Escaping Behavior of Sperms on the Biomimetic Oviductal Surface

Before fertilization, sperms adhere to oviductal epithelium cells, and only a restrictive number of winner sperms can escape to reach the egg. To study the sperm escape behavior from the oviductal surface, we developed a microfluidic chip to fabricate an adhesive surface and to create a gradient of progesterone (P₄) for mimicking the oviduct microenvironment in vivo. We identified three sperm motion patterns in such a microenvironment─anchored spin, run-and-spin, and escaped mode. By using kinetic analysis, we verified the hypothesis that the responsive rotation energy anchored with the adhered sperm head determines whether the sperm is trapped or detaching, which is defined as the hammer flying strategy of successful escape after accumulating energy in the process of rotating. Intriguingly, this hammer-throw escaping is able to be triggered by the P₄ biochemical stimulation. Our results revealed the tangled process of sperm escape before fertilization in the ingenious microfluidic system.

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.

Self-propelled micro/nanobots: A new insight into precisely targeting cancerous cells through intelligent and deep cancer penetration

Cancer overlooks are globally one of the most dangerous and life-threatening tribulations. While significant advances have been made in the targeted delivery of anti-cancer medications over the last few years, several challenges, such as low efficacy and strong toxic effects, remain to be addressed. Micro/nanomotors have been thoroughly studied for both effective cancer detection and treatment, as demonstrated by significant advancements in the architecture of smart and functional micro/nanomotor biomedical systems. Able to self-propelled within fluid media, micro/nanomotors have attractive vehicles to maximize the efficacy of tumor delivery. Here, we present the current developments in the delivery, detection, and imaging-guided treatment of micro/nanomotors in the clinical field, including cancer-related specific targeted drug delivery, and then discuss the barriers and difficulties encountered by micro/nanomotors throughout the medical process. Furthermore, this paper addresses the potential growth of micro/nanomotors for medical applications, and sets out the current drawbacks and future research directions for more advancement.

Selection of healthy sperm based on positive rheotaxis using a microfluidic device

For conception, sperm cells travel towards the oocyte. This journey is accomplished by only a few sperm cells, following various guidance mechanisms. Of these mechanisms, rheotaxis plays a significant role in guiding the sperm over a long distance. By taking advantage of this natural rheotaxis behavior of sperm, we have developed a microfluidic chip that isolates healthy sperm cells. The developed chip consists of different chambers separated by microchannels that facilitate separation of motile sperm cells from unprocessed semen samples with the help of fluid flow. The sperm cells are subjected to different velocities in different parts of the chip that direct functional sperm towards the collection chamber utilizing positive rheotaxis. The results from the developed microfluidic chip (with 0.5 μL min^-1 flow rate) have shown almost 100% motility, a significantly higher percentage of morphologically normal sperm cells with lesser sperm DNA fragmentation than the control (no-flow) and raw semen sample. This chip satisfies the need of a clinical setting as it is low-cost, easy to operate and uses a small semen volume for sperm sorting.

Prospective randomized controlled study of a microfluidic chip technology for sperm selection in male infertility patients

The purpose of this study is to evaluate the impact of a microfluidic approach for spermatozoon selection in male infertility patients undergoing intracytoplasmic sperm injection (ICSI). This research enrolled 128 individuals who had ICSI for male-factor infertility. The patients were separated into two groups according to the method used to pick the spermatozoa: group I (n = 64), which used traditional swim-up procedures, and group II (n = 64), which used the Fertile Chip for spermatozoon selection during ICSI therapy. Fertilization rates and embryo quality were the major outcomes. The rates of pregnancy, clinical pregnancy and live birth were used as secondary outcomes. As a result, there was no statistically significant difference between the two groups in terms of fertilization rate, total grade 1 and 2 embryos. Implantation rate was significantly higher in the Fertile Chip group than in the control group (50% vs. 31%, p = 0.02). The Fertile Chip group had considerably greater pregnancy rates, clinical pregnancy rates (CPR) and live birth rates than the control group (62.5% vs. 45.3%, p = 0.038; 59.4% vs. 35.9%, p = 0.006 and 46.8% vs. 25%, p = 0.009). Fertile Chip had no effect on fertilization rates or embryo quality in male-factor infertility couples. However, the Fertile Chip group had a statistically higher pregnancy rate, CPR and live birth rate.

Lower reactive oxygen species production and faster swimming speed of human sperm cells on nanodiamond spin-coated glass substrates

The sperm selection stage is what assisted reproductive technologies have in common and is crucial as it affects the success of the treatment cycle. The employment of microfluidic platforms for sperm selection has emerged showing promising results. In microfluidic platforms, sperm cells encounter micro-confined environments meanwhile having contact with channel walls and surfaces. Modification of contact surfaces using nanoparticles leads to the alteration of surface characteristics which in turn affects sperm behavior especially motility which is an indicator for sperm health. In this article, we present the results of investigating the motility parameters of sperm cells in contact with surface-modified glass substrates using nanodiamond particles. The results show that the sperm swimming velocities are significantly improved within the range of 12%-52% compared to the control surface (untreated). Reactive oxygen species production is also decreased by 14% justifying the increase in swimming speed. Taken together, bonding these modified surfaces to sperm selection microfluidic devices could enhance their efficiency and further improve their outcomes offering new solutions to patients facing 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.

Sperm Inspection for In Vitro Fertilization via Self-Assembled Microdroplet Formation and Quantitative Phase Microscopy

We present a new method for the selection of individual sperm cells using a microfluidic device that automatically traps each cell in a separate microdroplet that then individually self-assembles with other microdroplets, permitting the controlled measurement of the cells using quantitative phase microscopy. Following cell trapping and droplet formation, we utilize quantitative phase microscopy integrated with bright-field imaging for individual sperm morphology and motility inspection. We then perform individual sperm selection using a single-cell micromanipulator, which is enhanced by the microdroplet-trapping procedure described above. This method can improve sperm selection for intracytoplasmic sperm injection, a common type of in vitro fertilization procedure.

Cross flow coupled with inertial focusing for separation of human sperm cells from semen and simulated TESE samples

A triplet spiral channel coupled with cross-flow filtration has been designed and fabricated in an effort to separate sperm cells from either semen or simulated testicular sperm extraction (TESE) samples. This device separates a fraction of cells from the sample by taking advantage of inertial focusing combined with hydrodynamic filtration in multiple micro-slits. Compared to the conventional swim-up technique, the proposed microfluidic device is capable of efficiently separating sperm cells without any tedious semen sample processing and centrifugation steps with a lower level of reactive oxygen species and DNA fragmentation. The device processing capability on the simulated TESE samples confirmed its proficiency in retrieving sperm cells from the samples with an approximate yield of 76%. Conclusively, the introduced microfluidic device can pave the path to proficiently separate sperm cells in assisted reproductive treatment cycles.

Simulating nature in sperm selection for assisted reproduction

Sperm selection in the female reproductive tract (FRT) is sophisticated. Only about 1,000 sperm out of millions in an ejaculate reach the fallopian tube and thus have a chance of fertilizing an oocyte. In assisted reproduction techniques, sperm are usually selected using their density or motility, characteristics that do not reflect their fertilization competence and, therefore, might result in failure to fertilize the oocyte. Although sperm processing in in vitro fertilization (IVF) and intrauterine insemination (IUI) bypasses many of the selection processes in the FRT, selection by the cumulus mass and the zona pellucida remain intact. By contrast, the direct injection of a sperm into an oocyte in intracytoplasmic sperm injection (ICSI) bypasses all natural selection barriers and, therefore, increases the risk of transferring paternal defects such as fragmented DNA and genomic abnormalities in sperm to the resulting child. Research into surrogate markers of fertilization potential and into simulating the natural sperm selection processes has progressed. However, methods of sperm isolation - such as hyaluronic acid-based selection and microfluidic isolation based on sperm tactic responses - use only one or two parameters and are not comparable with the multistep sperm selection processes naturally occurring within the FRT. Fertilization-competent sperm require a panel of molecules, including zona pellucida-binding proteins and ion channel proteins, that enable them to progress through the FRT to achieve fertilization. The optimal artificial sperm selection method will, therefore, probably need to use a multiparameter tool that incorporates the molecular signature of sperm with high fertilization potential, and their responses to external cues, within a microfluidic system that can replicate the physiological processes of the FRT in vitro.

Viscous Cervical Environment-on-a-Chip for Selecting High-Quality Sperm from Human Semen

When ejaculated sperm travels through the vagina to the uterus, mucus secreted by the cervical canal generally filters out sperm having low motility and poor morphology. To investigate this selection principle in vivo, we developed a microfluidic sperm-sorting chip with a viscous medium (polyvinylpyrrolidone: PVP) to imitate the biophysical environment mimic system of the human cervical canal. The material property of the PVP solution was tuned to the range of viscosities of cervical mucus using micro-viscometry. The selection of high-quality human sperm was experimentally evaluated in vitro and theoretically analyzed by the convection-diffusion mechanism. The convection flow is shown to be dominant at low viscosity of the medium used in the sperm-sorting chip when seeded with raw semen; hence, the raw semen containing sperm and debris convectively flow together with suppressed relative dispersions. Also, it was observed that the sperm selected via the chip not only had high motilities but also normal morphologies and high DNA integrity. Therefore, the biomimetic sperm-sorting chip with PVP medium is expected to improve male fertility by enabling the selection of high-quality sperm as well as uncovering pathways and regulatory mechanisms involved in sperm transport through the female reproductive tract for egg fertilization.

Rheotaxis-based sperm separation using a biomimicry microfluidic device

Sperm selection is crucial to assisted reproduction, influencing the success rate of the treatment cycle and offspring health. However, in the current clinical sperm selection practices, bypassing almost all the natural selection barriers is a major concern. Here, we present a biomimicry microfluidic method, inspired by the anatomy of the female reproductive tract, that separates motile sperm based on their rheotaxis behavior to swim against the flow into low shear rate regions. The device includes micropocket geometries that recall the oval-shaped microstructures of the female fallopian tube to create shear protected zones for sperm separation. Clinical tests with human samples indicate that the device is capable of isolating viable and highly motile sperm based on their rheotaxis responses, resulting in a separation efficiency of 100%. The device presents an automated alternative for the current sperm selection practices in assisted reproduction.

Sperm Selection and Embryo Development: A Comparison of the Density Gradient Centrifugation and Microfluidic Chip Sperm Preparation Methods in Patients with Astheno-Teratozoospermia

In recent years, microfluidic chip-based sperm sorting has emerged as an alternative tool to centrifugation-based conventional techniques for in vitro fertilization. This prospective study aims to compare the effects of density gradient centrifugation and microfluidic chip sperm preparation methods on embryo development in patient populations with astheno-teratozoospermia. In the study, the semen samples of the patients were divided into two groups for preparation with either the microfluidic or density gradient methods. Selected spermatozoa were then used to fertilize mature sibling oocytes and the semen parameters and embryo development on days 3 and 5 were assessed. While the density gradient group was associated with a higher sperm concentration, motility (progressive and total) was significantly higher in the microfluidic chip group. No significant differences were observed in the fertilization rates or grade 1 (G1) and grade 2 (G2) proportions of the third-day embryos. Furthermore, while the proportions of the poor, fair and good blastocysts on day 5 did not differ significantly, excellent blastocysts (indicating high-quality embryos) were observed in a significantly higher proportion of the microfluidic chip group. When compared to the classical density gradient method, the microfluidic chip sperm preparation yielded sperm with higher motility and higher quality blastocysts at day 5; in patients with astheno-teratozoospermia.

Advances in sperm analysis: techniques, discoveries and applications

Infertility affects one in six couples worldwide, and fertility continues to deteriorate globally, partly owing to a decline in semen quality. Sperm analysis has a central role in diagnosing and treating male factor infertility. Many emerging techniques, such as digital holography, super-resolution microscopy and next-generation sequencing, have been developed that enable improved analysis of sperm motility, morphology and genetics to help overcome limitations in accuracy and consistency, and improve sperm selection for infertility treatment. These techniques have also improved our understanding of fundamental sperm physiology by enabling discoveries in sperm behaviour and molecular structures. Further progress in sperm analysis and integrating these techniques into laboratories and clinics requires multidisciplinary collaboration, which will increase discovery and improve clinical outcomes.

A microfluidic sperm-sorting device reduces the proportion of sperm with double-stranded DNA fragmentation

Sperm DNA fragmentation can be produced in one (ssSDF) or both (dsSDF) DNA strands, linked to difficulties in naturally achieving a pregnancy and recurrent miscarriages, respectively. The techniques more frequently used to select sperm require centrifugation, which may induce sperm DNA fragmentation (SDF). The objective of this study was to assess whether the microfluidic-based device FertileChip® (now ZyMot®ICSI) can diminish the proportion of sperm with dsSDF. First, in a blinded split pilot study, the semen of nine patients diagnosed with ≥60% dsSDF, was divided into three aliquots: not processed, processed with FertileChip®, and processed with swim up. The three aliquots were all analyzed using neutral COMET for the detection of dsSDF, resulting in a reduction of 46% (P < 0.001) with FertileChip® (dsSDF: 34.9%) compared with the ejaculate and the swim up (dsSDF: 65%). Thereafter, the FertileChip® was introduced into clinical practice and a cohort of 163 consecutive ICSI cycles of patients diagnosed with ≥60% dsSDF was analyzed. Fertilization rate was 75.41%. Pregnancy rates after the first embryo transfer were 53.2% (biochemical), 37.8% (clinical), 34% (ongoing) and the live birth rate was 28.8%. Cumulative pregnancy rates after one (65.4% of patients), two (27.6% of patients) or three (6.4% of patients) transfers were 66% (biochemical), 56.4% (clinical), 53.4% (ongoing) and the live birth rate was 42%. The selection of spermatozoa using Fertile Chip® significantly diminishes the percentage of dsSDF, compared with either the fresh ejaculate or after swim up. Its applicability in ICSI cycles of patients with high dsSDF resulted in good laboratory and clinical outcomes.

Progressive bovine sperm separation using parallelized microchamber-based microfluidics

Motility is one of the most important factors in sperm migration toward an egg. Therefore, sperm separation based on motility might enhance sperm selection for infertility treatments. Conventional centrifugation-based methods increase the risk of damage to sperm cells. Microfluidic systems, on the other hand, can sort sperm in a less intrusive way, but their efficiency and throughput still needs improvement, especially in low-concentration samples (oligozoospermia). Here, a microchamber-based microfluidic platform is demonstrated that can separate progressively motile sperm from non-viable sperm and debris, and trap nonprogressive sperm in microchambers. This platform can be operated in a short period of time (<10 min) with an excellent degree of controllability with no sample preparation. Sperm were screened in a 384-microchamber platform. The mean average-path velocity of the motile sperm in the collected sample increased significantly, from 57 ± 10 μm s^-1 in the raw semen sample to 81 ± 13 μm s^-1. The DNA Integrity of the separated sperm showed 20% improvement over the raw sample which indicated that separated sperm were of higher quality. We began with a 22.5 μL raw bovine sperm sample which had a concentration of 8.5 million sperm per milliliter (M mL^-1) with 38% motility. After separation, the concentration of the collected sperm was 2.1 M mL^-1 with a motility rate of 90%. This corresponds to a 75% retrieval efficiency and the selection of approximately 5.2 × 10⁴ progressively motile spermatozoa. Our results show that the microchamber depth does not affect the residence time of motile sperm; therefore, it is possible to inspect higher sample volumes within the same time frame. This microfluidic platform may provide an easy-to-implement solution for high-throughput, robust, and efficient, collection of progressive sperm with the DNA integrity needed for assisted reproductive technologies (ARTs). However, further studies are necessary to show the implications of this method in human cases.

Clinical values and advances in round spermatid injection (ROSI)

Azoospermia is defined as the complete absence of sperm cells in the ejaculate. Approximately 10-15 % of infertile men display azoospermia. Azoospermia can be subdivided into two types, obstructive azoospermia (OA) and non-obstructive azoospermia (NOA). NOA azoospermia might be the result due to primary testicular damage, secondary testicular damage, or incomplete testicular development. NOA azoospermia accounts for a considerable proportion of male infertility. A significant percentage of men with NOA azoospermia have foci of active spermatogenesis up to the stage of round spermatid. Round spermatid injection (ROSI) is a technique of assisted in-vitro fertilization (IVF) in assisted reproductive technology (ART). ROSI technique involves the injection of haploid germ cells derived from testicular biopsies into the recipient oocytes. The present study demonstrates that more participants and long-term follow-up studies are required to assess the reliability of the ROSI technique. In order to increase the success rate of the ROSI technique, round spermatids should be correctly evaluated and selected. Our study refers to the clinical values, challenges, and innovations in round spermatid injection (ROSI).

Selection of high-quality sperm with thousands of parallel channels

Sperm selection is essential for successful fertilization and embryo development. Current clinical sperm selection methods are labor-intensive and lack the selectivity required to isolate high-quality sperm. Microfluidic sperm selection approaches have shown promise but present a trade-off between the quality and quantity of selected sperm - clinicians demand both. The structure of the female reproductive tract helps to isolate a sufficient quantity of high-quality sperm for fertilization with densely folded epithelium that provides a multitude of longitudinally oriented pathways that guide sperm toward the fertilization site. Here, a three-dimensionally structured sperm selection device is presented that levers this highly parallelized in vivo mechanism for in vitro sperm selection. The device is inserted in a test tube atop 1 mL of raw semen and provides 6500 channels that isolate ∼100 000 high-DNA-integrity sperm for assisted reproduction. In side-by-side clinical testing, the developed approach outperforms the best current clinical methods by improving the DNA integrity of the selected sperm subpopulation up to 95%. Also, the device streamlines clinical workflow, reducing the time required for sperm preparation 3-fold. This single-tube, single-step sperm preparation approach promises to improve both the economics and outcomes of assisted reproduction practices, especially in cases with significant male-factors.

Curvature in the reproductive tract alters sperm-surface interactions

The fallopian tube is lined with a highly complex folded epithelium surrounding a lumen that progressively narrows. To study the influence of this labyrinthine complexity on sperm behavior, we use droplet microfluidics to create soft curved interfaces over a range of curvatures corresponding to the in vivo environment. We reveal a dynamic response mechanism in sperm, switching from a progressive surface-aligned motility mode at low curvatures (larger droplets), to an aggressive surface-attacking mode at high curvatures (smaller droplets of <50 µm-radius). We show that sperm in the attacking mode swim ~33% slower, spend 1.66-fold longer at the interface and have a 66% lower beating amplitude than in the progressive mode. These findings demonstrate that surface curvature within the fallopian tube alters sperm motion from a faster surface aligned locomotion in distal regions to a prolonged physical contact with the epithelium near the site of fertilization, the latter being known to promote capacitation and fertilization competence.

FertDish: microfluidic sperm selection-in-a-dish for intracytoplasmic sperm injection

The selection of high quality sperm is critical for intracytoplasmic sperm injection (ICSI), a prevalent assisted reproduction technology. However, standard selection methods are time-consuming and fail to recover the most viable sperm, thereby limiting the ICSI success rate. Microfluidics enables rapid selection of viable sperm in a manner representing in vivo processes, however, existing platforms lack clinical applicability. Here, we present FertDish, which integrates the clinically established ICSI Petri dish with a film featuring an array of sperm-selecting microchannels for selection of sperm directly from semen. The FertDish format mimics the clinician-familiar ICSI dish setup, and provides rapid (<10 min) single stage sperm preparation that circumvents standard labour-intensive multi-stage sperm processing steps. Tests with human donor and patient semen samples show that FertDish enables the selection of a high quality sperm sub-population, featuring improvements in DNA fragmentation index of more than 91% (donor) and 74% (patient) versus raw semen and 50% (donor) and 63% (patient) versus standard methods, and a distribution of more than 97% sperm with viable and high level DNA. The FertDish enables a high sperm recovery rate (>3.3 × 105 sperm per mL), and is readily adaptable to the clinical workflow with potential to improve ICSI outcomes.

Hemp-Based Microfluidics

Hemp is a sustainable, recyclable, and high-yield annual crop that can be used to produce textiles, plastics, composites, concrete, fibers, biofuels, bionutrients, and paper. The integration of microfluidic paper-based analytical devices (µPADs) with hemp paper can improve the environmental friendliness and high-throughputness of µPADs. However, there is a lack of sufficient scientific studies exploring the functionality, pros, and cons of hemp as a substrate for µPADs. Herein, we used a desktop pen plotter and commercial markers to pattern hydrophobic barriers on hemp paper, in a single step, in order to characterize the ability of markers to form water-resistant patterns on hemp. In addition, since a higher resolution results in densely packed, cost-effective devices with a minimized need for costly reagents, we examined the smallest and thinnest water-resistant patterns plottable on hemp-based papers. Furthermore, the wicking speed and distance of fluids with different viscosities on Whatman No. 1 and hemp papers were compared. Additionally, the wettability of hemp and Whatman grade 1 paper was compared by measuring their contact angles. Besides, the effects of various channel sizes, as well as the number of branches, on the wicking distance of the channeled hemp paper was studied. The governing equations for the wicking distance on channels with laser-cut and hydrophobic side boundaries are presented and were evaluated with our experimental data, elucidating the applicability of the modified Washburn equation for modeling the wicking distance of fluids on hemp paper-based microfluidic devices. Finally, we validated hemp paper as a substrate for the detection and analysis of the potassium concentration in artificial urine.

Microfluidic sperm selection yields higher sperm quality compared to conventional method in ICSI program: A pilot study

An appropriate preparation technique, should be capable of isolating highquality spermatozoa for intracytoplasmic sperm injection (ICSI). The aim was to assess sperm quality parameters, DNA integrity, embryo development, and clinical outcomes using a practical and accessible Microfluidic Sperm Sorting (MSS) technique. A total of 95 ICSI cases performed using sperm samples were prepared with our MSS (group 1) or by Direct Swim Up (DSU; control) method (group 2). Both sperm quality parameters and sperm DNA fragmentation (SDF) were compared between the groups. DNA fragmentation was assessed using Sperm Chromatin Dispersion (SCD) test and fine morphology was assessed using Motile Sperm Organelle Morphology Examination (MSOME). Embryo development and clinical outcomes were compared between the groups. In the MSS group, progressive motility and the fraction of Class I sperm morphology sperm were significantly higher compared to DSU group (P < 0.01 and P < 0.001, respectively). Moreover, the rates of DNA fragmentation and immotile spermatozoa were significantly lower in MSS when compared to DSU group (P < 0.001). Also, higher rates of high-quality embryo formation (P < 0.001), implantation (P = 0.04) and pregnancy (P = 0.05) were achieved in the MSS compared to DSU groups. The MSS technique proved to be a noninvasive, disposable, easy to use, and inexpensive method for separation of high-quality spermatozoa. Both laboratory parameters and clinical outcomes were improved with application of MSS for neat sperm collection in ICSI.AbbreviationsICSI: Intracytoplasmic Sperm Injection; MSS: Microfluidic Sperm Sorting; Sperm DNA Fragmentation (SDF); SCD: Sperm Chromatin Dispersion; MSOME: Motile Sperm Organelle Morphology Examination; DGC: Density Gradient Centrifugation; DSU: Direct Swim Up; ROS: Reactive Oxygen Species; ART: Assisted Reproducetive Technology.

Does the use of microfluidic sperm sorting for the sperm selection improve in vitro fertilization success rates in male factor infertility?

AIM

To evaluate the clinical outcome of assisted reproductive technology (ART) cycles in couple with male infertility, where the spermatozoa were selected using either a conventional gradient-density centrifugation technique or microfluidic sperm sorting.

METHODS

A total of 181 patients who underwent in vitro fertilization (IVF) because of male factor infertility at the IVF center of Bezmialem and Yeditepe University Hospital were included in this study. All patients were divided into two groups according to the sperm selection method: group I (n = 91): microfluidic sperm-sorting chip; group II (n = 90): density-gradient centrifugation. Data collected included male and female age, type of infertility, duration of infertility, previous IVF attempts, smoking, antral follicle count, total dosage of gonadotropins, maximum estradiol levels, duration of stimulations, endometrial thickness on human chorionic gonadotropin day, total number of oocytes retrieved, number of mature oocytes retrieved, number of pronuclear (PN), sperm parameters, clinical PR and ongoing PR.

RESULTS

There was no statistically significant difference in clinical PR and ongoing PR between groups (49.5% vs 40%, P = 0.2; 44% vs 36.7%, P = 0.3; respectively). The improvement in pregnancy rate was more prominent in patients where the female partner's age is higher than 35 (P = 0.09) and men have a total motile sperm count between 1 and 5 million (P < 0.01).

CONCLUSION

Microfluidic devices, "labs-on-a-chip," are a disposable, easy to use, and inexpensive method for sperm sorting. Our results show that IVF success rates might improve with the use of a microfluidic sperm-sorting chip for sperm selection in male infertility.

High DNA integrity sperm selection using surface acoustic waves

Male infertility is a global reproductive issue, several clinical approaches have been developed to tackle it, but their effectiveness is limited by the labour-intensive and time-consuming sperm selection procedures used. Here, we present an automated, acoustic based continuous-flow method capable of selecting high quality sperm with considerably improved motility and DNA integrity compared to the initial raw bull semen. The acoustic field translates larger sperm and guides highly motile sperm across the channel width. The result is the selection of sperm with over 50% and 60% improvement in vitality and progressive motility and more than 38% improvement in DNA integrity, respectively, while providing a clinically relevant volume and selected sperm number for the performance of in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) by selecting over 60 000 sperm in under an hour.

Medical Micro/Nanorobots in Precision Medicine

Advances in medical robots promise to improve modern medicine and the quality of life. Miniaturization of these robotic platforms has led to numerous applications that leverages precision medicine. In this review, the current trends of medical micro and nanorobotics for therapy, surgery, diagnosis, and medical imaging are discussed. The use of micro and nanorobots in precision medicine still faces technical, regulatory, and market challenges for their widespread use in clinical settings. Nevertheless, recent translations from proof of concept to in vivo studies demonstrate their potential toward precision medicine.

Round Spermatid Injection

From a fertility perspective, men with azoospermia represent a challenging patient population. When no mature spermatozoa are obtained during a testicular sperm extraction, patients are often left with limited options, such as adoption or the use of donor sperm. However, it has been reported that round spermatids can be successfully injected into human oocytes and used as an alternative to mature spermatozoa. This technique is known as round spermatid injection (ROSI). Despite the limitations of ROSI and diminished clinical success rates, the use of round spermatids for fertilization may have potential as a treatment modality for men with azoospermia.

Sperm Cell Driven Microrobots-Emerging Opportunities and Challenges for Biologically Inspired Robotic Design

With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots - a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end.

Review on Sperm Sorting Technologies and Sperm Properties toward New Separation Methods via the Interface of Biochemistry and Material Science

Successful fertilization in mammals requires spermatozoa to efficiently traverse the female reproductive tract to meet the egg. This process naturally selects high quality sperm cells for fertilization, but when artificial reproductive technologies are used such as in vitro fertilization, intracytoplasmic sperm injection, or intrauterine insemination, other methods of sperm selection are required. Currently, technology enables sperm sorting based on motility, maturity as defined by zeta potential or hyaluronic acid binding site expression, absence of apoptotic factors, appropriate morphology, and even sex. This review summarizes current knowledge on all known methods of sperm cell sorting, compares their efficiency, and discusses the advantages and limitations of each technique. Scope for further refinement and improvement of current methods are discussed as is the potential to utilize a variety of materials to innovate new methods of sperm separation.

Two-dimensional planar swimming selects for high DNA integrity sperm

Selection of high-quality sperm is critical to the success of assisted reproductive technologies. Clinical screening for top sperm has long focused on sperm swimming ability when following boundaries or when fully free of constraints. In this work, we demonstrate a sperm selection approach with parallel 2 μm tall confined selection channels that prohibit rotation of the sperm head and require planar swimming. We demonstrate that a planar swimming subpopulation of sperm capable of entering and navigating these channels has DNA integrity superior to the freely-swimming motile or raw sperm populations over a wide range of semen sample qualities. The DNA integrity of the selected sperm was significantly higher than that of the corresponding raw samples for donor samples and clinical patient samples, respectively. In side-by-side testing, this method outperforms current clinical selection methods, density gradient centrifugation and swim-up, as well as sperm selected via general motility. Planar swimming represents a viable sperm selection mechanism with the potential to improve outcomes for couples and offspring.

IVF-on-a-Chip: Recent Advances in Microfluidics Technology for In Vitro Fertilization

In vitro fertilization (IVF) has been one of the most exciting modern medical technologies. It has transformed the landscape of human infertility treatment. However, current IVF procedures still provide limited accessibility and affordability to most infertile couples because of the multiple cumbersome processes and heavy dependence on technically skilled personnel. Microfluidics technology offers unique opportunities to automate IVF procedures, reduce stress imposed upon gametes and embryos, and minimize the operator-to-operator variability. This article describes the rapidly evolving state of the application of microfluidics technology in the field of IVF, summarizes the diverse angles of how microfluidics has been complementing or transforming current IVF protocols, and discusses the challenges that motivate continued innovation in this field.

Use of microfluidic sperm extraction chips as an alternative method in patients with recurrent in vitro fertilisation failure

PURPOSE

It is known that sperm preparation techniques in in vitro fertilisation (IVF) are intended to select the best-quality sperm. The aim of this study is to compare sperm the density gradient method and microfluidic chip (Fertile Plus) method in infertile patients by analysing fertilisation rates, pregnancy rates, and sperm morphology and DNA fragmentation rates posed by these two methods.

METHODS

Using semen samples obtained from the patients, sperms were prepared with gradient (n = 312) and microfluidic chip methods (n = 116). Fertilisation and pregnancy rates were compared in the first time and in the recurrent IVF trial patients. In addition, the morphology and DNA fragmentation comparison of sperm samples were evaluated by Toluidine blue in situ chemical staining method.

RESULTS

There was no statistically significant difference between fertilisation and pregnancy rates when compared with study groups in first-time IVF treatment patients. However, in recurrent IVF failure patients, there was a significant difference in fertilisation rates but no statistically significant difference was found in pregnancy rates. The microfluidic chip method significantly decreased sperm DNA fragmentation index according to density gradient method.

CONCLUSIONS

Microfluidic chip method may be recommended in patients with recurrent unsuccessful in vitro trials. The sperm DNA fragmentation test prior to the treatment will be helpful in selecting the appropriate sperm-washing method.

Bacterial chemotaxis in a microfluidic T-maze reveals strong phenotypic heterogeneity in chemotactic sensitivity

Many microorganisms have evolved chemotactic strategies to exploit the microscale heterogeneity that frequently characterizes microbial habitats. Chemotaxis has been primarily studied as an average characteristic of a population, with little regard for variability among individuals. Here, we adopt a classic tool from animal ecology - the T-maze - and implement it at the microscale by using microfluidics to expose bacteria to a sequence of decisions, each consisting of migration up or down a chemical gradient. Single-cell observations of clonal Escherichia coli in the maze, coupled with a mathematical model, reveal that strong heterogeneity in the chemotactic sensitivity coefficient exists even within clonal populations of bacteria. A comparison of different potential sources of heterogeneity reveals that heterogeneity in the T-maze originates primarily from the chemotactic sensitivity coefficient, arising from a distribution of pathway gains. This heterogeneity may have a functional role, for example in the context of migratory bet-hedging strategies.

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.

Effects of the microfluidic chip technique in sperm selection for intracytoplasmic sperm injection for unexplained infertility: a prospective, randomized controlled trial

PURPOSE

The new-generation spermatozoon selection method, microfluidic technique called Fertile Chip^® gives the chance to select spermatozoa with lower DNA fragmentation indexes. We aimed to determine the effect of microfluidic techniques for spermatozoon selection in ICSI treatment in patients with unexplained infertility.

METHODS

This prospective randomized controlled study was conducted at a university hospital. One hundred twenty-two couples with unexplained infertility were included, in which 61 of them were treated with conventional swim-up techniques (control group) and another 61 with the microfluidic technique (study group) for spermatozoon selection in IVF treatment. The fertilization rates and the quality of embryos were the primary outcomes, and clinical pregnancy (CPR) and live birth rates (LBR) were the secondary outcomes of our study.

RESULTS

CPR in the study group and control group were 48.3% and 44.8% (p = 0.35) and LBR were 38.3% and 36.2% (p = 0.48), respectively. The fertilization rates were similar (63.6% and 57.4%, p = 0.098). A total number of grade 1 embryos were significantly higher in microfluidic technique group than in control group (1.45 ± 1.62 vs. 0.83 ± 1.03, p = 0.01). There were more surplus top quality embryos leftover to freeze in the study group (0.71 ± 1.48 vs. 0.22 ± 0.69, p = 0.02).

CONCLUSION

Our study showed that the microfluidic technique does not change fertilization, CPR, and LBR during IVF treatment for couples with unexplained infertility. Despite the fact that the total number of grade 1 embryos after ICSI treatment and the surplus number of grade 1 embryos after embryo transfer were higher in the microfluidic technique group, the study was not powered to detect this difference.

TRIAL REGISTRATION

NCT02488434.

On-chip oocyte denudation from cumulus-oocyte complexes for assisted reproductive therapy

Human infertility can be treated using assisted reproductive technology (ART) such as intracytoplasmic sperm injection (ICSI). But current ART techniques suffer from multiple cumbersome processes requiring technically skilled personnel. Microfluidics technologies offer unique opportunities to streamline ART procedures, reduce stress imposed upon gametes and embryos, and minimize the operator-to-operator variability. However, there have been no automated and continuous processing systems that can reduce the dependence on well-trained embryologists to obtain ICSI-ready oocytes from patients. In this study, using mouse models, we developed a microfluidic device to denude oocytes from the surrounding cumulus-corona cell mass, facilitating the evaluation of oocyte quality and the injection of sperm. Enzyme-treated cumulus-oocyte complexes pass through a series of jagged-surface constriction microchannels of optimized geometries. The jagged inner wall of constriction channels facilitates stripping off of the cumulus-corona cell mass. Oocytes that were denuded by the device showed comparable fertilization and developmental competence compared with mechanical pipetting. The device developed in this study achieves the automation of a manual process for oocyte denudation in a continuous flow, as well as improving standardization and ease-of-use. Our denudation-on-a-chip approach requires inexpensive and simple equipment, which represents one step forward towards improving the accessibility and affordability of assisted reproductive therapy.

Rheotaxis-based separation of sperm with progressive motility using a microfluidic corral system

The separation of motile sperm from semen samples is sought after for medical infertility treatments. In this work, we demonstrate a high-throughput microfluidic device that can passively isolate motile sperm within corrals inside a fluid channel, separating them from the rest of the diluted sample. Using finite element method simulations and proposing a model for sperm motion, we investigated how flow rate can provide a rheotaxis zone in front of the corral for sperm to move upstream/downstream depending on their motility. Using three different flow rates that provided shear rates above the minimum value within the rheotaxis zone, we experimentally tested the device with human and bovine semen. By taking advantage of the rheotactic behavior of sperm, this microfluidic device is able to corral motile sperm with progressive velocities in the range of 48-93 μm⋅s^-1 and 51-82 μm⋅s^-1 for bovine and human samples, respectively. More importantly, we demonstrate that the separated fractions of both human and bovine samples feature 100% normal progressive motility. Furthermore, by extracting the sperm swimming distribution within the rheotaxis zone and sperm velocity distribution inside the corral, we show that the minimum velocity of the corralled sperm can be adjusted by changing the flow rate; that is, we are able to control the motility of the separated sample. This microfluidic device is simple to use, is robust, and has a high throughput compared with traditional methods of motile sperm separation, fulfilling the needs for sperm sample preparation for medical treatments, clinical applications, and fundamental studies.

Live births from artificial insemination of microfluidic-sorted bovine spermatozoa characterized by trajectories correlated with fertility

Selection of functional spermatozoa plays a crucial role in assisted reproduction. Passage of spermatozoa through the female reproductive tract requires progressive motility to locate the oocyte. This preferential ability to reach the fertilization site confers fertility advantage to spermatozoa. Current routine sperm selection techniques are inadequate and fail to provide conclusive evidence on the sperm characteristics that may affect fertilization. We therefore developed a selection strategy for functional and progressively motile bovine spermatozoa with high DNA integrity based on the ability to cross laminar flow streamlines in a diffuser-type microfluidic sperm sorter (DMSS). The fluid dynamics, with respect to microchannel geometry and design, are relevant in the propulsion of spermatozoa and, consequently, ultrahigh-throughput sorting. Sorted spermatozoa were assessed for kinematic parameters, acrosome reaction, mitochondrial membrane potential, and DNA integrity. Kinematic and trajectory patterns were used to identify fertility-related subpopulations: the rapid, straighter, progressive, nonsinuous pattern (PN) and the transitional, sinuous pattern (TS). In contrast to the conventional notion that the fertilizing spermatozoon is always vigorously motile and more linear, our results demonstrate that sinuous patterns are associated with fertility and correspond to truly functional spermatozoa as supported by more live births produced from predominant TS than PN subpopulation in the inseminate. Our findings ascertain the true practical application significance of microfluidic sorting of functional sperm characterized by sinuous trajectories that can serve as a behavioral sperm phenotype marker for fertility potential. More broadly, we foresee the clinical application of this sorting technology to assisted reproduction in humans.