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

Straining Flow Effects on Sperm Flagellar Energetics in Microfluidic Cross-Slot Traps

Sperm need to effectively navigate the intricate pathways of the female reproductive tract, which are filled with various complex fluid flows. Despite numerous population-based studies, the effects of flow on the flagellar beating pattern of individual sperm remain poorly understood. In this study, a microfluidic cross-slot trap is employed to immobilize individual motile sperm for an extended period without physical tethering, thereby reducing potential cell damage and movement restriction compared to the conventional head-tethering method. The impact of pure straining flow on trapped single sperm is investigated. The experimental results demonstrate that at strain rates of 11.33 s-1 and higher, the periodic and repetitive beating pattern of the sperm flagellum changes to irregular movement. Furthermore, an increase in strain rate from 1.89 to 11.33 s-1 leads to a 35.4% reduction in beating amplitude and a 41.2% decrease in hydrodynamic power dissipation. These findings underscore the capability of the microfluidic cross-slot platform to trap sperm with high stability, contributing to a better understanding of sperm behavior in response to fluid flows.

A biomimetic sperm selection device for routine sperm selection

RESEARCH QUESTION

Can a biomimetic microfluidic sperm sorter isolate motile sperm while minimizing DNA damage in comparison with density gradient centrifugation (DGC)?

DESIGN

This was a two-phase study of 61 men, consisting of a proof-of-concept study with 21 donated semen samples in a university research laboratory, followed by a diagnostic andrology study with 40 consenting patients who presented at a fertility clinic for semen diagnostics. Each sample was split to perform DGC and microfluidic sperm selection (one-step sperm selection with 15 min of incubation) side-by-side. Outcomes evaluated included concentration, progressive motility, and DNA fragmentation index (DFI) of raw semen, and sperm isolated using DGC and the microfluidic device. Results were analysed using Friedman's test for non-parametric data (significant when P < 0.05). DFI values were assessed by sperm chromatin dispersion assay.

RESULTS

Sperm isolated using DGC and the microfluidic device showed improved DFI values and motility compared with the raw semen sample in both cohorts. However, the microfluidic device was significantly better than DGC at reducing DFI values in both the proof-of-concept study (P = 0.012) and the diagnostic andrology study (P < 0.001). Progressive motility was significantly higher for sperm isolated using the microfluidic device in the proof-of-concept study (P = 0.0061) but not the diagnostic andrology study. Sperm concentration was significantly lower for samples isolated using the microfluidic device compared with DGC for both cohorts (P < 0.001).

CONCLUSIONS

Channel-based biomimetic sperm selection can passively select motile sperm with low DNA fragmentation. When compared with DGC, this method isolates fewer sperm but with a higher proportion of progressively motile cells and greater DNA integrity.

OoTrap: enhancing oocyte collection and maturation with a field-deployable fluidic device

Assisted reproductive technologies (ART) are pivotal for contemporary reproductive medicine and species conservation. However, the manual handling required in these processes introduces stress that can compromise oocyte and embryo quality. This study introduces OoTrap, a novel fluidic device designed to streamline ART workflows by facilitating the capture and maturation of oocytes in a compact unit. The device also reintroduces mechanical forces similar to those in the in vivo environment, which are often missing in conventional systems. OoTrap operates in both static and perfusion-based modes, offering flexibility and optimal conditions for oocyte maturation. Notably, OoTrap achieved higher in vitro maturation (IVM) rates under perfusion, produced oocytes with fewer chromosomal abnormalities, and maintained spindle morphology integrity. The incorporation of a heating system and a 3D-printed syringe pump enabled IVM outside the incubator, making OoTrap suitable for field applications. The results highlight the potential of OoTrap to enhance ART outcomes by reducing manual handling, providing a controlled microenvironment, and offering a practical solution for field-based ART applications.

High-throughput selection of sperm with improved DNA integrity and rapidly progressive motility using a butterfly-shaped chip compared to the swim-up method

Microfluidics provides unique opportunities for the high throughput selection of motile sperm with improved DNA integrity for assisted reproductive technologies (ARTs). Here, through a parametric study on dimensions and geometrical angles, a butterfly-shaped chip (BSC) is presented to isolate sperm with high progressive motility and intact DNA at a separation rate of 1125 sperm per minute. Using finite element simulations, the flow field and shear rates in the device were optimized to leverage the inherent motility characteristics of sperm for maximum selection throughput. The device incorporates a triple selection mechanism in series, initially activating sperm rheotaxis by rotation against the semen flow, penetrating the counter buffer flow and swimming against the direction of the buffer flow, leaving dead cells and debris behind, and subsequently leveraging boundary-following behavior to direct progressively motile sperm to swim along the walls and reach the device outlet. The device selects over 4.1 million sperm per mL within 20 minutes, with 29.2%, 68.2%, and 57.3% improvement in total motility, DNA integrity, and velocity parameter (VCL), as compared with the conventional swim-up method, respectively. Overall, the performance of the device to separate sperm with approximately 95.9% total motility, 97.8% viability, and 96.6% DNA integrity at high concentrations demonstrates its potential for enhancing the efficiency of conventional treatment methods.

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.

Fallopian tube rheology regulates epithelial cell differentiation and function to enhance cilia formation and coordination

The rheological properties of the extracellular fluid in the female reproductive tract vary spatiotemporally, however, the effect on the behaviour of epithelial cells that line the tract is unexplored. Here, we reveal that epithelial cells respond to the elevated viscosity of culture media by modulating their development and functionality to enhance cilia formation and coordination. Specifically, ciliation increases by 4-fold and cilia beating frequency decreases by 30% when cells are cultured at 100 mPa·s. Further, cilia manifest a coordinated beating pattern that can facilitate the formation of metachronal waves. At the cellular level, viscous loading activates the TRPV4 channel in the epithelial cells to increase intracellular Ca2+, subsequently decreasing the mitochondrial membrane potential level for ATP production to maintain cell viability and function. Our findings provide additional insights into the role of elevated tubal fluid viscosity in promoting ciliation and coordinating their beating-a potential mechanism to facilitate the transport of egg and embryo, suggesting possible therapeutic opportunities for infertility treatment.

Making immotile sperm motile using high-frequency ultrasound

Sperm motility is a natural selection with a crucial role in both natural and assisted reproduction. Common methods for increasing sperm motility are by using chemicals that cause embryotoxicity, and the multistep washing requirements of these methods lead to sperm DNA damage. We propose a rapid and noninvasive mechanotherapy approach for increasing the motility of human sperm cells by using ultrasound operating at 800 mW and 40 MHz. Single-cell analysis of sperm cells, facilitated by droplet microfluidics, shows that exposure to ultrasound leads to up to 266% boost to motility parameters of relatively immotile sperm, and as a result, 72% of these immotile sperm are graded as progressive after exposure, with a swimming velocity greater than 5 micrometer per second. These promising results offer a rapid and noninvasive clinical method for improving the motility of sperm cells in the most challenging assisted reproduction cases to replace intracytoplasmic sperm injection (ICSI) with less invasive treatments and to improve assisted reproduction outcomes.

Making and selecting the best embryo in the laboratory

Over the past 4 decades our ability to maintain a viable human embryo in vitro has improved dramatically, leading to higher implantation rates. This has led to a notable shift to single blastocyst transfer and the ensuing elimination of high order multiple gestations. Future improvements to embryo culture systems will not only come from new improved innovative media formulations (such as the inclusion of antioxidants), but plausibly by moving away from static culture to more dynamic perfusion-based systems now made a reality owing to the breakthroughs in three-dimensional printing technology and micro fabrication. Such an approach has already made it feasible to create high resolution devices for intracytoplasmic sperm injection, culture, and cryopreservation, paving the way not only for improvements in outcomes but also automation of assisted reproductive technology. Although improvements in culture systems can lead to further increases in pregnancy outcomes, the ability to quantitate biomarkers of embryo health and viability will reduce time to pregnancy and decrease pregnancy loss. Currently artificial intelligence is being used to assess embryo development through image analysis, but we predict its power will be realized through the creation of selection algorithms based on the integration of information related to metabolic functions, cell-free DNA, and morphokinetics, thereby using vast amounts of different data types obtained for each embryo to predict outcomes. All of this will not only make assisted reproductive technology more effective, but it will also make it more cost effective, thereby increasing patient access to infertility treatment worldwide.

High-DNA integrity sperm selection using rheotaxis and boundary following behavior in a microfluidic chip

Rheotaxis, as one of the main natural guidance mechanisms in vivo, has been used in microfluidics to separate motile sperm. However, the lack of DNA integrity assessment and the inability to separate the cells in a specific reservoir have been the main limitations for the practical application of most of the devices using rheotaxis for sperm separation. Here, we present a microfluidic chip that can separate highly motile sperm using their inherent rheotaxis and boundary-following behavior in a network of boomerang-shaped microchannels. The device design is informed by our FEM simulation results to predict sperm trajectories. Experimental results demonstrate the device's performance to separate over 16 000 motile sperm in under 20 min, sufficient for droplet-based IVF. Separated cells are classified into two motility groups, highly motile (swimming speed > 120 μm s^-1) and motile (swimming speed < 120 μm s^-1). The device selects sperm with over 45%, 20%, and 80% improvement in motility, the number of highly motile sperm, and DNA integrity, respectively, suggesting promising potential for applications in assisted reproduction.

Sperm quality metrics were improved by a biomimetic microfluidic selection platform compared to swim-up methods

Sperm selection is an essential component of all assisted reproductive treatments (ARTs) and is by far the most neglected step in the ART workflow in regard to technological innovation. Conventional sperm selection methodologies typically produce a higher total number of sperm with variable motilities, morphologies, and levels of DNA integrity. Gold-standard techniques, including density gradient centrifugation (DGC) and swim-up (SU), have been shown to induce DNA fragmentation through introducing reactive oxygen species (ROS) during centrifugation. Here, we demonstrate a 3D printed, biologically inspired microfluidic sperm selection device (MSSP) that utilizes multiple methods to simulate a sperms journey toward selection. Sperm are first selected based on their motility and boundary-following behavior and then on their expression of apoptotic markers, yielding over 68% more motile sperm than that of previously reported methods with a lower incidence of DNA fragmentation and apoptosis. Sperm from the MSSP also demonstrated higher motile sperm recovery after cryopreservation than that of SU or neat semen. Experiments were conducted side-by-side against conventional SU methods using human semen (n = 33) and showed over an 85% improvement in DNA integrity with an average 90% reduction in sperm apoptosis. These results that the platform is easy-to-use for sperm selection and mimics the biological function of the female reproductive tract during conception.