Microfluidic Applications for Andrology

Can Microfluidics Improve Sperm Quality? A Prospective Functional Study

The same sperm selection techniques in assisted reproduction clinics have remained largely unchanged despite their weaknesses. Recently, microfluidic devices have emerged as a novel methodology that facilitates the sperm selection process with promising results. A prospective case-control study was conducted in two phases: 100 samples were used to compare the microfluidic device with Density Gradient, and another 100 samples were used to compare the device with the Swim-up. In the initial phase, a significant enhancement in progressive motility, total progressive motile sperm count, vitality, morphology, and sperm DNA fragmentation were obtained for the microfluidic group compared to Density Gradient. Nevertheless, no statistically significant differences were observed in sperm concentration and chromatin structure stability. In the subsequent phase, the microfluidic group exhibited significant increases in sperm concentration, total progressive motile sperm count, and vitality compared to Swim-up. However, non-significant differences were seen for progressive motility, morphology, DNA structure stability, and DNA fragmentation. Similar trends were observed when results were stratified into quartiles. In conclusion, in a comparison of microfluidics with standard techniques, an improvement in sperm quality parameters was observed for the microfluidic group. However, this improvement was not significant for all parameters.

Effects of sperm processing techniques on IVF pregnancy rates: a mini-review

Many factors associated with assisted reproductive technologies significantly influence the success of pregnancy after in vitro fertilization (IVF) either directly or indirectly. These factors include sperm processing techniques, egg retrieval, intrauterine artificial insemination, intracytoplasmic sperm injection, and embryo transfer. Among these technologies, sperm quality is one of the most critical factors for a successful IVF pregnancy. The method used for sperm processing plays a crucial role in determining the quality of sperm. Several widely used sorting techniques, such as conventional swim-up, density gradient centrifugation, magnetic activated cell sorting, and hyaluronic acid, have been extensively compared in various studies. Previous studies have shown that each sperm processing method causes varying degrees of sperm damage, particularly in sperm motility, concentration, morphological features, viability, and DNA integrity. However, sperm processing techniques have been developed slowly, and the impact of these methods on pregnancy rates is still unclear. Further exploration is needed. In this review, we aim to compare the results of different sperm processing techniques concerning sperm quality and IVF pregnancy rates. We will also discuss possible clinical approaches, such as microfluidics and integrated approaches, for testing and improving sperm quality.

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.

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.

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.

Microfluidic assessment of swimming media for motility-based sperm selection

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

Microfluidic mixing for sperm activation and motility analysis of pearl Danio zebrafish

Sperm viability in aquatic species is increasingly being evaluated by motility analysis via computer-assisted sperm analysis (CASA) following activation of sperm with manual dilution and mixing by hand. User variation can limit the speed and control over the activation process, preventing consistent motility analysis. This is further complicated by the short interval (i.e., less than 15 s) of burst motility in these species. The objectives of this study were to develop a staggered herringbone microfluidic mixer to: 1) activate small volumes of Danio pearl zebrafish (Danio albolineatus) sperm by rapid mixing with diluent, and 2) position sperm in a viewing chamber for motility evaluation using a standard CASA system. A herringbone micromixer was fabricated in polydimethylsiloxane (PDMS) to yield high quality smooth surfaces. Based on fluorescence microscopy, mixing efficiency exceeding 90% was achieved within 5 s for a range of flow rates (from 50 to 250 μL/h), with a correlation of mixing distances and mixing efficiency. For example, at the nominal flow rate of 100 μL/h, there was a significant difference in mixing efficiency between 3.5 mm (75±4%; mean±SD) and 7 mm (92±2%; P=0.002). The PDMS micromixer, integrated with standard volumetric slides, demonstrated activation of fresh zebrafish sperm with reduced user variation, greater control, and without morphologic damage to sperm. Analysis of zebrafish sperm viability by CASA revealed a statistically higher motility rate for activation by micromixing (56±4%) than manual activation (45±7%; n=5, P=0.011). This micromixer represented a first step in streamlining methods for consistent, rapid assessment of sperm quality for zebrafish and other aquatic species. The capability to rapidly activate sperm and consistently measure motility with CASA using the PDMS micromixer described herein will improve studies of germplasm physiology and cryopreservation.

A practical novel method for ensuring stable capacitation of spermatozoa from cryopreserved C57BL/6J sperm suspension

A large number of genetically modified mouse strains have been produced in recent years. Sperm cryopreservation is the most effective means of preserving these valuable strains, most of which have a C57BL/6 genetic background. However, the fertilization efficiency of sperm from several cryopreserved strains, including C57BL/6, is quite low. While new and improved methods of cryopreservation have been developed, the majority of sperm stocks have already been cryopreserved using traditional methods, such as storage in 18% raffinose and 3% skim milk (R18S3). Therefore, new thawing methods for these frozen stocks are needed. We have developed a new thawing method that involves selective collection of motile sperm and a preincubation medium that enhances capacitation. Motile sperm are selected simply by collecting a sample from the center of a dish, and capacitation is induced by the addition of methyl-beta-cyclodextrin, D-penicillamine, sodium citrate, and hypotaurine to modified Tyrode's solution. The fertilization rate of sperm prepared using this method was increased significantly compared to that of sperm thawed using the traditional method (63.9 vs 16.5%, P<0.01). These results demonstrate that this new in vitro fertilization method is an effective means of reviving C57BL/6 sperm cryopreserved in R18S3.

Sperm motion in a microfluidic fertilization device

Microfluidics has shown promise as a new platform for assisted reproduction. To assess the potential of microfluidics for fertilization, we studied sperm and fluid motion in microchannels to better understand the flow characteristics in a microfluidic device, how sperm interacted with this flow, and how sperm-oocyte attachment occurs in the device. There is a threshold fluid velocity where sperm transition from traveling with the fluid to a regime in which the sperm can move independently of the flow. A significant population of sperm remained in the inlet well area. Based on the lack of progressive forward movement, it was presumed that these sperm may have defects. Also of extreme interest was the tendency of sperm to travel along surface contours. These observations provide an improved understanding of sperm motion in microchannels and provide a basis for improved device designs that take advantage of the sperm/flow and sperm/geometry interactions.

The origins and the future of microfluidics

The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.