Faster sperm selected by rheotaxis leads to superior early embryonic development in vitro.

To understand the impact of sperm speed as they swim against the flow on fertilization rates, we created conditions similar to the female reproductive tract (FRT) on a microfluidic platform for sperm selection. Selected sperm were evaluated based on early development of fertilized embryos. Bovine and human spermatozoa were selected at various fluid flow rates within the device. We found that the speed of bovine spermatozoa increases as the flow rate increases and that the amount of DNA fragmentation index is lowered by increasing the flow rate. Bovine spermatozoa selected by our platform at low (150 µL h-1, shear rate 3 s-1), medium (250 µL h-1, shear rate 5 s-1), and high flow rates (350 µL h-1, shear rate 7 s-1) were used for fertilization and compared to sperm sorted by centrifugation. The samples collected at the highest flow rate resulted in the formation of 23% more blastocysts compared to the control. While selecting for higher quality sperm by increasing the flow rate does result in lower sperm yield, quality improvement and yield may be balanced by better embryonic development.

Screening the Degradation of Polymer Microparticles on a Chip.

Enzymatic degradation of polymers has advantages over standard degradation methods, such as soil burial and weathering, which are time-consuming and cannot provide time-resolved observations. We have developed a microfluidic device to study the degradation of single microparticles. The enzymatic degradation of poly (1,4-butylene adipate-co-terephthalate) (PBAT) microparticles was studied using Novozym 51032 cutinase. PBAT microparticles were prepared via an oil-in-water emulsion solvent removal method, and their morphology and chemical composition were characterized. Then, microparticles with varying diameters of 30-60 µm were loaded into the microfluidic chip. Enzyme solutions at different concentrations were introduced to the device, and changes in the size and transparency of PBAT microparticles were observed over time. The physicochemical properties of degraded products were analyzed by FT-IR, NMR, mass spectrometry, and differential scanning calorimetry. The degradation process was also performed in bulk, and the results were compared to those of the microfluidic method. Our analysis confirms that the degradation process in both bulk and microfluidic methods was similar. In both cases, degradation takes place on aliphatic and soft segments of PBAT. Our findings serve as a proof of concept for a microfluidic method for easy and time-resolved degradation analysis, with degradation results comparable to those of conventional bulk methods.

Rheotaxis quality index: a new parameter that reveals male mammalian in vivo fertility and low sperm DNA fragmentation.

The female reproductive tract simultaneously guides and selects high-quality sperm using rheotaxis in mammalian species. Sperm quality, however, is traditionally evaluated only by their movement velocities and concentration using computer-assisted sperm analysis (CASA), which ignores sperm rheotaxis. Here, by mimicking the female reproductive tracts' dimensions and hydrodynamic features, a new method is introduced to quantify sperm rheotaxis ability for evaluating semen quality. The combination of our RHEOtaxis quaLity indEX (RHEOLEX) and motile sperm concentration is able to predict sperm fertility levels in artificial insemination at various shear rates within 5 minutes. This means that RHEOLEX could be a biomarker for determining male in vivo fertility, unlike conventional semen quality parameters which fail to provide statistically significant predictions. In addition, a high RHEOLEX is associated with a low DNA fragmentation index (DFI), showing that this new parameter is able to identify low-DFI samples. Not only does this work highlight the importance of rheotaxis in determining male in vivo fertility, but it also provides a solid benchmark for developing fast microfluidic devices for male fertility prediction as well as DFI. Last, the data imply that the female reproductive tract might use rheotaxis to keep sperm with fragmented DNA from reaching the fertilization site.

Non-contact ultrasound oocyte denudation.

Cumulus removal (CR) is a central prerequisite step for many protocols involved in the assisted reproductive technology (ART) such as intracytoplasmic sperm injection (ICSI) and preimplantation genetic testing (PGT). The most prevalent CR technique is based upon laborious manual pipetting, which suffers from inter-operator variability and therefore a lack of standardization. Automating CR procedures would alleviate many of these challenges, improving the odds of a successful ART or PGT outcome. In this study, a chip-scale ultrasonic device consisting of four interdigitated transducers (IDT) on a lithium niobate substrate has been engineered to deliver megahertz (MHz) range ultrasound to perform denudation. The acoustic streaming and acoustic radiation force agitate COCs inside a microwell placed on top of the LiNbO3 substrate to remove the cumulus cells from the oocytes. This paper demonstrates the capability and safety of the denudation procedure utilizing surface acoustic wave (SAW), achieving automation of this delicate manual procedure and paving the steps toward improved and standardized oocyte manipulation.

Rolling controls sperm navigation in response to the dynamic rheological properties of the environment.

Mammalian sperm rolling around their longitudinal axes is a long-observed component of motility, but its function in the fertilization process, and more specifically in sperm migration within the female reproductive tract, remains elusive. While investigating bovine sperm motion under simple shear flow and in a quiescent microfluidic reservoir and developing theoretical and computational models, we found that rolling regulates sperm navigation in response to the rheological properties of the sperm environment. In other words, rolling enables a sperm to swim progressively even if the flagellum beats asymmetrically. Therefore, a rolling sperm swims stably along the nearby walls (wall-dependent navigation) and efficiently upstream under an external fluid flow (rheotaxis). By contrast, an increase in ambient viscosity and viscoelasticity suppresses rolling, consequently, non-rolling sperm are less susceptible to nearby walls and external fluid flow and swim in two-dimensional diffusive circular paths (surface exploration). This surface exploration mode of swimming is caused by the intrinsic asymmetry in flagellar beating such that the curvature of a sperm's circular path is proportional to the level of asymmetry. We found that the suppression of rolling is reversible and occurs in sperm with lower asymmetry in their beating pattern at higher ambient viscosity and viscoelasticity. Consequently, the rolling component of motility may function as a regulatory tool allowing sperm to navigate according to the rheological properties of the functional region within the female reproductive tract.

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.

Biological small-molecule assays using gradient-based microfluidics.

Studying the potency of small-molecules on eukaryotic and prokaryotic cells using conventional biological settings requires time-consuming procedures and large volumes of expensive small-molecules. Microfluidics could significantly expedite these assays by enabling operation in high-throughput and (semi)automated modes. Here, we introduce a microfluidics platform based on multi-volume microchamber arrays that can produce a wide range of small-molecule concentrations with a desired gradient-based profile for rapid and precise biological testing within a single device with minimal hands-on time. The concept behind this device is based on introducing the same amount of a small-molecule into microchambers of different volumes to spontaneously generate a gradient concentration profile via diffusion. This design enables to obtain an unprecedented concentration range (e.g., three orders of magnitude) that can be easily adjusted, allowing us to pinpoint the precise effect of small-molecules on pre-loaded prokaryotic and eukaryotic cells. We also propose a comprehensive relationship for determining the loading time (the only required parameter for implementing this platform) in order to study the effects of any small-molecule on a biological species in a desired test. We demonstrate the versatility of this microfluidics platform by conducting two small-molecule assays-antimicrobial resistance and sugar-phosphate toxicity for both eukaryotic and prokaryotic biological systems.

Theoretical study of the photothermal behaviour of self-assembled magnetic-plasmonic chain structures.

We study the field-directed self-assembly and photothermal behavior of one-dimensional (1D) chains of core-shell Fe3O4@Au magnetic-plasmonic nanoparticles. Monte Carlo analysis is used to predict the self-assembly of the nanoparticles when they are subjected to a uniform magnetic field and confined to a fluidic nanochannel. A coupled photonic and thermodynamic analysis is performed to analyze the optical and photothermal properties of the 1D chain structures. We show for the first time that the assembled chain structures exhibit a pronounced dip in their absorption spectrum at a wavelength that is strongly sensitive to changes in the refractive index of the surrounding medium. The plasmon enhanced features of these structures are well suited for a variety of theranostic modalities as we discuss.