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Key Points Sperm swim using periodic but time-irreversible and unidirectional flagellar motion. When sperm swim near a boundary, hydrodynamic sperm–wall interactions result in surface accumulation and boundary-following behaviour Microfluidic techniques paired with high-speed imaging have resolved the full 3D swimming patterns of sperm in bulk fluid and revealed a 2D slither swimming mode for sperm near surfaces Microfluidics show promise in studying sperm rheotaxis and chemotaxis. Future research needs to focus on developing high-throughput platforms with single-cell-analysis capabilities to study human sperm chemotaxis Microfluidic technologies are emerging as rapid and low-cost diagnostic alternatives for at-home and clinical male fertility testing, and technologies for additional, automated morphological analysis of sperm are needed Microfluidic platforms enable selection of high-quality sperm by mimicking the in vivo process. These technologies show promise for near-term advances in both understanding male infertility and clinical implementation Translation of microfluidic technologies for male infertility into the consumer market and clinical practices has been slow. A combination of multidisciplinary collaborations and market opportunity will speed up this process Many emerging opportunities exist for microfluidics in male infertility diagnosis and treatment, and promising microfluidic approaches are under investigation for addressing male infertility. In this Review, the authors describe and discuss these approaches for sperm analysis and selection. Infertility is a growing global health issue with far-reaching socioeconomic implications. A downward trend in male fertility highlights the acute need for affordable and accessible diagnosis and treatment. Assisted reproductive technologies are effective in treating male infertility, but their success rate has plateaued at ∼33% per cycle. Many emerging opportunities exist for microfluidics — a mature technology in other biomedical areas — in male infertility diagnosis and treatment, and promising microfluidic approaches are under investigation for addressing male infertility. Microfluidic approaches can improve our fundamental understanding of sperm motion, and developments in microfluidic devices that use microfabrication and sperm behaviour can aid semen analysis and sperm selection. Many burgeoning possibilities exist for engineers, biologists, and clinicians to improve current practices for infertility diagnosis and treatment. The most promising avenues have the potential to improve medical practice, moving innovations from research laboratories to clinics and patients in the near future.

Fluctuating light is the norm for photosynthetic organisms, with a wide range of frequencies (0.00001 to 10 Hz) owing to diurnal cycles, cloud cover, canopy shifting and mixing; with broad implications for climate change, agriculture and bioproduct production. Photosynthetic growth in fluctuating light is generally considered to improve with increasing fluctuation frequency. Here we demonstrate that the regulation of photosynthesis imposes a penalty on growth in fluctuating light for frequencies in the range of 0.01 to 0.1 Hz (organisms studied: Synechococcus elongatus and Chlamydomonas reinhardtii ). We provide a comprehensive sweep of frequencies and duty cycles. In addition, we develop a 2 nd order model that identifies the source of the penalty to be the regulation of the Calvin cycle – present at all frequencies but compensated at high frequencies by slow kinetics of RuBisCO.

Sperm migration through the female tract is crucial to fertilization, but the role of the complex and confined structure of the fallopian tube in sperm guidance remains unknown. Here, by confocal imaging microchannels head-on, we distinguish corner- vs. wall- vs. bulk-swimming bull sperm in confined geometries. Corner-swimming dominates with local areal concentrations as high as 200-fold that of the bulk. The relative degree of corner-swimming is strongest in small channels, decreases with increasing channel size and plateaus for channels above 200 μm. Corner-swimming remains predominant across the physiologically-relevant range of viscosity and pH. Together, boundary-following sperm account for over 95% of the sperm distribution in small rectangular channels, which is similar to the percentage of wall swimmers in circular channels of similar size. We also demonstrate that wall-swimming sperm travel closer to walls in smaller channels (~100 μm), where the opposite wall is within the hydrodynamic interaction length-scale. The corner accumulation effect is more than the superposition of the influence of two walls and over 5-fold stronger than that of a single wall. These findings suggest that folds and corners are dominant in sperm migration in the narrow (sub-mm) lumen of the fallopian tube and microchannel-based sperm selection devices.

The level of airway constriction in thin slices of lung tissue is highly variable. Owing to the labor-intensive nature of these experiments, determining the number of airways to be analyzed in order to allocate a reliable value of constriction in one mouse is challenging. Herein, a new automated device for physiology and image analysis was used to facilitate high throughput screening of airway constriction in lung slices. Airway constriction was first quantified in slices of lungs from male BALB/c mice with and without experimental asthma that were inflated with agarose through the trachea or trans-parenchymal injections. Random sampling simulations were then conducted to determine the number of airways required per mouse to quantify maximal constriction. The constriction of 45 ± 12 airways per mouse in 32 mice were analyzed. Mean maximal constriction was 37.4 ± 32.0%. The agarose inflating technique did not affect the methacholine response. However, the methacholine constriction was affected by experimental asthma ( p  = 0.003), shifting the methacholine concentration–response curve to the right, indicating a decreased sensitivity. Simulations then predicted that approximately 35, 16 and 29 airways per mouse are needed to quantify the maximal constriction mean, standard deviation and coefficient of variation, respectively; these numbers varying between mice and with experimental asthma.

The role of excessive airway constriction in the hyperresponsiveness to nebulized methacholine in mice with experimental asthma is still contentious. Yet, there have been very few studies investigating whether the increased in vivo response to methacholine caused by experimental asthma is associated with a corresponding increase in ex vivo airway constriction. Herein, the responses to nebulized methacholine in vivo and airway constriction in lung slices ex vivo were studied in 8‐ to 10‐week‐old male mice of two strains, BALB/c and C57BL/6. Experimental asthma was induced by administering house dust mites (HDM) intranasally, once daily, for 10 consecutive days. Complementary ex vivo studies were conducted with excised tracheas to measure and compare isometric force. As expected, the in vivo response to methacholine, and especially the hyperresponsiveness caused by HDM, was greater in BALB/c than in C57BL/6 mice. In contrast, there were no differences in maximal airway constriction between mouse strains, and the hyperresponsiveness to nebulized methacholine caused by HDM in both mouse strains was not associated with a corresponding increase in ex vivo airway constriction. The experiments with excised tracheas demonstrated no differences in isometric force between strains and between mice with and without experimental asthma. It is concluded that the hyperresponsiveness to nebulized methacholine in an acute mouse model of asthma induced by repeated HDM exposures is not associated with excessive airway constriction ex vivo. What is the central question of this study? In this study, we investigated the association between the in vivo response of the respiratory system to nebulized methacholine and the ex vivo responsiveness of airways in two mouse strains with and without experimental asthma induced by repetitive intranasal exposures to house dust mites. The ex vivo assays included measurements of airway constriction in lung slices and measurements of isometric force with excised tracheas. What is the main finding and its importance? Although striking differences in the in vivo response to methacholine were observed between mouse strains and between mice with and without experimental asthma, these changes were not matched by corresponding changes in ex vivo airway responsiveness.

This study was undertaken to determine whether a smaller lung volume or a stiffer lung tissue accounts for the greater lung elastance of C57BL/6 than BALB/c mice. The mechanical properties of the respiratory system and lung volumes were measured with the flexiVent and compared between male C57BL/6 and BALB/c mice (n = 9). The size of the excised lung was also measured by volume liquid displacement. One lobe was then subjected to sinusoidal strains in vitro to directly assess the mechanical properties of the lung tissue, and another one was used to quantify the content of hydroxyproline. In vivo elastance was markedly greater in C57BL/6 than BALB/c mice based on 5 different readouts. For example, respiratory system elastance was 24.5 ± 1.7 vs. 21.5 ± 2.4 cmH 2 O/mL in C57BL/6 and BALB/c mice, respectively (p = 0.007). This was not due to a different lung volume measured by displaced liquid volume. On the isolated lobes, both elastance and the hydroxyproline content were significantly greater in C57BL/6 than BALB/c mice. These results suggest that the lung elastance of C57BL/6 mice is greater than BALB/c mice not because of a smaller lung volume but because of a stiffer lung tissue due to a greater content of collagen.

A platform compatible with microtiter plates to parallelize environmental treatments to test the complex impacts of multiple stressors, including parameters relevant to climate change and point source pollutants is developed. This platform leverages (1) the high rate of purely diffusive gas transport in aerogels to produce well‐defined centimeter‐scale gas concentration gradients, (2) spatial light control, and (3) established automated liquid handling. The parallel gaseous, aqueous, and light control provided by the platform is compatible with multiparameter experiments across the life sciences. The platform is applied to measure biological effects in over 700 treatments in a five‐parameter full factorial study with the microalgae Chlamydomonas reinhardtii. Further, the CO2 response of multicellular organisms, Lemna gibba and Artemia salina under surfactant and nanomaterial stress are tested with the platform. A high‐throughput experimental platform capable of investigating environmental multistressors is demonstrated. Adapting a long‐range gradient generator and a projector to microtiter plates enables experiments with parallel control of multiple gaseous, aqueous, and light parameters. The platform is compatible with experiments involving microorganisms, as well as experiments with small multicellular plants and animals.

The following study investigates splashing of impinging water droplets on superhydrophobic surfaces with and without the presence of a stagnation flow. Droplets were accelerated by either gravity or gravity and co-flow. By changing the height and the air flow velocity different combinations of stagnation flow and droplet velocity were created. The spreading diameter, spreading velocity and contact time were studied for different air and droplet speeds. It was clearly observed that for a fixed impact velocity (i.e. constant Weber number), the presence of the stagnation flow promotes splashing and formation of satellite droplets. Consequently, for the co-flow droplet impact experiments, the mass of the recoiled droplet is significantly smaller than that of the impinging droplet in still air.

As legalization of cannabis increases worldwide, vaping cannabis is gaining popularity due to the belief that it is less harmful than smoking cannabis. However, the safety of cannabis vaping remains untested. To address this, we developed a physiologically relevant method for in vitro assessment of cannabis vapor on alveolar epithelial cell cultures. We compared the transcriptional response in three in vitro models of cannabis vapor exposure using A549 epithelial cells in submerged culture, pseudo-air liquid interface (ALI) culture, and ALI culture coupled with the expoCube™ advanced exposure system. Baseline gene expression in ALI-maintained A549 cells showed higher expression of type 2 alveolar epithelial (AEC2) genes related to surfactant production, ion movement, and barrier integrity. Acute exposure to cannabis vapor significantly affected gene expression in AEC2 cells belonging to pathways related to cancer, oxidative stress, and the immune response without being associated with a DNA damage response. This study identifies potential risks of cannabis vaping and underscores the need for further exploration into its respiratory health implications. Graphical Abstract • Vaporizing cannabis is increasingly popular but remains largely untested. • We used three in vitro models to assess the effects of cannabis vapor on alveolar epithelial cells. • Cannabis vapor exposure alters pathways linked to cancer and metabolism, without causing DNA damage.

The ability of large datasets of simple metrics (i.e. growth rate, lipid accumulation) to contribute to the understanding of microalgal photosynthesis is explored in this thesis. Specifically, three tools were developed, (i) a microfluidic multiplexed irradiance assay, which was composed of a microfluidic chip and a liquid crystal display; (ii) a second order mathematical model which can predict the growth under fluctuating light for periods ranging from a day to one under second and; (iii) a combinatorial assay for studying the mixed effect of light and nitrogen on growth and lipid accumulation. The multiplexed microfluidic irradiance assay (Microalgae on display) was capable of producing a large number of independent light treatments (200+), while avoiding the self-shading typical of flask-scale experiments. A set of linear ordinary differential equations were capable of capturing a second order behavior of photosynthetic growth, specifically a penalty at intermediate frequencies. This behavior lies outside the prevailing understanding of a high and low frequency limit. Lastly, the interplay between irradiance intensity and ammonium was resolved, showing that ammonium concentration plays a role at high light intensities only.