Making immotile sperm motile using high-frequency ultrasound

Collective sperm movement in mammalian reproductive tracts

Mammalian sperm cells travel from their origin in the male reproductive tract to fertilization in the female tract through a complex process driven by coordinated mechanical and biochemical mechanisms. Recent experimental and theoretical advances have illuminated the collective behaviors of sperm both in vivo and in vitro. However, our understanding of the underlying mechano-chemical processes remains incomplete. This review integrates current insights into sperm group movement, examining both immotile and motile states, which are essential for passive transport and active swimming through the reproductive tracts. We provide an overview of the current understanding of collective sperm movement, focusing on the experimental and theoretical mechanisms behind these behaviors. We also explore how sperm motility is regulated through the coordination of mechanical and chemical processes. Emerging evidence highlights the mechanosensitive properties of a sperm flagellum, suggesting that mechanical stimuli regulate flagellar beating at both individual and collective levels. This self-regulatory, mechano-chemical system reflects a broader principle observed in multicellular systems, offering a system-level insight into the regulation of motility and collective dynamics in biological systems.

Reconfiguring Surface Acoustic Wave Microfluidics via In Situ Control of Elastic Wave Polarization

We demonstrate in situ control of the elastic wave polarization in a surface acoustic wave (SAW). It allows us to create highly reconfigurable SAW microfluidics that can be switched on demand between the acoustohydrodynamic (AHD) regime and electrohydrodynamic (EHD) regime for manipulating particles and cells. The control of wave polarization comes from our experimental and theoretical identification of an unexpected shear-horizontal (SH) wave mode in a conventional Rayleigh (R) wave design, which is stereotyped to excite only vertically polarized Rayleigh SAWs. The SH wave mode is predominantly horizontally polarized and can be selectively excited to propagate in the same direction as the Rayleigh SAW. Such a selective wave generation between the SH mode and R mode allows for reconfiguration between AHD and EHD regimes that leads to unprecedented colloidal patterns and assembly dynamics. Such a reconfiguration of the particle manipulation mechanism can be explained by the controllable competition or synergism between the coexisting acoustic and electric fields. Remarkably, in the EHD regime, a virtual zero-boundary electric quadrupole is created, and a novel colloidal diamond-shaped assembly is observed in this piezoelectric-quadrupole trap, which was rarely reported in acoustic or electric microfluidics. The presented in situ control of polarization revolutionizes our understanding of SAW and acoustofluidics, expands its potential by assuming the advantages of AHD and EHD on demand, and inspires new strategies in micro- and nanoscale manufacturing and manipulation, with applications beyond fundamental scientific interest.

Repeated pulses of ultrasound maintain sperm motility

Sperm motility is a primary criterion for selecting viable and functional sperm in assisted reproduction, where the most motile sperm are used to increase the likelihood of successful conception. Traditional chemical agents to enhance motility pose embryo-toxicity risks, necessitating safer alternatives. This study investigates the use of low-intensity pulsed ultrasound exposure as a non-invasive treatment within an acoustofluidic device to maintain sperm motility. We utilized a droplet-based platform to examine the effects of repeated ultrasound pulses on single human sperm cells. Our findings demonstrate that repeated pulsed ultrasound maintains sperm motility over an hour, with significant improvements in motility parameters by at least 25% as compared to non-exposed sperm. Moreover, we show that the motility enhancements by repeated pulsed ultrasound are more significant in initially non-progressive sperm. Importantly, this method did not compromise sperm viability or DNA integrity. These results suggest a viable, sperm safe approach to enhance and maintain sperm motility, potentially improving assisted reproduction outcomes.

Acoustic enrichment of sperm for in vitro fertilization

Assisted reproductive technology (ART) has emerged as a crucial method in modern medicine for tackling infertility. However, the success of fertilization depends on the quality and quantity of sperm, often necessitating invasive surgical intervention, which presents challenges for non-invasive in vitro fertilization. Acoustic microfluidics technology has found widespread application across various biological contexts. In this paper, we propose to introduce a novel approach using asymmetric acoustic streaming generated by a single interdigital transducer (IDT) to enhance sperm concentration and improve fertilization in vitro, particularly in cases of moderate oligozoospermia. The concentration of particles increased approximately 6-fold in the central region after acoustic enrichment. Moreover, sperm motility was significantly improved without additional DNA fragmentation, and all the oocytes remained viable after 5 min of acoustic enrichment. Notably, acoustic enrichment accelerated fertilization and embryo development, leading to a higher fertilization rate and faster cleavage speed. Specifically, within 36 hours, the multiple-cell embryo ratio was significantly increased compared to the control group. This finding further validates the feasibility and non-invasiveness of acoustic enrichment for sperm fertilization in vitro. This work provides a promising tool for in vitro fertilization, holding significant implications for assisted reproduction.

Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation

Crescent-shaped hydrogel microparticles are shown to template uniform volume aqueous droplets upon simple mixing with aqueous and oil media for various bioassays. This emerging "lab on a particle" technique requires hydrogel particles with tunable material properties and dimensions. The crescent shape of the particles is attained by aqueous two-phase separation of polymers followed by photopolymerization of the curable precursor. In this work, the phase separation of poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40 000) for tunable manufacturing of crescent-shaped particles is investigated. The particles' morphology is precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rates of various streams. The fabricated particles with variable dimensions encapsulate uniform aqueous droplets upon mixing with an oil phase. The particles are fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color-coded particles. The blue fluorescent dye shows a moderate response to the pH change. The fluorescently labeled particles are able to tolerate an extremely acidic solution (pH 1) but disintegrate within an extremely basic solution (pH 14). The particle-templated droplets are able to effectively retain the disintegrating particle and the fluorescent signal at pH 14.