Separation of motile human sperms in a T-shaped sealed microchannel

Microfluidics as an emerging paradigm for assisted reproductive technology: A sperm separation perspective

Millions of people are subject to infertility worldwide and one in every six people, regardless of gender, experiences infertility at some period in their life, according to the World Health Organization. Assisted reproductive technologies are defined as a set of procedures that can address the infertility issue among couples, culminating in the alleviation of the condition. However, the costly conventional procedures of assisted reproduction and the inherent vagaries of the processes involved represent a setback for its successful implementation. Microfluidics, an emerging tool for processing low-volume samples, have recently started to play a role in infertility diagnosis and treatment. Given its host of benefits, including manipulating cells at the microscale, repeatability, automation, and superior biocompatibility, microfluidics have been adopted for various procedures in assisted reproduction, ranging from sperm sorting and analysis to more advanced processes such as IVF-on-a-chip. In this review, we try to adopt a more holistic approach and cover different uses of microfluidics for a variety of applications, specifically aimed at sperm separation and analysis. We present various sperm separation microfluidic techniques, categorized as natural and non-natural methods. A few of the recent developments in on-chip fertilization are also discussed.

Bio-inspired progressive motile sperm separation using joint rheotaxis and boundary-following behavior

Infertility, as a daunting ever-increasing challenge, poses a worldwide issue to both couples and the healthcare sector. According to the World Health Organization, half of infertility cases are attributed to male factor infertility, either partly or completely. Semen parameters of concern including sperm count, morphology, and motility are deemed to play a vital role in the insemination process. Density gradient centrifugation, being a clinically established procedure for improving on the mentioned parameters, has long been proven to inflict damage on the DNA content of the sperm cells, inducing DNA fragmentation. Herein, a bio-inspired microfluidic device is proposed that capitalizes on the geometry of the uterotubal junction (UTJ) of the female reproductive tract, which can act as a rheological barrier. The device leverages sperm rheotaxis and boundary-following behavior which have been considered as major migratory mechanisms used by sperm during the fertilization process in the female body. The device consists of a series of parallel channels that guide progressive motile sperms into the main sorting channel, where the hydrodynamic barriers created by two consecutive UTJ-like constrictions select sperms based on their propulsive velocity and linearity of motion. The sequential sorting employed here allows for the fractionation of the sperm population into two subpopulations with varying degrees of motility. Both sorted populations showed a significant increase in straight line velocity, reaching 63.4 ± 14.4 μm s-1 and 74 ± 13.8 μm s-1 in the first and second pools, respectively from 35.2 ± 27.2 μm s-1 in raw semen. Additionally, sorted populations demonstrated over 30% reduction in DNA fragmentation index, an indication that the proposed device selects for undamaged sperms with high quality. Apart from the biological superiority of the sorted sperms, this device presents itself as an easy and clinically-applicable method for the separation of progressive motile sperms, while at the same time, benefiting from a straightforward procedure for sperm retrieval.

Lab-on-chip (LoC) application for quality sperm selection: An undelivered promise?

Quality sperm selection is essential to ensure the effectiveness of assisted reproductive techniques (ART). However, the methods employed for sperm selection in ART often yield suboptimal outcomes, contributing to lower success rates. In recent years, microfluidic devices have emerged as a promising avenue for investigating the natural swimming behavior of spermatozoa and developing innovative approaches for quality sperm selection. Despite their potential, the commercial translation of microfluidic-based technologies has remained limited. This comprehensive review aims to critically evaluate the inherent potential of lab-on-chip technology in unraveling sophisticated mechanisms encompassing rheotaxis, thermotaxis, and chemotaxis. By reviewing the current state-of-the-art associated with microfluidic engineering and the swimming of spermatozoa, the goal is to shed light on the multifaceted factors that have impeded the broader commercialization of these cutting-edge technologies and recommend a commercial that can surmount the prevailing constraints. Furthermore, this scholarly exploration seeks to enlighten and actively engage reproductive clinicians in the profound potential and implications of microfluidic methodologies within the context of human infertility.