Selection of Functional Human Sperm with Higher DNA Integrity and Fewer Reactive Oxygen Species

Abstract

Fertilization and reproduction are central to the survival and propagation of a species. Couples who cannot reproduce naturally have to undergo in vitro clinical procedures. An integral part of these clinical procedures includes isolation of healthy sperm from raw semen. Existing sperm sorting methods are not efficient and isolate sperm having high DNA fragmentation and reactive oxygen species, and suffer from multiple manual steps and variations between embryologists. Inspired by in vivo natural sperm sorting mechanisms where vaginal mucus becomes less viscous to form microchannels to guide sperm towards egg, we present a chip that efficiently sorts healthy, motile and morphologically normal sperm without centrifugation. Higher percentage of sorted sperm show significantly lesser reactive oxygen species and DNA fragmentation than the conventional swim-up method. The presented chip is an easy-to-use high throughput sperm sorter that provides standardized sperm sorting assay with less reliance on embryologist’s skills, facilitating reliable operational steps.

Predominance of sperm motion in corners

“…With respect to the geometry, the fallopian tube becomes remarkably folded and confined with narrow lumen and corners as the sperm progresses along its journey56. Emerging assisted reproduction methods also employ microconfined geometries to mimic the female tract for in vitro sperm selection16171819 and to coordinate fertilization20212223. There is a lack, however, of quantitative understanding of how geometrical complexity and confinement influence sperm motion.…”

Recent advances in microfluidic diagnostic and treatment systems for assisted reproductive technologies in developing countries

“…In sections 4.4. and 4.5., we summarized evidence that sorted motile sperm possess higher DNA integrity, as indicated by studies of microfluidic devices without centrifugation [57,58,62,63,85]. Developments and applications of microfluidics have contributed markedly to improvements in ART over the past 20 years.…”

“…This disadvantage of low recovered motile sperm concentrations follows dilution of semen to control viscosity for laminar flow adjustments. Hence, motile sperm were sorted using microfluidic channels equipped with micro-pore filters (pore size: 4-20 µm) to separate non-motile sperm from those that swim up in a vertical direction, and motility and morphology of sorted sperm were greater than in unsorted sperm [62,63]. Because sorted motile sperm concentrations have not been discussed previously, it remains unclear whether this device can recover motile sperm concentrations sufficiently for IUI [63].…”

Sperm selection before intracytoplasmic sperm injection

“…Two recent papers developed lab-on-a-chip microfluidic devices for sorting sperm through microchannels (100) or a microfluidic sperm sorter (101). Nosrati et al (100) reported the one step purification of a sperm subpopulation with high viability and DNA integrity from 1ml of semen in less than 20 minutes, whereas Asghar et al (101) sorted sperm with significantly lower oxidative stress and DNA fragmentation compared to the conventional swim-up method. Although, these novel methods were still not applied in ART, their results are particularly impressive as they outperform the best currently applied clinical procedures and indicate that the interaction between different branches of science may open a new era in sperm selection for ART.…”