In vitro survival kinetics of microfluidic-sorted bovine spermatozoa.

Abstract

The isolation and characterization of sperm subpopulations that can achieve fertilization is a major challenge of assisted reproduction methods. We focused on the microfluidic sperm sorter as a novel tool for collecting highly motile spermatozoa from heterogeneous semen samples. This study primarily aims to obtain baseline information on sorted spermatozoa according to its characteristics and in vitro life span. Frozen-thawed bull semen was subjected to microfluidic sperm sorting using diffuser-type microfluidic sperm sorter (DMSS). After sorting, samples were collected as the sorted spermatozoa and unsorted residual spermatozoa and incubated at 37°C for subsequent evaluation. The samples were assessed at different time points (0 or 1, 6, and 24h) in terms of motility, which was measured by computer-assisted sperm analysis (CASA), membrane integrity, mitochondrial function, and adenosine triphosphate (ATP) production after sorting (0h). To determine the characteristics and efficiency of DMSS sorting, the sorted spermatozoa were compared with samples collected using the swim-up method, a conventional method in motile sperm selection. A comparison between the sorted and residual spermatozoa demonstrated significantly higher motility parameters, membrane integrity, and mitochondrial function of the sorted spermatozoa until 6h after incubation. The time course decrement of membrane and mitochondrial status were subjected to curve fitting and theoretically supported. Sperm ATP production measured immediately after sorting showed higher ATP generation of the sorted spermatozoa compared with the unsorted, frozen-thawed spermatozoa. The motility parameters and mitochondrial activity of DMSS-sorted spermatozoa were higher than the swim-up-collected spermatozoa (p<0.05). These results indicate that DMSS sorting can strictly select highly motile spermatozoa with the ability to maintain its membrane integrity and mitochondrial function related to ATP production. We speculate that the device that is able to sort high-quality spermatozoa can have great potential in assisted reproduction.