In natural fertilisation, stringent selection mechanisms favour genetically competent spermatozoa. In contrast, current spermatozoa preparation protocols used in assisted reproductive technologies (ART) lack the ability to select highly competent spermatozoa with similar precision. Conventional methods like swim-up and density gradient centrifugation are limited in removing apoptotic or DNA-damaged spermatozoa, affecting fertilisation success and embryo viability. Therefore, biomimetic approaches are urgently needed to improve ART outcomes.
We developed and validated a surface-engineered spermatozoa selection device incorporating a microchannel-based architecture that mimics natural selection processes in the female reproductive tract, including immune-mediated clearance. Microchannels (~50 µm deep, ~100 µm wide) were patterned onto glass slides using a diamond saw to promote directional motility and limit passive drift of compromised spermatozoa. Surfaces were coated with plasma-polymerised polyoxazoline, a biocompatible interface characterised via X-ray photoelectron spectroscopy and ellipsometry. Gold-nanoparticles were covalently attached to enhance surface topography and spermatozoa interaction.
To enable selective elimination of apoptotic spermatozoa, anti-phosphatidylserine (anti-PS) antibodies were immobilised near the channel inlet, simulating immune cell recognition. Progesterone also adsorbed at the outlet facilitated chemotactic retrieval of competent spermatozoa, showing time-dependent release from GNP-coated surfaces peaking at 20.7± 6.3 ng/mL at 60 minutes (competitive ELISA).
Optimising surface chemistry, geometry, and topography led to enrichment of spermatozoa with high DNA integrity. After 45 minutes of processing, spermatozoa collected at the outlet showed significantly improved spermatozoa motility and lower DNA fragmentation (0.6± 0.5% vs. 16.6± 1.6% in swim-up; P<0.0001, N=3). Annexin V-positive spermatozoa were also significantly reduced (3.9± 0.2% vs. 15.7± 4.6% in swim-up, P<0.05, N=3). Addition of microchannels provided a substantial improvement compared to previous models without microchannels, where DNA fragmentation rates averaged 4.5± 1.5% (N=5).
These data highlight the added value of microchannels in a channeled-slide format and support the translational potential of this non-invasive, efficient spermatozoa selection platform for ART.