Femtosecond laser is effective tool for zona pellucida engraving and tagging of preimplantation mammalian embryos

Purpose Our purpose was to study whether application of femtosecond laser pulses for alphanumeric code marking in the volume of zona pellucida ( ZP ) could be effective and reliable approach for direct tagging of preimplantation embryos. Methods Femtosecond laser pulses (wavelength of 514 nm, pulse duration of 280 fs, repetition rate of 2.5 kHz, pulse energy of 20 nJ) were applied for precise alphanumeric code engraving on the ZP of mouse embryos at the zygote stage for individual embryo marking and their accurate identification. Embryo quality assessment every 24 h post laser-assisted marking as well as immunofluorescence staining (for ICM/TE cell number ratio calculation) were performed. Results Initial experiments have started with embryo marking in a single equatorial plane. The codes engraved could be clearly recognized until the thinning of the ZP prior to hatching. Since embryo may change its orientation during the ART cycle, multi-plane code engraving seems to be more practical for simplifying the process of code searching and embryo identification. We have marked the ZP in three planes, and no decrease in developmental rates as well as no morphological changes of embryos post laser-assisted engraving have been observed as compared to control group embryos. Conclusions Our results demonstrate the suitability of femtosecond laser as a novel tool for noninvasive embryo tagging, enabling embryo identification from day 0.5 post coitum to at least early blastocyst stage. Thus, the versatility and the potential use of femtosecond lasers in the field of developmental biology and assisted reproduction have been shown.