A step towards the automation of intracytoplasmic sperm injection: real time confirmation of mouse and human oocyte penetration and viability by electrical resistance measurement

Objective: To evaluate if oocyte penetration and viability can be confirmed by an electrical resistance increase. Automated (robotic) intracytoplasmic sperm injection (ICSI) requires confirmation of oolemma penetration before sperm injection. Visual assessment using image processing algorithms have been developed but remain unreliable. We hypothesized that an increase in electrical resistance upon oolemma piercing during ICSI can serve as an objective tool to confirm oocyte penetration and viability. Design: Experimental study. Setting: Research laboratory in an academic center. Patients/Animals: Oocytes from female mice and women undergoing oocyte retrieval procedure. Intervention: Oolemma piercing attempts with the ICSI pipette were performed by advancing the pipette towards mature (metaphase II) oocytes collected from 6 to 12-week-old mice and immature (germinal vesicle stage and metaphase I) oocytes donated by women who underwent oocyte retrieval. Electrical resistance was measured using a conventional electrophysiological setup that includes an electrical resistance meter and two electrical wires located in the lumina of the holding and ICSI pipettes. Main Outcome Measure(S): The measure of interest was the change in electrical resistance (ΔR) before and after advancing the ICSI pipette in an attempt to penetrate an oocyte. The experiments of resistance measurements were done in 3 steps: Step 1 (proof of concept), penetrated vs. non-penetrated mouse oocytes. Step 2, mouse oocytes with visually intact oolemma vs. fragmented mouse oocytes. Step 3, human oocytes with visually intact oolemma vs. fragmented human oocytes. For each group, median and range (in parenthesis) of ΔR were determined in MΩ. Mann-Whitney test was performed to compare the two groups in each step. Results: In Step 1, the penetrated mouse oocytes showed a statistically significant resistance increase compared to the non-penetrated ones (n = 20, median ΔR = 7.79 [2.57 – 106.00] vs. n = 15, median ΔR = 0.10 [-0.06 – 0.69], respectively. In Step 2, the mouse oocytes with visually intact oolemma showed a statistically significant resistance increase compared to the fragmented ones (n = 45, median ΔR = 6.5 [0.1 – 191.7] vs. n = 13, median ΔR = 0.1 [-0.3 – 2.2], respectively. In Step 3, the human oocytes with visually intact oolemma showed a statistically significant resistance increase compared to the fragmented ones (n = 96, median ΔR = 1.92 [-0.05 – 6.70] vs. n = 17, median ΔR = 0.11 [0.00 – 0.30], respectively. Conclusions: An electrical resistance increase can serve as a reliable tool to confirm oocyte penetration and viability, independent of optical visualization. Following further validation and safety assessment, this technology can potentially be integrated into manual and robotic ICSI systems.