Effects of procedure manipulation and induced nucleation on sperm cryopreservation

BACKGROUND: Sperm cryopreservation is essential for assisted reproductive technologies, yet current methods face challenges regarding cryoprotectant toxicity and protocol standardization. OBJECTIVE: To develop an optimized cryopreservation system by investigating cryoprotective mechanisms and establishing standardized freezing protocols without using any animal-derived material. MATERIALS AND METHODS: Thermodynamic analysis was performed to evaluate the cryoprotectant efficacy of glycerol (i.e., its ice crystal inhibition properties). An optimized formulation combining 10% glycerol with recombinant human serum albumin (rHSA) was developed to replace traditional egg yolk components. A novel freezing protocol incorporating gradient cooling and precise nucleation at −8.5°C was implemented using a custom-designed automated cryopreservation device (±1°C precision). RESULTS: The optimized formulation significantly reduced the melting enthalpy while it maintained post-thaw sperm motility of 75.4 ± 3.2% and DNA fragmentation index <15%. The freezing protocol achieved 82.6 ± 4.1% recovery rate and reduced ice crystal formation by 62.3%. Preclinical study demonstrated significant improvements versus conventional methods (increased motility by 27.8% and enhanced DNA integrity by 34.6%, both p < 0.01). CONCLUSION: The study established a standardized, pathogen-free cryopreservation system with demonstrated efficacy in preserving sperm quality. The findings provide both technical solutions for clinical practice and fundamental insights into cryoprotective mechanisms.