Transmission electron microscopy of a thin-sectioned freeze-substituted suspension of human sperm cryopreserved in conventional straws (0.25ml capacity). The cryoprotectant used was glycerol/egg yolk. Ice was nucleated within the straw at -7°C. The sample was then cooled at 10°C per minute to -100°C and then transferred to liquid nitrogen. When viewed by electron microscopy the freeze concentrated material was electron dense due to the protein components of the egg yolk included in the cryoprotectant. Sperm cells embedded within the freeze concentrated material were similar to unfrozen controls - there was no evidence of osmotic shrinkage or of the presence of ice voids within the heads of the spermatozoa, although some shrinkage is observed in distal sections.
