A new technique is presented (The EAPO Pat.No007992. 05.10.2006) allowing to obtain and utilize sterile and biologically safe empty microspheres for efficient cryopreservation of solitary spermatozoa in IVF/ICSI programmes.
Isaev D.A., Zaletov S.Y., Zaeva V.V., Zakharova E.E., Shafei R.A., Krivokharchenko I.S. Artificial microcontainers for cryopreservation of solitary spermatozoa. Abstracts for 23th Annual Meeting of the ESHRE. Human Reproduction. 2007. V. 22, Suppl. 1. P. i154-i155.

The problem of single sperm cryopreservation can be solved by use of the microcontainers that prevent loss during manipulations. Zonae pellucidae of human and mammalian eggs are the best microcontainers, but their use is limited by risk of contamination with infectious and genetical foreign material. Alternative variants, such as cryoloops, are too labour-consuming and are not widespread. In our work we describe the technique of individual spermatozoon cryoprezervation in artificial microspheres made out of agarose gel. Agarose it is nontoxic, biologically inert and does not induce acrosome reaction. Post-thaw motility of spermatozoa cryopreserved in agarose microspheres was 64%.
Isaev, D.A. Zaletov, S.Y. Single sperm cryopreservation. Problemy Reproduktsii. 2006. V. 12; № 5, P. 43-47. (Russian) ISSN 1025-7217