Cryopreservation and xenografting of human ovarian fragments: medulla decreases the phosphatidylserine translocation rate oleh Vladimir Isachenko, Plamen Todorov, Evgenia Isachenko, Gohar Rahimi, Bettina Hanstein, Mahmoud Salama, Peter Mallmann, Andrey Tchorbanov, Paul Hardiman, Natalie Getreu, Markus Merzenich