Scientists in Japan developed a method to freeze dry mouse sperm on sheets of specially-prepared paper. The sheets are stored in a "sperm book" and the samples could then be removed and attached to a postcard for mailing. The technique enables the sperm to be sent around to other researchers cheaply and safely. The University of Yamanashi scientists' work builds on their previous efforts to preserve sperm in glass ampules to be transported to the International Space Station for experiments. Unfortunately, the ampules would break easily, requiring them to be protected with bulky cushions that took up room that could be used for more sperm. From ScienceDaily:
With the new method of preservation, thousands of mouse strain's sperm could be stored in a single book, dubbed the "sperm book" by the scientists. The book was stored in a freezer at -30°C until further use for experiments.
[The team] wanted to figure out if the sperm would still be potent after being mailed tens of miles and, to their delight, it was. The scientists were able to mail the mouse sperm from the "sperm book" as postcards by attaching the plastic sheet to the postcard with no protection. One scientist even sent another a "Happy New Year" card with mouse sperm attached as a gift.