Currently, donor tissue is preserved in refrigerators, floating within a special solution that keeps it viable for about a month.

Currently, donor tissue is preserved in refrigerators, floating within a special solution that keeps it viable for about a month.
The Missouri Osteochondral Allograft Preservation System (MOPS) uses a new solution and specially designed containers. Another major benefit apart from doubling the lifetime is that it does not require refrigeration.
Source-Medindia