They used a specialised solution to protect the liver sinusoids and epithelial cells from the potential damage of freezing and ice crystals. Polyethylene glycol (PEG) was used to protect the epithelial cells and a glucose derivative 3-O-methyl-D-glucose (3-OMG) was used to protect from supercooling.

More information can be found from the study here:
http://www.nature.com/nm/journal/v20/n7/full/nm.3588.html