Vitrification (not freezing) can preserve biological structure very well. Adding high concentrations of chemicals called cryoprotectants to cells permits tissue to be cooled to very low temperatures with little or no ice formation. The state of no ice formation at temperatures below -120°C is called vitrification. It is now possible to physically vitrify organs as large as the human brain, achieving excellent structural preservation without freezing.

• http://www.alcor.org/AboutCryonics/