Cryoprotectants

are substances that avoid crystallization during the freezing process. They are especially important when using a serum-free medium and interact, for example, with water molecules or increase the solubility of salts which also avoids cellular damage ^{47, 48}. The protectants themselves, however, are harmful to the cells. Cell damage increases with increased time of contact. For this reason freeze and thaw should be conducted as quickly as possible in order to minimize the contact time of protectant and cells. See cryoconservation.