Freeze-thaw by liquid nitrogen promotes platelet-derived growth factor-AA and transforming growth factor-β1 release 
Li Hong-tao, Duan Jian-min, Zhou Mou, Ma Yu-xia, Katayama Tadashi
Chinese Journal of Tissue Engineering Research . 2010, (36): 6755 -6758 .  DOI: 10.3969/j.issn.1673-8225.2010.36.025