Thermal analysis of liposome suspensions was performed to study their freezing behavior and effect of trehalose distributed across the membranes. Cooling scan of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) liposome suspensions showed exotherm peaks of bulk (heterogeneous ice nucleation, -15 to -25℃) and intraliposomal (homogeneous ice nucleation, approx. -45℃) solution freezing. Changing size of the intraliposomal ice formation peak indicated dehydration of liposomes after the bulk solution freezing. Liposomes of larger size and/or lower membrane fluidity showed slower rate of dehydration upon the bulk solution freezing. Addition of trehalose before and after the liposome preparation resulted in their different distribution across the membrane and varied freezing behaviors.
