Temperature-Sensitive Nonionic Vesicles Prepared from Span 80 (Sorbitan Monooleate)

Abstract

Different types of nonionic vesicles were prepared from commercial Span 80 (also called sorbitan monooleate), as an inexpensive, biocompatible alternative to conventional phospholipid-based vesicles (liposomes). The vesicles were characterized by different techniques and comparison was made with vesicles formed from POPC (1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine) or DOPC (1,2-dioleoyl- sn-glycero-3-phosphocholine). Dynamic light scattering measurements, electron microscopy analyses, and two types of fusion assays indicate that Span 80 vesicles are stable for at least 7 days at 4 or 25 degrees C, while storage at 42 degrees C causes irreversible vesicle fusion. This indicates that Span 80 vesicles are thermoresponsive with vesicle fusion occurring at elevated temperature. This property may be related to headgroup dehydration and is certainly not directly linked to the phase transition temperature (Tm) of the vesicles, since the Tm is below -30 degrees C, as determined by differential scanning calorimetry (DSC). The measured Tm value for Span 80 vesicles is lower than in the case of DOPC or POPC, correlating with a higher fluidity of Span 80 vesicles as compared to POPC or DOPC vesicles, as determined with DPH (1,6-diphenyl-1,3,5-hexatriene) as fluorescent membrane probe. High fluidity correlates with increased leakage of entrapped water-soluble dye molecules. Addition of cholesterol and soybean phosphatidylcholine lowers the extent of leakage, allowing a tuning of the bilayer permeability.

Molecular Dynamics Simulation of Sorbitan Monooleate Bilayers

“…3a) the bilayer was in a liquid crystalline phase with a large lateral diffusion constant (Table 1). This is expected as the phase transition temperature of Span 80 was determined to be 254 K, 11 which is much lower than the simulation temperature (298 K) of the present work. The APL was 0.343 nm ).…”

Physico-chemical Studies on the Interaction of Dendrimers with Lipid Bilayers. 1. Effect of Dendrimer Generation and Liposome Surface Charge

“…Cholesterol is one of the active component of cell membranes. It is known to control the fluidity/rigidity of membrane bilayers 25 . It is, therefore, proposed to undertake the studies on the interaction of dendrimers with the membrane mimetic systems which will resemble more closely to the biological systems.…”

Inter-vesicle polymerization using nonionic oxyethylene-hydrogenated castor oil

“…However, the aggregation of electrically neutral vesicles cannot be explained by the conventional DLVO theory, and several investigations have pointed out the importance of the so-called hydration force (as opposed to an electrostatic repulsive interaction) for the stability of electrically neutral vesicles [25][26][27]. For instance, Walde and co-workers [28] studied the interactions of nonionic vesicles, reporting that the aggregation and fusion of the nonionic vesicles is temperature dependent. Huang and co-workers [29] observed a catanionic-vesicle aggregation induced by a temperature increase, suggesting that the increase in the temperature promotes the removal of hydration water, which in turn results in a decrease in the hydration repulsion between vesicles.…”