(221a) Dynamic Surface Tensions (DSTs) of Dipalmitoylphosphatidylcholine (DPPC) Dispersions at Physiological Conditions
AIChE Annual Meeting
Tuesday, November 18, 2008 - 8:35am to 8:55am
Dipalmitoylphosphatidylcholine (DPPC) is the major lipid ingredient of natural lung surfactant, which stabilizes the lung alveoli by reducing greatly the surface tension at the air/liquid interface. The effect of the buffer compositions on the dynamic surface tension (DST) and vesicle sizes of aqueous DPPC was studied. The DPPC dispersions prepared with extensive sonication produced low tension minima (γmin), lower than 10 mN/m, in PBS (without Ca2+ or with Ca2+) or in HEPES buffer with calcium. Tensiometry results indicate that DPPC dispersions in HEPES buffer produce lower DSTs and achieve low DSTs faster at pulsating area conditions than the DPPC in the other buffers. The DLS and ST results suggest that the DPPC vesicle sizes in HEPES buffer are much smaller than those in the other buffers, consistently with the DLS results.
The effect of concentration on the DST of DPPC in PBS with Ca2+ was also studied. At 1000 ppm concentration, DPPC dispersions produced low tension minima (γmin), lower than 10 mN/m, after 10 minutes pulsation, which is the fastest compared with other concentrations. The γmin also reached to the value, lower than 10 mN/m, after 20 minutes pulsation at pulsating rate of 20 rpm right after generating bubble.
The effect on the ability of DPPC to lower the DSTs in water, PBS, PBS with Ca2+, and HEPES with Ca2+ was also studied with another method of preparing the DPPC dispersions, devised by Bangham and others. The DPPC dispersions prepared with the Bangham method can produce low tension minima (γmin), lower than 10 mN/m, in all conditions except with PBS solutions. The time it takes to reach DSTs below the 10 mN/m limit is longer than with the new method by 10 minutes. The effect on the DPPC vesicle size was also examined. The diameter of the DPPC vesicles is larger than with the new method, and especially in HEPES with Ca2+, the diameter is 980 nm whereas the one prepared with new method is 70 nm. In addition, while the new method's DPPC vesicles remained about the same for one month, the other method's vesicles increased day by day. The results show the dispersions for the new method are much more stable. These results have implications for designing efficient protocols of lipid dispersion preparation and for effective administration of lung surfactant replacement formulations for treating alveolar respiratory diseases.