Aggregation of dipalmitoylphosphatidylcholine vesicles

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Dipalmitoylphosphatidylcholine (DPPC) vesicles are model systems for studying lipid membrane behavior.
• Understanding vesicle aggregation and fusion is crucial for drug delivery and biomaterial design.
• The gel-liquid-crystalline phase transition significantly impacts lipid vesicle properties.

Purpose of the Study:

• To investigate the aggregation kinetics of DPPC vesicles below their phase transition temperature.
• To determine the influence of vesicle concentration, temperature, and size on aggregation and fusion.
• To develop a model for vesicle-aggregate interactions and fusion mechanisms.

Main Methods:

• Quasi-elastic light scattering (QELS) was employed to analyze vesicle size and aggregation.
• 90-degree light scattering was used to monitor changes in aggregate formation.
• Experiments were conducted across varying DPPC vesicle concentrations, temperatures, and initial vesicle sizes.

Main Results:

• Vesicle concentration influenced the number of aggregates, suggesting a bimolecular collisional mechanism for fusion.
• Increased temperature reduced aggregation, as the disaggregation rate surpassed the aggregation rate.
• Aggregation varied with vesicle size, decreasing for smaller vesicles (up to 700 A) and increasing for larger ones (950 A).

Conclusions:

• A model was proposed where aggregation precedes fusion in DPPC vesicles below the phase transition.
• Collisions between vesicle aggregates act as a trigger for fusion.
• Temperature and vesicle size are critical factors modulating the aggregation-fusion pathway.