Pluronic^®-bile salt mixed micelles.

Area of Science:

• Polymer Science
• Biophysical Chemistry
• Materials Science

Background:

• Bile salts are crucial for physiological processes, including lipid digestion and absorption.
• Ethylene polyoxide-polypropylene polyoxide (PEO-PPO-PEO) triblock copolymers, like Pluronics®, self-assemble into micelles with tunable properties.
• Understanding the interaction between bile salts and polymer micelles is essential for developing drug delivery systems and comprehending biological functions.

Purpose of the Study:

• To investigate the interaction between two bile salts, sodium cholate (NaC) and sodium deoxycholate (NaDC), and three PEO-PPO-PEO triblock copolymers.
• To elucidate the effect of pH on the formation and properties of mixed micelles.
• To compare the behavior of moderately hydrophobic Pluronic® P123 with very hydrophobic L121 and very hydrophilic F127 in the presence of bile salts.

Main Methods:

• Small-angle neutron scattering (SANS) to determine micelle size and structure.
• Cloud point (CP) measurements to assess solution stability.
• Nuclear Overhauser effect spectroscopy (NOESY) to probe molecular interactions and location within micelles.

Main Results:

• Both NaC and NaDC increased the cloud point and decreased the apparent hydrodynamic diameter of copolymer solutions.
• SANS revealed that P123 forms small spherical micelles, decreasing in size with increasing bile salt concentration.
• NaDC, being more hydrophobic, showed a more pronounced effect than NaC. NaC induced micellar growth in acidic conditions due to bile acid formation, while NaDC led to phase separation at higher concentrations.

Conclusions:

• Bile salts interact with PEO-PPO-PEO copolymers to form smaller, bile salt-rich mixed micelles.
• pH significantly influences the micellar behavior, with acidic conditions promoting micellar growth for NaC via bile acid formation.
• The hydrophobicity of both bile salts and copolymers dictates the nature and extent of their interactions, providing insights into bile salt solubilization and physiological roles.