Quantifying Binding of Ethylene Oxide-Propylene Oxide Block Copolymers with Lipid Bilayers

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers are utilized for cell membrane stabilization and permeabilization.
• Understanding the interaction mechanism between these copolymers and lipid membranes is crucial for optimizing their applications.

Purpose of the Study:

• To investigate how polymer structure influences the association of PPO-PEO block copolymers with lipid bilayers.
• To quantify the binding percentage and liposome surface coverage of these copolymers.

Main Methods:

• Utilized 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) unilamellar liposomes as model membranes.
• Employed pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) to probe polymer diffusion in the presence and absence of liposomes.
• Quantified polymer-lipid bilayer association by fitting PFG-NMR echo decay curves to a biexponential model.

Main Results:

• PFG-NMR echo decay curves transitioned from single to biexponential in the presence of liposomes, indicating polymer binding.
• Increased total molecular weight and hydrophobicity of PPO-PEO copolymers significantly enhanced polymer-lipid bilayer association.
• Higher polymer concentrations led to increased liposome surface coverage, eventually reaching a saturation limit.

Conclusions:

• The hydrophobic PPO block likely inserts into the lipid bilayer, driving copolymer-membrane association.
• PFG-NMR provides a robust method for quantifying polymer-lipid bilayer interactions.
• Systematic variation of polymer structure offers a means to tune copolymer-membrane association for specific applications.