Bimodal polymer mushrooms: compressive forces and specificity toward receptor surfaces

Area of Science:

• Biomaterials Science
• Nanotechnology
• Surface Chemistry

Background:

• Poly(ethylene glycol) (PEG) chains are crucial for extending nanoparticle circulation time.
• Optimizing PEG structure for enhanced target specificity in nanomedicine remains a challenge.

Purpose of the Study:

• To investigate the impact of bimodal poly(ethylene glycol) (PEG) chain lengths on nanoparticle targeting specificity.
• To measure specific and nonspecific forces between grafted polymer layers and model receptor surfaces.

Main Methods:

• Utilized the surface force apparatus to compress supported lipid membranes with varying PEG chain lengths against streptavidin surfaces.
• Modeled bimodal mixtures of grafted polymer mushrooms with controlled fractions of biotin-ligated PEG.

Main Results:

• Longer 5000 Da PEG chains increased steric repulsion, reducing net adhesion when shorter chains were ligated.
• The 5000 Da chain did not alter the initial ligand-receptor binding distance.
• Flexible PEG tethers allowed ligand-receptor bond formation beyond the equilibrium mushroom layer edge under static and dynamic flow.

Conclusions:

• Liposome targeting is enhanced by grafting ligands with a contour length exceeding the bimodal mushroom layer's equilibrium height.
• Understanding polymer brush structure is key to designing effective targeted nanoparticles.