Surfactant modification of the surface energetics of hydrophobic polymers and protein adsorption

Abstract

A low interfacial free energy between a polar surface and water is expected to lead to a smaller amount of protein adsorbed. However, nonpolar surfaces have high interfacial free energies with water. They can acquire lower interfacial free energies by modifying the polar and dispersion components of their surface free energy so that they approach those of water. The two-phase method, in which an aqueous solution of surfactant and chloroform constitute the two-phase system, can be used for the modification of the hydrophobic surface. The hydrophobic polymer is immersed for a short time in chloroform (which is a solvent for the polymer). This allows disentanglement of the surface chains. Subsequently, the polymer is pulled out through the solvent-water interface and further through the water phase. The monolayer of adsorbed surfactant present at the water-chloroform interface is thus transferred to the surface of the polymer. The hydrophobic chains of the surfactant and polymer entangle and the polar head groups orient towards the water phase. Protein adsorption experiments carried out with albumin and fibrinogen showed that the amounts of protein adsorbed on unmodified PMMA surfaces can be significantly higher than those on SDS- and Brij 35-modified surfaces. The sequence for adsorption is unmodified surface > SDS-modified surface > Brij 35-modified surface.

Keywords:

• Surface modification
• surfactant
• hydrophobic polymer
• protein adsorption