Surface modification of a perfluorinated ionomer using a glow discharge deposition method to control protein adsorption

Nafion™ is the membrane material preferred for in situ glucose sensors. Unfortunately, surface properties of Nafion promote random protein adsorption and eventual foreign body encapsulation thus leading to loss of glucose signal over time. Here we detail surface modifications made by RF plasma deposition to Nafion with the intent to prevent random protein adsorption while providing enough functional sites (hydroxyl groups) to bind a biologically active peptide known to induce cellular adhesion (YRGDS). Nafion surfaces were modified by RF plasma polymerizing five different combinations of (1) tetraethylene glycol dimethyl ether (tetraglyme) and (2) 2-hydroxyethyl methacrylate (HEMA): pure tetraglyme, 2.5% HEMA with 97.5% tetraglyme, 5% HEMA with 95% tetraglyme, 10% HEMA with 90% tetraglyme, and pure HEMA. Resultant surfaces were characterized by XPS (low and high resolution), dynamic contact angle, and atomic force microscopy. Protein adsorption and retention was determined and correlated to surface layer composition. The ability to bind a cell adhesion peptide was also determined and correlated well with surface layer composition.