AVS 49th International Symposium
    Biomaterials Monday Sessions
       Session BI-MoM

Paper BI-MoM9
Hydration Forces on a Switchable Bioactive Surface

Monday, November 4, 2002, 11:00 am, Room C-201

Session: Theoretical Studies of Biosurfaces/Biotribology and Biorheology
Presenter: B.-I. Kim, Sandia National Laboratories
Authors: B.-I. Kim, Sandia National Laboratories
M.A. Samara, Sandia National Laboratories
D.L. Huber, Sandia National Laboratories
J.E. Houston, Sandia National Laboratories
B.C. Bunker, Sandia National Laboratories
Correspondent: Click to Email
Poly(n-isopropyl acrylamide) (PNIPAM) monolayers can be thermally switched between hydrophobic and hydrophilic states at a phase transition temperature of 35°C. Protein adsorption studies indicate that the hydrophilic state represents an anti-fouling state, while biomolecules form adherent monolayers on the hydrophobic state. We have used a scanning probe system called the interfacial force microscope (IFM) to probe the mechanisms for protein adsorption on this switchable polymer surface. With the IFM, we have simultaneously measured both normal and friction forces between a silica tip and a surface functionalized with PNIPAM as a function of separation distance. The results show that at room temperature, there is a repulsive hydration force between the tip and the substrate. As the phase transition temperature is approached, the repulsive force collapses, allowing the tip and substrate to come into adhesive contact. The transition from repulsive to attractive adhesive forces is accompanied by a doubling in lateral friction forces. IFM results obtained at different tip speeds at different temperatures suggest that the repulsive hydration force observed at room temperature is associated with the presence of ordered water structures within the polymer that break down at higher temperatures. Experiments are in progress with chemically-functionalized tips to provide us with fundamental insights of the parameters controlling the stability of this ordered water and its role in protein adsorption.