IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Biomaterials Wednesday Sessions
       Session BI+SS-WeM

Paper BI+SS-WeM5
Orientational Effects and Surface Free Energies in the Amino Acids Adsorption Process onto Silicon-based Surfaces

Wednesday, October 31, 2001, 9:40 am, Room 102

Session: Biological Interface & Surface Science
Presenter: C. Satriano, University of Catania, Italy
Authors: G.L. Gambino, University of Catania, Italy
C. Satriano, University of Catania, Italy
G. Marletta, University of Catania, Italy
Correspondent: Click to Email
The present paper deals with the study of the adsorption process of Lysine (Lys) and Cysteine (Cys) from aqueous solutions as a function of the substrate structure and solutions pH. The substrate effect has been studied for three silicon-based substrates, i.e. silicon dioxide, poly(hydroxymethyl)siloxane (PHMS) and oxygen plasma-treated PHMS. The pH role on the adsorption process has been investigated by performing the incubations in the amino acid solutions both at their isoelectric pH and at the physiological pH, i.e. pH = 7.4. The in situ characterization of the substrates-amino acids molecules interaction was performed by means of the Quartz Crystal Microbalance with Dissipation (QCM-D) technique. On the other hand, ex-situ measurements were performed by means of Angular Resolved X-Ray Photoelectron Spectroscopy (ARXPS) and Contact Angle (CA) measurements. In particular, ARXPS, by varying the sampling depth from @tdA@10 nm to @tdA@2 nm, allowed to elaborate a coverage model, while the CA technique, by using three test liquids, allowed to calculate the surface free energies and their relative dispersive and acid-base contributions. QCM-D data shows that Lys and Cys strongly adsorb onto the plasma-treated PHMS while on the untreated PHMS surfaces the adsorption of both amino acids does not occur. ARXPS measurements indicate that the adsorbed molecules exhibit a preferential orientation respect to the plane of the surface, however no uniform coverage is obtained for any kind of substrate. Finally, the CA measurements indicate that the polar component of the surface free energy is directly related to both the amount and the orientation of the adsorbed amino acid molecules.