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    Surface-immobilized PAMAM-dendrimers modified with cationic or anionic terminal functions: physicochemical surface properties and conformational changes after application of liquid interface stress

    Year: 2011

    Journal: Journal of Colloid and Interface Science 2012, 366 (1) pp 179-190, 20121211

    Authors: Verena Katzur, Mirjam Eichler, Erika Deigele, Christiane Stage, Peter Karageorgiev, Jürgen Geis-Gerstorfer, Gottfried Schmalz, Stefan Ruhl, Frank Rupp, Rainer Müller

    Organizations: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany, Section Medical Materials and Technology, Department of Prosthodontics, University Hospital Tübingen, Osianderstr. 2-8, 72076 Tübingen, Germany, Department of Operative Dentistry and Periodontology, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany, Department of Oral Biology, School of Dental Medicine, State University of New York at Buffalo, 3435 Main Street, Buffalo, NY 14214, USA

    Functionalization of surfaces with highly branched dendrimer molecules has gained attractiveness for various applications because the number of functional groups exceeds those of surfaces functionalized with self-assembled monolayers. So far, little is known about the physicochemicalproperties of dendrimer functionalized surfaces, especially if the flexibility of dendrimer structure remains after covalent immobilization. Therefore, the purpose of this study was to covalently immobilize polyamidoamine (PAMAM) dendrimer molecules exhibiting terminal amine and carboxyl groups to silicon model surfaces and to explore their properties and structure at the solid–air and solid–liquidinterface. Our results show that the surface free energy is higher for PAMAM coatings than for analogously terminated SAMs and also higher for carboxyl than amine functionalized coatings. Furthermore, several findings suggest that conformational freedom of the dendrimers was preserved aftersurface immobilization. Wet compared to dry PAMAMNH2surfaces show reduced hydrophilicity and increased contact angle hysteresis, whereas PAMAMCOOH surfaces become more hydrophilic and showed decreased hysteresis. Streaming current measurements showed an unexpected behavior for PAMAMCOOH surfaces in that they reveal a net positive surface charge over a wide pH range in spite of the carboxylated periphery. All of these results indicate a certain degree of masking, burrowing, back-folding and unfolding of functional groups upon environmental changes.