Biomimetic surfaces via dextran immobilization : grafting density and surface properties

Biomimetic surfaces were prepared by chemisorption of oxidized dextran (Mw = 110 kDa) onto SiO2 substrates that were previously modified with aminopropyl-tri-ethoxy silane (APTES). The kinetics of dextran oxidation by sodium metaperiodate (NaIO4) were quantified by 1H NMR and pH measurements. The extent of oxidation was then used to control the morphology of the biomimetic surface. Oxidation times of 0.5, 1, 2, 4, and 24 hours resulted in <20, ~30, ~40, ~50 and 100% oxidation, respectively. The surfaces were characterized by contact angle analysis and atomic force microscopy (AFM). Surfaces prepared with low oxidation times revealed a more densely packed "brushy" layer when imaged by AFM than those prepared at low oxidation times. Finally, the contact angle data revealed, quite unexpectedly, that the surface with the greatest entropic freedom (0.5 h) wetted the fastest and to the greatest extent (THETAAPTES > THETA1h > THETA2,4h > THETA0.5h).