ABSTRACT
Dextran surface grafting density was systematically varied via a two-step process involving SiO(2) amination by aminopropyltriethoxy silane (APTES) followed by oxidized dextran (M(w) = 110 kDa) chemisorption. Dextran oxidation kinetics with sodium metaperiodate (NaIO(4)) were quantified by (1)H NMR and pH measurements. Aldehyde group formation increased with increasing oxidation time. For 0.5 h oxidation time, dried film ellipsometric thickness was constant for solution concentrations ranging from 1 to 4 mg/mL. Dextran layers with the lowest grafting density wetted fastest and displayed the lowest contact angle (theta(APTES) > theta(1 h) > theta(2,4 h) > theta(0.5 h)). Under aqueous conditions, AFM force versus displacement measurements on 0.5 and 4.0 h surfaces exhibited a single displacement jump upon retraction. The 1.0 and 2.0 h surfaces showed two jumps consistent with two populations of chains, namely, loosely and strongly bound dextran. Overall, film morphology and wetting behavior were relatively invariant with grafting density, confirming the method's robustness for preparing biomimetic coatings with consistent properties.
