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    Cross-Linked Bioreducible Layer-by-Layer Films for Increased Cell Adhesion and Transgene Expression

    Year: 2010

    Journal: J. Phys. Chem. B, 2010, 114 (16), pp 5283–5291, 20100827

    Authors: Blacklock J. *†‡, Sievers T.K. ‡, Handa H. §, You Y-Z, Oupick D., Mao G. §, Möhwald H. ‡

    Last authors: Helmuth Möhwald

    Organizations: Department of Biomedical Engineering, Wayne State University, Detroit, Michigan 48202, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Potsdam, D-14424, Germany, Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan 48202, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202

    Country: USA, US, United States of America

    The effect of cross-linking layer-by-layer (LbL) films consisting of bioreducible poly(2-dimethylaminoethyl methacrylate) (rPDMAEMA) and DNA is examined with regard to rigidity, biodegradability, cell adhesion, and transfection activity using 1,5-diiodopentane (DIP) cross-linker. DIP chemically reacts with the tertiary amines of rPDMAEMA, altering the chemical composition of these LbL films. The result is a change in surface morphology, film swelling behavior, and film rigidity, measured with AFM and ellipsometry. It is found that the apparent Young’s modulus is increased more than 4 times its original value upon cross-linking. Cross-linking mass is additionally confirmed with a quartz crystal microbalance with dissipation (QCM-D). Comprehensive analyses of these experimental values were investigated to calculate the degree of cross-linking using the rubber elasticity theory and the Flory−Rehner theory. Additionally, the Flory−Huggins parameter, χ, was calculated. Good agreement in the two methods yields a cross-linking density of 0.82 mmol/cm3. The Flory−Huggins parameter increased upon cross-linking from 1.07 to 1.2, indicating increased hydrophobicity of the network and formation of bulk water droplets within the films. In addition, the effects of cross-linking on film disassembly by 1,4-dithiothreitol (DTT) are found to be insignificant despite the alteration in film rigidity. Mouse fibroblast cells and smooth muscle cells are used to study the effect of cross-linking on cell adhesion and cell transfection activity. In vitro transfection activity up to seven days is quantified using secreted alkaline phosphatase (SEAP) DNA. Film cross-linking is found to enhance cell adhesion and prolong the duration of cellular transfection. These results contribute to the development of bioreducible polymer coatings for localized gene delivery.