Functionalization of fibers using azlactone-containing polymers: layer-by-layer fabrication of reactive thin films on the surfaces of hair and cellulose-based materials

Abstract

We report an approach to the functionalization of fibers and fiber-based materials that is based on the deposition of reactive azlactone-functionalized polymers and the "reactive" layer-by-layer assembly of azlactone-containing thin films. We demonstrate (i) that the azlactone-functionalized polymer poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) can be used to modify the surfaces of a model protein-based fiber (horsehair) and cellulose-based materials (e.g., cotton and paper), and (ii) that fibers functionalized in this manner can be used to support the fabrication of covalently cross-linked and reactive polymer multilayers assembled using PVDMA and poly(ethyleneimine) (PEI). The growth, chemical reactivity, and uniformity of films deposited on these substrates were characterized using fluorescence microscopy, confocal microscopy, and scanning electron microscopy (SEM). In addition to the direct functionalization of fibers, we demonstrate that the residual azlactone functionality in PVDMA-treated or film-coated fibers can be exploited to chemically modify the surface chemistry and physicochemical properties of fiber-based materials postfabrication using amine functionalized molecules. For example, we demonstrate that this approach permits control over the surface properties of paper (e.g., absorption of water) by simple postfabrication treatment of film-coated paper with the hydrophobic amine n-decylamine. The azlactone functionality present in these materials provides a platform for the modification of polymer-treated and film-coated fibers with a broad range of other chemical and biological species (e.g., enzymes, peptides, catalysts, etc.). The results of this investigation thus provide a basis for the functionalization of fibers and fiber-based materials (e.g., textile fabrics or nonwoven mats) of potential utility in a broad range of consumer, industrial, and biomedical contexts.

Figure 1

A) Chemical structures of polymers used in this study (see Materials and Methods for additional information regarding extent of fluorescent labeling). B) Fluorescence microscopy image of horsehair after immersion in a solution of PVDMA_TMR followed by vigorous rinsing (see text). C) Fluorescence microscopy image of untreated horsehair. D) Fluorescence microscopy image of horsehair treated with polymer 1 followed by rinsing. E–F) Fluorescence microscopy images of PVDMA-treated horsehair before (E) and after (F) exposure to dansyl cadaverine. G) An uncoated horsehair fiber treated with dansyl cadaverine. Scale bars = 500 µm.

Figure 2

A–F) Fluorescence microscopy images of horsehair coated with A) 0, B) 2, C) 4, D) 6, E) 8, and F) 10 bilayers of PEI/PVDMA_dan. G) Confocal fluorescence microscopy image of hair coated with 10 bilayers of PEI/PVDMA_dan. (H–I) Fluorescence microscopy images of strands of (H) horsehair coated with 10 PEI/PVDMA bilayers treated with dansyl cadaverine and (I) uncoated horse hair. (J) Plot of fluorescence intensity as a function of the number of PEI/PVDMA_dan bilayers deposited on horsehair fibers. Scale bars: A–F, H, I) 500 µm; G) 50 µm.

Figure 3

A) Low and B) high magnification SEM images of a strand of horsehair coated with 10 PEI/PVDMA bilayers. C) Low and D) high magnification SEM images of an uncoated strand of horsehair. Scale bars: A–C) 20 µm, D) 10 µm.

Figure 4

A–C) Fluorescence microscopy images of sections of (A) cotton thread, (B) a cotton ball, and (C) the edge of a piece of filter paper that were coated with 10 PEI/PVDMA bilayers and subsequently treated with TMR-cadaverine. (D) Digital picture of a strip of gauze coated with 10 PEI/PVDMA bilayers (left) and an uncoated strip of gauze (right), subsequently treated with TMR-cadaverine. Scale bars = (A–C) 500 µm; (D) scale in centimeters.

Figure 5

Digital pictures of uncoated filter paper (A–B) and filter paper coated with 1 PEI/PVDMA bilayer (C–D), 1.5 PEI/PVDMA bilayers (E–F), 10 PEI/PVDMA bilayers (G–H), and 10.5 PEI/PVDMA bilayers (I–J) that were functionalized with decylamine and spotted with droplets (~2 µL) of an aqueous solution of methyl blue dye. Images were acquired immediately after placing the water droplets on the surface of the paper (left column) and after standing at room temperature for approximately 8 minutes (right column).