Highly swellable free-standing hydrogel nanotube forests

Well-ordered arrays of high aspect ratio nanotubes display structural anisotropy, high surface area, and functionalizable surface morphology. We demonstrated, for the first time, the vapor deposition synthesis of well-ordered arrays of hydrogel nanotubes (i.e. nanotube forest structures) with controllable swelling properties using anodic aluminium oxide (AAO) membranes. Initiated chemical vapor deposition (iCVD) enabled templating of hydrogel nanotubes from 2-hydroxyethyl methacrylate (HEMA) monomers with systematically tuned crosslinking ratios. Water uptake and the swelling ratios of the nanotubes monotonically decreased with the crosslink density. For a given crosslinked hydrogel composition, the degree of swelling for the nanotubes was observed to be significantly higher than for the planar films. Furthermore, protein adsorption is systematically moderated through the crosslinking density on nanotube samples, making them potential templates for biomaterials.