title: Bioinspired water-enhanced mechanical gradient nanocomposite films that mimic the architecture and properties of the squid beak.
abstract: Inspired by the water-enhanced mechanical gradient character of the squid beak, we herein report a nanocomposite that mimics both the architecture and properties of this interesting natural material. Similar to the squid beak, we have developed nanocomposites where the degree of cross-linking is controlled along the length of the film. In this study, we utilized tunicate cellulose nanocrystals as the nanofiller that are functionalized with allyl moieties. Using photoinduced thiol-ene chemistry, we have been able to cross-link the CNC nanofiller. In the dry state where strong CNC interactions can occur, only a small mechanical contrast is observed between the cross-linked and uncross-linked samples. However, when the films are exposed to water, which "switches off" the noncovalent CNC interactions, a significant mechanical contrast is observed between the same films. For example, at 20 wt % CNC (in the dry film), an increase in wet modulus from 60 to 300 MPa (∼500% increase) is observed after photoirradiation. Furthermore, we show that the wet modulus can be controlled by altering the UV exposure time which allows access to mechanical gradient films.
authors.affiliation: Department of Macromolecular Science and Engineering, Case Western Reserve University , 2100 Adelbert Road, Kent Hale Smith Building, Cleveland, Ohio 44106-7202, United States.
authors.forename: Justin D
authors.initials: JD
authors.lastname: Fox
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Capadona
authors.forename: Paul D
authors.initials: PD
authors.lastname: Marasco
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Rowan
mesh_terms: D000818:Animals; D001502:Beak / Q000737:chemistry; D032701:Biomimetics; D003432:Cross-Linking Reagents / Q000737:chemistry; D049832:Decapodiformes / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D015394:Molecular Structure; D053761:Nanocomposites / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D014867:Water