Squid Beak Inspired Cross-Linked Cellulose Nanocrystal Composites

Abstract

Bioinspired cross-linked polymer nanocomposites that mimic the water-enhanced mechanical gradient properties of the squid beak have been prepared by embedding either carboxylic acid-or allylfunctionalized cellulose nanocrystals (CNC) into an alkene-containing polymer matrix (poly(vinyl acetate-co-vinyl pentenoate), P(VAc-co-VP)). Cross-linking is achieved by imbibing the composite with a tetrathiol cross-linker and carrying out a photoinduced thiol−ene reaction. Central to this study was an investigation on how the placement of cross-links (i.e., within matrix only or between the matrix and filler) impacts the wet mechanical properties of these materials. Through cross-linking both the CNCs and matrix, it is possible to access larger wet mechanical contrasts (E′ stiff /E′ soft = ca. 20) than can be obtained by just cross-linking the matrix alone (where contrast E′ stiff /E′ soft of up 11 are observed). For example, in nanocomposites fabricated with 15 wt % of allyl-functionalized tunicate CNCs and P(VAc-co-VP) with about 30 mol % of the alkene-containing VP units, an increase in the modulus of the wet composite from about 14 MPa to about 289 MPa at physiological temperature (37 °C) can be observed after UV irradiation. The water swelling of the nanocomposites is greatly reduced in the cross-linked materials as a result of the thiol−ene cross-linking network, which also contributes to the wet modulus increase. Given the mechanical turnability and the relatively simple approach that also allows photopatterning the material properties, these water-activated bioinspired nanocomposites have potential uses in a broad range of biomedical applications, such as mechanically compliant intracortical microelectrodes.

Photolithographic Fabrication of Mechanically Adaptive Devices

“…We used the DW process to fabricate a functionally graded film with a pattern of alternating angled stripes created by low (6000 mJ/cm 2 ) and high (16 000 mJ/cm 2 ) doses, mirroring the design of reported bending actuators (Figure S9). , Figure c and d shows that the object indeed bends after exposure to emulated physiological conditions, as expected on the basis of inhomogeneous swelling. The possibility to preprogram actuation into a mechanically adaptive polymer by a simple DW process should be useful to impart cortical devices with active deployment options that are activated post implantation or for self-wrapping electrode–nerve interfaces for peripheral nervous system applications …”

Relatively Independent Motion of a Continuous Nanocellulose Network in a Polymer Matrix

“…Nanocellulose, such as cellulose nanofibers, − cellulose nanocrystals, − and bacterial cellulose, , has attracted enormous attention as a biobased reinforcing agent for synthetic polymers due to its sustainability, renewability, lightweight, high specific surface area, high elastic modulus, and low coefficient of thermal expansion . Normally, hydrophobic modification on hydrophilic nanocellulose is needed to obtain a homogeneous dispersion in nonpolar monomers or hydrophobic polymers, facilitating the interfacial compatibility between nanocellulose and hydrophobic polymers, thus avoiding aggregation of nanocellulose in hydrophobic polymer matrices that would lead to poor mechanical property. , In ideal nanocellulose/polymer composites, nanocellulose should maintain its original dimension, especially the diameter, and move together with the polymer matrix under tensile or compressive force to consume the applied energy and substantially improve the mechanical performance of the composites.…”

Bioinspired Macromolecular Materials

“…Stuart Rowan offers another route to augment and tune the mechanical properties of hydrated network materials through the creation of nanocomposite networks comprising polymers embedded with cellulose nanocrystals. 14 These materials, inspired by the impressive mechanical properties found in the beaks of squid, exhibit tunable mechanical properties and swelling which is dependent on the topology used for lightmediated cross-linking as well as the duration of applied light. Finally, Hans Boerner describes a strategy to screen a pool of monomers in pursuit of customized polymeric solubilizers of a photosensitizer.…”

“…These materials are converted to a sol upon UV-irradiation, while thermal relaxation leads to rapid hydrogel recovery. Stuart Rowan offers another route to augment and tune the mechanical properties of hydrated network materials through the creation of nanocomposite networks comprising polymers embedded with cellulose nanocrystals . These materials, inspired by the impressive mechanical properties found in the beaks of squid, exhibit tunable mechanical properties and swelling which is dependent on the topology used for light-mediated cross-linking as well as the duration of applied light.…”