This feature article discusses three remarkable protein fi bers: spider dragline, lacewing egg stalk and mussel byssus. Sequence-structure-function relationships of selected proteins in the fi bers are highlighted and the potential of these proteins for use as new materials is summarized.
Gradients are a natural design principle in biological systems that are used to diminish stress concentration where materials of differing mechanical properties connect. An interesting example of a natural gradient material is byssus, which anchors mussels to rocks and other hard substrata. Building upon previous work with synthetic polymers and inspired by byssal threads, protein gradient films are cast using glycerine-plasticized gelatine and fibroin exhibiting a highly reproducible and smooth mechanical gradient, which encompasses a large range of modulus from 160 to 550 MPa. The reproducible production of biocompatible gradient films represents a first step towards medical applications.
The nonwetting and self‐cleaning properties of the lotus depend on microscale and nanoscale roughness provided in part by a covering of epicuticular waxes that crystalize on the surface of its leaves. Wax deposition is driven by the evaporation of water, which carries waxes to the surface as it moves through the epidermis and cuticle. If the wax layer is damaged, repair occurs through the same mechanism. The experiments described herein have exploited this principle to establish a completely biologically derived system based on silk and lotus epicuticular wax, showing that it is possible to coat silk surfaces with waxes and thereby change their wetting characteristics and tensile properties. The robustness of the material is also documented by crystal regrowth after damage to the wax layer through abrasion (scratching and rubbing), resistance to water‐jetting, and UV exposure. To further characterize this system, the diffusion of natural and synthetic waxes through two types of silk films, Bombyx mori fibroin and engineered spider silk are studied, showing that the extent of wax diffusion through silk membranes depends upon wax type and protein structure, which remains unchanged through the process. Making use of the simple passive phenomenon of advection, these studies represent a method of low‐energy fabrication of completely biological, lotus‐inspired membranes with tunable surfaces.
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