Abstract
Nature's design of functional materials relies on smart combinations of simple components to achieve desired properties. Silk and cellulose are two clever examples from nature-spider silk being tough due to high extensibility, whereas cellulose possesses unparalleled strength and stiffness among natural materials. Unfortunately, silk proteins cannot be obtained in large quantities from spiders, and recombinant production processes are so far rather expensive. We have therefore combined small amounts of functionalized recombinant spider silk proteins with the most abundant structural component on Earth (cellulose nanofibrils (CNFs)) to fabricate isotropic as well as anisotropic hierarchical structures. Our approach for the fabrication of bio-based anisotropic fibers results in previously unreached but highly desirable mechanical performance with a stiffness of ∼55 GPa, strength at break of ∼1015 MPa, and toughness of ∼55 MJ m-3. We also show that addition of small amounts of silk fusion proteins to CNF results in materials with advanced biofunctionalities, which cannot be anticipated for the wood-based CNF alone. These findings suggest that bio-based materials provide abundant opportunities to design composites with high strength and functionalities and bring down our dependence on fossil-based resources.
Highlights
Lightweight structural materials from renewable resources offer properties that can surpass the performance of their components by several orders of magnitude.[1]
We applied the concept of mixing cellulose nanofibrils (CNFs) and recombinant spider silk proteins (RSPs) in a hydrocolloidal dispersion, where the stability of the dispersion is controlled by supramolecular interactions[26] (Figure 1a)
When comparing the surface morphologies of the films prepared from CNF and CNF/silk dispersions, no clear difference is observed from scanning electron microscopy (SEM)
Summary
Lightweight structural materials from renewable resources offer properties that can surpass the performance of their components by several orders of magnitude.[1]. Cellulose nanofibrils obtained from trees have received remarkable scientific and commercial attention lately as it is a renewable resource available in larger volumes, yielding materials combining several favorable features such as biodegradability and low toxicity along with impressive mechanical properties.[22] The high aspect ratio (>150) and stiffness (∼138 GPa) of the crystalline regions of cellulose nanofibrils (CNFs) make this material ideal as a reinforcing element in composites.[23−26] lack of bioactive nature is limiting its use in biomedical applications.[27] Integrating CNF with recombinant spider silk proteins (RSPs) will lead to future advanced products having properties that can benefit a wide range of applications, given the possibility to functionalize the material.[28]. Compared to other reported bio-based composites,[1,31] the nanstructured materials exhibit simultaneous outstanding stiffness (elastic modulus ∼55 GPa), toughness ∼55 MJ m−3 (strain-to-failure ∼10%), and strength (strength at break ∼1015 MPa)
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