Biopolymer nanofibrils exhibit exceptional mechanical properties with a unique combination of strength and toughness, while also presenting biological functions that interact with the surrounding environment. These features of biopolymer nanofibrils profit from their hierarchical structures that spun angstrom to hundreds of nanometer scales. To maintain these unique structural features and to directly utilize these natural supramolecular assemblies, a variety of new methods have been developed to produce biopolymer nanofibrils. In particular, cellulose nanofibrils (CNFs), chitin nanofibrils (ChNFs), silk nanofibrils (SNFs) and collagen nanofibrils (CoNFs), as the four most abundant biopolymer nanofibrils on earth, have been the focus of research in recent years due to their renewable features, wide availability, low-cost, biocompatibility, and biodegradability. A series of top-down and bottom-up strategies have been accessed to exfoliate and regenerate these nanofibrils for versatile advanced applications. In this review, we first summarize the structures of biopolymer nanofibrils in nature and outline their related computational models with the aim of disclosing fundamental structure-property relationships in biological materials. Then, we discuss the underlying methods used for the preparation of CNFs, ChNFs, SNF and CoNFs, and discuss emerging applications for these biopolymer nanofibrils.

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Partially deacetylated α-chitin nanofibers/nanowhiskers mixtures (DEChNs) and TEMPO-oxidized α-chitin nanowhiskers (TOChNs) that had positive and negative charges, respectively, were transformed into hydrogels with mass concentrations of 0.2, 0.4, 0.6, 0.8, and 1.0% under ammonium hydroxide or hydrochloric acid "gas phase coagulation". To the best of our knowledge, 0.2% is the lowest mass content reported for the successful preparation of physical self-standing hydrogels based on chitin nanofibers/nanowhiskers. The even and uniform coagulation under "gas phase" is one of the key aspects of preparing hydrogels with quite low mass content. The storage modulus achieved the highest value of 8.35 and 3.73 KPa for DEChN and TOChN hydrogels, respectively, at the mass concentration of 1.0%, and these are known to be the highest values reported in the literature for hydrogels at the same mass concentration of chitin nanofibers/nanowhiskers. The equilibrium swelling ratio (ESR) of both DEChN and TOChN hydrogels decreased with increasing mass content at neutral pH. As the pH increased from 2 to 10, the swelling degree of DEChN hydrogels decreased from 268 to 130, whereas the swelling degree of TOChN hydrogels increased from 128 to 242. Additionally, due to the electrostatic attraction between the hydrogels and dyes, DEChN hydrogels had significant adsorption of Reactive Blue 19, while TOChN hydrogels had effective adsorption of Basic Green 4. The different pH-dependent swelling behavior and adsorption affinity of the DEChN and TOChN hydrogels were related to their designed opposite surface charges corresponding to the surface amino groups on the DEChNs and carboxyl groups on the TOChNs.

A ubiquitous feature of natural silk fibers is the presence of well‐organized mesostructures, including microfibrils, nanofibrils, and nanoparticles. These mesoscale building blocks are typically well organized into sophisticated arrangements and contribute robust mechanical performance and functions as part of natural silk fibers. However, it remains a major challenge to directly isolate these mesostructures for engineering applications. Here, an environmentally friendly and scalable “partial dissolution and physical dispersion” strategy is developed to exfoliate silk fibers into different mesostructures, including microfibrils, nanofibrils, nanorods, and nanoparticles. On the basis of the advantages of these mesosilks in tunable sizes, sharp size distributions, high modulus, excellent redispersibility, as well as versatile processability, the applications of these mesosilks in electronic and environmental fields are further explored, including water treatment, recycling organic solvent, paper sensors, and nanofertilizers. These explorations open a new avenue for silk fiber applications while also providing a pathway to help address critical issues in electronic and environmental fields.

Tensan silk, a natural fiber produced by the Japanese oak silk moth ( Antherea yamamai, abbreviated to A. yamamai), features superior characteristics, such as compressive elasticity and chemical resistance, when compared to the more common silk produced from the domesticated silkworm, Bombyx mori ( B. mori). In this study, the "structure-property" relationships within A. yamamai silk are disclosed from the different structural hierarchies, confirming the outstanding toughness as dominated by the distinct mesoscale fibrillar architectures. Inspired by this hierarchical construction, we fabricated A. yamamai silk-like regenerated B. mori silk fibers (RBSFs) with mechanical properties (extensibility and modulus) comparable to natural A. yamamai silk. These RBSFs were further functionalized to form conductive RBSFs that were sensitive to force and temperature stimuli for applications in smart textiles. This study provides a blueprint in exploiting rational designs from A. yamanmai, which is rare and expensive in comparison to the common and cost-effective B. mori silk to empower enhanced material properties.