Constructing Stiff ß-Sheet for Self-Reinforced Alginate Fibers.

The application of alginate fibers is limited by relatively low mechanical properties. Herein, a self-reinforcing strategy inspired by nature is proposed to fabricate alginate fibers with minimal changes in the wet-spinning process. By adapting a coagulation bath composing of CaCl2 and ethanol, the secondary structure of sodium alginate (SA) was regulated during the fibrous formation. Ethanol mainly increased the content of ß-sheet in SA. Rheological analysis revealed a reinforcing mechanism of stiff ß-sheet for enhanced modulus and strength. In combination with Ca2+ crosslinking, the self-reinforced alginate fibers exhibited an increment of 39.0% in tensile strength and 71.9% in toughness. This work provides fundamental understanding for ß-sheet structures in polysaccharides and a subsequent self-reinforcing mechanism. It is significant for synthesizing strong and tough materials. The self-reinforcing strategy involved no extra additives and preserved the degradability of the alginate. The reinforced alginate fibers exhibited promising potentials for biological applications.

Self-Assembly Reinforced Alginate Fibers for Enhanced Strength, Toughness, and Bone Regeneration.

Material reinforcement commonly exists in a contradiction between strength and toughness enhancement. Herein, a reinforced strategy through self-assembly is proposed for alginate fibers. Sodium alginate (SA) microstructures with regulated secondary structures are assembled in acidic and ethanol as reinforcing units for alginate fibers. Acidity increases the flexibility of the helix and contributes to enhanced extendibility. Ethanol is responsible for formation of a stiff ß-sheet, which enhances the modulus and strength. The structurally engineered SA assembly exhibits robust mechanical compatibility, and thus reinforced alginate fibers possess an improved tensile strength of 2.1 times, a prolonged elongation of 1.5 times, and an enhanced toughness of 3.0 times compared with SA fibers without reinforcement. The reinforcement through self-assembly provides an understanding of strengthening and toughening mechanism based on secondary structures. Due to a similar modulus with bones, reinforced alginate fibers exhibit good efficacy in accelerating bone regeneration in vivo.

Hierarchical nano-helix as a new reinforcing unit for simultaneously ultra-strong and super-tough alginate fibers.

Fabricating alginate fibers of high strength and toughness remains a great challenge because of the difficulty in improving both strength and toughness simultaneously. Herein, this work reported the hierarchical assembly of sodium alginate nano-helix and its potential application as a new reinforcing unit for alginate fibers. Contributed from the hierarchical structures of α-helix, ß-sheet and tertiary helical alignment of nanofibrils, nano-helix improved the tensile strength of fibers with enhanced modulus, and prolonged elongation through unravelling the tertiary structures. Thus, the strength, elongation and toughness of alginate fibers were all enhanced by >200 %, solving the tradeoff of strength and toughness. The mechanical performance of nano-helix engineered alginate fibers is superior to present alginate fibers and even some other biomass-based fibers. The assembly of nano-helix provides a feasible reinforcing strategy for polysaccharide based materials, achieving simultaneous improvement of strength and toughness.