Bioinspired Structural Design For Mechanically Enhanced Nanocomposite Macrofibers

Nature gave perfect directions towards creating structural materials by precisely controlling the assembly process of nanoscale/molecular scale building blocks to form a highly ordered architechture.This multiscale construction strategy endows natural materials with exceptional properties in mechanical strength,optical performances and many other fields.Inspired by the typical structural characteristics as well as the strengthening and toughning mechanisms found in widespread biosynthesized fibers,scientists apply rational biomimetic assembly approach with engineering designs to fabricate high-performance structural fiber materials.In this dissertation,we will first review the research progress in biomimetic structural materials,and discuss several representative assembly approaches in manufacturing structural fiber materials.Then,we will present the research status of biomimetic structural fiber materials and its applications in biomedical and tissue engineering.Finally,we will set the common biological strucutural materials like bone,wood,spider silk and animal hairs as models to fabricate biomimetic mechanical reinforced nanocomposite macrofibers under the guidance of uniaxial paralleled and hierarchical helix structures in common design motifs of natural fibers.We will refer to the strengthening and toughning mechanisms of the hierarchical helical structures across multiple length scales with stiff anmatricesd strong nanoscale fibrous building blocks embedded in softer and energy dissipating.We will also analysis the assembly process-structure-property relationship in our designed system.The main achievements in this dissertation are as follow:1.Using wet spinning and confined drying methods,we prepare three different nanocomposite macrofibers with distinct nanofiber building blocks.We obtain bacterial cellulose-sodium alginate(BC-Alg),carbon nanotube-sodium alginate(CNT-Alg)and Xonotlite-sodium alginate(Xonotlite-Alg)nanofiber-based macrofibers with highly coaxial orientation structure under fluid shear.We also study the relation between mechanical properties of the designed macro fibers and the influence factors(such as the kinds of building blocks,nanofiber aspect ratio,extrusion speed and the draw ratio)during the wet-spinning and drying process.2.With regard to the general problem of low elongtation or brittleness of previously reported cellulose-based macrofibers,we reported a bioinspired hierarchical helical and nanocomposite structural design strategy to fabricate mechanically robust bacterial cellulose-sodium alginate(BC-Alg)macrofibers via combining a facile wet-spinning process with a subsequent multiple wet-twisting together.The resultant macrofibers exhibit a hierarchical helical structure with good alignment of BC nanofibers embedded in a soft Alg matrix in the macrofibers,with maximum tensile strength of?535MPa,elongation of?16%and toughness of?45 MJ·m'3.The structural feature is recognized to give rise to the unique property combination of the resultant nanocomposite macrofibers.The bioinspired structural design strategy presented here is simple,mild and cost-effective,representing a promising platform for the development of high-performance nanocomposite fiber materials for future structural or functional applications.