Materials Construction,structure And Properties Of Native Protein With Hierarchical Structure

The utilization of biomass from nature resource has attracted increasing public attention because of the needs for sustainable development and low carbon economy.Natural protein such as silk fibroin and collagen has been widely used in food,packaging,environment,biomedical,tissue engineering and other fields.Designing and optimizing the “structure–property–function” relationship of these materials remains a key problem.In this thesis,silk fibroin and collagen with hierarchical structure as the targets were used to fabricate protein materials,and their “structure–property–function” relationships was studied to provide theoretical basis to construct biopolymer-based materials.The main contents of this thesis are as follows:(1)The heat-induced self-assembly of silk fibroin(SF)is studied by combing fluorescence assessment,infrared nanospectroscopy,wide-angle X-ray scattering,and Derjaguin-Muller-Toporov coupled with atomic force microscopy.Several fundamental issues regarding the formation,structure,and mechanical performance of silk nanofibrils(SNFs)under heat-induced self-assembly are discussed.Accordingly,the formation of SNFs occurs through nucleation-dependent aggregation,but the assembly period is variable and irregular.The long-term assembly of SF,however,mainly involves an elongation growth process.SNFs produced by different methods,such as ethanol treatment and heat incubation,have similar secondary structure and mechanical properties.These investigations improve the in-depth understanding of fundamental issues related to self-assembly of SNFs,and thus provide inspiration and guidance in designing of silk nanomaterials.(2)The hydrothermal treatment was used to treat SF solution and SNF.The experimental conditions for structural transformation of silk induced by hydrothermal treatment were explored by changing the treatment time and temperature.The self-assembly behavior was studied at different solid-liquid interfaces.The results showed that the time and temperature of hydrothermal treatment were 160 ℃/12 h.On the surface of gold and carbon,the ordered structure cannot be formed.On the surface of silicon wafer and glass wafer,the self-assembly ordered array structure can be observed.The solid-liquid interface self-assembly process was affected by external force,which was a process influenced by kinetics,but still determined by thermodynamics.These studies have improved the understanding of protein self-assembly at solid-liquid interfaces.(3)The collagen fibers were exfoliated from bovine skin using a sodium hydroxide Na OH/urea aqueous system with freeze-thaw cycles based on the hierarchical structure of natural collagen.These isolated collagen fibers were then utilized as building blocks to fabricate free-standing collagen membranes,which exhibited good stability in water,acid and alkali solutions.The results showed that the diameter of the collagen fiber was 135-185 nm,and the length of the collagen fiber was >121 μm.The tensile strength of the membrane is in the range of 0.44-1.10 MPa and the tensile strain is in the range of 42-68%.p H-triggered aggregation and dispersion of collagen fibers endowed reversible transparency for collagen membrane.This work provides a new approach for collagen processing and material construction.