Construction Of Novel Materials Based On Chitin And Evaluation Of Their Application In Biomedical Field

Nowadays, renewable resource has become one of the most important subjects in chemistry, responding to the strategy of sustainable development. As the second most abundant biomass except cellulose, chitin is a nontoxic, biocompatible and biodegradable biopolymer from ocean, which is an ideal ingredient for the fabrication of newly designed biomedical and functional materials. Chitin has abundant-OH and certain amount of-NH2 and acetyl amino groups, which are feasible for various modification and chelation with metal ions. Thus chitin could also be applied as catalyst supports, biosensors, foodstuff additives and so on.This thesis focuses on the fabrication of functional materials involving the extraction of chitin nanowhisker and nanofibers by chemical and mechanical methods, as well as dissolution of chitin in NaOH/urea aqueous solvent. Wide-angle X-ray diffraction (XRD), solid state 13C NMR, Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), florescent microscope, water contact angle (CA) measurement, differential scanning calorimeter (DSC), thermogravimetric analysis (TG), UV-Vis (UV) spectra, rheometer, X-ray photoelectron spectra (XPS), etc have been used for the characterization of their structure and properties. Moreover, cytological and zoological experiments have been conducted to evaluate their potential applications in biomedical field, which would largely broaden the application scope of chitin based materials.The major innovations of this thesis include the following aspects:(1) Chitin whiskers with high crystallinity was prepared by acid hydrolysis and displayed remarkable mechanical reinforcement to cellulose films. (2) Based on the pH dependence of chitin whiskers, alginate/chitin whisker polyelectrolyte hydrogels were fabricated and applied as a scaffold for the osteoblast adhesion and proliferation. (3) The chitin whiskers were hydrophobically modified and their thickening effect in edible oil was evaluated. (4) Partially deacetylated chitin nanofibers were utilized as both reductant and stabilizer for synthesis of gold nanoparticles and their application in glucose detection was studied. (5) Regenerated chitin fibers and chitin nonwoven were fabricated form NaOH/urea aqueous solution for the first time and tested as wound dressing for full-thickness cutaneous wound model in rabbits.Chitin whiskers with mean length and width of 300 and 20 nm were successfully prepared by acid hydrolysis. Cytocompatible nanocomposite films were prepared by blending a-chitin whiskers and cellulose solution in NaOH/urea. Structure and properties of the chitin/cellulose composite films were characterized by FT-IR, XRD, 13C NMR, SEM, UV-Vis, TGA, and tensile tests. The results revealed that the chitin whiskers were dispersed homogeneously, leading to good miscibility and properties of the chitin/cellulose composite films. By varying the chitin whisker content, the tensile strength and elastic modulus of the films can be controlled. HeLa and 293T cells were seeded onto the surfaces of the nanocomposite films, showing that the composite films were nontoxic to both cell types and that the addition of chitin whiskers promoted cell adhesion and proliferation.Novel nanocomposite hydrogels composed of poly electrolytes alginate and chitin whiskers with biocompatibility were successfully fabricated based on the pH dependence of chitin whiskers. The chitin whiskers were uniformly dispersed in negatively charged sodium alginate aqueous solution, leading to the formation of the homogeneous nanocomposite hydrogels. The experimental results indicated that their mechanical properties were significantly improved compared to alginate hydrogel and the swelling trends were inhibited as a result of the strong electrostatic interactions. The nanocomposite hydrogels exhibited certain crystallinity and hierarchical structure with nanoscale chitin whiskers, similar to the structure of the native extracellular matrix. Moreover, the nanocomposite hydrogels were successfully applied as bone scaffolds for MC3T3-E1 osteoblast cells, showing their excellent biocompatibility and low cytotoxicity. The results of fluorescent micrographs and SEM images revealed that the addition of chitin whiskers markedly promoted the cell adhesion and proliferation of the osteoblast cells. The biocompatible nanocomposite hydrogels have potential application in bone tissue engineering.A facile approach was developed to modify chitin whiskers by reaction with bromohexadecane, and the potential application of the modified whiskers in structuring oil was evaluated. The results of FT-IR, XRD, elemental analysis, solid 13C NMR, and DSC confirmed that the long alkyl chains were successfully introduced to the chitin whiskers and endowed them with improved hydrophobicity and thermal transition. By hot pressing the modified whiskers, the highly hydrophobic whisker sheets were constructed, showing high contact angles close to 150°. The hydrophobic interaction between the long alkyl chains and chitin backbone induced the crystal alignment with micro-nano structure, leading to the surface roughness and high hydrophobicity of the sheets. Furthermore, the modified whiskers could form a stable dispersion in the sunflower oil, displaying a remarkable thickening effect. The viscosity of the oily suspension exhibited temperature dependence and shear-thinning behavior, suggesting great potentials to fabricate oleogel without adding any saturated fat. Furthermore, the intrinsic biocompatibility of a-chitin structure benefits its application in foodstuff, cosmetics, and medical fields.Partially deacetylated chitin nanofibrils (CNFs) were successfully prepared by surface cationization and applied as supporting matrix for nano gold particles (AuNPs). Due to the reducibility and chelation function of the amino groups, CNFs played as both reductant and stabilizer in the in-situ synthesis and subsequent immobilization of AuNPs. Thus the resultant CNF-AuNPs suspension displayed high stability against flocculation. The size and shape of AuNPs were tunable by adjusting parameters like concentration of CNFs, reaction temperature and so on. In addition, the CNF-AuNPs displayed peroxidase mimic behavior and catalyzed the reaction of TMB and H2O2 to produce a blue solution. When combined with glucose oxidase, the CNF-AuNPs suspension was available for detection of glucose with a limit of detection of 94.5nM. This detection was highly specific, cheap and visible with low contamination, which has potential application in clinical medicine, food analysis and related fields.Pure chitin fibers with fine appearance and relatively high mechanical strength were prepared for the first time. From a chitin solution dissolved in a 11 wt% NaOH/4 wt% urea aqueous system via freezing/thawing, the chitin fibers were spun directly by coagulating with 15wt% H2SO4 on a simplified laboratory spinning frame via "green" pathway. Subsequently, chitin nonwoven fabrics were constructed from the fresh wet fibers by hot pressing. The results from FT-IR, XRD,13C NMR and SEM indicated that chitin fibers had lustrous surface and circular section, and retained the intrinsic structure of a-chitin, because the dissolution and regeneration of chitin were physical processes. Furthermore, the chitin nonwoven fabrics designed for the use as wound dressing showed excellent ability to accelerate healing and more remarkable effects than traditional gauze in the wound healing test for rabbits, as a result of the inherent antimicrobial properties of chitin. This work would open up a new pathway for fabricating biocompatible chitin filaments, which is very potential in the biomedical material fields.In this thesis, chitin was utilized as the raw materials for the fabrication of nanostructures with different scales and nanocomposites for various applications, especially in the biomedical field. At the same time, NaOH/urea aqueous solution was utilized for the preparation of regenerated chitin fibers and chitin nonwoven fabrics, which could be expected as novel biomedical raw materials to replace the cellulose analogy. since the above mentioned materials all retained the intrinsic structure and bioactivity of the original chitin, as a component of living organism, these materials are expected to be widely applied in cell scaffolds, tissue engineering, wound dressing, food and cosmetics, biosensors and so on. This work not only broadened the application routes and scope of chitin based materials, but also contributed some neat ideas to turn the seafood waste into wealth. This research accords well with the principles of sustainable development and thus exhibit both scientific significance and prospects of applications.