| β-glucan is the major component of yeast cell wall, which self-assemble into triple helical structure through non-covalent bonding, providing mechanical support to yeast in a dynamic manner. β-glucan also has immunomodulatory effect: it can bond to the receptor Dectin-1 on macrophages to stimulate the immune system and have the final effect of anti-infection, anti-virus, anti-cancer, wound healing. Although β-glucan has unique structure and bioactivity, its application in biomaterials is rather limited due to its poor processability. In this study, β-glucan is chemically modified to improve its processability and to adjust its hydrophilicity. Thus it can meet the requirements of biomaterials in processability and stability in physiological environment and to further expand its fields of application especially in targeted drug delivery and tissue repair and regeneration.First β-glucan was chemically modified in a regioseletive way and characterized. In the triple helical structure of β-glucan, the hydroxyl groups of O-6 and O-4 positions exist on the exterior of the helices and the hydroxyl groups of O-2 position exist in the interior and are interlocked by hydrogen bonding. Considering its helical structure,the hydroxyl groups of O-6 and O-4 positions of β-glucan were formylized in a heterogeneous way while keeping the helical structure intact. Then the helices were disassembled in pyridine solution and the rest of the hydroxyl groups were further acetylated. After de-formylation in hot water, regioselectively modified β-glucan acetate with O-2 position fully acetylated and O-4 position half acetylated was obtained. The β-glucan acetate has amphiphilic structure and it exhibits interesting self-assembly behavior. Nanosheets structure with an average diameter of 25 nm and thickness of 0.7 nm were obtained by adding water into its dilute DMSO solutions,possibly driven by hydrophobic interaction and hydrogen bonding. The nanosheets may packed in a way that the hydrophobic acetyl groups hidden inside of the sheets and the hydrophilic hydroxyl groups exposes outside of the sheets. The nanosheetscan further self-assemble into more complex structures. After sonicating under room temperature, the nanosheets assembled into vesicular structure with an average diameter of 300 nm. The vesicular structure may assembled from the packing and merging of nanosheets due to the hydrophobic interaction and hydrogen bonding.After analyzing the intermediates during the self-assembly process, it was found that nanosheets assemble into a ring-like structure before assemble into vesicles. In addition, the nanosheets can also assemble into cubes and ribbon like structure. The modification did not undermine its immune stimulating effect and the dispersity in water was improved. β-glucan was found to up-regulate the phagocytosis function of mice peritoneal macrophages and increase the expression of IL-1,IL-6 and TNF-α by RAW 264.7 cells.By one step esterification reaction, β-glucan esters including acetate, propionate,butyrate, butyrate, valerate were obtained, all of which have excellent solubility in organic solutions. By using hexafluoroisopropanol as only solvent, fibrous membranes consisting of β-glucan esters were obtained by electrospinning, which have average diameters of 150, 149, 410, 1236 nm. Except that β-glucan valerate fibers have defect structure, all the other β-glucan ester fibers have good morphology free of branching or beads structure. β-glucan acetate fibers are very hydrophilic with water retaining abilities while β-glucan butyrate are very hydrophobic. Mimicking the human skin structure, bilayer fibrous wound dressing containing β-glucan acetate and butyrate was obtained by electrospinning. Mechanical testing found that the wound dressing has appropriate tensile strength in either dry or wet state and have excellent integrity. The wound dressing support the adhesion and growth of 3T3 fibroblast cells.In a 14 day mice full thickness skin defect repair study, the β-glucan bilayer dressing was found to improve wound healing and the histology analysis(H&E, Masson staining) found that the β-glucan group has better regenerated skin compared with control and gauze group.The above results suggest that esterified β-glucan has not only maintained itsimmunological activity but also can self-assemble into vesicles or can be electrospun into fibrous membranes. The scope of biomedical applications of β-glucan can be expanded especially in drug delivery vehicles targeted the immune system or wound healing dressings. |
