Study On Preparation Of Nanocellulose And Its Enhanced Sodium Alginate Hydrogel

Sodium alginate hydrogel is considered as an ideal biomedical material due to its good swelling rate,biocompatibility and biodegradability.It can be widely used in the field of biomass materials such as tissue engineering.However,the single sodium alginate hydrogel has disadvantages such as poor mechanical properties,which limits its further application in tissue engineering.We choose natural cellulose as a raw material to construct functional nanofibrillar crystals and electrospun fiber membranes,and add them to hydrogels to obtain functional sodium alginate hydrogels with good mechanical properties and biocompatibility.It shows a wide range of application prospects in the field of medical dressings and tissue engineering.Firstly,the cellulose nanocrystal-Ag@AgCl(CNC-Ag@AgCl)was prepared by adding silver nitrate to cellulose solution with PVP,then hydrolyzed using sulfuric acid under visible light.In this method,Ag@AgCl could be firmly attached to CNC surface without using any reducing agent.Experimental data obtained from energy dispersive spectrometry,X-ray photoelectron spectroscopy and X-ray diffraction confirmed the presence of Ag@AgCl on the surface of CNC.The antifouling performance of CNC-Ag@AgCl composites was tested by a model methyl orange-degradation experiment under visible light.The composites could almost completely degrade methyl orange in 180 min,while the composite fabricated in the solution with PVP was more stable.After three experimentation cycles,the degradation efficiency remained at 85%.Also,the composite exhibited excellent antibacterial properties in a test of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus.Secondly,based on the sodium alginate(SA)hydrogel,in order to improve the mechanical properties and antibacterial properties of the hydrogel,the CNC-Ag@AgCl prepared in Experiment 1 was added as a physical blend,and then tannic acid was added to adjust the homogeneity of the cross-link density of the hydrogel.Through the result of FTIR,XRD,XPS,TGA,SEM,swelling rate and water retention test experiments,CNCAg@AgCl was uniformly dispersed in the sodium alginate and formed a stable double-network hydrogel through intermolecular hydrogen bonding.At the same time,the hydrogel maintained good water retention and swelling ratio.By testing the tensile properties of hydrogel materials through a universal testing machine,we found that the toughness of sodium alginate/CNC-Ag@AgCl hydrogel(SACA)and sodium alginate/CNCAg@AgCl/tannic acid hydrogel(SACAT)series hydrogel materials have been significantly improved.With the increase of CNC-Ag@AgCl content,the elongation at break of hydrogel composites increased significantly.The 0.05-SACAT hydrogel material was the best,and its elongation at break was 16 times that of pure sodium alginate hydrogel.The experimental results of counting method and bacteriostatic zone method proved that SACA and SACAT series hydrogel materials had good antibacterial properties.The antibacterial properties of SACA and SACAT series hydrogel materials showed a significant increase with the increase in CNCAg@AgCl content;0.2-SACAT hydrogel materials had the best antibacterial properties,while pure sodium alginate hydrogels had no obvious antibacterial effect.At the same time,it was found that the sterilization effect of the hydrogel composite on Escherichia coli(gramnegative bacteria)was slightly better than that of Staphylococcus aureus(gram-positive bacteria).Finally,an electrospun nanofiber membrane was obtained by electrospinning and added to the sodium alginate hydrogel in a layered form to improve the mechanical properties of the hydrogel.In addition,gelatin and disodium hydrogen phosphate were added to the sodium alginate aqueous solution,and then biomimetic mineralization was performed after calcium ion cross-linking to improve the biocompatibility of the sodium alginate hydrogel.The results of FTIR,XRD,TGA,SEM,water retention and swelling rate test proved that after biomimetic mineralization,more bone-like apatite was generated inside the hydrogel,and the hydrogels had good water retention and swelling rates.The biocompatibility of the hydrogel was significantly improved.The results of the compressive properties of hydrogel materials tested by a universal testing machine showed that we found that the addition of electrospun nanofiber membranes to the hydrogel in a layered form had a significant effect on the compression strength of the hydrogel.As the number of fiber membrane layers increased,the higher the compression modulus.However,adding too many layers of fiber membranes caused internal defects of the hydrogel to reduce its compression modulus.The tensile properties of hydrogel materials were studied by universal testing machine.We found that compared to pure sodium alginate/gelatin hydrogel(SAG),the elongation at break of mineralization-sodium alginate/gelatin hydrogel(MSAG)was significantly increased,and the elongation at break and tensile strength of SAG-C hydrogel were both enhanced.In vitro degradation performance test results showed that SAG series hydrogels had good degradation performance,and the dry degradation rate and wet degradation rate reached the highest value after the ninth week.In vitro cell experiments found that sodium alginate/gelatin-cellulose hydrogel(SAG-C)?M-SAG and M-SAG-C hydrogel had no obvious cytotoxicity.At the same time,the introduction of bone-like apatite into M-SAG-C hydrogel made the cells have better adhesion and proliferation ability on the composite surface.The higher the degree of mineralization,the better the cell compatibility of the hydrogel material.