| Nano-lignin has excellent UV light absorption properties,anti-oxidation,antibacterial and non-cytotoxic characteristics,and can replace non-renewable inorganic nanoparticles in the field of tissue engineering and regenerative medicine materials.Chitosan has good biocompatibility,non-toxicity,antibacterial,degradability,and accelerates wound healing properties.Therefore,chitosan is widely used in the fields of drug composite films,food packaging materials and drug hydrogels.However,film and hydrogel materials prepared by pure chitosan have disadvantages such as single performance and poor mechanical properties.In this study,agricultural and forestry wastes were used as raw materials to prepare nano-lignin by pretreating the raw materials using p-toluenesulfonic acid(p-Ts OH)and diluting the hydrolysate using adding water.Take advantage of nano-lignin's reproducibility,antibacterial properties,nano-effects and strong affinity with chitosan,nano-lignin was blend with chitosan under acetic acid-water system to prepare nano-lignin/chitosan functional materials(composite films and hydrogels)with excellent performance,overcoming the inherent defects of the single chitosan-based material.The specific research contents are as follows:(1)Preparation and structure control of nano-ligninp-TsOH was used to dissolve lignin in the pretreatment hydrolysate by pretreating corn stover and wood processing residues(poplar wood).Subsequently,the lignin in the hydrolysate was self-assembled into lignin nanoparticles by means of dilution and sedimentation.Then the effects of pretreatment temperature,hydrolysis solution dilution sequence,hydrolysis droplet acceleration and mechanical stirring speed on the characteristics of nano-lignin particle size,chemical structure and molecular weight distribution were studied,and the two sources of nano-lignin were compared.The optimal conditions for preparing corn stover nano-lignin and poplar nano-lignin were as follows: The pretreatment temperature of p-Ts OH was 140 °C,the dilution method was that the pretreatment hydrolyzate was added dropwise to water,the dilution rate was0.15 m L/min,and the mechanical stirring speed was 500 r/min.Ultimately,corn stover nano-lignin with the particle size of 101.9 nm and poplar nano-lignin with the particle size of 174.4 nm were prepared.In addition,the nano-lignins from both sources were spherical particles with uniform shapes.The structure of nano-lignin prepared under optimal conditions was characterized,and the results showed that: Poplar nano-lignin contained relatively low element S(0.16%)and carboxyl group(0.06 mmol/g).However,the nano-lignin of corn stover contained relatively high element S(0.29%)and carboxyl group(0.35 mmol/g).The molecular weight of poplar nano-lignin(4917 Da)was higher than that of corn stover nano-lignin(3856 Da).And the Zeta potential of poplar nanolignin(-32.6 m V)was lower than that of corn stover nano-lignin(-31.6 m V),it showed that poplar nano-lignin contained relatively high negative surface charge.(2)Preparation and performance study of nano-lignin/chitosan composite filmThe nano-lignin/chitosan composite films were prepared by blending the nanolignin of corn stover or the nano-lignin of poplar wood with chitosan.The effects of the type and amount of nano-lignin on the mechanical properties,antibacterial properties,fruit freshness and drug slow-release properties of the composite film were also studied.The electrostatic attraction and hydrogen bonding between nano-lignin and chitosan molecules made the chaotic chitosan molecules orderly and tightly arranged together.Additionally,the thickness of the chitosan film was reduced,and the mechanical strength of the chitosan film was improved.When the addition amount of the two types of nanolignins was 0.5%,the resulting composite film had the highest tensile strength and the lowest thickness,among them,the improvement effect of poplar nano-lignin was better.Due to the hydrophobic effect of nano-lignin,the prepared chitosan composite film had high hydrophobicity,among them,the poplar nano-lignin/chitosan composite film had higher hydrophobicity.The addition of the two types of nano-lignin significantly improved the antibacterial performance of chitosan film against Escherichia coli(E.coli),and the antibacterial properties were increased from 22.9%(pure chitosan film)to98.6%(corn stover nano-lignin/chitosan composite film)and 63.8%(poplar nanolignin/chitosan composite film),respectively.The addition of nano-lignin also had a strong effect on improving the antibacterial properties of Staphylococcus aureus(S.aureus).The antibacterial properties were increased from 82.4%(pure chitosan film)to99.4%(corn stover nano-lignin/chitosan composite film)and 98.8%(polplar nanolignin/chitosan composite film),respectively.The prepared two-source nanolignin/chitosan composite film also had good fresh-keeping ability on fruits(grapes),and the performance was similar to that of commercial fresh-keeping film.With meloxicam as the model drug,the effect of nano-lignin addition on its slow-release performance was studied.The results showed that after the addition of nano-lignin,the drug encapsulation rate of the composite film was increased by 11.8%(corn stover nanolignin/chitosan composite film)and 1.6%(poplar nano-lignin/chitosan composite film).In PBS with the pH of 5.8,the addition of two nano-lignins significantly reduced the burst of pure chitosan drug film,and increased the drug sustained release time of the drug film from 10 h to 24 h.Similarly,in PBS with the pH of 5.8,both nano-lignins increased the maximum drug release of the drug film,and the maximum drug release increased from 67.5%(pure chitosan film)to 79.3%(corn sover nano-lignin/chitosan composite film)and 72.8%(poplar nano-lignin/chitosan composite film).(3)Preparation and performance study of nano-lignin/chitosan composite hydrogelPolyethylene glycol diglycidyl ether(PEGDE)was used as the cross-linking agent.The nano-lignin/chitosan composite hydrogel was prepared by cross-linking corn stover nano-lignin or poplar nano-lignin with chitosan.In this study,the effects of the type and amount of nano-lignin on the strain performance,pH response and drug release performance of the composite film were studied.Simultaneously,the sustained-release property of the hydrogel was explored by using the model drug meloxicam.Expectedly,the addition of two types of nano-lignin enhanced the compressive strength of the film,and the maximum compressive strength was increased from 122 k Pa(pure chitosan hydrogel)to 209 k Pa(corn stover nano-lignin/chitosan composite hydrogel)and 203 k Pa(poplar nano-lignin/chitosan composite hydrogel),respectively.Both nano-lignins improved the elastic recovery ability of hydrogels.Under the condition of 30% strain,the composited hydrogels were not deformed after 5 and 10 cycles of loading-unloading tests.Additionally,all three hydrogels had good biocompatibility,and the cell survival rate in the in vitro cytotoxicity study was higher than 80%.Moreover,the addition of two types of nano-lignins significantly improved the pH response of the hydrogel.When the hydrogel was alternately placed in the acid or base solution,the hydrogel undergoed cyclic swelling or shrinking,respectively.With meloxicam as a model drug,the effect of the addition of nano-lignin on its slow-release performance was studied.The results showed that the addition of two nano-lignins in PBS(pH=5.8)increased the sustained release time of the hydrogel from 24 h(pure chitosan hydrogel)to 48 h(two types of nano-lignin/chitosan composite film).Since the addition of the two types of nano-lignins effectively increased the pores of the hydrogel.Therefore,the maximum drug release of the two composite hydrogels increased,and the maximum drug release increased from78.7%(pure chitosan hydrogel)to 97.6%(corn stover nano-lignin/chitosan composite hydrogel)and 91.9%(poplar nano-lignin/chitosan composite hydrogel),respectively.In PBS with the low pH(5.8),the sustained drug release of the drug hydrogel belonged to the Ficks diffusion mechanism.And the sustained drug release of the drug hydrogel belonged to the synergistic mechanism of Ficks diffusion and erosion in PBS(pH=7.4). |
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