Preparation Of Porous Materials By Glycyrrhizin Acid-based Foam Templates And Their Application In Controlled Release Of Active Cargos

In recent years,aqueous foams have been widely used in daily life,such as food,personal care,cosmetics and detergent products.Porous materials prepared by aqueous foam templates have high specific surface area,high load capacity and other advantages,which show a great application value in the fields of biomedical transportation and functional food.In this study,Glycyrrhizic acid(GA),a natural triterpenoid saponin,was used as raw material,mixed with Cellulose nanocrystals(CNCs),Hydroxyethyl Cellulose(HEC),and zein-pectin(ZP)particles to prepare foam templates and porous materials.The formation and stability mechanisms of the composite nanofiber foam were investigated,and the hydrophobic/hydrophilic active cargos were encapsulated and transported.The main conclusions are as follows:(1)Natural and nanoscale GA nanofibers and CNCs were used to prepare homogeneous,super-stable and thermally responsive aqueous foams.GA adsorbed around the bubble to form a multi-layer fiber network.At the same time,GA and CNCs could form a high viscoelastic composite hydrogel network through hydrogen bonding in continuous phase.The formation of the gel network in the interface and bulk phase could effectively prevent the liquid drainage,bubble coarsen and coalescence.Therefore,the super-stable composite aqueous foam was formed.The addition of Na Cl could further strengthen the composite hydrogel network and improve the stability of foam.In addition,GA-CNCs composite foam had excellent thermal response.High temperature(T>T_m)could cause rapid instability of the foam,and by simply changing the heating medium or adjusting the strength of the network inside the foam,the instability behavior of the foam could be effectively controlled.(2)GA-HEC aqueous foam template was prepared by combining HEC.The effects of HEC addition on the structure,formation and stability of GA foam hydrogel network and the stability of GA-HEC aqueous foam in the freeze-drying process were studied.We also evaluated the structural properties of porous materials prepared by composite aqueous foams and studied its controlled release properties of riboflavin sodium phosphate.The results showed that by adding HEC,GA and HEC formed intermolecular hydrogen bonds,which could form a high viscoelastic composite hydrogel network in the continuous phase.The network structure in the interface and continuous phase was more compact and orderly.Therefore,bubbles were well separated,and the drainage of foam was effectively prevented,thus improving the stability of the foam.The aqueous foam had a good stability in the freeze-drying process,so the porous foams with good compressive performance and mechanical adaptability which could encapsulate hydrophilic active factors was prepared.GA-HEC composite foam formed bubbles with small pore size and uniform distribution due to the enhancement of network structure,which made the diffusion path of riboflavin sodium phosphate become longer,so the release of riboflavin sodium phosphate can be prolonged.(3)A composite foam template was prepared by combining GA,HEC and ZP particles.The effects of ZP on the formation and stability of GA-HEC aqueous foam system were studied.The porous material was prepared by using composite aqueous foam as the template.We studied the release properties of hydrophilic/hydrophobic active materials.The results showed that GA adsorbed in the multilayer interface to stabilize the bubbles,while ZP was distributed in the continuous phase,which made the aqueous foam have higher yield stress and storage modulus.Therefore,the foam drainage was effectively prevented,and the coarsening and aging of bubbles were significantly slowed down.ZP encapsulated the hydrophobic active cargo curcumin,while GA encapsulated the hydrophilic active cargo Vitamin B12.The foam template can be used as a soft material with the capability of simultaneously loading hydrophilic and hydrophobic active cargos,which could control the release of the active materials.With the increase of ZP concentrations,the release rate and the amount of the active cargos increased.Compared with GA-HEC-ZP composite foam,GA-HEC-ZP hydrogel has higher release rate and the amount of release.By controlling the concentrations of ZP and the pore structure of porous materials,the release of active cargos can be effectively controlled.