Assembly Mechanism Of Electrospun Layer-by-Layer Self-Assembled Nanofibers And Its Application

Electrospinning is a simple and versatile technique for producing nanofibers with diameters in the range from nanometers to micrometers through an external electric force.Due to large surface-to-volume ratio,ultrafine structures and highly porous structure,the nanofibers have been used in multiple fields,including active packaging,drug delivery,enzyme immobilization,and tissue engineering.Recently,it has been reported that by combining the layer-by-layer self-assembly technique,multilayer nanofibers can be fabricated through sequential adsorption of active substances on the nanofibers via various molecular interactions,resulting in the adjustable porosity,thickness,and mechanical strength of the self-assembled nanofibers.In this work,we firstly evaluated the effects of driveless physical deposition on the application characteristics of multilayer nanofibrous films.Then,multilayer nanofibers of bioactive delivery systems were fabricated by various methods such as physical deposition,electrostatic interactions,electrostatic interactions and post-covalent cross-linking,electrostatic-metal coordination interactions,and electrostatic-reversible covalent interactions.The aim of this study is to elucidate the effects of molecule interactions on the physicochemical properties of nanofibers and its modulation of bioactive molecules such as curcumin,lysozyme etc.,and the related mechanisms were discussed.The main contents and results of this article were summarized as follows:1.Mechanism and application characteristics of multilayer nanofibrous films fabricated by driveless physical depositionElectrospinning technique was utilized to fabricate a multilayer film with ethylcellulose nanofibers as the outer layer and curcumin-loaded gelatin nanofibers as the inner layer,a model of driveless physical deposition was constructed.Fieldemission scanning electronic microscopy observations showed that the outer and inner layers had a smooth surface and clear boundary.The hydrophobic outer layers decreased the water vapor permeability and improved the water contact resistance of the hydrophilic inner layer,and the intimate interactions of hydrogen bonds between two adjacent layers enhanced the thermal stability.The gelatin film exhibited a release of 10.8%curcumin with 150 min after burst release in the initial 30 min.However,the multilayer film showed a sustained release of the encapsulated curcumin for 96 h,and the maximal release ratio of curcumin from the film was 11.69%.In addition,the antioxidant activities of the released curcumin from the multilayer film were well retained within 96 h.2.Mechanism and application characteristics of multilayer nanofibers fabricated by electrostatic self-assemblyElectrospinning and layer-by-layer self-assembly techniques were used to fabricate multilayer nanofibers with lysozyme and sodium alginate(SA)as selfassembled layers,a model of electrostatic self-assembly was constructed.With the increasing number of layers,the nanofibers presented an increased average fiber diameter from 364 to 611 nm.The enhanced thermal stability was observed due to the layer-by-layer electrostatic deposition,as well as the formation of hydrogen bonds in the case of the self-assembled nanofibers.The immobilized lysozyme exhibited the improved pH and temperature resistance,excellent storage stability,and retained over 70%of its initial activity after reusing 4 cycles.Moreover,these self-assembled nanofibers resulted in a substantial decrease in Staphylococcus aureus colonies in ultrahigh temperature milk at 4℃ and 25℃,respectively.The highest inhibition rates of the nanofibers against Staphylococcus aureus at 4℃ and 25℃ were 69.31%and 69.82%,respectively.3.Mechanism and application characteristics of multilayer nanofibers fabricated by electrostatic self-assembly and post-covalent cross-linkingElectrospinning and layer-by-layer self-assembly techniques were used to fabricate multilayer nanofibers with lysozyme and dextran sulfate sodium salt(DS)as self-assembled layers,a model of electrostatic self-assembly and post-covalent crosslinking was constructed.The non-heated self-assembled nanofibers presented the increased average fiber diameter from 397 to 501 nm with increasing number of layers,but an improved thermal stability was induced by Maillard reaction due to the formation of covalent bonds.After heating,the immobilized lysozyme lost less than 40%of its initial activity,but exhibited the enhanced temperature tolerance and storage stability,and retained over 55.6%of its original activity after 12 reuses.Moreover,the heated nanofibers showed substantially higher antibacterial activities against Staphylococcus aureus(54.3%)and Escherichia coli(15.0%),compared to the non-heated ones.4.Mechanism and application characteristics of multilayer nanofibers fabricated by electrostatic-metal coordination self-assemblyElectrospinning and layer-by-layer self-assembly techniques were used to fabricate multilayer nanofibers with Ag+and polydopamine(PDA)as self-assembled layers,a model of electrostatic-metal coordination self-assembly was constructed.The surface morphology and composition analysis confirmed that the reduction of Ag+to AgNPS and the successful deposition of PDA and AgNPS.With the increasing number of layers,the self-assembled nanofibers presented an improved thermal stability and deformation resistance due to electrostatic and metal coordination interactions.The self-assembled nanofibers with AgNPS outermost layer were higher antibacterial activities against Staphylococcus aureus and Escherichia coli than the nanofibers with PDA as the outermost layer.The highest inhibition rates of the self-assembled nanofibers against Staphylococcus aureus and Escherichia coli were 60.19%and 58.59%,respectively.5.Mechanism and application characteristics of multilayer nanofibers fabricated by electrostatic-metal coordination self-assemblyElectrospinning and layer-by-layer self-assembly techniques were used to fabricate multilayer nanofibers with chitosan-dialdehyde-β-cyclodextrin-curcumin(CS-DCD-CUR)and alginate dialdehyde(ADA)as self-assembled layers,a model of electrostatic-reversible covalent self-assembly was constructed.With the increasing number of layers,the self-assembled nanofibers showed an increased average fiber diameter from 441 to 576 nm and had relatively rough surfaces.The improved thermal stability and tensile strength of self-assembled nanofibers were attributed to Schiff base bond and electrostatic attraction between CS-DCD-CUR and ADA.The self-assembled nanofibers exhibited pH-sensitive release characteristics under acidic conditions due to the hydrolysis of Schiff-base in acid solution.Moreover,the self-assembled nanofibers showed slow and sustained release of curcumin within 620 min and maintained the antioxidant activities.The highest radical scavenging activities against ABTS and DPPH radicals of the nanofibers were 24.75%and 83.56%,respectively.