Fabrication Of The Advanced Gel Materials Based On Electrospun Nanofibers And Their Applications

Gel materials including aerogels and hydrogels are the materials which have been widely used in many fields such as separation and purification,heat insulation,wave absorption,sensing,biomedicine,daily chemicals,etc.,and have broad development prospects.However,there are still some outstanding problems to be solved although they have been developed so far.For example,common aerogels and hydrogels have the problems of notable brittleness and poor compression resistance property,and hydrophobic aerogels possess poor oil antifouling property.Stimulus-responsive hydrogels have slow response rate.These existing problems greatly weaken their application effect in some fields.In order to solve these problems,three types of advanced gel materials(superhydrophilic nanofibrous aerogels,temperature-responsive hollow nanofibrous hydrogels with ultrafast response rate and excellent compression elasticity and near infrared(NIR)light responsive hollow nanofibrous hydrogels with fast response rate)were fabricated using electrospun nanofibers in this thesis.The relationships between their structures and performances were studied.Moreover,their application potentials in the separation of surfactant-stabilized water-in-oil emulsions,temperature or NIR light controlled drug release and photothermal/chemical synergistic postoperative therapy for solid tumor were explored,respectively.The detailed research purposes and contents and the obtained research results of this thesis mainly include following three aspects:(1)In order to solve the problems of poor oil antifouling property of the reported hydrophobic nanofibrous aerogel in the separation of water-in-oil emulsion and using organic solvent to wash for regeneration,superhydrophilic PVA/SiO₂ hybrid nanofibrous aerogel was prepared using polyvinyl alcohol(PVA)and tetraethylorthosilicate(TEOS)as main raw materials by electrospinning,freeze-shaping and thermal crosslinking processes.It was observed by scanning electron microscope(SEM)that the aerogel has a hierarchical porous structure composed of interpenetrating macropores and micropores,which have the sizes of ca.20?m and ca.1?m,respectively,and its constituent nanofibers are cemented with each other.The characterization results obtained by Fourier transformation infrared(FTIR)show that silica-based crosslinking structure was formed between the PVA molecular chains through hydrolysis of TEOS and polycondensation reaction during the heat treatment process,so the prepared nanofibrous aerogel has good stability and compression elasticity.The PVA/SiO₂ hybrid nanofibrous aerogel with better separation property was obtained by investigating the effects of the factors,such as alcoholysis degree of PVA,TEOS amount,PVA concentration in the spinning solution etc.,on the separation flux and separation efficiency of separating surfactant-stabilized water-in-oil emulsion.When it was used for gravity-driven separation of the surfactant Span 80 stabilized water-in-gasoline emulsion,the flux is 2022 L m^-2 h^-1,the separation efficiency approaches 99.8%and the purity of the separated gasoline reaches as high as 99.994%.During the separation process,the water layer hindering the separation was not formed between the emulsion to be separated and the aerogel.Additionally,the nanofibrous aerogel could be recycled by simple washing and drying after separating surfactant-stabilized water-in-oil emulsion and its separation performance of the aerogel was not change after ten times of regeneration.Differing from other separation materials,the nanofibrous aerogel simultaneously has filtration and adsorption effect in the separation process of surfactant-stabilized water-in-oil emulsion.The deemulsification of its constituent hydrophilic nanofibers and the capillary force of its internal micropores could be the main factors to achieve highly efficient separation of the emulsions.(2)To further increase the response rate and improve compression resistance property of temperature-responsive hydrogels for their more effective application in temperature-controlled drug release,the hollow nanofibers were prepared by coaxial electrospinning technique combined with an extracting process,using the thermally cross-linkable temperature-responsive polymer poly(N-isopropylacrylamide-co-N-hydroxymethylolacrylamide)as a fiber-forming polymer.The inner diameter and shell thickness of the hollow nanofibers were controlled by changing the flow rate ratio of the core spinning solution and the shell spinning solution.Then,the hollow nanofibrous hydrogel with good stability and compression elasticity was fabricated by high-speed dispersion,freeze-shaping and heat treatment process.SEM results show that the hydrogel precursor has a hierarchical porous structure similar to above-mentioned aerogel,and FTIR results confirm that chemical cross-linking structures were formed within the nanofiber shells and between the nanofibers.The prepared hollow nanofibrous hydrogel has remarkable temperature responsiveness,and the response rate is faster than that of the solid nanofibrous hydrogel with the same chemical composition,which increases with decreasing the shell thicknesses of its constituent hollow nanofibers.When the ambient temperature was raised from 20°C to 55°C,the shortest time for the hollow nanofibrous hydrogel to reach its deswelling equilibrium state is 14 s,and the one for returning to its swelling equilibrium is 27 s,which are greatly shorter than those of the temperature-responsive hydrogels reported previously(the shortest time to reach a deswelling equilibrium state is about 4 min).Through preparing samples by rapidly freezing the hydrogel and observing its morphological structures before and after its phase transition in response to temperature change,it is speculated that the hydrophobic interaction between its constituent fibers and the rapid expelling of the water molecules from its interpenetrating macropores and micropores and the fiber cavities are the main reasons for its rapid temperature response.During coaxial electrospinning,dextran marked by fluorescein isothiocyanate(FITC)(FITC-dextran),as a hydrophilic macromolecular model drug,was loaded into the shells of the temperature-responsive hollow nanofibers.When the ambient temperature was alternately changed between 15°C and47°C,the resulted drug-loaded temperature-responsive hollow nanofibrous hydrogel can release its loaded FITC-dextran in an?on/off?switchable fashion.In vitro cell cytotoxicity test results demonstrate that the prepared drug loaded temperature-responsive nanofibrous hydrogel is biocompatible.(3)To improve the response speed and compression resistance property of NIR light responsive hydrogel for the application of photothermal/chemical synergistic postoperative therapy of tumor,the synthesized monodisperse gold nanorods(AuNRs)with the longitudinal surface plasma resonance wavelength close to 808 nm were firstly introduced into the shells of temperature-responsive hollow nanofibers by coaxial electrospinning.Then,NIR light responsive hollow nanofibrous hydrogel with hierarchical porous structure and excellent compression elasticity was constructed through high-speed dispersion,freeze-shaping and heat treatment processes.It was observed by transmission electron microscopy(TEM)that AuNRs are aligned along the fiber axis within the hollow nanofiber shells.FTIR results show that there is an interaction between AuNRs and the polymer within the fiber.The resulted hydrogel can respond to NIR light of 808 nm wavelengths,and their response speed increases with the increase of its AuNRs content.The shortest time for the nanofibrous hydrogel to reach its deswelling equilibrium state is 24 s.During the coaxial electrospinning process,paclitaxel(PTX),an anti-cancer drug,was loaded into the shells of temperature-responsive hollow nanofibers.The obtained PTX loaded hollow nanofibrous hydrogel can respond to 808 nm NIR light irradiation or non-irradiation to release the drug in controllable?on/off?mode.The results of in vitro cytotoxicity experiment and animal experiment demonstrate that the PTX-loaded NIR light responsive hollow nanofibrous hydrogel can kill in vitro 4T1 breast cancer cells and postoperative residual tumor in mice through photothermal and chemical synergistic effects when they were irradiated by 808 nm NIR light of1.5 W/cm² power density.After three times of the irradiation,the residual cancer cells in the mice can be completely killed,without recurrence.In addition,H&E histological analysis results confirm that the hydrogel has high biological safety during photothermal/chemical synergistic therapy of tumor.