| As an effective and low-cost technique which could produce continuous sub-micron or nano-scale fibrous films,it has drawn much attention from researchers and it has been widely used in encapsulation of bioactive compounds.Chitosan,a nature polysaccharide,which is non-toxic and have high biocompatibility,is an ideal wall material.However,pure chitosan is hard to electrospin and need to be mixed with a special co-spinning agent which could improve electrospinnablity of chitosan,hence,choosing a suitable co-spinning agent is a challenge.The aim of this research was to fabricate a composite electrospun nanofibers,in which chitosan was a raw material and pullulan was a co-spinning agent.In this study,we researched the effect of processing parameters on morphology of nanofibers and proved the potential of chitosan/pullulan composite nanofiber films as a kind of fast dissolving oral film.Moreover,in order to enhance its properties and maintain its stability in application,we crosslinked nanofiber films by heating and cinnamaldehyde and characterized the crosslinked nanofiber films.The main research contents and results of the paper are as follows:?1?Processing parameters on nanofibersIn this study,we investigated the effects of processing parameters like voltage,feed ing rate and spinning distance.The results showed that as the voltage rose from 10 k V to 25 k V,the diameter of nanofiber fell significantly?P<0.05?.However,much higher voltage could make distribution of diameters uneven,spindle nanofibers and small droplets appeared.As feeding rate increased from 0.5 m L/h to 2.0 m L/h,the diameter of nanofiber increased,but the difference was not significant?P>0.05?.If the feeding rate was too fast,nanofibers would fused with each other.As the spinning distance rose from 7 cm to 16 cm,the diameter of nanofiber fell significantly?P<0.05?,but much longer distance resulted in coexistence of very thin and thick nanofibers,and the nanofibers became sparse.?2?Characterization and application of fast dissolving chitosan/pullulan composite nanofiber filmsIn this study,Chitosan/pullulan composite nanofiber which has been used as fast dissolving oral films?FDOFs?were prepared via electrospun technology.The ratio of chitosan/pullulan?C/P?had an influence on solution property and nanofiber morphology,with the increa se of chitosan,viscosity and conductivity of solutions increased significantly?P<0.05?,the difference of surface tension was not significant?P>0.05?.The morphology obtained by scanning electron microscopy indicated that the diameter of nanofibers decreased initially then increased.The Fourier transform infrared spectra indicated hydrogen bond interactions between chitosan and pullulan molecules.X-ray diffraction analysis proved that electrospun process decreased the crystallinity of materials.With the addition of chitosan content in the FDOF,DSC?differential scanning calorimetry,DSC?showed that melting point increased from 167.33 to 170.75?.TG?thermo gravimetric?showed the maximum decompose rate increased from 309.70 to 313.56?.DMTA?dynamic mechanical thermal analysis,DMTA?showed glass transition temperature increased from 73.88 to 112.84?.Water solubility test proved that the FDOF can dissolve in water completely within 60 seconds.Finally,in order to prove its practicability in future,a model drug of aspirin was encapsulated in the FDOF successfully.?3?Enhancing physical properties of chitosan/pullulan electrospun nanofibers via green crosslinking strategiesIn this study,electrospun chitosan/pullulan nanofiber films were cros slinked by two green methods?heating and cinnamaldehyde?.As for thermal crosslinking C/P?TCP?nanofiber films,with the increase of chitosan content from 10%to 30%,the morphology results indicated that the nanostructures of TCP nanofiber films were more stable after crosslinked films were immersed in water;water contact angle increased from 31.8°to 54.1°significantly?P<0.05?;weight loss decreased from 83.65%to 45.31%;swelling ratio increased from 32.11%to 263.45%;water vapor permeability decreased 3.49×10-10 g m-1 s-1 Pa-1 to 2.77×10-10 g m-1 s-1 Pa-1;tensile strength increased from 2.95 MPa to 3.86 MPa;elastic modulus increased from 97.61MPa to 115.00 MPa,but the difference was not significant?P>0.05?;elongation at break decreased from 5.24±0.40%to 3.57±0.84%;the maximum decompose rate increased from 305.53?to 309.54?.As for cinnamaldehyde crosslinking C/P?CCP?nanofiber films,with the increase of chitosan content from 10%to 30%,the morphology results indicated that the nanostructures of CCP nanofiber films were more stable after crosslinked films were immersed in water;water contact angle increased from 87.9°to 112.7°?P<0.05?;weight loss decreased from 23.42±4.76%to 15.58±2.16%;swelling ratio decreased from 73.15%to 47.44%;water vapor permeability decreased from 2.29×10-10g m-1 s-1 Pa-1to 1.60×10-10 g m-1 s-1 Pa-1;tensile strength increased from 11.36 MPa to 22.55MPa;elastic modulus increased from 344.31 MPa to 1150.95 MPa;elongation at break decreased from 4.53%to 2.83%;the maximum decompose rate increased from 309.13?to 312.85?.These results showed that the stability of nanostructure,hydrophobic properties,resistance to water,barrier properties,mechanical and thermal properties of TCP and CCP films were enhanced as the weight ratio of chitosan increased,furthermore,these properti es of CCP films were more excellent than TCP films.The Fourier transform infrared spectra indicated the occurrence of Maillard reaction during the thermal crosslinking process and Schiff base reaction during the cinnamaldehyde crosslinking process. |
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