The Regulation Of The Structure Of Electrospun Nanofibrous Nonwoven Mats And Application

Electrospinning is a simple and versatile technique for the production of nanofibers with diameters ranging from nanometers to micrometers.Electrospun nanofibers have attracted great attention owing to their unique features such as high specific surface areas,high porosity,and interconnected pore structure,allowing them to be used in filtration,tissue engineering,textiles,sensing,and fabrication of wearable electronic devices.Although nonwoven mats of polymer nanofibers can meet most of the requirements needed for the aforementioned applications,the inadequate mechanical strength critically limits their further development.Most nonwoven mats of electrospun nanofibers are formed via physical stacking(without inter-fiber connection),resulting in relatively weak mechanical properties.Besides,high junction resistance between fibers further limited their applications in electric device.In order to overcome the above problems.The objective is to achieve the welding only occurred at the cross points,with no significant changes to the topological and geometric structures of the nanofibers away from the intersection.These methods will extend the application fields of electrospun nanofibers.In this study,overall welding,local welding and gradient welding were achieved by solvent vapor,laser induced and swelling.Based on these methods,the systematic study of welding and the applications of welded electrospun nanofibers mats has been explored.We believe that the work has both notable academic value and application potential.We firstly describes a simple and effective method for welding electrospun nanofibers at the cross points to enhance the mechanical properties of their nonwoven mats.The welding is achieved by placing a prepared nonwoven mat of the nanofibers in a capped vial with the vapor of a proper solvent.For polycaprolactone(PCL)nanofibers,the solvent is dichloromethane(DCM).The welding can be managed in a controllable fashion by simply varying the partial pressure of DCM and/or the exposure time.Relative to the pristine nanofiber mat,the mechanical strength of the welded PCL nanofiber mat can be increased by as much as 200%.Meanwhile,such a treatment does not cause any major structural changes,including morphology,fiber diameter,and pore size.This study provides a generic method for improving the mechanical properties of nonwoven nanofiber mats,holding great potential in various applications.Solvent vapor to weld only globally rather than locally has limited their further development.Hence,we demonstrate a controllable and low-cost technique to weld polymer fiber into large interconnected networks by locally heating,which generated by Au nanocages(Au NCs)upon irradiation of near-infrared region(NIR)laser.Since polymer fibrous mats cannot directly utilize light to generate heat as it only weakly absorbs visible and near-infrared light.Through this process,the welding of polycaprolactone(PCL)and poly(vinylidene fluoride)(PVDF)fibrous mats at junctions were achieved.Besides,the selected over welded could obtain transparent film with different patterns on the fibrous mats,which can extend this technique to the applications of thermal paper and laser printing.The output voltage of Au NC/PVDF fibrous mat can reach to 25.2 V,since the overall resistivity is reduced.This method may open new opportunities for developing welded polymer fibrous mats as a potential candidate applied for the aforementioned applications with low-cost and less damage.Devices based upon piezoelectric and pyroelectric poly(vinylidene fluoride)(PVDF)films have attracted great attention owing to their mechanical flexibility and superior energy harvesting capability.However,the performance of such devices still need to be greatly improved owing to the relatively low content of ? phase in the films.In addition,PVDF cannot directly utilize light to generate electricity as it only weakly absorbs visible and near-infrared light,preventing effective conversion from light to heat.In this report,we address both issues by directly incorporating Au nanocages(Au NCs)into PVDF nanofibers prepared by electrospinning.The incorporation of Au NCs improved both the piezoelectric and pyroelectric responses of a hybrid device by more than 17 folds,making them promising for the fabrication of self-powered devices,tactile sensors,and infrared detectors.The repair of tendon to bone has been a challenge in orthopedic surgery,since the lack of a hierarchically scaffold that could mimic the change of gradient decreasing orientation and increasing mineralization at the tendon to bone insertion site.By utilized of controlled ethanol solution-vapor mediated welding on the electrospun poly(lactic-co-glycolic acid)(PLGA)fibrous mats and the dissolution of hydroxyapatite(HAp)by acid.We have successfully demonstrated the construction of a fibrous mat with gradient organization and mineralization from aligned to random that mimic the structural organization and composition of collagen fibers at the tendon to bone insertion site.Importantly,compared to mineral deposition,the diameter of fibers was not significant effected by acid dissolution.MC3T3-E1 cells cultured on these scaffolds exhibited highly organized and randomly oriented morphologies,and increased expression of alkaline phosphate(ALP),respectively,from the aligned to random portions.Besides,the mechanical properties were enhanced by welding at the junctions of fibers.These results indicated that the electrospun fibrous mat with gradient organization and mineralization holds great potential to induce gradient organized and differentiation of MC3T3-E1 cells for tendon to bone healing.