Study On Preparation Of Polycitrate-based Microspheres And Micronanofiber Membranes By Pickering Emulsion

Poly(1,8-octanediol-co-citric acid)(POC)as a thermosetting bioelastomer,has attracted much attention due to the simple and non-toxic synthesis process,controllable mechanical properties,uniform degradation rate,high shape retention rate,and good biocompatibility.But the thermoset nature makes it relatively difficult to form.The emulsion formed by solid particles instead of traditional surfactants is called Pickering emulsion.Considering the utilization of green and safe particle emulsifiers,which are able to avoid the toxic side effects of traditional emulsifiers,Pickering emulsion shows important application prospects in the field of medical materials.Based on this,this paper hopes to use POC prepolymers to construct Pickering emulsion to achieve molding processing of POC elastomer materials,thereby expanding their application areas.In this paper,the Pickering emulsion was constructed with the synthesized POC prepolymer as the oil phase,the biocompatible and biodegradable chitin nanocrystalline whisker(CW)as the particle-based emulsifier,and the pullulan(PUL)aqueous solution as the aqueous phase,then prepared the POC-based microspheres and micro-nanofiber membranes by spray drying technology and electrospinning technology respectively,in order to expand the application scope of POC-based materials.The main research work is as follows:1.The POC prepolymer,as the oil phase,was prepared by melting and polymerizing,and then dissolved in the dimethyl carbonate(DMC)at the ratio of 50 wt%.The CW prepared by acid solution method was used as emulsifier,and fabricated into different concentration of CW aqueous dispersions.The POC oil-in-water type(O/W)Pickering emulsion was prepared by ultrasonic emulsification at the ratio of 1:1,and the macroscopic and microscopic characterization of the emulsion was carried out.It was concluded that when the proportion of CW/POC was greater than 7%,stable pickering emulsion can be constructed.The diameter of the droplets decreases gradually with the concentration of whiskers increases.2.With the 50 wt% POC dissolved in the DMC as the oil phase,20 wt% of the PUL aqueous solution as the aqueous phase,and CW as the emulsifier,the POC/PUL O/W Pickering emulsions with different oil/water volume ratio of 1:4,2:3 and 1:1 were prepared and denoted as O1/W4,O2/W3 and O1/W1,respectively.The results showed that the emulsion structure was stable and the droplet particle size was in the micron-level range.3.The POC/PUL O/W Pickering emulsion(1:4,v/v)was spray dried and cured to form POC/CW/PUL microspheres which show the average diameter of the beads was 3.84±1.79 ?m.And then the PUL of the shell layer was removed by water washing,obtaining POC/CW elastomer microspheres with an average diameter of 1.95±1.08 ?m.The application of microspheres was preliminarily studied.First of all,chitosan(CS)and polycaprolactone(PCL)were blended and modified by POC/CW/PUL microspheres and POC/CW microspheres.The results showed that POC/CW/PUL microspheres improved the toughness of CS membranes,and POC/CW microspheres increased the elongation at break of PCL membranes and reduced rigidity.And then,the oil-water phase of POC/PUL O/W Pickering emulsion was spray dried and heat cured to obtain drug-carrying POC/CW/PUL microspheres.According to the vitro release studies,the POC/CW/PUL microspheres could achieve double-layer drug release.The hydrophobic drug release in the core layer followed the non-Fickian diffusion mechanism,while the cortical hydrophilic drug release followed the Fickian diffusion mechanism.4.POC/CW/PUL fiber membranes were prepared from the O1/W4,O2/W3,O1/W1 emulsions through electrospinning and curing processes,and the PUL of the cortex was washed to obtain POC/CW fiber membrane.The structure and properties of fiber membranes are characterized by SEM,TEM,DSC,DMA and other methods.In addition,POC/CW/PUL drugcarrying fiber film was prepared from the drug-carrying emulsion through electrospinning.The results indicate that all three emulsions can be electrospun,among which the O1/W4 shows the best.And the fiber diameter gradually increases with the increase of the proportion of POC in the core layer.Besides,curing time has a certain impact on the mechanical properties of the fiber membranes.If the curing time is too short,the mechanical properties of the fiber film will get poor.If the curing time is too long,the fiber film will become hard and brittle.The three POC/CW fiber membranes did not appear viscous flow at high temperatures,and all exhibited the characteristics of elastomers.