Core-sheath Nanofibers As Drug Delivery System For Thermoresponsive Controlled Release

With nanotechnology developed rapidly,nanofibers had gradually become the hotspots in the research areas recently.Electrospinning technology is the most simply and easily method to prepare nano-materials.As the electrostatic spinning explores,coaxial electrospinning and hollow electrostatic spinning has gradually become the mainstream.This method is based on the electrostatic spinning and only a small part of the improvement,however,it have larger surface area,higher porosity and better biocompatibility than traditional spinning.Electrospun fibers have many applications in biological,as well as in the field of biomedical,such as drug delivery carrier,tissue engineering scaffold and wound dressings.As a novel drug delivery system,a special core-shell structure of the coaxial electrospinning can make the drug loaded core and the shell wrapped with other functional materials,which to achieve the control of drug release.In this work,hydrophobic ethyl cellulose(EC)and hydrophilic polyvinyl pyrrolidone(PVP)were choose to used as shell materials.Poly-N-isopropy-lacrylamide(PNIPAAm)was choose to used as core materials.And ethanol as solvent to dissolve three materials.In order to improve the spinning properties of PNIPAAm and control the drug sustain release slowly,the PNIPAAm and EC or PVP can be spun by coaxial electrospinning,respectively.The specific research contents are as follows:(1)The PNIPAAm/EC and PNIPAAm/PVP coaxial nanofibers and the drug-loaded coaxial nanofibers were prepared successfully.(2)The morphologies of coaxial nanofibers and drug-loaded coaxial nanofibers were observed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that the two kinds of coaxial nanofibers are homogeneous and have no obvious beading and the diameter distribution is concentrated.The coaxial nanofibers have obvious core-shell structure: the inner layer is PNIPAAm fiber and the outer layer is EC or PVP fiber.And the surface of coaxial nanofibers were smooth and uniform,the core nanofibers with drug loaded have nodrug precipitation and phase separation.The PNIPAAm/EC and PNIPAAm/PVP coaxial nanofiber membranes have been successfully prepared by X-ray diffraction(XRD)and infrared spectroscopy(FTIR).(3)The contact angle of coaxial nanofibers and drug-loaded nanofibers were tested under a series of temperature gradient.The results show that when the temperature was below the LCST,the PNIPAAm/EC and PNIPAAm/PVP coaxial nanomaterials and drug-loaded nanofibers have a small contact angle and was hydrophilic.When the temperature was under LCST,the coaxial nanofiber membrane had a large contact angle and was hydrophobic.It is indicated that coaxial nanostructures don't change the temperature-sensitive properties of the thermosensitive polymer and change a transition from hydrophilic to hydrophobic.(4)The experiments of cell compatibility of coaxial nanofibers and drug-loaded coaxial nanofibers were carried out by MTT assay.The results showed that coaxial nanofibers and drug-loaded coaxial nanofibers have no toxic and side effect on the cells.(5)In vitro release of coaxial nanofibers with drug-loaded at two different temperatures.The result shows that the temperature is 25 ?(below the LCST),the release rate of PNIPAAm/EC coaxial nanofibers was about 45% within 5 hours.The release rate of PNIPAAm/EC was only 70% in 5 to 10 hours and remained unchanged after 10 hours.The release of PNIPAAm/PVP coaxial nanofiber reached 60% in first5 h.Followed by a sustained increase in drug release,PNIPAAm/PVP with drug-loaded coaxial nanofibers reached 80%,and after 10 h remained basically unchanged.When the temperature was increased to 37 ?(higher than the LCST value),the drug release of the two kinds of coaxial fibers appeared release slowly.The release of PNIPAAm/EC coaxial nanofibers up to 50% in 20 hours,and sustain release after 20 h.However,the drug release of PNIPAAm/PVP coaxial nanofibers reached 60% at 20 h and continued to release after 20 h.The results show that the controlled release of coaxial fiber temperature-sensitive drug is related to the hydrophobic property of the shell in coaxial nanofibers.The effect of PNIPAAm/EC coaxial nanofibers have a slower drug release than PNIPAAm/PVP coaxialnanofiberscan during the different temperature.