Chitosan/Pullulan Nanofiber Mats Via Electrospinning

Chitosan is a modified natural polymer mainly produced from another natural polysaccharide called chitin,which is one of the most abundant organic materials all over the world.Chitosan has good biocompatibility,biodegradability,and antimicrobial properties,which provide great potentials in biomedical applications such as tissue engineering,drug delivery,and wound dressing,etc.Pullulan is a neutral linear,fungal exopolysaccharide produced from starch by aureobasidium pullulans.Besides the common advantages of natural polysaccharides,such as non-toxic,biocompatible and biodegradable,the typical linkage pattern of pullulan provides unique physical properties,including excellent water solubility,high water absorbing capability,adhesive properties and capability to form strong and resilient films and fibers.Pullulan can be easily molded and has been proven to be effective for nanofiber formation.Recently pullulan is being investigated for several biomedical applications such as targeted drug and delivery,tissue engineering and wound dressing.Electrospinning has proved to be a relatively simple,versatile technique to produce functional nanofibers and nanofibrous membranes.The exceptional characteristics of electrospun nanofiber mats include high surface area to volume ratio,high porosity,flexibility and adjustable pore size distribution,which make them more suitable candidates in a wide range of applications especially in biomedicine and tissue engineering.As we know,the electrospinning of chitosan is very difficult due to the protonation of amino groups on the back bone of chitosan,and chitosan nanofibers were often produced from toxic or corrosive solvents like trifluoroacetic acid,DMSO and concentrated acetic acid,which will affect the applications of chitosan in the field of biomaterials.In this work,we prepared chitosan/pullulan nanofiber mats using low concentration of acetic acid.As the electrospinning of chitosan is very difficult so we used pullulan as carrier polymer to improve the electrospinnability of the chitosan.We used two electrospinning techniques such as blend electrospinning and co-axial electrospinning and compared the properties of the nanofiber mats prepared by both methods.For blend electrospinning different ratios of chitosan and pullulan were taken i.e.30:70,20:80,50:50 and 70:30.And for co-axial electrospinning pullulan was taken 17% and chitosan concentration were changed like 1%,2%,3%,and 4%.As both chitosan and pullulan are hydrophilic in nature,dopamine was used as crosslinker to improve the water stability of the nanofiber mats.The effects of dopamine content and crosslinking modes(sodium hydroxide or ammonium carbonate)on the structure of nanofiber mats were discussed.The nanofiber mats were characterized by Fourier transform infrared spectroscopy(FTIR),field emission electron microscopy(FESEM),X-ray diffraction(XRD),thermo gravimetric analysis(TGA),water contact angle(WCA),and water absorption test.The results showed that using pullulan as carrier polymer improved the electrospinnability of chitosan and produced nano-sized fibers.The temperature and humidity also had a great impact on the electrospinnability of chitosan.The incorporation of dopamine into chitosan/pullulan spinning dope followed by crosslinking in the vapor of ammonium carbonate endowed nanofiber mats with a good water stability.The co-axial electrospinning was successfully performed with chitosan solution as a core and pullulan solution as a shell,and the obtained nanofiber exhibited a large diameter than that from blend electrospinning,and less stable in water though after crosslinking by dopamine.Thus,the blend electrospinning is more preferable for preparation of chitosan/pullulan nanofiber mats.