Coaxial electrospinning of polycaprolactone@chitosan: Characterization and silver nanoparticles incorporation for antibacterial activity Kaleemullah Kalwar, Wen-Xiu Sun, Da-Li Li, Xue-Ji Zhang, Dan Shan ⁎ Sino-French Laboratory of Biomaterials and Bioanalytical Chemistry, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China abstract article info Article history: Received 8 April 2016 Received in revised form 31 August 2016 Accepted 31 August 2016 Available online 01 September 2016 In this work, Polycaprolactone@Chitosan (PCL@CS) coaxial nanofibers (NFs) were successfully prepared by co- electrospinning technique. Feed rate, solvent ratio 0.6 mL/h and 3:1 was optimized, respectively. Furthermore, coaxial nanofibers were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC); also contact angle was checked, CS has higher hydrophilicity than PCL@CS and PCL. Silver nanoparticles (AgNPs) were synthe- sized and immobilized on the coaxial nanofibers. Gram negative Escherichia coli BH5α (E. coli) and Gram positive Staphylococcus aureus (S. aureus) were tested against modified coaxial nanofibers for antibacterial activity, 13 mm inhibition zone was measured against E. coli which was higher than S. aereus. © 2016 Elsevier B.V. All rights reserved. Keywords: Coaxial nanofibers Polycaprolactone Chitosan Silver nanoparticles Antibacterial activity 1. Introduction Polymeric fibers can be synthesized with the size from few nm to a number of μm in diameter by using novel electrospinning technique [1–3], that is widely used for the production of high performance nano- fibers with different conditions like large surface area to volume ratio and high porosity with tiny pore size [4]. Polycaprolactone (PCL) known as a aliphatic polyester, is frequently employed in biomedical uses because of its biocompatibility, slow biodegradability, low-cost, non-toxicity and good mechanical properties [5,6]. PCL has good com- patibility with various medications and can be manipulated in different formulations anticipated to drug delivery and tissue engineering [7,8]. Nanofabrication of PCL was discussed in previous literature [9–11] etc. Moreover, synthesis of Chitosan nanofibers is limited by high revolt- ing forces in the middle of ionic groups inside the polymer, that occur throughout the application of high electric field in the course of electrospinning [12]. It is previously studied that researchers have gained 330 nm nanofibers of chitosan from a mixture solution of chito- san, dichloromethane and triflouroacetic acid. Another approach is con- cerned with the fabrication of amalgam materials such as chitosan/ polyvinyl alcohol [13], chitosan/polyethylene oxide [14] etc. Aforemen- tioned amalgam materials have a number of benefits over pure chitosan e.g. higher mechanical strength, biocompatibility and antibacterial properties [15]. It is well known that PCL has hydrophobic properties [16], which may strictly limit its use in some applications. Mixing of PCL with a hy- drophilic polymer may considerably enhance the whole material char- acteristics. Chitosan is a natural polysaccharide extracted from chitin that can deliver the hydrophilicity and the capability to assist the bio- compatibility of PCL [16–21]. Therefore, the combination of PCL with the Chitosan may prove helpful for the occurrence of inventive materials. Furthermore, for the surface functionalization of nanofibers with nanomaterials and manufacturing of antimicrobial coating can be car- ried out by using chemical reactions with functional groups [22],A number of antimicrobial agents or antibiotics can be comprised in nano- fibers for the prevention of microbial infection [23,24], such as elemen- tal silver, Ag-GODs and its formulation to produce NPs are most efficient antimicrobial agents [25,26]. In this paper, the co-electrospinning technique was applied to man- ufacture PCL@CS core@shell NFs, where PCL, CS form core and shell layer, respectively. PCL was selected as a core material because of its properties. CS of high molecular weight was employed for the synthesis of shell. As CS was unsuccessfully electrospun; thus, the use of PCL as a core of coaxial nanofibers is expected to increase the electrospinning ca- pability of CS. In addition, by co-eletrospun method, CS is fully accumu- lated on the shell of nanofibers which shows better CS revelation than PCL@CS blend fabrication. The influence of concentration on the core, feed rate of coaxial fibers process, solvent concentration, morphology, core/shell structure, properties such as contact angel measurements, Reactive and Functional Polymers 107 (2016) 87–92 ⁎ Corresponding author. E-mail addresses: danshan@njust.edu.cn, danshan@yzu.edu.cn (D. Shan). http://dx.doi.org/10.1016/j.reactfunctpolym.2016.08.010 1381-5148/© 2016 Elsevier B.V. All rights reserved. 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