(395g) Controlled Released Antibacterial Ag/Poly (L-lactic acid)/Poly(vinyl alcohol) (Ag/PLLA/PVA) Core–Shell Nanofibers Prepared By Cold Atmospheric Plasma (CAP) Treatment and Electrospinning

Introduction: Electrospinning is a well-established process for the fabrication of nanofiber mats of high surface areas and high porosities. This process has been widely used for low-cost wound dressing production [1]. Silver is another widely-used and recognized effective anti-bacterial agent. Generally, the simplest and most commonly used method for incorporating silver nanoparticles into electrospun nanofibers is by the suspension of silver nanoparticles into polymer solutions. However, nanofibers produced by this method have reduced antibacterial properties due to silver nanoparticle aggregation. In order to avoid this problem, the objective of the present study was to utilize cold atmospheric plasma (CAP) [2], which is an ionized gas with ions, electrons, and excited atoms, as a reducing agent for photosensitive silver salts.

Materials and methods: Highly porous core-shell nanofibers were generated by rapid phase separation during the electrospinning process. A 10% PLLA solution was prepared using poly (L-lactic acid) (Sigma, U.S) with 1% silver nitrate (w/w) (Sigma, U.S). Then, the core-shell nanofiber was electrospun with a two-fluid coaxial spinneret (Inovenso Ltd. Co, Turkey), inner tube diameter of 1.2 mm, and outer diameter 1.4 mm, at a voltage ranging from 12-15 kV applied at the tip of the spinneret. The spun fibers were collected on a rotating collector at a speed of 300 rpm. Samples were then treated by cold atmospheric plasma at different times (30s, 60s, 90s, and 180s). Treated and untreated samples were observed by scanning electron microscopy (Hitachi, S-3700N, US). Anti-bacterial experiments and cell cytotoxicity studies will be conducted and reported later. All experiments were run in triplicate and repeated three times for each group with statistics analyzed by ANOVA followed by student t-tests.

Results and discussion: The topography of the fibers plays an important role in regulating initial cell behavior (such as cell adhesion and proliferation) due to changes in surface energy. SEM images of untreated and CAP treated nanofibers showed that the diameter of electrospun nanofibers ranged from 400 nm to 900 nm. Nanopores could be observed on the nanofiber surface, which indicated higher surface areas compared to nanofibers without nanopores. The diameter of nanopores on the untreated surface ranged from 5 nm to 20 nm. However, the nanopores became larger as CAP treated time increased. For 30s of CAP treatment, nanopores on the surface enlarged to about 30 nm in diameter, and 40 nm with 60s of CAP treatment. In addition, it is clear that the color of the electrospun polymer matrix gradually turned darker with increased durations of CAP exposure, indicating that silver nanoparticles were generated during CAP treatment.

Conclusions: In this study, a nanoporous core-shell nanofiber matrix was fabricated by an electrospinning method. Anti-bacterial silver nanoparticle reduction was successfully prepared by CAP treatment of the electrospun scaffold. In addition, results here showed for the fist time that the CAP treatment process is an effective tool to increase nanopore size on the surface of the nanofibers, resulting in increased surface areas, which will affect surface energy, initial protein adsorption events and cell adhesion as well as proliferation.

Acknowledgement: This study was supported by Northeastern University.

References: [1] D. Reneker, A. Yarin. Polymer, 2008, 49 (10), 2387â??425.

[2] M. Wang, X. Cheng, W. Zhu, et al. Tissue engineering: part A, 2014, 5(20), 1060-1071.