Synthesis of Polylactic Acid Membranes Loaded With Silver Nanoparticles by Electrospinning Technique

Polylactic acid (PLA) is a biodegradable and biocompatible thermoplastic aliphatic material that could stimulate tissue regeneration and drug release in tissue engineering. It is successfully applied to electrospinning of membranes in biomedical field due to its biocompatibility [1]. Selection of non-hazardous solvents for PLA and their optimal ratio is highly important for biomedical applications and membrane formation. The nanofibers formation and spinnability of solution highly depends on considered mixed-solvent system of polymer [1,2]. In this study we varied polymer concentration, and ratio of solvents (acetone (AC), dimethylformamide (DMF) and chloroform (CHL)) in polymer solution to find effect on the fiber diameter and morphology. The appropriate solvent selection depends on the type of polymer should optimize the electrospinning process to produce homogeneous membranes [3]. 
The mixture of solvents that are nonpolar – CHL (the dielectric constant lower than 5) and polar – AC and DMF (the dielectric constant higher than 20) used to meet the electrical property criteria. PLA is better dissolved in CHL, but addition of a solvents with higher dielectric constant, like AC and DMF created more charges on the jet surface that enhances the stability of the charged jet facilitating the formation of fibers.
At the first stage was solution preparation for electrospinning. Polylactic acid was dissolved step by step in CHL, AC and DMF in following ratios: 
   sample #1: (5% PLA+10 mL CHL+ 5 mL AC + 5 mL DMF)
   sample #2: (5% PLA+10 mL CHL+ 10 mL AC)
   sample #3: (5% PLA+10 mL CHL+ 7 mL AC + 3 mL DMF)
   sample #4: (5% PLA+10 mL CHL+ 3 mL AC + 7 mL DMF)
   sample #5: (10% PLA+10 mL CHL+ 5 mL AC + 5 mL DMF)
The solution of silver nanoparticles with concentration 3 g/L was added dropwise to the polymer-solvents solutions for increasing antibacterial properties of obtained membranes.
The morphology of obtained membranes and fibrils structure were investigated by SEM (SEO-SEM Inspect S50-B) equipped with energy dispersive spectrometer AZtecOne with detector X-MaxN20 (Oxford Instruments plc.) for element analysis. 
The main factors that influenced on fibers morphology are voltage and the flow rate. Such parameters should be varied for different polymer solutions. It was observed that fibrils diameter was decreased with increase of voltage. The increase of PLA concentration to 10% leads to increasing fiber diameter.  It was concluded that by varying of PLA solution concentrations and electrospinning parameters membranes with oriented fibrils and required diameter will be obtained.