Electrospinning of continuous poly (L-lactide) yarns: Effect of twist on the morphology, thermal properties and mechanical behavior.

Electrospinning PLLA solutions from two oppositely charged nozzles gives a triangle of fibers, also called E-triangle, that assemble into yarns at the convergence point. The formed yarn at the E-triangle was taken up by a unit comprising a take up roller and coupled twister plate, which twist rate can be varied. At all twist rates, uniform and smooth fibers without any beads were formed. The apex angle of the deposited fibers at the E-triangle was larger at higher twist rates. By increasing the twist rate from 80rpm to 320rpm the orientation angle of fibers in the yarn changes from 18.8° to 41.5°. Increasing the twist rate revealed a higher polymer crystallinity likely due to the polymer orientation by the applied tension to the fibers. The ultimate strength and modulus of electrospun yarns were higher when prepared at higher twist rates. However, at the highest twist rates, the strength and modulus of electrospun yarns leveled off and even decreased slightly. The results revealed that the mechanical properties not only depend on the polymer crystallinity but also on the alignment of the fibers in the yarn and the angle at which they were deposited. These biodegradable materials are promising materials to be used in a wide range of applications where environmentally friendly products are required.

Drug release behavior of electrospun twisted yarns as implantable medical devices.

In this study, twisted drug-loaded poly(L-lactide) (PLLA) and hybrid poly(L-lactide)/poly(vinyl alcohol) (PLLA/PVA) yarns were produced using an electrospinning technique based on two oppositely charged nozzles. Cefazolin, an antibiotic drug was incorporated in the yarn fibers by addition to the PLLA electrospinning solution. Morphological studies showed that independent of the twist rate, uniform and smooth fibers were formed. The diameter of the electrospun fibers in the yarns decreased at higher twist rates but produced yarns with larger diameters. At increasing twist rates the crystallinity of the fibers in the yarns increased. In the presence of cefazolin the fiber diameter, yarn diameter and crystallinity were always lower than in the non-drug loaded yarns. In addition the yarn mechanical properties revealed a slightly lower strength, modulus and elongation at break upon drug loading. The effect of the twist rate on the cefazolin in vitro release behavior from both PLLA and hybrid yarns revealed similar profiles for both types of drug-loaded yarns. However, the total amount of drug released from the hybrid PLLA/PVA yarns was significantly higher. The release kinetics over a period of 30 d were fitted to different mathematical models. Cefazolin release from electrospun PLLA yarns was governed by a diffusion mechanism and could best be fitted by Peppas and Higuchi models. The models that were found best to describe the drug release mechanism from the hybrid PLLA/PVA yarns were a first-order model and the Higuchi model.

Influence of the solvent type on the morphology and mechanical properties of electrospun PLLA yarns.

An electrospinning technique based on the use of two oppositely charged nozzles was applied to fabricate continuous twisted yarns of poly(L-lactide) (PLLA) nano/micro fibers. In this study, the effect of solvent on the electrospinning of PLLA fibrous yarns was investigated. For this purpose, yarns were electrospun using chloroform, dichloromethane or 2,2,2-trifluoroethanol as solvents at a PLLA concentration of 7 wt%. The analysis of the morphology, diameter, crystallinity and mechanical properties of electrospun yarns revealed that the vapor pressure of the solvent plays an important role. Whereas the fiber diameter decreased, the crystallinity of the fibers increased using a solvent with lower vapor pressure. In addition, mechanical properties (e.g., tensile strength and modulus) revealed that the yarns composed of fibers with smaller diameters showed higher tensile strength and modulus. In summary, fine-tuning solvent properties resulted in a modulation of fiber diameter, crystallinity, and thereby yarn mechanical properties, and are important factors to consider in the fabrication and application of electrospun yarns.