Influence of spinline stress on release properties of a coaxial controlled release device based on EVA polymers.

ABSTRACT

PURPOSE: To investigate the influence of the extrusion parameters on the polymeric structure and release properties of polyethylene vinyl acetate (EVA) coaxial fibers, used for controlled release of steroids. METHODS: Coaxial fibers were prepared under various extrusion conditions. Both spinline stress and release properties were determined. The polymeric structure of the membrane was investigated with wide angle X-ray scattering (WAXS). RESULTS: Upon leaving the spinneret, the polymeric fiber exhibits a large die swell. As a consequence, it is necessary to apply a force to draw the fiber to its desired diameter. A larger drawing force is needed at lower extrusion temperature, at a smaller air gap, or at a higher spinning velocity. It was found that the release rate of a steroid from the coaxial fiber increases, when the fibers are prepared at a higher spinline stress. X-ray measurements reveal that at higher spinline stress, the crystalline volume fraction of the membrane decreases. As a result of a decreasing crystallinity, the permeability of the polymer increases. CONCLUSIONS: It is demonstrated that the extrusion parameters and spinline stress have a significant influence on the polymeric structure of the membrane and hence the release properties. Higher spinline stress results in a higher release rate.