Physical-chemical aspects of a coaxial sustained release device based on Poly-Eva

Abstract

Sustained release of dugs offers several advantages like increased efficacy, safety, compliance and convenience. As a consequence sustained drug delivery is often preferred above daily administration of drugs. Furthermore, drug delivery systems can be designed to deliver one or more drugs at a specified rate, for a specific period of time and even at a desired location. In this thesis a sustained release device is described that is manufactured from a non-degradable polymer, namely polyethylene vinyl acetate (EVA). EVA polymers exhibit excellent permeability properties for various drugs and can be obtained in various grades. The sustained release device consists of a coaxial fiber that is based on two types of EVA polymers and is used for sustained release of steroids. These coaxial fibers are manufactured by means of a coextrusion process. Polyethylene vinyl acetate polymers are semi-crystalline. This means that the polymeric structure consists of alternating crystalline and amorphous regions. Because the molecular distances within the polymer crystals are normally smaller than the molecular size of the drug to be released the diffusion process of the drug molecules takes place in the amorphous domains. The presence, size and orientation of the crystalline and amorphous regions are influenced by the manufacturing and storage conditions of the coaxial fibers. As a consequence the release rate of a drug is influenced by the manufacturing and storage conditions of the coaxial fiber. The aim of the study reported in this thesis is to obtain more insight into the mechanisms and factors that influence the release properties of a drug from a coaxial controlled release device based on polyethylene vinyl acetate