- Polymer-based delivery systems are being used increasingly as a method of drug administration. However, few systems have been developed where the release rates can be externally regulated or made to increase as time progresses. To address this issue, we have developed a system composed of ethylene-vinyl acetate copolymer, drug, and magnetic beads. The release of proteins from these polymer matrices can be repeatedly modulated by exposing them to oscillating magnetic fields. The effects of changing the strength and orientation of embedded magnets, and the frequency and amplitude of the magnetic field have been investigated. We report here the effect of the polymer properties on the extent of modulation. Ethylene vinyl acetate (EVAc) copolymers of varying vinyl-acetate content were used and a correlation between the rigidity of the polymer and the extent of modulation was examined.