a polymeric device releasing biologically active , water - soluble materials having a molecular weight of less than 1000 in a controlled , continuous and linear manner over an extended period of time . insoluble polymer matrixes can be defined in any shape , size and drug content . when applied to medical use , biocompatible polymers are used so that the device is implantable . the device is made by modifying prior art devices based on diffusion of fluid into a polymeric matrix containing dispersed biologically active molecules to yield a polymer device which can be placed in a fluid environment , so that fluid is absorbed by the device and the water soluble molecules diffuse into the fluid environment , leaving behind pores and channels , where the rate of diffusion is limited by an impermeable coating over a portion of t the u . s . government has rights in this invention by virtue of this research supported in part by n . i . h . grant gm26698 .