Active agent containing hydrogel devices wherein the active agent concentration profile contains a sigmoidal concentration gradient for improved constant release, their manufacture and use

Claim 1

An active agent containing controlled release diffusion device comprising a swellable hydrogel matrix in the non-swollen state, interpenetrated with an active agent solute having a stable concentration distribution increasing in a gradient normal to the surface of th device and between the surface and the core thereof, said gradient being in the form of a substantially continuous, inflection point containing, sigmoidal curve, wherein the core is substantially uniformly loaded with active agent and extends outwardly from the center of the device to about 1 to about 60 percent of the radius of the device; the sigmoidal concentration gradient of the active agent extending gradient of the active agent extending outwardly from said core to cover about 99 to about 30 percent of the radius of the device, the remainder, up to about 10 percent of the outermost portion of the radius to the surface of the device, contains a concentration of active agent of no more than 10 weight percent per unit volume as compared to the core concentration of active agent, such that the device, when placed in an aqueous hydrogel swelling environment, releases said active agent in a controlled continuous manner by diffusion for a predetermined period of time into said aqueous environment.