Production of sustained released system

Claim 1

A process for producing a dispensing system capable of releasing a substance at a substantially constant rate in an environment that depletes said substance, said process comprising the steps of: A. forming a capsule which defines an intracapsular volume and comprises a membrane defining a multiplicity of pores of a size sufficient to permit passage of molecules of said substance, said capsule being formed by first preparing a shape-retaining sphere comprising a water-soluble polymer comprising plural cationic or anionic groups and subsequently contacting said sphere with a first polymer comprising plural groups having a charge opposite that of said water-soluble polymer; B. placing said capsule in a solution containing a concentration of said substance for a time sufficient to permit said solution and said substance to diffuse into said intracapsular volume to produce a capsule loaded with said substance; and C. reducing the dimensions of the pores defined by the membrane of said loaded capsule to a degree sufficient to limit the rate at which molecules of said substance pass therethrough by exposing the capsule to a second polymer comprising a multiplicity of groups having a charge opposite that of said water-soluble polymer.