a cost - effective , scalable technique for producing microspheres loaded with biologically active solid proteins is provided . the microspheres degrade over time and release biologically active vegf , as demonstrated by the proliferation of huvecs in vitro compared to negative controls . a defined concentration of microspheres can deliver a quantifiable level of vegf with known release kinetics . the invention can be used with other growth factors and applied to tissue engineering applications such as the regeneration of peripheral nerve , bone , adipose tissue , and solid organs . the method of the invention includes the steps of dissolving a polymer with an organic solvent to produce a polymer solution ; adding a biologically effective amount of a bioactive substance to the solution to produce a mixture of the polymer and the bioactive substance ; vibrating the mixture to produce a bioactive substance - polymer complex ; emulsifying the mixture to produce an emulsion comprising the bioactive substance - polymer complex ; and extracting the organic solvent from the emulsion to produce microspheres comprising the polymer - bioactive substance complex , wherein the bioactivity of the bioactive substance is usefully preserved .