Micro-sized particles having a polymeric structure of cells are provided. Also provided is a method of producing micro-sized particles having a polymeric structure comprising: (1) forming a homogenous solution by heating a mixture of a high molecular weight polymer and a low molecular weight material, wherein said low molecular weight material makes up at least about 50% by weight of the homogenous solution, (2) forming a dispersed solution by dispersing the homogenous solution formed in step (1) into an inert material, (3) cooling the dispersed solution to cause the high molecular weight polymer to phase separate from the low molecular weight material, (4) forming solid particles comprised of said low molecular weight material trapped inside a structure of cells of said high molecular weight polymer, and (5) removing the solid particles from the dispersed solution.