Abstract: A method for controlling generation of biologically desirable voids in a composition placed in proximity to bone or other tissue in a patient by selecting at least one water-soluble inorganic material having a desired particle size and solubility, and mixing the water-soluble inorganic material with at least one poorly-water-soluble or biodegradable matrix material. The matrix material, after it is mixed with the water-soluble inorganic material, is placed into the patient in proximity to tissue so that the water-soluble inorganic material dissolves at a predetermined rate to generate biologically desirable voids in the matrix material into which bone or other tissue can then grow.