Abstract: Compositions for sustained delivery of a biomolecule including an anionic polymer and a cationic polymer which ironically interact with each other and, optionally, with the biomolecule. Methods for making the compositions, including the step of combining the negatively charged polymer with the positively charged polymer to form an ionic complex are also provided. The biomolecule may be complexed with one of the polymers before it is complexed with the oppositely charged polymer. The complex is exposed to conditions that cause the formation of precipitated microcarriers, such as a change in pH or the addition of a complexing molecule. The compositions are preferably formulated into microcarriers.