Specific examples of suitable polymers include polysaccharides such as dextran or cellulose; chitin; chitosans; proteins; aliphatic polyesters; poly(lactides); poly(glycolides); poly(??-caprolactones); poly(hydroxybutyrates); poly(anhydrides); aliphatic polycarbonates; poly(orthoesters); poly(amino acids); poly(ethylene oxides); and polyphosphazenes.