the present invention relates to a method of preparing microcapsules suitable for encapsulation of therapeutic and diagnostic agents . the capsular coats are prepared from biodegradable polymers . in a particular aspect of the invention , surface charge of the polymeric material is altered by conjugation of an amino acid ester to the polymer , providing targeting to specific tissue cells . encapsulation of hydrophilic radiodiagnostic agents in 1 μm capsules provides improved opacification . encapsulation of cytotoxic agents in 100 μm capsules is useful in chemoembolization procedures .