methods for making comb - type antithrombotic conjugate wherein substantially all side chains of water soluble poly are extended by ring - opening polymerization to form a copolymer wherein substantially all terminals are conjugated to an antithrombotic molecule . in addition , a method is provided for applying a coating comprising a comb - type anti - thrombotic conjugate to at least a portion of an implantable device to prevent or reduce the formation of thrombosis on the surface of the device . a first or sub - layer of the coating is prepared by mixing a polymeric material and a biologically active agent with a solvent , thereby forming a homogeneous solution . a second or outer layer comprising a comb - type anti - thrombotic conjugate may be applied over the inner drug - containing layers using , for example , a dip coating or spray coating process . alternatively the comb - type antithrombotic conjugate may be used as a matrix material to encapsulate a pharmaceutical agent to form microspheres or nanospheres before depositing the microspheres or nanospheres onto a medical device .