Patent ID: 8715622

Claim:
An echogenic polymer microcapsule or nanocapsule comprising: (a) a hardened outer surface consisting of (1) a hardened non water soluble polymer and (2) pores in the hardened outer surface of the microcapsule or nanocapsule formed by removal of a non-water soluble sublimable substance; and (b) a hollow core formed by removal of a water soluble sublimable substance, wherein said hollow core is encapsulated by the hardened outer surface, wherein said echogenic polymer microcapsule or nanocapsule is made from (i) an outer surface forming mixture consisting of a non water soluble polymer and the non-water soluble sublimable substance dissolved in one or more volatile non-polar solvents and (ii) an inner surface forming mixture comprising the water soluble sublimable substance dissolved in water; wherein said microcapsule or nanocapsule has a diameter from about 400 nanometers to about 1.6 microns.