Introduction In drug delivery applications for chemotherapeutics, a promising approach is the use of drug carriers to reduce the total amount of cytostatics while minimizing side effects. In addition, the carriers, loaded with the drug, can be guided to the tumorous tissue via the vascular system, allowing a local drug release. In our case, drug release is activated due to the sonosensitive behavior of the nanospheres by inertial cavitation caused by focused ultrasound. For measuring the

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... ion effect, a passive cavitation detection (PCD) setup has been employed. So far, the nano carriers were simply filled in laboratory vessels, which did not mimic blood vessels in tissue. Now, we designed flow-through tissue mimicking phantoms to investigate the cavitation behavior in thin vessels as well as to verify our drug delivery approach for its clinical suitability. Methods The flow-through tissue-mimicking phantoms feature a square cross sectional layout which each having a centrally extending channel representing a blood vessel. The phantoms have lateral edge lengths of 20, 40, and 60 mm, the diameters dc of the vessel mimicking flow-through channels are 1, 2, and 3 mm, respectivly, which are typical blood vessel diameters. The phantoms' material consist of a polyvinyl alcohol-water mixture whose sound velocity and acoustic wave impedance are comparable to the corresponding values of biological tissue. Cavitation is excited by a burst signal with the characteristic parameters burst length = 0.6 ms, duty cycle = 0.02%, frequency f = 750 kHz, wavelength ≈1.5 mm, negative pressure amplitude = 1.25 MPa yielding the mechanical Index MI ≈ 1.44. Thus, the maximal MI = 1.9, allowed for diagnostic ultrasound levels, is not exceeded. During the cavitation investigation, the nanospheres are pumped through the phantom. The flow velocities correspond to the physiological velocities in blood vessels (vf = 0.05 m/s -0.1 m/s). Results Investigations have shown that the drug releasing cavitation effect associated to the sonosensitive and biocompatible nanospheres also occures in fine vessel structures, even in the case of vessel diameters dc < . These results confirm the applicability of our drug delivery approach in chemotherapy.