MICROSCALE HYDRODYNAMIC CAVITATION AND ITS APPLICATIONS
Osman Yavuz Perk
Mechatronics, MSc Program, 2012
Assoc. Prof. Ali Koşar (Thesis Supervisor), Assoc. Prof. Devrim Gözüaçık, Asst. Prof. Alpay Taralp, Prof. Dr. Ali Rana Atılgan, Assoc. Prof. Asiye Işın Doğan Ekici
Date &Time: August 7th, 2012 – 11:30
Place: FENS L055
Keywords: Hydrodynamic cavitation, biomedical treatment, microchannel, cavitation damage, kidney stone erosion
Micro flows find applications in a variety of topics covering biomedical, cooling, electronics and MEMS (micro-electro-mechanical-systems) applications. Hydrodynamic cavitation, which is one of the types of cavitation, is based on vaporization, bubble formation and bubbles implosion at low pressures. When the local static pressure of the liquid drops below the vapor pressure of the medium at the operating temperature, cavitating flow is generated. The collapses of the cavities give rise to serious damage to the exposed surfaces. Catastrophic damage and destructive nature of hydrodynamic cavitation has been preferred to be used in various biotechnological areas, but yet not for biomedical purposes. Therefore, in this study it is focused on its effect on biological samples to determine its feasibility and controllability for biomedical usage.
The objective of this study is to reveal the potential of micro scale hydrodynamic bubbly cavitation for the use of kidney stone treatment, and to reveal the effects on prostate cells and benign prostatic hyperplasia (BPH) tissue. Hydrodynamically generated cavitating bubbles were targeted to the surfaces of 18 kidney stone samples made of calcium oxalate, and their destructive effects were exploited in order to remove kidney stones in in vitro experiments. Phosphate buffered saline (PBS) solution was used as the working fluid under bubbly cavitating conditions in a 0.75 cm long micro probe of 147 μm inner diameter at 9790 kPa pressure. The surface of calcium oxalate type kidney stones were exposed to bubbly cavitation at room temperature for 5 to 30 min. The eroded kidney stones were visually analyzed with a high speed CCD camera and using SEM (scanning electron microscopy) techniques. The results showed that at a cavitation number of 0.017, hydrodynamic bubbly cavitation device could successfully erode stones with an erosion rate of 0.31mg/min. It was also observed that the targeted application of the erosion with micro scale hydrodynamic cavitation may even cause the fracture of the kidney stones within a short time of 30 min. The proposed treatment method has proven to be an efficient instrument for destroying kidney stones.
In cell culture experiments, hydrodynamic cavitation caused a dramatic decrease in cell number. Moreover, late response of hydrodynamic cavitation was checked with various cell death assays; however, no effect was observed in terms of cell death activation. In addition to prostate cells, the destructive effect of hydrodynamic cavitation was investigated on human tissues. Hydrodynamic cavitation exposure resulted in a deep cavity on the targeted area of BPH tissue without giving any damage to the surrounding area. All these new findings support the idea of usage of hydrodynamic cavitation as a novel therapeutic method for ablating tumor tissues.