ID: 2193

• Title:
  Characterization of shock and expansion waves for medical applications
  
  Authors:
  

  Nakajo,Ryuichi- Graduate School of Science and Technology, Kumamoto University
  Hosano,Nushin - Biomaterials and Bioelectrics Department, Institute of Industrial Nanomaterials
  Sakugawa,Takashi - Biomaterials and Bioelectrics Department, Institute of Industrial Nanomaterials, Kumamoto University
  Hosano,Hamid - Biomaterials and Bioelectrics Department, Institute of Industrial Nanomaterials, Kumamoto University

  
  
  Abstract:
  Clinical application of shock waves, as a completely non-invasive procedure, has been expanded during the past decades. Recent investigations have revealed further interesting therapeutic and diagnostic potentials of shock waves. While the effects of shock waves on cells and tissue have been extensively studied, little is known about the effects of short duration and high intensity pulse expansion waves. Furthermore, it is imperative to have knowledge about effects of pulse expansion waves on tissue, as focused shock waves are always followed by an expansion wave, and shock wave reflects as an expansion wave from low acoustic impedance tissue, like fat. Meanwhile, tensile stress is more effective than compression to permeabilize/porate cells, which makes expansion waves further interesting.
  
  Pressure measurements, flow visualization, and cell experiments were made to investigate underwater shock waves. A magnetic pulse compression circuit (MPC) developed by our group was used as the power source for the underwater pulse discharge. Two electrodes made of a tungsten rod was used to generate the shock wave. Underwater expansion waves were generated by reflection of shock waves from a low acoustic impedance air boundary. The large difference in acoustic impedance between water and air makes it possible to generate strong expansion wave. A natural rubber membrane was placed at the boundary between the water/cell-medium and air to separate the boundaries. Shock waves, expansion waves, and cavitation behind the expansion waves were visualized by the Schlieren and shadowgraph methods using a high-speed frame camera (50~300 kfps). Shock wave and expansion wave pressures were measured by a FOPH (fiber optic probe hydrophone) pressure transducer. U937 cells were used to evaluate effects of shock and expansion waves.
  
  We observed a series of phenomena after propagation of expansion waves, especially growth, collapse, secondary shock wave generation, and repulsion of bubbles. Cavitation, which was not seen so much after the shock wave passage, was seen in large quantities after the expansion wave passage. In the pressure measurement, the shock and expansion waves values increased as the output voltage was increased, and their effects on viability and growth of U937 cells were studied.
  
  Pressure measurements and visualization experiments confirmed the pressure values of shock waves and expansion waves and their relationship to cavitation. The specific effects of the shock wave and the expansion wave were confirmed by the cell experiments.
  
  Keywords:
  Shock waves, Expansion waves, Cell poration and permeabilization
  
  Refs:
  
  
  Topic 1:
  12. Biomedical applications
  
  Topic 2:
  4. Diagnostics, analytics, experimental techniques