Measured bioeffects of tone-burst ultrasound in combination with poly(propyl acrylic) acid (PPAA)

In this study, high intensity focused ultrasound (HIFU) is combined with the pH-sensitive cell membrane disrupting polymer PPAA (poly-propyl acrylic acid) at sublethal doses to achieve hemolysis of human erythrocytes and sonoporation of suspended cells. For our studies, a 1 mL sample of cells suspended in phosphate buffered saline (PBS) was simultaneously exposed to 1.1 MHz acoustic tone bursts and PPAA at a temperature of 37°C. We vary the pH of the suspension fluid and amount of PPAA added to assess the influence of its structural conformation, functionality, and concentration upon measured bioeffects. For hemolysis study, we suspended erythrocytes at a final concentration of 10⁸ cells/mL. Damage to the cell suspension was determined by measuring the amount of hemoglobin released using a spectrophotometer. A passive cavitation detection system was utilized to monitor the acoustic emissions from the cell suspension during exposure to ultrasound. In the presence of PPAA, there is a significant increase in cavitation and bioeffects during ultrasound exposure at more acidic pH levels. This polymer/ultrasound synergy is pH independent, unlike the synergy of ultrasound with poly(ethyl acrylic acid). The levels of cavitation and hemolysis measured from HIFU/PPAA synergy was compared with levels measured from HIFU/Optison(R) synergy to assess the effectiveness of the polymer in an acoustic field