Cell characterization using high frequency ultrasound

Abstract

BAKSHI, SAURABH SANJEEV. Cell Characterization Using High Frequency Ultrasound. (Under the direction of Dr.Xiaoning Jiang.) Cell characterization has acquired increasing attention and significance as one of the key steps in tissue engineering and genetic study. This thesis presents a new method of characterizing human stem cells quantitatively and in real-time, by establishing a wellstudied relationship between the electric impedance of a piezoelectric transducer and the acoustic properties of the matching layer. In this case, the matching layer is represented by the stem cell layer, and the cell acoustic impedance is thus obtained by measuring the electric impedance of the piezoelectric resonator on which the cells were grown and chemically induced to undergo osteogenic differentiation. Experiments were conducted with human adipose derive stem cells (hASC) growing on lead magnesium niobate-lead titanate (PMN-PT) resonator plates under in-vitro conditions. A clear change in the electrical impedance of the piezoelectric transducer was observed over a period of 14 days, during which the cells began to deposit calcium, causing a change in the resonator acoustic load. This observed phenomenon is simulated mathematically by the use of a Mason model for transducer design. A MATLAB program was developed based on the Mason equivalent circuit for a piezoelectric resonator behaving under loaded conditions. Cell thickness, sound speed and densities were required as input parameters for running simulations. These were obtained by conducting pulse-echo experiments on the cell layer growing separately in culture wells using a 50 MHz piezoelectric transducer. The simulation was able to show similar resonator behavior as observed from the impedance experiments. This work is thus an initial step in developing a new technique for characterizing cells based on their mechanoacoustic properties.