Online

Karki, Alina

Materials Science Graduate Program

2022

Ph. D.

The ability of ultrasound to localize acoustic energy deposition and induce a biological effect within a target is examined in three novel biomedical applications: sonoporation, osteoporosis diagnosis, and biofilm mitigation.Ultrasound can excite encapsulated microbubbles, causing an acoustic cavitation effect in the vicinity of cells, temporarily increasing membrane permeability, and allowing cells to uptake foreign molecules. This non-viral transfection technique is called sonoporation. Our experimental study demonstrated that it could be effective for small interfering RNA (siRNA) delivery into an isolated mouse and human T-cells, which is a complex process despite its importance in treating numerous diseases. T-cells are non-proliferating, while siRNA is a large, negatively charged, unstable molecule. Using flow cytometry, we determined the optimal ultrasound parameters for sonoporation, under which stable linear acoustic cavitation of bubbles occurs. We used the western blot technique to examine the inhibition of methylation-controlled J protein (MCJ) expression in sonoporated mouse and human CD8 T-cells. Ultrasound parameters (velocity and attenuation) and bone porosity are sensitive to osteoporotic bone conditions, and hence investigating their relationship can be of potential use for diagnostic purposes. These parameters were measured for twenty one cancellous bone samples via in vitro ultrasonic spectroscopy through transmission mode using three center frequency transducers covering 1-7.8 MHz range frequencies. The results established the nonlinear relationship of porosity-attenuation coefficients and a linear relationship of porosity-velocity at all frequencies, with their maximum values at the lowest porosity and gradual decrease with increasing values of porosity for the range of porosities in our samples for all frequencies. We also obtained detailed measurements of the effect of ultrasound waves of three different frequencies and three amplitudes on the diffusion of nanoparticles of three different diameters in an agarose hydrogel, which mimics the porous structure of the extracellular polymeric substance matrix developed within a biofilm. The acoustic diffusion coefficients were higher than molecular diffusion coefficients, and there was a significant effect on diffusion coefficients with an increase in frequency and amplitudes for all size particles. The results agreed with the continuous-time random walk (CTRW) model of oscillatory diffusion by Balakrishnan and Venkataraman (1981), suggesting that nanoparticles undergo the phenomena of oscillatory diffusion under acoustic excitation, leading to oscillatory flow and retention of the particles by the porous medium. These results indicated that low-intensity ultrasound (< 3W/cm2) could be an effective physical method to enhance the transport rate of antimicrobial drugs into the biofilm.