@phdthesis{shangguan96e,
  author = {H. Shangguan},
  title = {Local Drug Delivery with Microsecond Laser Pulses: \emph{In vitro} Studies},
  school = {Portland State University},
  year = {1996},
  abstract = {Photomechanical drug delivery is a technique for localized drug delivery using laser-induced hydrodynamic pressure following cavitation bubble expansion and collapse. This dissertation presents \textit{in vitro} studies of photomechanical drug delivery. The main goals were investigate the possibility of photomechanical drug delivery as a new means of localized drug delivery to thrombus for enhancement of laser thrombolysis and to address some of the questions regarding the physical processes during photomechanical drug delivery. \vskip2mm A parametric study was performed to characterize laser-induced cavitation phenomena that take place in absorbing liquids or on soft targets using time-resolved flash photography, high-speed shadowgraphy, particle image velocimetry. The laser-induced cavitation bubble dynamics depended where the bubble was formed. The bubble expansion and collapse could cause the surrounding flow motion at a speed of up to 12\,m/s. A theoretical model was used to estimate the bubble volumes formed in absorbing liquids. This model assumed vaporization of the entire disk of absorbing liquids under a delivery fiber, rather than vaporization of a fraction of the disk. Good agreement was found between the model and experimental results. \vskip2mm Photomechanical drug delivery into soft materials (gelatin or thrombus) were studied using solutions of oil and dye or 1\,$\mu$m fluorescent microspheres. The drug could be driven into thrombus several hundred micrometers and even few millimeters in both axial and radial directions when the gelatin structures were fractured. The results of using thrombus phantoms were comparable to those obtained using porcine clots. The cavitation bubble formation is the governing mechanism for photomechanical drug delivery. \vskip2mm The ablation process is profoundly affected by whether the optical fiber tip is inside a catheter or is in contact with the thrombus when the laser light is delivered through an optical fiber to the thrombus. The contact ablation efficiency of porcine clot was at least three times greater than the non-contact ablation efficiency. The mass ablated was correlated with the expansion pressure of the cavitation bubble. The fluorescent microspheres penetrated the mural clot the same distance for both ablation methods. The kinetic energy generation depended on the total delivered energy regardless of the light delivery methods.},
}