Acoustic characterization of geometrically and biochemically targeted optical breakdown effects for biomedical applications.

摘要

Femtosecond laser-induced optical breakdown (LIOB) enables nonlinear energy deposition on micron and submicron spatial scales and has the potential to produce precise tissue effects in a number of medical and biological systems. LIOB occurs only where the breakdown threshold is exceeded, and may be manipulated both geometrically (through laser beam focusing) and biochemically (through metal/dendrimer nanocomposite (DNC) targeting) for selective photodisruption within tissues while minimizing thermal and mechanical damage to surrounding material. Measurable effects of localized breakdown, shock wave emission and microbubble formation, signal targeted areas and generate an object for sensitive acoustic detection and potential manipulation.; Experimental studies were performed to investigate femtosecond LIOB effects in transparent and semi-transparent biological material. Photodisruption at the focus of a near-infrared, ultrafast laser source was monitored using a high-frequency (≥ 50 MHz) acoustic technique. Ultrasonic recordings detected breakdown and illustrated laser-induced microbubble characteristics and dynamics. Studies in tissue-mimicking, gelatin phantoms demonstrated that laser pulse fluence, number, and period may be varied to deposit energy in a specific temporal manner, creating and stabilizing microbubbles with particular characteristics. Studies in porcine skin demonstrated that possibilities to precisely photodisrupt deeply localized areas in scattering tissue, however, are limited with geometrically targeted LIOB. The application of an index-matching agent improved penetration depth, and high numerical aperture focusing produced precise subsurface breakdown up to 150 micron focusing depths.; LIOB with biochemically targeted metal/dendrimer nanocomposites (DNCs) enables precise and selective photodisruption by locally reducing breakdown thresholds up to three orders of magnitude. Studies in DNC solutions demonstrate that DNC metal content markedly influences solution threshold reduction, while DNC terminal group (and thus net surface charge) and solution concentration influence the details of breakdown at these reduced fluences. A DNC construct targeted to the KB tumor cell line through the folate receptor successfully demonstrated targeted intracellular reduction in breakdown threshold. This research contributes to the framework for LIOB applications that precisely manipulate tissue and cells and produce a microbubble for acoustic manipulation and further therapeutic effects.