Sonoporation

Sonoporation is performed with a dedicated sonoporator. Sonoporation may also be performed with custom-built piezoelectric transducers connected to bench-top function generators and acoustic amplifiers. Standard ultrasound medical devices may also be used in some applications. Measurement of the acoustics used in sonoporation is listed in terms of mechanical index, which quantifies the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a non-thermal action based on pressure. ==Microbubble contrast agents==

Microbubble contrast agents are generally used in contrast-enhanced ultrasound applications to enhance the acoustic impact of ultrasound. For sonoporation specifically, microbubbles are used to significantly enhance membrane translocation of molecular therapeutics. General features The microbubbles used today are composed of a gas core and a surrounding shell. The makeup of these elements may vary depending on the preferred physical and chemical properties. Microbubble shells have been formed with lipids, galactose, albumin, or polymers. The gas core can be made up of air or heavy gases like nitrogen or perfluorocarbon. Mechanism of action Microbubble gas cores have high compressibility relative to their liquid environment, making them highly responsive to acoustic application. As a result of ultrasound stimulation, microbubbles undergo expansion and contraction, a phenomenon called stable cavitation. If a microbubble is attached to the cell membrane, the microbubble oscillations produced by ultrasound stimulation may push and pull on the membrane to produce a membrane opening. These rapid oscillations are also responsible for adjacent fluid flow called microstreaming which increases pressure on surrounding cells producing further sonoporation to whole cell populations. The physical mechanisms supposedly involved with microbubble-enhanced sonoporation have been referred to as push, pull, microstreaming, translation, and jetting. == Membrane translocation mechanism ==

The mechanism by which molecules cross cellular membrane barriers during sonoporation remains unclear. Different theories exist that may potentially explain barrier permeabilization and molecular delivery. The dominant hypotheses include pore formation, endocytosis, and membrane wounds. Pore formation Pore formation following ultrasound application was first reported in 1999 in a study that observed cell membrane craters following ultrasound application at 255 kHz. Later, sonoporation mediated microinjection of dextran molecules showed that membrane permeability mechanisms differ depending on the size of dextran molecules. Microinjection of dextran molecules from 3 to 70 kDa was reported to have crossed the cellular membrane via transient pores. In contrast, dextran molecules of 155 and 500 kDa were predominantly found in vesicle-like structures, likely indicating the mechanism of endocytosis. This variability in membrane behavior has led to other studies investigating membrane rupture and resealing characteristics depending on ultrasound amplitude and duration. Endocytosis Various cellular reactions to ultrasound indicate the mechanism of molecular uptake via endocytosis. These observed reactionary phenomena include ion exchange, hydrogen peroxide, and cell intracellular calcium concentration. Studies have used patch clamping techniques to monitor membrane potential ion exchange for the role of endocytosis in sonoporation. Ultrasound application to cells and adjacent microbubbles was shown to produce marked cell membrane hyperpolarization along with progressive intracellular calcium increase, which is believed to be a consequence of calcium channels opening in response to microbubble oscillations. These findings act as support for ultrasound application inducing calcium-mediated uncoating of clathrin-coated pits seen in traditional endocytosis pathways. Other work reported sonoporation induced the formation of hydrogen peroxide, a cellular reaction that is also known to be involved with endocytosis. The membrane resealing process has been shown to be calcium-dependent. This property may suggest that the membrane repair process involves a cell's active repair mechanism in response to the cellular influx of calcium. == Preclinical studies ==

In vitro The first study reporting molecular delivery using ultrasound was a 1987 in vitro study attempting to transfer plasmid DNA to cultured mouse fibroblast cells using sonoporation. This successful plasmid DNA transfection conferring G418 antibiotic resistance ultimately led to further in vitro studies that hinted at the potential for sonoporation transfection of plasmid DNA and siRNA in vivo. In vivo In vivo ultrasound mediated drug delivery was first reported in 1991 == References ==