Nanobubble Mediated Gene Delivery in Conjunction With a Hand-Held Ultrasound Scanner

Ketamine is usually used for murine anesthesia in animal experiments with other anesthetics for its sedation and analgesic effects. However, ketamine was categorized as a narcotic drug in Japan on January 1, 2007. After this act came into effect, a narcotic handling license became necessary for using and possessing ketamine. Pentobarbital sodium, which is also used for laboratory animal experiments as Nembutal, is no longer being manufactured. For these reasons, other anesthetic agents that can be used without a license are needed. In this paper, we examined the use of anesthetics other than ketamine and pentobarbital sodium. A combination anesthetic (M/M/B: 0.3/4/5) was prepared with 0.3 mg/kg of medetomidine, 4.0 mg/kg of midazolam, and 5.0 mg/kg of butorphanol. The anesthetics were administered to male ICR mice by intraperitoneal injection. In order to assess anesthetic depth and duration, we stimulated the mice directly after loss of righting reflexes to recovery of these same reflexes and then recorded four parameters--a tail pinch reflex, a pedal withdrawal reflex in the forelimbs, a pedal withdrawal reflex in the hindlimbs, and corneal reflex. Each parameter was scored, and the anesthetic depth, expressed by the total score, was summed. The surgical anesthesia duration of M/M/B: 0.3/4/5 mg/kg was almost identical to the surgical anesthetic duration with a ketamine and xylazine mixture (80-8 mg/kg). These data suggested that mice can be anesthetized by M/M/B: 0.3/4/5 as an alternate to ketamine. We thus can recommend M/M/B: 0.3/4/5 for murine surgical anesthesia.

We follow the history of nanobubbles from the earliest experiments pointing to their existence to recent years. We cover the effect of Laplace pressure on the thermodynamic stability of nanobubbles and why this implies that nanobubbles are thermodynamically never stable. Therefore, understanding bubble stability becomes a consideration of the rate of bubble dissolution, so the dominant approach to understanding this is discussed. Bulk nanobubbles (or fine bubbles) are treated separately from surface nanobubbles as this reflects their separate histories. For each class of nanobubbles, we look at the early evidence for their existence, methods for the production and characterization of nanobubbles, evidence that they are indeed gaseous, or otherwise, and theories for their stability. We also look at applications of both surface and bulk nanobubbles.

Ultrasound (US) is one of the most frequently used diagnostic methods. It is a non-invasive, comparably inexpensive imaging method with a broad spectrum of applications, which can be increased even more by using bubbles as contrast agents (CAs). There are various different types of bubbles: filled with different gases, composed of soft- or hard-shell materials, and ranging in size from nano- to micrometers. These intravascular CAs enable functional analyses, e.g., to acquire organ perfusion in real-time. Molecular analyses are achieved by coupling specific ligands to the bubbles’ shell, which bind to marker molecules in the area of interest. Bubbles can also be loaded with or attached to drugs, peptides or genes and can be destroyed by US pulses to locally release the entrapped agent. Recent studies show that US CAs are also valuable tools in hyperthermia-induced ablation therapy of tumors, or can increase cellular uptake of locally released drugs by enhancing membrane permeability. This review summarizes important steps in the development of US CAs and introduces the current clinical applications of contrast-enhanced US. Additionally, an overview of the recent developments in US probe design for functional and molecular diagnosis as well as for drug delivery is given.