RajDev Adeps*, B.Brahmaiah, Sreekanth Nama, Prasanna Kumar Desu
Department of Pharmaceutics, Priyadarshini Institute of Pharmaceutical Education and Research (PIPER),
Pulladigunta, Kornepadu (V), Vatticherukuru (M), Guntur-522017, Andhra Pradesh, India
Gas filled microbubbles are well known as ultrasound contrast agents for medical ultrasound imaging and for non-invasive delivery of drugs and genes to different tissues. Microbubbles designate air or gas filled microspheres suspended in a liquid carrier phase which generally results from the introduction of air or gas. The liquid phase contains surfactants to control the surface properties as well as stability of the bubble. Microbubbles are manufactured from biocompatible materials, so they can be injected intravenously. Microbubbles have an average size (1-8 µm) less than that of RBC’s i.e. they are capable of penetrating even into the smallest blood capillaries & releasing drugs or genes, incorporated on their surface, under the action of ultrasound. Ultrasound radiation are used which are non hazardous. Most of the physicians today prefer imaging with ultrasound in combination with microbubbles compared to other diagnostic techniques for low cost and rapidity. The ultrasonic field can be focused at the target tissues and organs; thus, selectivity of the treatment can be improved, reducing undesirable side effects. Recently, targeting ligands are attached to the surface of the microbubbles, which have been widely used in cardiovascular system, tumour diagnosis and therapy. This review focuses on the characteristics of microbubbles that give them therapeutic properties and some important aspects of ultrasound parameters that are known to influence microbubble-mediated drug delivery. In addition, current studies involve discussion of novel therapeutical application of microbubbles.
Key words: Microbubbles, Ultrasound, Contrast agent, Targeted drug delivery
The main goal of drug delivery and targeting by microbubble is to improve the efficiency of drug action in the region, where the disease cells are arised and reducing undesired adverse effects, such as toxicity, in the healthy tissues. For the drug action and/or deposition in the targeted region various external energy field applied, like light (photodynamic therapy), neutron beam (boron neutron capture therapy), magnetic field (targeted accumulation of magnetic drug carrier in the tissues close to the magnet) or mechanical energy. In order to improve drug action we applied mechanical energy in form of ultrasound irradiation. Ultrasound improves drug delivery into tissue and cells.
Microbubbles are known as contrast agents for ultrasound (US) diagnostics and imaging presence of ultrasound energy deposition foci in the tissues. They increase the cell permeability by perturbing cell membranes. Recently, Microbubbles are anticipated to find further uses in therapy as efficient and safe targeted deliverers of drugs and genes. Microbubbles are gas-filled colloidal particles, with a size range of 100 μm . The intrinsic compressibility of microbubbles is approximately 17,000 times more than water. They also scatter ultrasound very strongly, so they are known as ultrasound contrast agent.
Gas-filled microbubbles administered by intravascular route can serve as cavitation nuclei. So they have wide range of ultrasound- mediated drug delivery applications . The main application of ultrasound and microbubbles is to targeted drug and gene delivery in specific region of disease. Under exposure of sufficiently high-amplitude ultrasound, these targeted microbubbles would carry a drug or gene to a specific area of interest and then ultrasound is used to burst the microbubbles, causing site-specific delivery of the bioactive material.