U ltrasound guided microbubble technology – guiding the future of drug delivery

Anurag Khirwal^*, R. N. Gupta

Birla Institute of Technology, Mesra, Ranchi – 835215, Jharkhand, India.

*Corresponding author:

Dr. R. N. Gupta, Professor, Department of Pharmaceutical Sciences, Birla Institute of Technology, Mesra- 835215, India.

E-mail: roopgupta@sify.com, Tel: +91-9431383013.

ABSTRACT

Current research supports ultrasound being a future method for treatment using micro bubble technology. A lipid shell coats the micro bubble to give it stability in the human vascular system and allows for gradual reabsorption with no harm to the patient. Micro bubbles work by excitation; the bubbles expand and contract rapidly when exposed to the pressure changes exerted by ultrasound waves, and thus resonates with the ultrasound. The increased resonance causes the bubbles to be several thousand times more reflective then regular tissue and this enhances grey-scale and Doppler imaging. The size of micro bubbles allows unopposed passage through the capillaries. Although micro bubbles were originally developed to enhance diagnostic testing, they can also be used as vectors for pharmaceutical and genetic materials. Properly designed Microbubble avoids extravasation to normal tissues and recognition by reticulo-endothelial system cells, which prolongs their circulation time after systemic injection. This allows their use in targeting cancerous or inflamed tissues. Passive targeting is based on enhanced permeability of defective microvasculature that allows extravasation of drug-loaded nanoparticles through large interendothelial gaps. In addition to enhanced vascular permeability, tumours demonstrate poor lymphatic drainage, this positive effect provides for a long retention of the extravagated particles in tumour tissue. Potent tumour accumulation of the nanoparticles requires sufficient particle residence time in circulation, for which it is commonly coated with polyethylene oxide chains.

Keywords: Ultrasound Therapy, Micro bubbles, Ligand Binding, Micro vessels, Pharmaceutical delivery.