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.