11 October 2011
A polymer product that can temporarily block blood vessels during surgery has been approved in the US. The product, called LeGoo, is liquid at room temperature, but rapidly forms a gel when warmed by the body, creating a firm plug and halting blood flow.
The key ingredient is a poloxamer, a polymer comprising three distinct ‘blocks’ of repeating monomers, a hydrophobic block of polypropyleneglycol sandwiched between two hydrophilic blocks of polyethyleneglycol. At higher temperatures, the hydrophilic arms align, and in this conformation the molecules form micelles, leading to an increase in viscosity and a phase change from liquid to gel. This process is reversed when the product is cooled, after which the molecules dissolve in the blood and pass harmlessly out of the body. Afterwards, the poloxamer can’t reform as a gel because the concentration is too low. The key to the success of LeGoo is that the viscosity changes over a relatively narrow temperature range of only a few degrees. This means that the vessel can be unblocked by simply applying a little ice.
Poloxamers are biocompatible, and their ability to form micelles has made them attractive to researchers interested in new drug delivery mechanisms.
Blood vessels are normally blocked for surgical procedures using clamps that apply mechanical force across the opening. LeGoo leads to less trauma on the vessels, says John Merhige from Pluromed, the company that makes the product. In addition, it maintains the shape of the vessel, making suturing more straightforward.
In addition to LeGoo, Pluromed makes Backstop, a product designed to prevent kidney stones slipping in the wrong direction during their removal. The company says the market for its products is worth over $2 billion (£1.3 billion).
Alun Davies, professor of vascular surgery at Imperial College London, UK, has used LeGoo. He says that it won’t replace clamps entirely. Clamps are comparatively cheap because they can be reused so many times. But LeGoo is useful in arteries that have become calcified, when the force of the clamp breaking up the chalky residue can lead to damage.