Surgery for cardiovascular problems often requires the implantation of vascular grafts and stents to prop open failing or narrowed blood vessels. However, while this solves the immediate problem of restoring blood flow, it introduces the risk of blood clots.

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This artist’s impression shows the coating on the inside of the improved vascular graft (in the magnified section).
Image credit: ITMO University/Yulia Chapurina

Now, in a new study published in the Journal of Medicinal Chemistry, chemists from ITMO University in St. Petersburg, Russia, describe how they developed and tested a new type of artificial blood vessel coating that resists blood clot formation.

The coating is a thin film of densely packed nanorods made of aluminum oxide blended with a substance that activates a clot-busting enzyme – the substance is called urokinase-type plasminogen activator.

When the team used this film to coat the inner surface of a vascular graft, it generated a stable concentration of plasmin – an enzyme that dissolves blood clots.

The unique properties of the film arise from its structure – a porous matrix that holds the plasminogen activator. The matrix protects the plasminogen activator while at the same time allowing it to react – through the system of pores – with plasminogen in the blood.

When the plasminogen – a substance that occurs naturally in the blood – meets with the plasminogen activator inside the matrix of pores, it produces the clot-dissolving enzyme plasmin.

The team ran several experiments to test the properties of the new film-coated vascular grafts. For example, for one test they grew artificial clots made of blood plasma mixed with thrombin and placed them inside the graft.

Lead author and lab researcher Yulia Chapurina, who set up the experiments, says:

“The results of the experiment amazed us. Very soon the clot started to dissolve and leak through the graft. In reality, our coating would destroy clots at the stage of formation, constantly ensuring an unobstructed blood flow in the graft.”

The new film promises to be an improvement on the latest types of grafts and stents – the so-called “drug-eluting” types. These are coated with drugs that are slowly released into the blood, but their lifetime is limited by the amount of drug they store.

The team believes their system, because it is based on the entrapment of the drug inside a porous protective shell, will last much longer, offering a practically “unlimited” lifetime for the artificial blood vessels.

Senior author Vladimir Vinogradov, who heads the international lab the study team works in, says their findings are not restricted to artificial blood vessels but to any kind of implants. It all depends on the type of drug you use in the coating, as he explains:

For example, after the implantation of an artificial ureter, urease crystals often start to grow inside and doctors do not know how to deal with this problem. It is possible to apply a similar drug-containing coating that dissolves urease.”

“The same approach may be used for kidney or liver surgery, but these are plans for the future,” he concludes.

Meanwhile, another study that Medical News Today recently reported found that the process of aging may protect blood vessels from oxidative stress.

In The Journal of Physiology, researchers from University of Missouri School of Medicine say their findings suggest healthy aging spurs a natural, adaptive response that counteracts the effect of oxidative stress on blood vessels.