Vascular implants can cause inflammatory reactions, such as restenosis and thrombosis, inside the body. This is because the body reacts to the implants and produces an excess of endothelial cells (which line the inside of blood vessels). These cells then begin to "stick" to the surface of the devices.

Restenosis happens when vascular smooth muscle cells (VSMCs), which surround the endothelial layer in cells, proliferate profusely and secrete a lot of extracellular matrix proteins that re-narrow the artery that has been treated. Thrombosis is caused by proliferation of the endothelial cells themselves.

One way to overcome these problems is to use drug-eluting stents that stop or slow down VSMC growth, but such devices can delay blood-vessel healing and cause thrombosis later on. Ideally, a stent should not prevent endothelial cells from moving about, but at the same time stop VSMCs from growing. A team led by Tejal Desai of UCSF is now saying that stents made from nickel-titanium (or “Nitinol”) coated with tube-like structures, also made of Nitinol, might be just the answer here.

Pro-healing surface

Nitinol is FDA-approved and is one of the three most common materials used in biomedical devices (along with stainless steel and cobalt-chromium). Nitinol-based stents are also superelastic and kink resistant and so are better in this respect.

“The tubular coating on Nitinol creates a pro-healing surface that allows endothelial cells to migrate but reduces the proliferation of smooth muscle cells that can cause restenosis,” Desai tells nanotechweb.org. “The surface does this by actually down-regulating the production of extracellular matrix proteins typically produced by the muscle cells.”

The researchers hope that their work, which is detailed in Nano Lett., will help in the development of new stent materials and architectures that reduce neointimal hyperplasia without the use of drugs.

The team is already testing its new nanotubular stents on animals.