Together with the U.S. Army and neurosurgeons at the Walter Reed National Military Medical Center (Bethesda, MD), researchers at Purdue University (West Lafayette, IN) are trying to develop a new type of bioactive coating for stents used to treat brain aneurysms, including those caused by head trauma from bomb blasts. Portions of stents are being designed using bioactive coatings to attract magnetized cells to repair blood vessels damaged as a result of trauma.
Currently, aneurysms are treated by performing brain surgery, opening the skull and clipping the balloon-like sac, or inserting a catheter through an artery into the brain and implanting a metallic coil into the sac. The problem with these procedures is that they involve major complications, including massive bleeding or the formation of potentially fatal blood clots. In such procedures, the survival rate is about 50/50 or worse, and those who do survive could be impaired, explains Jean Paul Allain, an associate professor of nuclear engineering at Purdue.
In contrast, the new research involves using ion beams to modify stent coatings with a magnetic material. The beams are also being used to create biomimetic surface textures that are designed to promote cellular proliferation and repair damaged vessels. "Stents coated with a bioactive coating might be inserted at the site of an aneurysm to help heal the inside lining of the blood vessel," Allain says. "We're talking about using a regenerative approach, attracting cells to reconstruct the arterial wall."
Cells needed to repair blood vessels are influenced by both the surface texture and the surface chemistry of the stent materials. Surface texture can include features such as bumps and irregular shapes as small as 10 nm wide. "We are learning how to regulate cell proliferation and growth by tailoring both the function of surface chemistry and topology," Allain notes. "There is correlation between surface chemistry and how cells send signals back and forth for proliferation. So the surface needs to be tailored to promote regenerative healing." Irradiating materials with the ion beams causes surface features to self-organize and also influences the surface chemistry."
The stents are made of nonmagnetic materials, such as stainless steel and an alloy of nickel and titanium. Only a certain part of them is rendered magnetic to direct the proliferation of cells to repair a blood vessel where it begins bulging to form the aneurysm. The coating's surface is functionalized so that it interacts properly with the blood-vessel tissue. Some of the cells are magnetic naturally, and 'magnetic nanoparticles' would be injected into the bloodstream to speed tissue regeneration. The researchers also intend to engineer the stents so that they show up in medical imaging to reveal how the coatings survive in the bloodstream.