Shape Memory Foams Plug Brain Aneurysms

Polyurethane-based shape memory polymer (SMP) foams could be the basis for a more effective and less risky method for treating potentially fatal brain aneurysms.

Developed by researchers at Texas A&M University (College Station, USA) the SMP foams have the ability to be made into a primary shape and then transformed into another shape with an increase in temperature. The SMP foam remains in a temporary crimped shape so that it can be inserted into a blood vessel and delivered to the aneurysm with the use of a microcatheter. Once at the aneurysm site, the foam is triggered to expand and fill the aneurysm sac by laser light from an optical fiber. Similar to a sponge, the SMP foam enables blood to fill the aneurysm, forming a clot and promoting the growth of endothelial cells that work to heal the aneurysm.

Test results show that the SMP foams promote long-term health of the areas of the blood vessel affected by the aneurysm, reducing the chances of the aneurysm reforming, as evident by the formation of endothelial cells and collagen tissue that lead to a more stabilized healing than fibrin, a short-term “patch” abundant in aneurysms treated with coils. The researchers also implanted SMP polyurethane foams in a porcine aneurysm model to determine biocompatibility, localized thrombogenicity, and stability. The degree of healing was evaluated via gross observation, histopathology, and low vacuum scanning electron microscopy imaging after 0, 30, and 90 days.

The researchers found that clotting was initiated within the SMP foam less than one hour from exposure to blood, partial healing was observed at 30 days, and almost complete healing had occurred at 90 days in vivo, with minimal inflammatory response. The researchers compared this to cerebral aneurysms treated by traditional endovascular methods using platinum coils, which have a tendency to be unstable, either due to chronic inflammation, compaction of coils, or growth of the aneurysm. The study was published in the May 2013 issue of the Journal of Biomaterials Research.

“Not only do we see a lower inflammatory response, the foams are promoting a more aggressive healing response within the aneurysm,” said lead author Duncan Maitland, PhD, of the department of biomedical engineering. “We are seeing an unprecedented level of healing with regard to this lack of an inflammatory response and the promotion of collagen and cellular growth that lead to long-term healing of the aneurysm.”

SMPs include foams, scaffolds, meshes, and other polymeric substrates that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape triggered by an external stimulus, such as temperature change, an electric or magnetic field, light, or a solution. As well as polymers in general, SMPs also cover a wide property-range from stable to biodegradable, from soft to hard, and from elastic to rigid, depending on the structural units that constitute the SMP.

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