Treating Brain Aneurysms with Polymer Foam

Texas A&M University, College Station, TX

A team of engineers at Texas A&M University, led by Duncan Maitland, a professor of biomedical engineering, along with the Mayo Clinic Medical School, aims to use special polyurethane-based shape memory polymer foams (SMPs) as a more effective and less risky method for treating aneurysms. Aneurysms fill with blood and form bulges in the walls of blood vessels, which can rupture and cause severe or even fatal neurological damage.

Fig. 1 – A crimped SMP foam device is delivered to an aneurysm via catheter and then expands to a permanent shape within the aneurysm where it stabilizes the aneurysm and promotes healing.

The researchers say that typical treatment involves implanting platinum coils to reduce pressure on the vessel walls so that healing can occur before the aneurysm ruptures. However, these coils can pose risks by causing inflammation that inhibits healing, or can compact over time and cause subsequent rupture or re-rupture or lead to the formation of aneurysms adjacent to the original aneurysm.

Their research involves filling the bulge with polyurethane-based SMP foam instead of platinum coils. The foams can be formed into a primary shape and then transform into another shape when the temperature increases, making them ideal for filling aneurysms, they explain. (See Figure 1)

Initially, the SMP foam is formed into a temporary crimped shape so that it can be inserted into a blood vessel and delivered to the aneurysm using a microcatheter. Once at the proper site, the foam is triggered to expand and fill the aneurysm sac by body temperature, they say. The foam allows blood to fill the aneurysm, forming a clot and accelerating healing through the volume of the aneurysm and, importantly, at the neck or opening of the aneurysm.

For a 2mm diameter coil, the surface area is 29 times more than the next best device, and the volume filling is 20 times better than the next best device, since a high surface area and improved volume filling lead to dramatically improved healing compared to bare platinum coils.

Test results reveal that SMP foams promote long-term health of the areas of the blood vessel affected by the aneurysm, and reduce the chances of the aneurysm reforming, as shown by the types of cells and tissue formed, for example, increased collagen presence, which is a far more mechanically stable tissue than fibrin.

In addition to promoting a healing response in aneurysms, the SMP foams show strong signs of biocompatibility, showing minimal inflammation once inserted into the aneurysm. Histology studies comparing SMP foams to two types of FDA-approved sutures used in vascular surgeries demonstrate that the foams to outperform both types of sutures.