Mechanical and radiographic properties of a shape memory polymer composite for intracranial aneurysm coils

An intracranial aneurysm can be a serious condition that can go undetected until the aneurysm ruptures, causing hemorrhaging within the subarachnoid space surrounding the brain. The typical treatment for large aneurysms is by embolization using platinum coils. However, in about 15% of the cases treated by platinum coils, the aneurysm eventually re-opens as a result of the bio-inertness of platinum. One solution to this is to develop suitable materials with increased bio-activity to use as coil implants. In this research, a shape memory polymer (SMP), Calomer™, produced by The Polymer Technology Group, Inc., was investigated as a candidate for aneurysm coils. The SMP was tested to determine its thermo-mechanical properties and the strength of the shape recovery force. Composite SMP specimens containing tantalum filler were produced and tested to determine the mechanical effect of adding this radio-opaque metal. Thermo-mechanical testing showed that the material exhibited a shape recovery force a few degrees above the glass transition temperature, T_g. The effects of the addition were small and included a decrease in T_g and recovery force. SMP coils deployed inside a simulated aneurysm model demonstrate that typical hemodynamic forces do not hinder the shape recovery process. The radio-opacity of the Ta-filled material was characterized with clinical fluoroscopy.