For the past 4 years, under the leadership of Dr. Duncan Maitland of Lawrence Livermore National Laboratory, CBST has been developing light-activated shape memory polymer (SMP)-based intravascular tools for the interventional surgery of life-threatening blood clots and aneurysms. SMP’s are a material that can be formed into a specific initial shape, reformed into a second shape, and then by heating, induce the material to recover its initial shape. The heating can be caused by light illumination, electric current, electromagnetic heating, and other methods. Often the SMP devices are deployed using a catheter that has incorporated a fiber optic cable capable of delivering laser light to the SMP device which in turn is heated to its transition temperature.

CBST is currently performing a proof-of-concept study of a shape memory polymer (SMP) device for occlusion of cerebral aneurysms, thereby preventing hemorrhagic strokes.  The long-term goal of this research is to deliver clinical prototype devices that can begin FDA clinical trials.  The proposed pilot study effort will focus on the validation of clinical prototype devices through a series of animal experiments at the University of California, Davis Medical Center.

Cerebral aneurysm rupture occurs in approximately 30,000 people per year in the United States, with devastating consequences.  Three-fourths of patients will end up either dead or neurologically debilitated. The shape memory polymer devices being developed are expected to have many significant improvements over the current treatment that uses metallic coils

In the past year this team has produced two milestone publications. The first (Polyurethane Shape-Memory Polymers Demonstrate Functional Biocompatibility In Vitro, M. Cabanlit, D. Maitland, T. Wilson, S. Simon, T. Wun, M. Gershwin, and J. Van der Water, Biomolecular Biosciences 2007, 7, 48) establishes  the excellent biocompatibility of this material as defined by inflammation, thrombogenesis, and the activation of either platelets and neutrophils. The critical conclusion is that these materials are unlikely to stimulate a negative in vivo response.

A second publication (Shape-Memory Behavior of Thermally Stimulated Polyurethane for Medical Applications, G. Baer, T. Wilso, D. matthews, and D. Maitland, Journal of Applied Polymer Science, 103, 3882, 2007) describes detailed measurements of the thermomechanical properties of these materials and establishes that these properties can be adjusted to be well suited for manufacturing interventional devices such as thromboembolic extractors , vascular stents, and aneurysm filling foams.

Pictures of the foam deploying in in vitro aneurysm model.  Foam starts in compressed form (upper left) and expands to fill 60% the aneurysm (lower right).  The time from the laser initiation to the final image was approximately 10 seconds.  The aneurysm, delivery catheter, and posterior cerebral arteries can be seen in all images.  The flow rate for this experiment was 60 ml/min measured at the inflow (basilar artery).  Similar foam deployments, actuation, and release in the aneurysms were performed for 0, 20, and 100 ml/min flow rates.

For more information about this article, please contact Duncan Maitland, PhD (LLNL) (maitland1@llnl.gov) or Jonathan Hartman, M.D. (UCDMC) (jonathan.hartman@ucdmc.ucdavis.edu)