Shape memory polymer embolization

Shape memory polymers make up another class of injectable biomaterials for vascular applications, yet are relatively new in the field of endovascular embolization. Shape memory polymers are chemically structured so that they are able to reversibly take on a different physical shape in response to some stimuli (Small et al, 2007). Usually these different shapes include a compact form and an expanded form of the polymer. In the case of endovascular embolization, the expanded polymer can be pre-formed to fit specific contours of an individual aneurysm (Ortega et al, 2007). Upon interacting with some type of stimuli, such as heat or cold, the material is compacted into a shape that can be delivered through a microcatheter. The process of using shape memory polymers to embolize an aneurysm is shown in Fig. 7.5, along with samples of expanded SMPs (Ortega et al, 2007). 

These materials have an obvious application to fusiform aneurysms, which are difficult to treat using coils or liquid embolics due to migration into the parent vessel. Shape memory polymers can potentially remove this limitation since the device is pre-formed to the aneurysm topography. Metcalf et al (2003) investigated a porous polyurethane shape memory polymer as an embolic device for fusiform aneurysms in an animal model. In this study, thick neointimal formation was found over aneurysm necks after a 12-week period. The porous nature of this material may have encouraged cell infiltration and neointimal growth to seal off the aneurysm from the rest of the vasculature (Metcalfe et al,... 

Shape memory polymers, as well as the other developmental embolic materials discussed here, represent insight into future procedures that may revolutionize the practice of endovascular embolization in order to better treat critical vascular conditions. 

Small, W., Buckley, P. R., Wilson, T., Benett, W. J., Hartman, J., Saloner, D. Maitland, D. (2007) Shape memory polymer stent with expandable foam a new concept for endovascular embolization of fusiform aneurysms. IEEE Transactions on Biomedical Engineering, 54, 1157—1160. 

Maitland, D. J., et al. (2007). Prototype laser-activated shape memory polymer foam device for embolic treatment of aneurysms. BIOMEDO, 12(3), 030504-030501-030504-030503. 

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