New expandable hydrogel-platinum coil hybrid device for aneurysm embolization

Abstract

This study introduces a new, hybrid embolic device that in addition to offering all the important attributes of existing detachable platinum coils also shows an enhanced ability to fill aneurysm cavities. The device consists of a carrier platinum coil coupled to an expandable hydrogel material, which undergoes a ninefold increase in volume when placed into a physiological environment. Distinct from previous devices aimed at speeding the organization of thrombus, the new device has been designed to entirely fill the aneurysm cavity, with complete or near-complete exclusion of thrombus. Unlike thrombus, the hydrogel material is stable and unaffected by natural thrombolytic processes and thus may diminish observed rates of aneurysm recanalization. We report the angiographic and histologic findings of the new, hybrid device used to treat experimental aneurysms in rabbits.

Fig 1.

Hybrid hydrogel-platinum coil device. Top, prehydration image shows initial profile of the device. Highly compact hydrogel material is wrapped around a platinum coil. Indentations between winds of the underlying platinum coil can be seen through the compact hydrogel material (straight white arrow). The outer diameter of the coil is 0.008 inch; the thickness of the hydrogel is approximately 0.001 inch, such that the outer diameter of the device is 0.010 inch. Bottom, post-hydration image of the device shows marked expansion of the hydrogel material, which has become translucent. The outer edges of the hydrogel are denoted by the curved white arrows. The platinum coil is denoted by the black arrow. The radial thickness of the expanded hydrogel is approximately 0.013 inch, such that the total outer diameter of the hydrated device is 0.035 inch.

Fig 2.

Study animal 4, 2-week implant. A, Anteroposterior digital subtraction angiogram of the brachiocephalic artery shows a narrow-necked 5.4-mm-wide 7.8-mm-high aneurysm (black arrow). B, Anteroposterior digital subtraction angiogram obtained immediately after embolization with a single complex coil and three hydrogel devices shows dense packing of the aneurysm dome, with persistent flow at the aneurysm neck (straight white arrow). C, Anteroposterior digital subtraction angiogram obtained 2 weeks after embolization shows progressive occlusion of the aneurysm cavity, with the neck now occluded (curved white arrow). D, Hematoxylin and eosin stain; original magnification, ×6.8. Coronal section obtained through the aneurysm cavity. The aneurysm cavity is filled with a mixture of unorganized thrombus (long straight arrow) and expanded hydrogel (short straight arrow). The hydrogel stains as faint, violet-colored, reticular material. There is no substantial inflammation. A thin fibrin membrane traverses the neck (curved arrow). Artifactual separation between the aneurysm wall and the coils and hydrogel occurred during processing (open arrow).

Fig 3.

Study animal 6, 1-month implant. A, Anteroposterior digital subtraction angiogram of the brachiocephalic artery shows a narrow-necked 4-mm-wide 7-mm-high aneurysm (black arrow). B, Anteroposterior digital subtraction angiogram obtained immediately after embolization with a single complex coil and two hydrogel devices shows dense packing of the aneurysm dome, with persistent flow at the aneurysm neck (straight white arrow). C, Anteroposterior digital subtraction angiogram obtained 1 month after embolization shows progressive occlusion of the aneurysm cavity, with the neck now occluded (curved white arrow). D, Hematoxylin and eosin stain; original magnification, ×2.5. Coronal section obtained through the aneurysm cavity. The sac is nearly completely filled with hydrogel, which stains as faint, violet-colored, reticular material. There is a small amount of organizing thrombus near the dome (arrow).

Fig 4.

Study animal 10, 3-month implant. A, Anteroposterior digital subtraction angiogram of the brachiocephalic artery shows a wide-necked 4-mm-wide 11-mm-high aneurysm (black arrow). B, Anteroposterior digital subtraction angiogram obtained immediately after embolization with a single complex coil and a single hydrogel device shows dense packing of the aneurysm dome, with persistent flow at the aneurysm neck (straight white arrow). C, Anteroposterior digital subtraction angiogram obtained 3 months after embolization shows progressive occlusion of the aneurysm cavity, with the neck now occluded (curved white arrow). D, Hematoxylin and eosin stain; original magnification, ×6.3. Coronal section obtained through the aneurysm cavity. The sac is nearly completely filled with hydrogel, which stains as faint, violet-colored, reticular material. There is a small amount of organized tissue near the neck (arrow).

Fig 5.

Study animal 16, 6-month implant. A, Anteroposterior digital subtraction angiogram of the brachiocephalic artery shows a wide-necked 5.5-mm-wide 8.5-mm-high aneurysm (black arrow). B, Anteroposterior digital subtraction angiogram obtained immediately after embolization with a single complex coil and a single hydrogel device shows dense packing of the aneurysm dome, with persistent flow at the aneurysm neck (straight white arrow). C, Anteroposterior digital subtraction angiogram obtained 6 months after embolization shows progressive occlusion of the aneurysm cavity, with the neck now occluded (curved white arrow). D, Hematoxylin and eosin stain; original magnification, ×6.8. Coronal section obtained through the aneurysm cavity. The sac is completely filled with hydrogel, which stains as faint, violet-colored, reticular material. A thin layer of organized tissue traverses the neck of the aneurysm (arrow).