Photo-cross-linking of PVA in concentrated aquous solution, and application to liquid embolic of cerebral aneurysms for subarachnoid hemorrhage

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A subarachnoid hemorrhage (SAH) is bleeding onto the surface of the brain, most often caused by a break in a blood vessel at the base of the brain. A blood vessel usually breaks at a weak spot called an aneurysm. This can cause a very severe neurological injury or even death. Traditionally this has involved a major brain operation with closure of the aneurysm using a surgical clip. Closure of such aneurysms can often be accomplished now through embolization using platinum GDC ○!R coils, and liquid embolics.The purpose of this project was to obtain objective data on control and behavior of photosensitive PVA with an in vitro simulation system of photosensitive PVA embolization for aneurysm. Photosensitive polyvinyl alcohols (PVA) containing photoactive units such as uracil, thymine, styryl pyridium (SbQ) were investigated as liquid embolics. As liquid embolics for cerebral aneurysm, the requirements are 1) strong adhesion to aneurysm, 2) the adhesion continue until formation of new blood vessel for 2 weeks, 3) viscosity of the solution is low for high injection rate. The contents of the photoactive unit in PVA should be high for the strong adhesion, but the content of the photoactive units should be low for low viscosity of the solution. In this study, glass simulation tube of cerebral aneurysm was used for measurements of viscosity and adhesion by photo-cross linking.For the high photosensitivity, the contents of the photoactive unit should be high. However; the high contents of the photoactive units made decrease the solubility of PVA in water. Therefore, polyethylene glycol units (TEG: tri(ethylene glycol)monomethylether) were introduced in PVA. By introduction of TEG unites, PVA contain about 10% units of SbQ units were soluble in water and gave high photosensitivity. The adhesion of PVA on cerebral aneurysm model was complete within 3-second irradiation of UV light, and no detachment was observed for 2 weeks under flow of physiological saline.