Type 1 collagen as an endovascular stent-graft material for small-diameter vessels: a biocompatibility study.

PURPOSE: To compare patency rates and degrees of neointimal hyperplasia between bovine type 1 collagen stent-grafts and uncovered control stents in small-diameter vessels (< or =4 mm). MATERIALS AND METHODS: Uncovered stainless-steel, balloon-expandable stents (n = 5) and type 1 collagen stent-grafts (n = 6) were implanted via the femoral arteries with use of 4-mm balloon catheters into the abdominal aorta of New Zealand White rabbits. Ten animals were available for follow-up. Subjects were followed for 1 month (three uncovered stents; three collagen stent-grafts) or 4 months (two uncovered stents; two collagen stent-grafts). Angiography was performed before animal sacrifice and luminal compromise was compared between groups. Histologic and immunohistochemical analysis was performed to determine presence of neointima and neointimal thickness and area; these parameters were also compared between groups. RESULTS: All stents and stent-grafts remained patent at both time points. Luminal compromise was not detectable angiographically in any subject. Maximum neointimal thickness was less than 5 mum for all subjects. Neointimal thickness and area were not statistically significantly different between groups. CONCLUSIONS: Type 1 collagen stent-grafts demonstrate excellent hemocompatibility and biocompatibility in small-diameter vessels in rabbits.

A collagen-based coil for embolization of saccular aneurysms in a New Zealand White rabbit model.

BACKGROUND AND PURPOSE: In the treatment of cerebral aneurysms, platinum coils often fail to elicit a fibrotic response. We tested the hypothesis that a new, collagen-based endovascular coil would improve angiographic and histologic outcomes as compared with those achieved with platinum coils in a rabbit model of saccular aneurysms. METHODS: Elastase-induced aneurysms were created in 12 New Zealand White rabbits (body weight, 3-4 kg). Embolization was performed either by use of collagen-based coils (n = 6) or platinum coils (n = 6). In both coil groups, subjects were kept alive for either 2 weeks (n = 3 [collagen], n = 3 [platinum]) or 10 weeks (n = 3 [collagen], n = 3 [platinum]) after embolization and then were sacrificed. Digital subtraction angiography (DSA) was performed immediately after embolization and immediately before sacrifice. Postmortem histologic analysis of all coils was performed. RESULTS: Collagen-based coils were loosely packed in all cases because of limitations in size of coils available for embolization. In all six aneurysms packed with collagen-based coils, progressive thrombosis was noted at follow-up (DSA). Platinum coil samples were densely packed in all six cases. Progressive thrombosis was seen in one case, and interval regrowth was present in one case. Two weeks after embolization, collagen-based coil samples showed a marked peri-coil cellular response. Ten weeks after embolization, collagen-based samples had dense connective tissue matrix deposition in two of three cases. Platinum coils had unorganized thrombus at 2 weeks; loose-matrix deposition was only seen in the 10-week samples. Smooth muscle actin-positive cells were seen across the neck of the aneurysm in four of six collagen-based coil cases. CONCLUSION: Collagen-based coils show a marked cellular response in animal-model aneurysms, with resultant high rates of progressive occlusion after embolization. Dense matrix deposition is commonly seen with collagen-based coils. This contrasts with low rates of progressive thrombosis and high rates of loose matrix deposition seen with platinum coils.