High-performance self-expanding stent graft: development and application to experimental aneurysms

Tissue Engineering at the Blood-Contacting Surface: A Review of Challenges and Strategies in Vascular Graft Development

Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.

Hemodynamic Study of Flow Remodeling Stent Graft for the Treatment of Highly Angulated Abdominal Aortic Aneurysm

This study investigates the effect of a novel flow remodeling stent graft (FRSG) on the hemodynamic characteristics in highly angulated abdominal aortic aneurysm based on computational fluid dynamics (CFD) approach. An idealized aortic aneurysm with varying aortic neck angulations was constructed and CFD simulations were performed on nonstented models and stented models with FRSG. The influence of FRSG intervention on the hemodynamic performance is analyzed and compared in terms of flow patterns, wall shear stress (WSS), and pressure distribution in the aneurysm. The findings showed that aortic neck angulations significantly influence the velocity flow field in nonstented models, with larger angulations shifting the mainstream blood flow towards the center of the aorta. By introducing FRSG treatment into the aneurysm, erratic flow recirculation pattern in the aneurysm sac diminishes while the average velocity magnitude in the aneurysm sac was reduced in the range of 39% to 53%. FRSG intervention protects the aneurysm against the impacts of high velocity concentrated flow and decreases wall shear stress by more than 50%. The simulation results highlighted that FRSG may effectively treat aneurysm with high aortic neck angulations via the mechanism of promoting thrombus formation and subsequently led to the resorption of the aneurysm.

Electrospun poly(L-lactic acid-co-ɛ-caprolactone) fibers loaded with heparin and vascular endothelial growth factor to improve blood compatibility and endothelial progenitor cell proliferation

Emulsion electrospinning is a convenient and promising method for incorporating proteins and drugs into nanofiber scaffolds. The aim of this study was to fabricate a nanofiber scaffold for anticoagulation and rapid endothelialization. For this purpose, we encapsulated heparin and vascular endothelial growth factor (VEGF) into the core of poly(L-lactic acid-co-ɛ-caprolactone) (P(LLA-CL)) core-shell nanofibers via emulsion electrospinning. The fiber morphology, core-shell structure and hydrophilicity of the nanofiber mats were analyzed by scanning electron microscopy, transmission electron microscopy and water contact angle. The blood compatibility was measured by hemolysis and anticoagulation testing. A CCK-8 assay was performed to study the promotion of endothelial progenitor cell (EPC) growth and was complemented by immunofluorescent staining and SEM. Our study demonstrates that heparin and VEGF can be incorporated into P(LLA-CL) nanofibers via emulsion. The released heparin performed well as an anticoagulant, and the released VEGF promoted EPC growth on the fiber scaffolds. These results imply that electrospun P(LLA-CL) nanofibers containing heparin and VEGF have great potential in the development of vascular grafts in cases where antithrombogenicity and accelerated endothelialization are desirable.

Preparation and characterization of a thrombin inhibitor grafted polyethersulfone blending membrane with improved antithrombotic property

A thrombin inhibitor grafted polyethersulfone membrane with improved antithrombotic property.

Occlusion of canine aneurysms using microporous self-expanding stent grafts: long-term follow-up

PURPOSE

The treatment of large or giant cerebral aneurysms by surgical and/or endovascular techniques is difficult and poses relatively high risks. Therefore, a microporous self-expanding (hybrid) stent graft composed of a thin, expandable, segmented polyurethane (SPU) membrane with micropores and a drug-delivery system was developed.

MATERIALS AND METHODS

A commercially available, self-expanding carotid stent was covered with a thin microporous SPU membrane fabricated by the dip-coating method and the excimer laser ablation technique, with an intraluminal coating of argatroban. Experimentally fabricated lateral-wall aneurysms in canine carotid arteries using venous pouches were occluded with the hybrid stent graft (bale-shaped pore density of 23.6%) on one side and a bare-metal stent on the other side without systemic antiplatelet therapy.

RESULTS

Angiography at 1, 6, and 12 months of stenting revealed that all arteries were patent without marked stenosis without systemic antiplatelet therapy. All aneurysms treated with hybrid stent grafts remained occluded throughout the 12-month period, while among those treated by bare-metal stents, 2 of 3 aneurysms were occluded at 6 months (67%) and only 1 of 3 aneurysms were occluded at 12 months (33%). Histology revealed that the novel hybrid stent graft had less intimal hyperplasia than the bare-metal stent. The hybrid stent graft was useful for the successful occlusion of these canine carotid aneurysms, even at 12 months.

CONCLUSIONS

The novel hybrid stent grafts are expected to overcome the disadvantages of fully covered stent grafts and simple bare-metal stents, while combining both their merits, and appear to be useful in the treatment of large or giant cerebral aneurysms.

Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia

Treatment of large (diameter 12-25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 μm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 μm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 μm) than the bare stents (341 ± 146 μm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 μm). A pore ratio of 23.6% was found to control intimal growth.

Autologous small-caliber "biotube" vascular grafts with argatroban loading: a histomorphological examination after implantation to rabbits

Functional autologous tubular tissues, termed "biotubes," have been developed as small-caliber vascular grafts. Biotubes can be easily and safely constructed in vivo by using a novel concept in regenerative medicine-in body tissue architecture technology, which requires neither clean specialized laboratories nor complex cell management. Biotubes with "anastomotic reinforcement cuffs" were prepared by embedding a silicone rod (diameter, 3 mm; length, 30 mm) as a mold in the dorsal subcutaneous pouches of rabbits. The rod was covered at both ends with 2 pieces of polyurethane sponge tubes (length, 3 mm), and it was removed when the grafts were harvested. These biotubes had homogeneous thin connective tissue walls (thickness: 76 +/- 37 microm) that were primarily composed of collagen and fibroblasts. The resulting cuff-impregnated biotubes were auto-implanted in the carotid arteries for predetermined periods of up to 12 weeks and then morphologically examined. On implantation of the biotubes after argatroban loading, the total patency was 9/11 without any instance of aneurysm formation or rupture. At 12 weeks after implantation, no significant neointimal thickening was observed (170 +/- 30 microm). In addition, minimal thrombus formation was observed on the luminal surfaces, which were completely covered with endothelial cells regularly oriented longitudinally. The regenerated vascular walls comprised multilayered smooth muscle cells and dense collagen fibers with regular circumferential orientation with few elastin fibers and were similar to native arteries. Biotubes with argatroban loading could thus be used as small-caliber vascular prostheses that greatly facilitate healing process and exhibit excellent biocompatibility.