Significance of porosity and compliance of microporous, polyurethane-based microarterial vessel on neoarterial wall regeneration

Abstract

The microporous structure of artificial vascular grafts, which increases compliance and porosity simultaneously, may enhance neoarterial regeneration. In order to differentiate these effects, three models of segmented polyurethane grafts (inner diameter, 1.5 mm; wall thickness, 100 microns) with or without micropores fabricated using an excimer laser ablation technique, were prepared, and their neoarterial regenerative potentials were studied upon implantation: Model I (microporous, permeable, compliant); Model II (smooth-surfaced, impermeable, compliant); and Model III (smooth-surfaced, impermeable, noncompliant). In Models I and II, the pore or groove size (diameter, 100 microns) and pore or groove arrangement were fixed, and consequently their compliances were almost identical. Irrespective of model, the luminal surfaces were coated with benzophenone-derivatized gelatin and subsequently photocured. Twenty grafts (length, 20 mm) of each model were implanted in the aortas of rats. Predetermined implantation periods were 4, 12, and 24 weeks. Total patency rate decreased in the order Model I (100%), II (87%), and III (59%) grafts. All patent grafts were completely endothelialized after 12 weeks of implantation, irrespective of model. After 12- and 24-week implantations, in Model I grafts, the neoarterial wall was thin, and smooth muscle cells (SMCs) were of the contractile phenotype. In Model II grafts, the neoarterial wall exhibited considerable thickening. In Model III grafts, the neoarterial wall exhibited marked thickening, and SMCs were of the synthetic phenotype. The neoarterial wall thickness at the midportion of the grafts after 24 weeks of implantation increased in the order Model I (48 +/- 8 microns), II (146 +/- 87 microns), and III (385 +/- 21 microns) grafts. These results strongly suggest that compliance matching and porosity synergistically resulted in neoarterial wall restoration without appreciable thickening.

Surface microarchitectural design in biomedical applications:In vivo analysis of tissue ingrowth in excimer laser-directed micropored scaffold for cardiovascular tissue engineering

“…That is, the thickness was almost the same among the proximal anastomosis site, midportion, and distal anastomosis site. This phenomenon is different from that observed in our previous implantation study of the microporous small-caliber artificial grafts, [69][70][71] in which neoarterial wall thickness decreased significantly with increasing distance from the distal anastomosis site to the midportion after 4 weeks of implantation in rat. The wall thickness at the midportion gradually increased with implantation period, whereas the thickness at the anastomosis site remained almost constant.…”

“…22 Based on these fundamental findings and techniques, we fabricated compliant microporous small-caliber artificial grafts with a well-defined pore size and distribution, and implanted them into the rat abdominal aorta. [69][70][71][72] The pores provided for rapid transmural vascular wall regeneration in the early stage after implantation with little occurrence of intimal hyperplasia in the later stage, probably owing to compliance matching with living tissue (mechanical compatibility).…”

Small-diameter compliant arterial graft prosthesis: Design concept of coaxial double tubular graft and its fabrication

“…Details of the procedures for microporing, preparation of photoreactive gelatin, and coating were described in our previous papers. [11][12][13][14] Young's modulus of micropored films was measured using a rheometer (RE-3305; Yamaden Co., Ltd., Tokyo, Japan) by a tensile-strength test. Coaxial double or triple tubular grafts were assembled by inserting the inner tube into the outer tube.…”

“…Measurements of the P-D relationship were as previously reported. 13 Briefly, one end of an arterial segment (length of more than 20 mm) was cannulated to a fixed stainless-steel connector for pressure loading and the other to a sliding connector. The vessel segment, immersed in Krebs-Ringers solution bubbled with a mixture of 95% oxygen and 5% carbon dioxide gas at 37°C, was gradually inflated with a pressurized intraluminal KrebsRingers solution.…”

Influence of fabrication process on the final properties of natural-rubber latex tubes for vascular prosthesis

“…Both must be completely controlled in the manufacturing process for the success of the tube-like implants [13]. The tubes must have regular and uniform walls, being available on a variety of sizes and diameters, and have to work in the vascular system as the original arteries to avoid thrombogenesis.…”