Differences in neointima formation between impervious and porous polytetrafluoroethylene vascular patch material

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure.

Hyaluronic acid biodegradable material for reconstruction of vascular wall: a preliminary study in rats

The objective of this preliminary study was to develop a reabsorbable vascular patch that did not require in vitro cell or biochemical preconditioning for vascular wall repair. Patches were composed only of hyaluronic acid (HA). Twenty male Wistar rats weighing 250-350 g were used. The abdominal aorta was exposed and isolated. A rectangular breach (1 mm × 5 mm) was made on vessel wall and arterial defect was repaired with HA made patch. Performance was assessed at 1, 2, 4, 8, and 16 weeks after surgery by histology and immunohistochemistry. Extracellular matrix components were evaluated by molecular biological methods. After 16 weeks, the biomaterial was almost completely degraded and replaced by a neoartery wall composed of endothelial cells, smooth muscle cells, collagen, and elastin fibers organized in layers. In conclusion, HA patches provide a provisional three-dimensional support to interact with cells for the control of their function, guiding the spatially and temporally multicellular processes of artery regeneration.

Mechanical properties of small-diameter polyurethane vascular grafts reinforced by weft-knitted tubular fabric

Polyester filament yarns of different Deniers were knitted into tubular fabrics with different densities and thicknesses on a specially designed weft-knitting machine. The developed tubular fabric was used to reinforce polyurethane vascular graft and thus a kind of composite vascular graft was fabricated with a small inner diameter of 4 mm. Tensile properties of the reinforced composite vascular grafts were compared with the control tubular fabric and the pure PU vascular grafts. Elasticity and strength of the reinforced vascular grafts were improved compared with the weft-knitted tubular fabrics. Strength of the reinforced composite vascular grafts was almost 5-10 times of the strength of the pure PU vascular grafts. As the PU content increased in the reinforced composite vascular grafts, the wall thickness of the vascular graft and its strength increased, but the initial modulus of the reinforced composite vascular grafts remained similar to that of the weft-knitted tubular fabric, and the PU content showed little influence on the initial modulus of the reinforced composite vascular grafts. Microporous structure can also be fabricated in the wall of the reinforced composite vascular grafts.

Transmural communication at a subcellular level may play a critical role in the fallout based-endothelialization of dacron vascular prostheses in canine

A microporous and permeable wall is important for the healing of vascular prostheses, however, the significance of its permeability to soluble substances at subcellular level has not been demonstrated. Polyester arterial prostheses were prepared in such a way that each of them contained three segments, of which at least one segment was impervious and another segment was permeable to water but impermeable to cells. Twenty graft segments were implanted in 7 dogs as a thoraco-abdominal bypass for 2 months. The prostheses were then harvested, photographed, and treated for histological and morphological studies. The low porosity graft capped by two thrombogenic segments was fully endothelialized, proving the fallout mechanism. The striking contrast with its impermeable counterpart demonstrated that a wall permeable to small substances of subcellular level was critical for the endothelial healing. A wide range of water permeabilities did not reveal advantages of high water permeable segments over low water permeable ones. Endothelial ingrowth from anastomoses was also jeopardized in the absence of wall permeability. In conclusion, transmural communication at a subcellular level may have played a critical role in the fallout based-endothelialization of arterial prostheses in canine. This highlights the potential function of perigraft cytokines and growth factors in endothelial healing.

Pore size, tissue ingrowth, and endothelialization of small-diameter microporous polyurethane vascular prostheses

Small-diameter microporous polyurethane vascular prostheses with an average pore size of between 5 and 30mum at the outer surfaces and 30mum at the luminal surface were prepared. Thirty-two PU and 8 expanded polytetrafluoroethylene (ePTFE) prostheses were implanted into the abdominal aorta of rats for periods ranging from 1 to 8 weeks. Harvested prostheses were analysed histologically and morphologically. The progress of endothelial-like cells and the extent of infiltration of perigraft tissues were quantified. All of the prostheses showed fast growth of endothelial-like cells in the second week, with the PU prostheses having an external pore size of 30mum producing the highest rate. It was also during the second week that perigraft tissue grew most significantly into the prosthetic structure. This coincident may suggest the importance of rapid tissue regeneration for the early endothelial healing. The role of the ingrowth perigraft tissues is likely to support and stabilize the neointima. The thickening of neointima was mainly located at the vicinity of the proximal anastomoses of some of the PU prostheses and was unrelated with the extent of perigraft tissue infiltration. In the PU prostheses, a complete lining of endothelial-like cells was achieved by the end of 4 weeks. Expanded PTFE prostheses displayed smooth, thin intima, very limited tissue ingrowth, and incomplete coverage of endothelial-like cells.