Evaluation of a polyepoxy compound fixed biological vascular prosthesis and an expanded polytetrafluoroethylene vascular graft

Antithrombogenicity is one essential requirement for the successful use of small caliber vascular prostheses. In this study, a polyepoxy compound fixed, heparinized 4 mm diameter Baxter Denaflex vascular graft was evaluated against a 4 mm diameter Gore-Tex expanded polytetrafluoroethylene (ePTFE) vascular graft in the canine model. In addition to the thromboresistant characteristic conferred by heparinization, the crosslinking agent allowed the Denaflex graft to retain the original color of the native artery. Six centimeter long graft segments were implanted into the carotid arteries bilaterally in 5 dogs. The patency rate at 3 months for the Denaflex graft was 100% (five out of five) whereas in the control ePTFE graft, it was 40% (two out of five). The explanted Denaflex grafts exhibited softness and flexibility, and their luminal surfaces maintained a white color like that before implantation. To the contrary, the patent ePTFE grafts felt hard, and red thrombi covered large portions on their inner surfaces. Under microscopic observation, neointima formation was limited to regions near the anastomotic sites for both types of grafts. This experiment showed that the Denaflex vascular graft has an excellent antithrombogenic property and has a compliance similar to native arteries.     

Lipid uptake in expanded polytetrafluoroethylene vascular grafts

Purpose: The mechanisms of vascular prosthesis failure are reported to be associated, in part, with an atherosclerotic degenerative process that is related to an abnormal lipid infiltration. The lipid uptake in expanded polytetrafluoroethylene (ePTFE) vascular grafts was reproduced in vitro, and the effect of time on the permeability of these prostheses was studied. Methods: Water permeability tests were carried out under dynamic flow conditions at various hydrostatic pressures. Lipid uptake was simulated by circulating a phosphatidylcholine suspension inside an expanded Teflon prosthesis under pulsatile or continuous transmural pressure ranging between 80 mm Hg and 180 mm Hg, at a flow rate of 500 mL/min and 2000 mL/min, for a duration ranging from 2 hours to 1 month. Results: Water permeability tests indicated that under hydrostatic pressures of 180 mm Hg and 300 mm Hg, water percolated through the prosthesis wall after an exposure of 720 minutes and 75 minutes, respectively. After exposing the prostheses to the lipid dispersion under the various flow conditions, the fluid convection through the wall occurred. Preferential convection pathways with a constant periodicity were observed across the length of each prosthesis and were, therefore, associated with regularly spaced perforations depicted in the structure of the devices. Phospholipids gradually agglomerated within the prosthesis wall, allowing a restrictive molecular mobility. Infrared spectroscopy results indicated that the lipid uptake depended on the transmural pressure and time of exposure. Conclusion: The occurrence of the membrane permeability may be associated with the dilatation and plastic deformation of the prosthesis. Lipid uptake occurs in ePTFE grafts after an aggressive kinetic process. (J Vasc Surg 1998;28:527-34.)     

Experimental study on the mechanism of serum leakage from expanded polytetrafluoroethylene (EPTFE) vascular prosthesis

Even in recent years, the Blalock-Taussig (B-T) shunt operation has been carried out in order to increase pulmonary blood flow in patients of low pulmonary flow congenital heart disease. In such a case, a modified B-T shunt using an EPTFE vascular prosthesis would be employed in order to prevent blood flow obstruction in the upper extremity, and occasionally serum leakage from EPTFE vascular prosthesis is a complication. This has often troubled cardiovascular surgeons the world over, and we attempted to elucidate the mechanism of serum leakage and to discover how to prevent the situation from occurring. Using scanning electron microscopy, the structure of EPTFE vascular prosthesis was found to consist of an average of 0.5 micro meter polytetrafluoroethylene (PTFE) fibers arranged in parallel 5.0 micro meters from each other. The reason why serum does not usually leak from these widely spaced fibers is due to the presence of a repellent force derived from the surface tension and the contact angle between the solid surface of PTFE and the liquid. When the contact angle is over 90 degrees, the repellent force is in effect, while when it is below 90 degrees, this force is decreased. The surface tension and contact angle of physiological saline on the surface of PTFE showed values of 71.6 dyn/cm and 114.0 degrees, respectively, while demonstrating a strong repellent force. On the other hand, the surface tension of heparinized blood on the surface of the PTFE was 56.5 dyn/cm and the contact angle was 90.6 degrees. Thus, heparinized blood was assumed to act on the surface of the PTFE with a weak repellent force and for that reason had a tendency to easily leak from the EPTFE vascular prosthesis. When the surface of the PTFE was in contact with blood, blood protein was fixed to the surface of the PTFE and the contact angle of blood was thereby decreased. When the inner pressure of the vascular prosthesis was increased, the wall was stretched easily in a circumferential direction but with great difficulty in a longitudinal direction. With the PTFE stretched and released repeatedly, the expanded circumference was enlarged progressively due to the plastic character of the PTFE and because the spaces between the PTFE fibers were widened. In order to examine the relationship between the space between fibers and the critical pressure leading to serum leakage, computer simulation was carried out and the results showed a reversed linear correlation between the density of the fibers and the minimal pressures responsible for serum leakage.(ABSTRACT TRUNCATED AT 400 WORDS)     

Analysis of urokinase immobilization on the polytetrafluoroethylene vascular prosthesis

The polytetrafluoroethylene (PTFE) vascular prosthesis is thrombogenic and therefore not an ideal artificial blood vessel. The immobilization of urokinase on the surface of this substance has the potential to render the PTFE thrombolytic. Urokinase was immobilized to PTFE using tridodecylmethyl-ammonium chloride as a surfactant. In this preliminary study, a success rate of 45 percent was observed for the immobilization of active urokinase to PTFE. A model is proposed wherein application of the graft to an in vivo system is discussed. The urokinase graft is expected to be most effective under conditions of reduced blood flow which otherwise might promote thrombogenesis. The systemic side effects of the immobilized urokinase are expected to be significantly less when compared with the side effects of urokinase infused for clot lysis. The model presented of the urokinase-bound graft suggests that development and further study of the graft will result in an improved PTFE vascular prosthesis.     

A small arterial substitute: expanded microporous polytetrafluoroethylene: patency versus porosity.

Eighty-nine grafts of expanded microporous polytetrafluoroethylene (PTFE) with a diameter of 4 mm, were placed in the carotid and femoral arteries of dogs. The animals were sacrificed at varying intervals beginning three days after operation. Four animals remain alive with patent grafts 10 months post-operatively. Twenty-four of 89 grafts were occluded, an overall patency of 73%. Fibril length (pore size) of the graft material was varied from 4 to 110 microns. Average pore size ranged from 9 to 65 microns. Wall thickness varied from 0.3 to 0.75 mm. Density ranged from 0.24 to 0.35 g/ml. Tissue ingrowth, neointimization and patency rate as compared to pore size, wall-thickness and density of expanded PTFE were observed. Pore size is the primary determinant of tissue ingrowth, neointimization and patency. Of 51 grafts with an average pore size of 22 microns or less, there were 6 occlusions, an 88% patency rate. There were 38 grafts with an average pore size of 34 microns or greater. In these 38 grafts, 18 occlusions were observed, a 53% patency rate. Patent grafts demonstrated tissue ingrowth, capillary formation an a thin neointima. Using small pore grafts, patency rates of 90% can be anticipated in the dog. Expanded microporous PTFE with its ease of handling, strength and pliability may be the vascular prosthesis of choice in man.     

Polyurethane vascular prostheses decreases neointimal formation compared with expanded polytetrafluoroethylene

Purpose: Synthetic grafts have been increasingly used for complex vascular reconstructions in patients with limited autologous vein availability. Materials currently in use induce increased stenosis and graft thrombosis compared with autologous vein, especially in smaller vessels. We examined whether grafts constructed of a porous biodegradation-resistant polycarbonate polyurethane (PU) exert better biocompatibility in terms of faster endothelialization and decreased chronic proliferation of intimal cells compared with expanded polytetrafluoroethylene (ePTFE). Methods: PU or ePTFE interposition grafts were implanted into the abdominal aortas of male Sprague-Dawley rats (PU, n = 37; ePTFE, n = 32). Grafts were removed at days 1, 7, 14, 28, and 56 and 6 months and were evaluated by immunohistochemical, electron microscopic, and morphometric techniques. Bromodeoxyuridine (BrdU) was injected at 1 and 24 hours before death to determine cellular proliferation. Endothelial cells and smooth muscle cells were identified with antibodies to von Willebrand factor and α-actin, respectively. Results:The luminal surface of PU grafts took 4 weeks to completely endothelialize, whereas ePTFE grafts took 24 weeks (P < .05). Neointimal cell proliferation was lower in PU grafts compared with ePTFE at 56 days (1.4 ± 0.1 versus 8.6 ± 1.5, P < .001) and at 6 months (0.15 ± 0.002 versus 3.4 ± 0.5, p < .001). Neointimal thickness at 6 months after implantation was 3.2 ± 0.8 μm for PU compared with 10.3 ± 3.1 μm for ePTFE (P < .05). Conclusion: Polycarbonate polyurethane small vascular prostheses promoted faster luminal endothelialization, induced less chronic intimal proliferation, and produced a significantly thinner neointima than ePTFE grafts. These findings suggest that aliphatic-polycarbonate urethanes may offer advantages over standard materials such as ePTFE for vascular graft construction. (J Vasc Surg 1999;29:168-76)     

Extensible expanded polytetrafluoroethylene vascular grafts for aortoiliac and aortofemoral reconstruction

The operative experience and medium-term outcome achieved with longitudinally extensible ('stretch') expanded polytetrafluoroethylene (ePTFE) bifurcated grafts in patients undergoing aortoiliac or aortofemoral reconstruction for occlusive disease at our institution was reviewed. Between 1991 and 1998, 242 patients received a bifurcated stretch graft. Forty-one patients (17%) required an aortic endarterectomy, and 63 (26%) underwent femoral artery endarterectomy. 228 patients were followed for a mean of 32 months. One patient (0.4%) died perioperatively. The perioperative morbidity included cardiac (3.7%), respiratory (2.5%), and renal (3.3%) complications. Three patients required early reoperation for bleeding. Four (1.7%) grafts thrombosed within 24h of surgery; eight additional grafts (3.3%) thrombosed 5-8 months later. There were three postoperative aortic graft infections, one inguinal infection, three inguinal pseudoaneurysms, and one aortic pseudoaneurysm. Ultrasonography during follow-up showed no periprosthetic fluid collections or graft dilatations. The bifurcated ePTFE stretch graft is suitable for aortoiliac and aortofemoral reconstruction, and its physical characteristics may help to reduce graft-related complications.     

Effects of fibronectin bonding on healing of high porosity expanded polytetrafluoroethylene grafts in pigs

BACKGROUND: We developed a new fibronectin bonding to expanded polytetrafluoroethylene (ePTFE) and previously reported that, in a dog carotid implant model, fibronectin bonding improves graft healing in high porosity ePTFE grafts. The purpose of this study was to further investigate the effect of the fibronectin bonding on graft healing in a pig carotid implant model. METHODS: Fifteen pigs received a high porosity ePTFE graft treated with the fibronectin bonding (fibronectin-bonded graft) on one side and an untreated graft (non-bonded graft) on the contralateral side. The grafts were explanted at intervals of 3 and 6 weeks and subjected to histological studies. RESULTS: At 3 weeks, the neointima of fibronectin-bonded grafts was better organized than that of non-bonded grafts. At 6 weeks, the morphologic features of the neointima were the same in fibronectin-bonded and non-bonded grafts. The neointima was completely organized. CONCLUSIONS: Together with the previous results with the dog model, fibronectin bonding could be expected to improve healing of the high porosity ePTFE grafts in humans.     

Octylcyanoacrylate tissue adhesive as an alternative to mechanical fixation of expanded polytetrafluoroethylene prosthesis

In minimally invasive incisional hernia repair positioning and fixation of the expanded polytetrafluoroethylene (ePTFE) mesh prosthesis on the deep surface of the abdominal wall may be facilitated using tissue adhesives. Octylcyanoacrylate (OCTYL), a new adhesive, forms a strong flexible bond with antimicrobial properties. In a rabbit model for incisional hernia we investigated characteristics of the bond created by OCTYL between ePTFE and abdominal wall musculature. We studied initial bond strength and the postoperative host response to the adhesive over a 6-week period. We compared sutured, stapled, and glued mesh prostheses and examined the tissue-prosthesis interface. The ePTFE mesh was fixed successfully to the abdominal wall with OCTYL and remained tightly attached at 6 weeks. Prostheses fixed with OCTYL and spiral tacks induced few intra-abdominal adhesions compared with sutured mesh. All prostheses were completely reperitonealized at 2 weeks. The force required to displace mesh fixed with sutures and staples was greater than mesh fixed with OCTYL. Analysis of the ePTFE/tissue interface by light and scanning electron microscopy showed host cellular migration into the interstices of the mesh with fixation by tacks and suture, whereas an inflammatory infiltrate was seen on the muscular surface with OCTYL fixation of the mesh.     

Bacterial infectibility of chronically implanted endothelial cell-seeded expanded polytetrafluoroethylene vascular grafts

Vascular prosthetic grafts become more resistant to infection as the interval between implantation and bacteremic challenge increases. Endothelial cell (EC) seeding of such grafts has been shown to improve measurably their ability to resist a bacteremic challenge several weeks after implantation, presumably by reducing the amount of thrombus-free area (TFA) on their luminal surface. However, no investigators have reported the impact of EC seeding on the ability of chronically implanted vascular prostheses to resist a late bacteremic challenge. Bilateral common carotid interposition grafts were placed in 15 adult mongrel dogs with a 4 mm internal diameter, experimental, expanded polytetrafluoroethylene (ePTFE) prosthesis. One animal died shortly after operation and the grafts in two dogs thrombosed, thereby leaving 12 animals with at least one patent graft for subsequent study. At a mean interval of 45 weeks after implantation, five dogs (seven patent grafts) were challenged with an intravenous infusion of 3 X 10(8) radiolabeled Staphylococcus aureus; bacterial adherence and the TFA of the graft's luminal surface were determined for each of the patent grafts. There was no statistically significant difference in bacterial adherence or TFA between EC-seeded and control grafts. At a mean interval of 53 weeks after implantation, the remaining seven dogs (14 patent grafts) received a similar bacterial infusion and the animals were allowed to recover. Five days later, the grafts were harvested and cultured. Once again, there was no significant difference in the infectibility of EC-seeded vs. control grafts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multicenter evaluation of a polytetrafluoroethylene vascular access graft as compared with the expanded polytetrafluoroethylene vascular access graft in hemodialysis applications

OBJECTIVES: The purpose of this study was to compare in a randomized, prospective, and controlled study, the performance of a multilayered, self-sealing polyurethane vascular access graft (PVAG) and expanded polytetrafluoroethylene (ePTFE) vascular access grafts in hemodialysis applications. Performance measures included graft survival, complications, time to early cannulation, and hemostasis times after cannulation.Study Design: A total of 142 patients were randomized equally to receive one of the two grafts after meeting all eligibility requirements. All patients were followed up prospectively to 12 months or to the end of secondary patency. Specifically, this study documented the performance of the PVAG and ePTFE grafts by determining the patencies and complications for both grafts. RESULTS: Patient characteristics between the two groups were similar with respect to risk factors and demographic characteristics (P >.05). Life-table patencies from the date of first dialysis were primary patency: PVAG 55% versus ePTFE 47% (6 months) and PVAG 44% versus ePTFE 36% (12 months) and secondary patency: PVAG 87% versus ePTFE 90% (6 months) and PVAG 78% versus ePTFE 80% (12 months). None of these differences were significant (P >.05). Both primary and secondary patencies were also not significantly different when the date of implantation was the starting point. Adverse events and complications were similar for the two groups, except the PVAG group had a higher incidence of technical complications manifested by graft kinking when compared with the control cohort (P <.05). Additionally, there was no significant difference in complication rates between these two groups with regard to infection and bleeding. When the time to hemostasis after cannulation was compared at 5minutes or less, there were more PVAG cannulation sites that achieved hemostasis compared with ePTFE sites, and this difference was significant (P <.0001). When time to first dialysis access was compared between the two grafts, 53.9% of all PVAG grafts were cannulated before 9 days versus none with the ePTFE grafts (P <.001). However, long-term graft survival was not significantly different when PVAG patients were stratified into early (< 9 days) and the late access (9 >/= days) groups (P =.29). CONCLUSIONS: The PVAG graft allows for early access without compromising long-term performance. Both PVAG and standard ePTFE grafts have similar long-term outcomes, despite early access with the PVAG vascular access grafts.     

One-year experience with a new expanded polytetrafluoroethylene vascular graft for hemodialysis

Hemodialysis access achieved through a prosthetic vascular graft has become more popular, especially in diabetic and older patients and those who have had several unsuccessful surgical accesses. From January to December 1996, we implanted a newly available expanded polytetrafluoroethylene (ePTFE) graft (DIASTAT Vascular Access Graft) that allows early cannulation in 18 patients (11 men and 7 women; mean age +/- SD, 63.7 +/- 11 years). Thirteen of these patients had at least one failed vascular access. All grafts were cannulated for dialysis within 7 days of implantation, with flow rates > or = 300 ml/min. The time to hemostasis after the first cannulation ranged from 2 to 4 min. The primary patency rate at one year was 56%. Four grafts developed thrombosis requiring surgical intervention; three were salvaged and one was removed. The one-year assisted or cumulative patency rate was 72%. One patient had persistent bleeding requiring graft revision immediately after surgery. The bleeding stopped and its origin was not determined. There were no graft infections or hematomas. Because of the early cannulation possible with the DIASTAT graft, as well as the lesser time to hemostasis than that generally achieved with standard ePTFE grafts, this prosthesis is a good alternative to autogenous access construction.     

In vivo study of an elastomer end-coated polytetrafluoroethylene vascular prosthesis.

Polyurethane end-coated polytetrafluoroethylene (PTFE) grafts (elastomer PTFE grafts) were implanted in 12 female adult mongrel dogs to assess patency, intimalization, tissue incorporation, and technical suitability of the material as a vascular graft. Each dog had bilateral aortoiliac grafts placed, one a standard PTFE and the other an elastomer PTFE graft. The length of the grafts was 7-8 cm and the diameter was 6 mm. The grafts were harvested at intervals to 120 days postoperatively. The elastomer PTFE grafts showed superior longitudinal elasticity, retention of shape, and no graft tearing with suture tension; however, no significant difference in bleeding was noted at the anastomoses between the standard and elastomer PTFE grafts. Satisfactory patency was obtained with both standard (8/10) and elastomer PTFE grafts (9/10) at 90-120 days. No significant difference in the thickness of intima and the length of pannus ingrowth was noted between the standard and elastomer PTFE grafts. No outer tissue incorporation was seen at the elastomer-treated graft segments as opposed to the well-incorporated untreated segments. In conclusion, elastomer end-coating of a PTFE vascular prosthesis provided excellent handling characteristics without detracting from patency; however, the lack of outer tissue incorporation may be a potential disadvantage in its clinical use.     

Microarterial prostheses of expanded polytetrafluoroethylene

Forty grafts of expanded polytetrafluoroethylene (PTFE) with an inside diameter of 1.5 mm were placed in the femoral arteries of rabbits. The telescoped technique was used for the anastomoses. The animals were sacrificed at intervals beginning the day after implantation. Four of the grafts lost patency and one graft had a remarkable degree of intimal hypertrophy. The remaining grafts developed thin neointimal formations and remained patent up to 7 months after implantation. The overall patency rate was 90%. Neointimization was established 35 to 90 days following surgery. The formation of neointima began at the anastomotic sites and extended into the grafts. It is concluded that PTFE prostheses can be used for grafting arteries as small as 1.0-1.2 mm in diameter, which up to now had been considered impossible.