Experimental evaluation of ten clinically used arterial prostheses

Evaluations for surrounding tissue incorporation after implantation of synthetic vascular prostheses in animal models

Incorporation of surrounding tissues after implantation of synthetic vascular prostheses potentially varies in accordance with implanted prostheses. To evaluate post-implant tissue incorporation, we examined surgical, histological and ultrastructural findings after implantation in animal models. Three types of commercially available prostheses were tested (Gelweave™; Group G, J Graft SHIELD NEO^®; Group J and Triplex^®; Group T). Prostheses were implanted into Sprague-Dawley rats subcutaneously or sutured on abdominal aorta of Japanese white rabbits. The tissues were surgically examined for adhesion and were subjected to histological evaluations for cellular and tissue infiltration and ultrastructural observations by scanning electron microscopy (SEM). Group G exhibited less tendency in adhesion formation in early phase (rat: G vs J, P < 0.0001; G vs T, P < 0.0001/rabbit: G vs J, P < 0.0001; G vs T, P = 0.059). In late phase, Group J showed highest adhesion (rat: G vs J, P = 0.0004; J vs T, P = 0.015/rabbit: G vs J, P = 0.0015; J vs T, P = 0.0044). In group G, a gap was observed between implants and surrounding tissues forming capsulation, whereas other groups exhibited tissue infiltration inside of the implants wall which were also confirmed by SEM. The tissue permeation toward the implants and adhesion was positively correlated (P < 0.0001). Surrounding tissue conformation varied in accordance with the type of prostheses. It is desirable to elucidate characteristics of each prosthesis to select suitable grafts for each patient to achieve a better surgical outcome.

Endothelial Cell Seeding to the Dog Vena Caval Prostheses Made of Different Materials and Configurations

Producing an early and complete prosthetic endothelialization is one of the best methods for improving performance of venous grafts. This study investigated the effect of graft material and configuration on the prosthetic endothelialization. Forty-two mongrel dogs were randomly divided into six groups. Four animals from each group were implanted with endothelial cell (EC)-seeded prostheses and 3 with unseeded ones in the inferior vena cava (IVC). ECs were harvested from autogenous omentum by enzymatic method yielding 1.65 ±0.43x106 ECs per gram of omentum. A 5-cm-long segment of IVC was resected, and an equal-dimension prosthesis was interposed. A femoral arteriovenous fistula (AVF) was created. Prostheses were explanted at ten days following surgery. All EC-seeded knitted Dacron prostheses and 3 seeded polytetrafluoroethylene (PTFE) ones were patent with complete endothelialization. All seeded woven Dacron prostheses were patent with partial endothelialization. Only 2 seeded and one control Silk prostheses were patent, and no EC lining could be detected. Light microscopy revealed that the neointima was thinner in the patent seeded PTFE grafts than that in controls (p<0.001) and in seeded knitted Dacrons (p < 0.02) . The neointima of seeded knitted Dacron grafts was thinner than that of controls (p<0.01). No marked difference was seen among the neointima formed on Meadox porous, Vascutek porous grafts (VP1200), or Vascutek sealed Gelsoft grafts. It was concluded that: (1) Excellent and early endothelialization of EC-seeded dog caval implants can be established with Vascutek VP1200, Gelsoft, Meadox knitted Dacron, and indigenous ePTFE. (2) Knitted Dacron is superior to woven Dacron in regard to EC seeding. (3) The gelatin-impregnated Gelsoft does not interfere with prosthetic endothelialization. (4) The woven Dacron, and especially the Silk prosthesis, seem unsuitable for EC seeding in the venous circuit.

Fibrinogen matrix deposited on the surface of biomaterials acts as a natural anti-adhesive coating

Adsorption of fibrinogen on the luminal surface of biomaterials is a critical early event during the interaction of blood with implanted vascular graft prostheses which determines their thrombogenicity. We have recently identified a nanoscale process by which fibrinogen modifies the adhesive properties of various surfaces for platelets and leukocytes. In particular, adsorption of fibrinogen at low density promotes cell adhesion while its adsorption at high density results in the formation of an extensible multilayer matrix, which dramatically reduces cell adhesion. It remains unknown whether deposition of fibrinogen on the surface of vascular graft materials produces this anti-adhesive effect. Using atomic force spectroscopy, single cell force spectroscopy, and standard adhesion assays with platelets and leukocytes, we have characterized the adhesive and physical properties of the contemporary biomaterials, before and after coating with fibrinogen. We found that uncoated PET, PTFE and ePTFE exhibited high adhesion forces developed between the AFM tip or cells and the surfaces. Adsorption of fibrinogen at the increasing concentrations progressively reduced adhesion forces, and at ≥2 μg/ml all surfaces were virtually nonadhesive. Standard adhesion assays performed with platelets and leukocytes confirmed this dependence. These results provide a better understanding of the molecular events underlying thrombogenicity of vascular grafts.

Irregular neointimal lining with prominent proliferative activity after carotid patch angioplasty: an autopsy case report

OBJECTIVE

Although the healing response after carotid balloon injury and carotid patch angioplasty injury has been well-documented in animal models, there is limited information about this process after carotid endarterectomy (CEA) in human patients.

CASE DESCRIPTION

We describe the autopsy results of a 79-year-old man who died 18 days after CEA with patch angioplasty. The treated carotid artery had an adequate luminal diameter. Elastica-Masson staining revealed that the treated portion was covered with neointima but the patch graft was exposed to the arterial lumen at 18 days after CEA. Immunohistochemistry staining for alpha-smooth muscle actin (α-SMA), von-Willebrand factor, and vascular endothelial growth factor receptor-2 revealed that the neointima was mainly composed of α-SMA-positive cells. In addition, the α-SMA-rich neointima had many more Ki-67-positive cells than did the internal carotid artery intima in the area beyond the CEA-treated portion.

CONCLUSIONS

This case report is the first to describe an entire carotid artery specimen in the acute stage after CEA with patch angioplasty. These findings suggest that an α-SMA-rich neointima with prominent proliferative activity covers the inner surface of the treated carotid artery, but patch grafts are left uncovered. The intrinsic arterial wall may have an important role in intimal regeneration after CEA, although the nature of the neointima and the mechanism by which it regulates proliferative activity remain unclarified.

Origin of the nonadhesive properties of fibrinogen matrices probed by force spectroscopy

The deposition of a multilayered fibrinogen matrix on various surfaces results in a dramatic reduction of integrin-mediated cell adhesion and outside-in signaling in platelets and leukocytes. The conversion of a highly adhesive, low-density fibrinogen substrate to the nonadhesive high-density fibrinogen matrix occurs within a very narrow range of fibrinogen coating concentrations. The molecular events responsible for this transition are not well understood. Herein, single-cell and molecular force spectroscopy were used to determine the early steps in the formation of nonadhesive fibrinogen substrates. We show that the adsorption of fibrinogen in the form of a molecular bilayer coincides with a several-fold reduction in the adhesion forces generated between the AFM tip and the substrate as well as between a cell and the substrate. The subsequent deposition of new layers at higher coating concentrations of fibrinogen results in a small additional decrease in adhesion forces. The poorly adhesive fibrinogen bilayer is more extensible under an applied tensile force than is the surface-bound fibrinogen monolayer. Following chemical cross-linking, the stabilized bilayer displays the mechanical and adhesive properties characteristic of a more adhesive fibrinogen monolayer. We propose that a greater compliance of the bi- and multilayer fibrinogen matrices has its origin in the interaction between the molecules forming the adjacent layers. Understanding the mechanical properties of nonadhesive fibrinogen matrices should be of importance in the therapeutic control of pathological thrombosis and in biomaterials science.

Time course of fibronectin in the peri-implant tissue and neointima formation after functional implantation of polyester-based vascular prostheses with different porosity in pigs

Intima hyperplasia, resulting from extracellular matrix (ECM) secretion, can lead to vascular prosthesis occlusion and is a major problem in vascular surgery. Fibronectin might contribute to ongoing ECM secretion. However, the exact role of fibronectin and its influence on neointima formation remains unclear. This study was aimed at investigating the time course of the fibronectin area fraction and neointima formation following the functional implantation of three different polyester vascular prostheses into pigs. The infrarenal aorta from 15 animals (n = 5/group) was replaced by prosthesis segments with low, medium and high primary porosity. After 7, 14, 21, 28 and 116 days, the prostheses were morphometrically examined. Overall, the fibronectin area fraction was inversely correlated with the neointima thickness, demonstrating high fibronectin levels in the early phase (days 7 and 14) and low levels in the later phase with almost complete neointima formation (days 21-116). Throughout the study, fibronectin levels were highest at the proximal anastomosis region. The low porosity prosthesis had the highest fibronectin area fraction and a delayed neointima formation in the middle phase (days 21 and 28) but the highest neointima lining on day 116. The results indicate a relationship between fibronectin and neointima formation with the prosthesis porosity, demonstrating the importance of the textile design for tissue reactions following implantation.

Plasminogen on the surfaces of fibrin clots prevents adhesion of leukocytes and platelets

BACKGROUND AND OBJECTIVES

Although leukocytes and platelets adhere to fibrin with alacrity in vitro, these cells do not readily accumulate on the surfaces of fibrin clots in vivo. The difference in the capacity of blood cell integrins to adhere to fibrin in vivo and in vitro is striking and implies the existence of a physiologic antiadhesive mechanism. The surfaces of fibrin clots in the circulation are continually exposed to plasma proteins, several of which can bind fibrin and influence cell adhesion. Recently, we have demonstrated that adsorption of soluble fibrinogen on the surface of a fibrin clot results in its deposition as a soft multilayer matrix, which prevents attachment of blood cells. In the present study, we demonstrate that another plasma protein, plasminogen, which is known to accumulate in the superficial layer of fibrin, exerts an antiadhesive effect.

RESULTS

After being coated with plasminogen, the surfaces of fibrin clots became essentially non-adhesive for U937 monocytic cells, blood monocytes, and platelets. The data revealed that activation of fibrin-bound plasminogen by the plasminogen-activating system assembled on adherent cells resulted in the generation of plasmin, which decomposed the superficial fibrin layer, resulting in cell detachment under flow. The surfaces generated after the initial cell adhesion remained non-adhesive for subsequent attachment of leukocytes and platelets.

CONCLUSION

We propose that the limited degradation of fibrin by plasmin generated by adherent cells loosens the fibers on the clot surface, producing a mechanically unstable substrate that is unable to support firm integrin-mediated cell adhesion.

Prospective randomized trial of ACUSEAL (Gore-Tex) vs Finesse (Hemashield) patching during carotid endarterectomy: long-term outcome

BACKGROUND

Several studies have reported that carotid endarterectomy with patch angioplasty is superior to primary closure. Conventional polytetrafluoroethylene (Gore-Tex, W. L. Gore & Associates, Flagstaff, Ariz) patching has been shown to have results similar to autogenous saphenous vein patching; however, it requires a longer hemostasis time. This study examined the long-term clinical outcome and incidence of restenosis after carotid endarterectomy using the new ACUSEAL (Gore-Tex) patching vs Hemashield Finesse (Boston Scientific Corp, Natick, Mass) patching.

METHODS

The study randomized 200 patients (1:1) undergoing carotid endarterectomy to 100 with ACUSEAL patching and 100 with Hemashield-Finesse patching. All patients underwent immediate and 1-month postoperative duplex ultrasound studies, which were repeated at 6-month intervals. Kaplan-Meier analysis was used to estimate the freedom from stroke, stroke-free survival, and the risk of restenosis for both groups.

RESULTS

The demographic and clinical characteristics, the mean operative diameter of the internal carotid artery, and the length of the arteriotomy were similar in both groups. The mean hemostasis time was 5.1 for the ACUSEAL patching vs 3.7 minutes for Finesse patching (P = .01); however, the mean operative times were similar for both groups (P = .61). The incidence of ipsilateral stroke was 2% for ACUSEAL patching (both early perioperative strokes) vs 3% for Finesse patching (2 early and 1 late stroke) at a mean follow-up of 21 months. The respective cumulative stroke-free rates at 1, 2, and 3 years were 98%, 98%, and 98% for ACUSEAL patching vs 97%, 97%, and 97% for Finesse patching (P = .7). The respective cumulative stroke-free survival rates at 1, 2, and 3 years were 97%, 92%, and 88% for ACUSEAL patching vs 96%, 96%, and 91% for Finesse patching (P = .6). The respective freedom from > or =70% carotid restenosis at 1, 2, and 3 years was 98%, 96%, and 89% for ACUSEAL patching vs 92%, 85%, and 79% for Finesse patching (P = .04).

CONCLUSIONS

Carotid endarterectomy with ACUSEAL patching and Finesse patching had similar stroke-free rates and stroke-free survival rates. The mean hemostasis time for the ACUSEAL patch was 1.4 minutes longer than that for the Finesse patch; however, the Finesse patch had higher restenosis rates than the ACUSEAL patch.

Vascular graft healing. III. FTIR analysis of ePTFE graft samples from implanted bigrafts

A bigraft, composed of a 30-microm internodal distance expanded polytetrafluoroethylene (ePTFE) arterial graft segment and a preclotted polyethylene terephthalate arterial graft segment, was used to study the healing process of two different materials in the same dog. Healing was followed by FTIR-ATR spectroscopy and correlated with ELISA analyses of selected growth factors and matrix proteins. The FTIR analyses of the ePTFE explants from 1 and 3 h; 3, 5, 7, 10, and 14 days; and 4 and 8 weeks showed that the ePTFE grafts did not heal (endothelialize), but appeared to remain in overlapping inflammation and proliferation stages of wound healing. Although FN was found in the fibrin layer coating the luminal surface of the ePTFE, VEGF was not present. The inability of VEGF to complex with FN may be the result of FN binding sites being blocked or hidden by the conformation of the fibrin clot that forms on ePTFE. Also, TGF-beta was not present beyond the initial clot formation at 3 h postimplantation. The absence of these two growth factors may be an important factor in the lack of healing of 30-microm ePTFE grafts, because both were found to be present during the early stages of healing for the preclotted polyester grafts that did endothelialize.

Prospective randomized trial of carotid endarterectomy with polytetrafluoroethylene versus collagen-impregnated dacron (Hemashield) patching: late follow-up

OBJECTIVE

To compare the late clinical outcome and incidence of recurrent stenosis after carotid endarterectomy (CEA) with polytetrafluoroethylene (PTFE) versus Hemashield patching.

SUMMARY BACKGROUND DATA

Several randomized trials have confirmed the advantages of patching over primary closure when performing CEA.

METHODS

Two hundred CEAs (180 patients) were randomized into 100 with PTFE patching and 100 with Hemashield. All patients underwent postoperative color duplex ultrasounds at 1, 6, and 12 months, and every year thereafter. The mean follow-up was 26 months. Kaplan-Meier analysis was used to estimate the risk of re-stenosis, stroke, and stroke-free survival. A multivariate analysis of various risk factors was also done.

RESULTS

Demographic and clinical characteristics were similar in both groups. The incidence of all ipsilateral strokes (early and late) was 8% (7% perioperative) for Hemashield versus 0% for PTFE patching. Both groups had similar mortality rates. The cumulative stroke-free rates at 6, 12, 24, and 36 months were 93%, 93%, 93%, and 89% for Hemashield versus 100%, 100%, 100%, and 100% for PTFE patching. The cumulative stroke-free survival rates at 6, 12, 24, and 36 months were 90%, 89%, 87%, and 79% for Hemashield versus 98%, 98%, 92%, and 92% for PTFE patching. Kaplan-Meier analysis also showed that freedom from 50% or greater re-stenosis at 6, 12, 24, and 36 months was 89%, 81%, 73%, and 66% for Hemashield versus 100%, 100%, 100%, and 92% for PTFE. Similarly, the freedom from 70% or greater re-stenosis at 6, 12, 24, and 36 months was 93%, 91%, 86%, and 78% for Hemashield versus 100%, 100%, 100%, and 100% for PTFE. Univariate and multivariate analyses of demographic and preoperative risk factors showed that only Hemashield was significantly associated with a higher incidence of 70% or greater recurrent stenosis.

CONCLUSIONS

PTFE patching was superior to Hemashield in lowering the incidence of postoperative ipsilateral strokes and late recurrent stenosis.

Prospective randomized study of carotid endarterectomy with polytetrafluoroethylene versus collagen-impregnated Dacron (Hemashield) patching: perioperative (30-day) results

PURPOSE

Several studies have reported that carotid endarterectomy (CEA) with patch angioplasty has results that are superior to primary closure. Polytetrafluoroethylene (PTFE) patching has been shown to have results comparable with autogenous vein patching; however, it requires a prolonged hemostasis time. Therefore, many surgeons are using collagen-impregnated Dacron patching (Hemashield [HP]). This study is the first prospective randomized trial comparing CEA with PTFE patching versus HP patching.

METHODS

Two hundred CEAs were randomized into two groups, 100 PTFE and 100 HP patching. All patients underwent immediate postoperative and 1-month postoperative color duplex ultrasound scanning studies. Demographic and clinical characteristics were similar in both groups, including the mean operative diameter of the internal carotid artery.

RESULTS

The perioperative stroke rates were 0% for PTFE, versus 7% for HP (4 major and 3 minor strokes, P =.02). The combined perioperative stroke and transient ischemic attack rates were 3% for PTFE, versus 12% for HP (P =.047). The operative mortality rate for PTFE was 0%, versus 2% for HP (P =.477). Five perioperative carotid thromboses were noted in patients undergoing HP patching, versus none in patients undergoing PTFE patching (P =.07). After 1 month of follow-up, 2% of patients in the PTFE group had a 50% or more restenosis, versus 12% of patients in the HP group (P =.013). The mean operative time for PTFE patching was 119 minutes, versus 113 minutes for HP patching (P =.081). The mean hemostasis time was significantly higher for PTFE patching than for HP patching, 14.4 versus 3.4 minutes (P <.001).

CONCLUSION

CEA with HP patching had a higher incidence of perioperative strokes, carotid thrombosis, and 50% or more early restenosis than CEA with PTFE patching. However, the mean hemostasis time was higher for PTFE patching than for HP patching.

Prospective controlled study of carotid endarterectomy with hemashield patch: is it thrombogenic?

The use of patch angioplasty after carotid endarterectomy (CEA) has been shown to have superior results to CEA with primary closure. Polytetrafluoroethylene (PTFE) patches have been shown to have comparable results to autogenous vein patching; however, PTFE has the disadvantage of prolonged hemostasis time. Therefore, many surgeons are using collagen-impregnated Dacron patches (Hemashield[HP]). We believe this is the first prospective controlled study of the use of HP in carotid endarterectomy. This study included 144 consecutive patients who had 151 CEAs with HP. Postoperative duplex ultrasounds were done at 1 month and every 6 months thereafter. The mean follow-up was 12 months (range: 1-30 months). Indications for CEA included symptomatic (64%) and asymptomatic (36%) stenoses. The overall incidence of ipsilateral stroke was 5% (4% perioperative), with a combined TIA and stroke rate of 12%. Incidence of > or =50% recurrent stenosis was 21% (7% symptomatic TIA/stroke) and > or =80% recurrent stenosis was 9%. Kaplan-Meier analysis showed that at 1 year and 2.5 years freedom from > or =50% recurrent stenosis was 78% and 57%, respectively, freedom from > or =80% recurrent stenosis was 92% and 77%, respectively, and a stroke-free survival rate of 94% and 72%, respectively. Women had a 22% and men a 14% recurrent stenosis rate (p=0.04). There was no correlation between other specific risk factors and recurrent stenosis except for hypertension (33% vs 12%, p=0.003). The authors concluded that CEA with HP had a higher incidence of recurrent stenosis (21%), and a higher perioperative stroke rate (4%) after a mean follow-up of 12 months than previously reported using PTFE or saphenous vein patching (2% and 9% recurrent stenosis rates, respectively, and 1% and 0% perioperative stroke rates, respectively after a mean follow-up of 30 months). This raises the question as to whether this patch is thrombogenic in this location. Therefore, a randomized controlled trial comparing this patch with other patches (PTFE or vein) is warranted.

The effect of differing rates and injection sites on the amount of protamine delivered before detection of hemodynamic alterations in dogs

OBJECTIVES

To determine the effect of the route and rate of protamine administration on the amount of protamine that could be delivered before a hemodynamic reaction occurred in dogs.

STUDY DESIGN

Prospective randomized experimental study.

ANIMALS

Twenty adult mixed-breed dogs weighing 25.1+/-2.5 kg.

METHODS

Before vascular surgery, the dogs were heparinized to reach an activated clotting time (ACT) of 300 seconds. After completion of the vascular surgery, protamine was administered intravenously until a hemodynamic reaction was recorded. The 4 groups of dogs were given protamine at 5 mg/min (slow) or 10 mg/min (fast) via the cephalic or the jugular veins. Systemic and pulmonary arterial pressures, central venous pressure (CVP), and pulmonary arterial occlusion pressure (PAOP) were recorded before and after protamine administration. The dose of protamine was recorded when a reaction occurred, which was defined as mean arterial pressure (MAP) <60 mm Hg or mean pulmonary arterial pressure (MPAP) >20 mm Hg or more than double the baseline value.

RESULTS

Significant decreases in systolic arterial pressure (SAP), MAP, and diastolic arterial pressure (DAP) and significant increases in systolic (SPAP), mean (MPAP), and diastolic (DPAP) pulmonary arterial pressures were recorded after protamine administration. The cephalic slow group had significantly fewer protamine reactions than other groups (chi-square = 8.57, P = .03, df = 3). Significantly more protamine could be delivered from the cephalic vein (52.5+/-14.5 mg) compared with the jugular vein (37.6+/-16 mg) before a reaction occurred (P = .048).

CONCLUSION

The rate of administration did not have an effect on the amount of protamine delivered. Adverse reactions were minimized when protamine was administered via the cephalic vein at a slow rate.

CLINICAL RELEVANCE

We would recommend delivering protamine after cardiopulmonary bypass or vascular surgery through a peripheral venous route.

Lipid uptake across the wall of an expanded polytetrafluoroethylene vascular graft

Previous studies have shown that vascular grafts were prone to inducing an atherosclerosis-like phenomenon, thus possibly jeopardizing their performance. Furthermore, lipid retention, observed in most synthetic arterial prostheses explanted from humans, appears to have an important role in the progression of this atherosclerotic process, therefore hindering the healing process and neo-intima formation of these synthetic conduits. The current study examined lipid concentration profiles across prosthesis membranes exposed to lipid dispersion under various transmural pressures, flow rates, and durations of exposure. It was demonstrated that the lipids rapidly permeated the prosthesis membrane, as lipid advection increased to a maximum, then steadily decreased until the membrane became completely impermeable to the fluid. The concentration of lipids within the grafts was monitored using FT-IR microspectroscopy, then correlated as a function of time in order to evaluate the mass transfer coefficients and lipid saturation concentration. Lipid sorption, as a function of time, was described by a mechanism taking into account two first-order kinetic models. The lipids were first rapidly adsorbed onto the Teflon(R), potentially influenced by the strong affinity of these lipids for the highly hydrophobic polytetrafluoroethylene polymer. This affinity then enhanced the germination of the lipid deposits that filled in the prosthesis wall. For lipid retention as a function of the transmural pressure and flow rate, no clear tendency was established.

Immunohistochemical analysis of vascular prostheses implanted with the left ventricular assist system

BACKGROUND

Dacron vascular prostheses are associated with thromboembolic complications and inflammatory responses; impregnation with bovine collagen reportedly stimulates additional inflammatory/immunologic complications. The Novacor (Baxter Healthcare Corp., Oakland, CA, USA) left ventricular assist system uses Dacron inflow and collagen-impregnated Dacron outflow prostheses.

METHODS

Explanted inflow and outflow prostheses were evaluated for inflammatory/immunologic, hemostatic, anticoagulant, and fibrinolytic pathways. Non-implanted prostheses immersed in whole blood or plasma were used as controls.

RESULTS

Immunoglobulins and complement components were observed in all prostheses with activated macrophages being present only in implanted prostheses. Antithrombin III was observed in all prostheses whereas fibrin, tissue plasminogen activator, and alpha-2 plasmin inhibitor were present only in implanted prostheses. Endothelial and smooth muscle cells associated with vascular structures containing collagen type IV and laminin were observed solely in implanted prostheses.

CONCLUSION

An inflammatory response occurs and key components of hemostatic, anticoagulant, and fibrinolytic pathways are present within implanted prostheses. These processes are accompanied by endothelial and smooth muscle cell infiltration which appear to lay the foundation for neovessel development.

In vivo biocompatibility and degradation studies of polyhydroxyoctanoate in the rat: a new sealant for the polyester arterial prosthesis

The present study examined the biocompatibility and degradation properties of poly (beta-hydroxy octanoate) (PHO) as an impregnation substrate on arterial prostheses. PHO-impregnated polyester grafts sterilized by ethylene oxide (EO) or gamma (gamma) radiation, and polyester Dacron(R) prostheses impregnated with fluoropolymer, gelatin, or albumin were implanted subcutaneously in rats for periods ranging from 2 to 180 days. The biocompatibility was assessed by quantifying the alkaline and acid phosphatase secretion while performing histological studies at the tissue/prosthesis interface. The degradation was determined by chemical analysis of the EO and gamma-sterilized PHO after implantation using differential scanning calorimetry (DSC), wide angle x-ray diffraction (WAXD), and size exclusion chromatography (SEC). Alkaline phosphatase activity by the sterilized PHO and by the gelatin and albumin grafts was significantly elevated early after implantation in contrast to that of the Dacron and fluoropolymer grafts that occurred later, at 7 and 5 days, respectively The peak of acid phosphatase activity for all of the grafts occurred between 5 and 10 days postimplantation, with the gamma-sterilized PHO grafts recording the greatest activity. Histological study revealed that the tissue incorporation into the graft wall was earlier and more complete for the Dacron and fluoropolymer grafts after 6 months than for the gelatin and albumin grafts, because the latter induced important inflammatory reactions during the resorption of the cross-linked protein substrates. The EO and gamma-sterilized PHO grafts exhibited a similar healing sequence characterized by the development of a collagenous tissue surrounding the prostheses. However, no infiltration of tissue into the graft wall was observed after 6 months, mainly because of the presence of the PHO. Degradation of the EO and gamma-sterilized PHO occurred preferentially by a hydrolytic mechanism as shown by a 30% molecular weight decrease after 6 months. In conclusion, PHO showed good biocompatibility in terms of enzyme activity and tissue reaction. Degradation was a slow, in vivo process controlled primarily by a random hydrolytic reaction and by a local enzymatic attack by macrophages and giant cells.

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.

Succinylated collagen crosslinked by thermal treatment for coating vascular prostheses

Vascular prostheses coated with collagen carefully prepared to avoid contamination were tested to see if it could induce endothelial cell lining throughout the graft surface in a natural way. The collagen fibers were succinylated. Hydrogel produced with the succinylated collagen was used for the sealant to reduce the amount of solid substance. To avoid contamination and the side effects of chemical reagents, the collagen thermally crosslinked under sterile conditions. A suspension of the collagen fibers was enmeshed in the interstices of Dacron fibers of fabric prostheses, which were then thermally crosslinked at 130 degrees C for 20 h. The prostheses were porous when the collagen fiber network was dry. Under wet conditions, however, the water permeability of the grafts was reduced to 0.1 ml/min from the 1,250 ml/min of the original prostheses. Three weeks after implantation in the abdominal aortas of dogs, 81.2 +/- 11% of the luminal surface was macroscopically thrombus free, and 56 +/- 14% was endothelialized. More than 95% of the coated collagen had been absorbed. Numerous fibroblasts had migrated into the graft walls, and capillary blood vessels had infiltrated the inside of the graft walls without foreign body reaction. In the controls, thrombus free areas averaged 9.0 +/- 5%, and endothelialized areas averaged 5.2 +/- 4%. Many giant cells, plasma cells, and lymphocytes had migrated into the graft walls, but no fibroblasts. These results suggest that rapid endothelialization is possible when clean collagen is used.

The Dialine II graft: a new collagen-impregnated warp-knitted polyester arterial prosthesis

The Dialine graft, a new prototype of knitted vascular prosthesis that uses a different brand of polyester fibers as an alternative to Dacron fibers, has been shown to offer excellent in vitro physical performance and in vivo healing. Although it still requires preclotting, the Dialine prosthesis was made impervious by impregnation of bovine type I collagen cross-linked with vapors of formalin. The purpose of the present investigation was to compare the in vitro physical characteristics of the Dialine II graft with those of the collagen-impregnated Hemashield graft. In addition, we studied the healing performance as a thoracoabdominal bypass in dogs for prescheduled periods of implantation ranging from 4 hours to 6 months. In vitro, the bursting strength, resistance to dilatation, and suture retention strength properties of the Dialine II prosthesis were all shown to exceed those of the Hemashield control graft. In the first weeks after implantation, the Dialine II grafts induced a discrete inflammatory response, as shown by the constant leukocyte counts observed both before implantation and when the animals were killed, as well as by the histologic observation of a few inflammatory cells in contact with the collagen. Consequently, the Dialine II grafts showed a slow rate of bioresorption of cross-linked collagen. At 1 month, a thin internal collagenous capsule was present at both anastomoses, laying over the original collagen coating. At 3 and 6 months, areas of thrombotic deposits and endothelialized areas were observed on the luminal surface. Because results of early clinical trials have been highly satisfactory, this prosthesis may be recommended for use without restriction as a medium- and large-diameter blood conduit.

Implant site influence on arterial prosthesis healing: a comparative study with a triple implantation model in the same dog

PURPOSE

The purpose of this study was to develop a cost-effective canine graft healing model that gives information on various implant sites and controls for variable factors between graft locations and between animals and to compare the influence of implant site (retropleural, retroperitoneal, and subcutaneous areas) on arterial graft healing in the same subject under such controlled study conditions.

METHODS

Five mongrel dogs were studied for 8 weeks, and one was studied for 3 years. Each received three porous Dacron grafts during the same surgery: a carotid-femoral bypass (C-FB) and interposition grafts in the descending thoracic aorta and abdominal aorta. To produce comparable shear stress calibers of the C-FB and abdominal aorta grafts were 2 mm less than those of the descending thoracic aorta, and a distal arterio-venous fistula was created to further increase the C-FB flow. For comparable blood aggregation status platelet aggregation was preevaluated and adjusted with antiplatelet agents. Graft flow surfaces were assessed for thrombus-free surface and endothelial-like cell coverage scores. Tissue samples were studied with hematoxylin-eosin, factor VIII/ von Willebrand factor, smooth muscle alpha-actin staining, and scanning electron microscopy and transmission electron microscopy.

RESULTS

All grafts were patent. Shear stress for the three grafts and platelet aggregation among the study subjects were comparable. Healing of descending thoracic aorta and abdominal aorta grafts was similar, but C-FB healing was slow, incomplete, and uneven, with a high incidence of seroma. Eight-week and 3-year results were comparable.

CONCLUSIONS

This model gives broad healing information about the areas where grafts are often implanted in humans. Eight weeks appears to be a sufficient period to reflect basic and general healing characteristics. Grafts heal better in the retropleural and retroperitoneal areas than in the subcutaneous tissues.

Biological response to Bard Clamshell Septal Occluders in the canine heart

BACKGROUND

The Clamshell Septal Occluder has been used to close various congenital heart defects. The purpose of this study was to evaluate the long-term biological response to this device after placement in the canine heart. Previous in vivo studies with device placement were limited to 60 days.

METHODS AND RESULTS

An atrial septal defect was created in dogs by blade septostomy followed by balloon dilation. Both old and new (redesigned) devices were placed. Angiographic follow-up was performed at 1, 3, and 6 months and 1 and 2 years after device placement with groups of dogs euthanitized at the same intervals. Gross and microscopic assessment was done on the explanted devices. The implants were covered at least 50% by neointima at 1 month and covered completely by 3 months. There was no thrombus formation. Areas of focal hemorrhage were evident at 1 month and were not present at 3 months. The fibrous capsule that covered the device became more densely organized and neovascularized by 2 years. A focal foreign body reaction at the device-tissue interface persisted for 2 years. There were no arm fractures with either the old or new devices in these dogs.

CONCLUSIONS

The Bard Clamshell Septal Occluder is well tolerated in the canine heart for at least 2 years and elicits a normal healing process.

An albumin-coated polyester arterial graft: in vivo assessment of biocompatibility and healing characteristics

The albumin-coated vascular graft (ACG) and its uncoated polyester substrate, the Vascular II (V-II), were evaluated in terms of biocompatibility and biofunctionality using two in vivo animal studies. Biocompatibility and immunoreactivity were assessed by implanting intraperitoneally in the rat small segments of the ACG and the V-II graft and harvesting them with their surrounding tissue 3d, 1, 2 and 4 weeks later. Cytofluorometric determination of total T cells (CD3), the ratio of CD4/CD8 subsets and the percentage of IL-2 receptor-positive T cells in the peripheral blood has revealed that no significant difference in any of the T cell populations was found between the ACG and the V-II graft. The cellular reactivity of the ACG in terms of acid phosphatase activity at the implant side was significantly greater at 3 d but not at longer periods. Biofunctionality was evaluated by implanting both grafts as a thoracoabdominal vascular bypass in dogs for 11 different periods ranging from 4 h to 6 months. The rate of albumin resorption was such that traces were still present at 1 month, but no longer observable at 2 months. Tissue incorporation into the graft wall was earlier for the V-II (2 weeks) than for the ACG (4 weeks), which showed complete encapsulation, tissue incorporation and endothelialization after 2 months in vivo. Only small differences were observed between both grafts in terms of platelet and fibrin uptake on the luminal surface. The prostacyclin/thromboxane A2 ratio increased to a level higher that 1.0 aorta within 1 month for the V-II and 4 months for the ACG. In conclusion, the Bard ACG has demonstrated excellent biocompatibility in terms of blood T cell behaviour and acid phosphatase activity at the implant site. Finally, its healing response is equivalent to that of the uncoated Dacron prosthesis once the albumin coating has been resorbed.

Histologic observation of continuity of transmural microvessels between the perigraft vessels and flow surface microostia in a porous vascular prosthesis

To ascertain the histologic relationship between flow surface microostia and perigraft vessels in the healing of a porous vascular prosthesis, a series of careful histologic examinations were carried out on a preclotted, knitted Dacron graft, 8 mm in diameter and 7 cm long, after implantation in the canine infrarenal abdominal aorta for 3 months. Four adjacent longitudinal tissue blocks were taken from the middle for evaluation by means of light microscopy, scanning electron microscopy, transmission electron microscopy, and immunocytochemical staining, and the remainder of the specimen was stained with silver nitrate to allow visualization of microostia and cell borders on the flow surface. Following identification of two microostia adjacent to the area where samples had been taken for general healing evaluation, a 3 x 8 mm full-thickness block containing the microostia was embedded in glycol methacrylate and stained with hematoxylin and eosin. Of 240 serial sections cut from this block, 80 were prepared and examined. Silver staining revealed 42 microostia on the flow surface. Light, scanning, and transmission electron microscopy with endothelial factor VIII/von Willebrand factor stain confirmed a single layer of endothelial cells on the flow surface, and beneath was a well-organized neointima containing fusiform cells confirmed as smooth muscle by alpha-actin stain. Light microscopy of the serial sections revealed transmural microvessels, lined with endothelium, extending continuously between the flow surface ostia and the perigraft vessels in this porous vascular prosthesis.

Effect of differential shear stress on platelet aggregation, surface thrombosis, and endothelialization of bilateral carotid-femoral grafts in the dog

PURPOSE

The purpose of this study was to determine the effects of increased shear stress on the aggregability of platelets as they traverse a long, small-caliber (6 mm) Dacron graft in the dog and on the surface thrombosis and endothelialization of such a graft.

METHODS

Each of nine dogs received bilateral carotid-femoral artery grafts, approximately 75 cm long, for 3 months; one graft of each pair had a distal femoral arteriovenous fistula to produce a higher shear rate than the contralateral graft. Platelet aggregation scores were determined on blood withdrawn from the external jugular vein and from the proximal and distal ends of the grafts in each animal. Graft flow rates, which were used in the computation of shear stress, and luminal pressure gradients through grafts were measured during surgery and specimen retrieval. Specimens were studied with light microscopy after hematoxylin and eosin and immunocytochemical staining and by scanning electron and transmission electron microscopy to evaluate the nature, composition, and thickness of the flow surface lining, as well as the transmural healing.

RESULTS

Two high-shear stress and two low-shear stress grafts occluded unilaterally; five dogs had bilaterally patent grafts, allowing comparative analyses. All subjects had low platelet aggregability with aspirin. Platelet aggregation scores taken from proximal and distal ends of the grafts were not significantly different. The high-shear stress grafts had significantly more endothelial-like cell coverage (p < 0.0371) than the low-shear stress grafts, less flow-surface thrombus (p < 0.0056), and a thinner surface lining (p < 0.0029), on both the neointima and pseudointima.

CONCLUSIONS

In subjects with low platelet aggregation scores, long Dacron grafts do not elevate platelet aggregability of blood flowing through them. High-shear stress grafts have less flow surface thrombus, more endothelialization, and a thinner surface lining than do low-shear stress grafts.

Carbodiimide cross-linked gelatin: a new coating for porous polyester arterial prostheses

The performance of a polyester arterial prosthesis impregnated with gelatin and cross-linked with carbodiimide (Uni-graft) was compared with its porous parent graft (Protegraft) using a canine thoraco-abdominal bypass model. The grafts were investigated in terms of their handling characteristics, imperviousness at implantation, surface thrombogenicity and healing behaviour. Prostheses 30 cm in length were implanted for the following periods: 4, 24 and 48 h, 1, 2 and 4 weeks, 2, 3, 4, 5 and 6 months. Both types of graft had good handling characteristics. The ready-to-use impregnated graft provided satisfactory haemostasis at implantation with no blood permeating through the wall after flow was restored. Both grafts exhibited low surface thrombogenicity, as determined by the uptake of labelled fibrin and platelets, and the healing sequence of the impregnated graft after resorption of the gelatin was equivalent to that of the preclotted control. Biodegradation of the gelatin was complete within 1 month of implantation with the subsequent development of a collagenous internal capsule at both anastomoses. Endothelial cells were observed between 4 and 6 months, but were confined to small islets distributed along the luminal surface. The prostacyclin/thromboxane A2 (PGI2/TXA2) ratio, which gives an indication of the level of endothelial cell activity, was greater than 1.0 after 1 week of implantation for the control graft. For the impregnated graft it reached 1.0 only after 3 months of implantation, but remained above 1.0 for periods of up to 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Sealing of a fabric vascular prosthesis with autologous adipose tissue: a preliminary report of its clinical application

A new method of sealing fabric vascular prostheses with autologous adipose tissue was clinically applied as an alternative to preclotting with fresh blood. Thirty-six patients with peripheral arterial occlusive disease were implanted with highly porous fabric prostheses. The prostheses were prepared by sealing the fabric pores with autologous adipose tissue that had been chopped up into small pieces and enmeshed in the fabric by forceful injection of the tissue suspension through a syringe. There was no complication related to the sealed graft such as graft bleeding after implantation. In-hospital mortality occurred in 4 patients: 1 case each of pneumonia, pulmonary infarction, sepsis, and acute myocardial infarction. During the period of 274 +/- 190 days, 3 prostheses were found to be occluded. All the other grafts were patent. The overall patency rate was 91.4%. Postoperative angiography revealed neither intimal thickening at the anastomotic sites nor irregularity of the prosthetic surface. The method proved safe and useful for implantation of smaller caliber artificial grafts.

Proof of fallout endothelialization of impervious Dacron grafts in the aorta and inferior vena cava of the dog

PURPOSE

The purpose of this study was to prove directly whether cells from the blood stream contribute to endothelialization of isolated, impervious Dacron vascular grafts in the dog.

METHODS

We designed an 18 cm, three-component graft with two parallel central Dacron limbs; one was made impervious with silicone rubber, and the other was preclotted. This model was implanted in the canine descending thoracic aorta with 30 microns polytetrafluoroethylene grafts anastomosed at each end. An 8 cm, three-component graft completely coated with silicone rubber was implanted in the canine abdominal aorta and inferior vena cava. Implant periods ranged from 4 to 12 weeks. Flow surfaces were studied by use of stereomicroscopy after being stained with silver nitrate, and by use of scanning and transmission electron microscopy, the inner wall and flow surface were studied by light microscopy after hematoxylin-eosin and immunocytochemical staining (the latter for endothelial and smooth muscle cells), and the full wall was studied by light microscopy after hematoxylin-eosin staining.

RESULTS

Effective prevention of pannus and transmural ingrowth into the impervious central test grafts was achieved, and scattered islands of endothelial cells were conclusively demonstrated on flow surfaces in each of the three implant sites 4 weeks after implantation. In the descending thoracic aorta, where these grafts were also implanted for 8 and 12 weeks, alpha-actin-positive cells and microvessels were found beneath some of the endothelial islands.

CONCLUSION

Fallout endothelialization of Dacron vascular grafts occurs in both the arterial and venous systems of the dog.

Effectiveness of fragmented autologous adipose tissue as a sealer of porous textile grafts: effect on endothelial development

PURPOSE

This study is designed to develop a sealing method for fabric vascular prosthesis with chopped tissue fragments.

METHODS

A highly porous fabric vascular prosthesis was invaginated, and a suspension of chopped autologous adipose connective tissue fragments was injected repeatedly until the pores were enmeshed with the fragments. Small tissue fragments oozed out from and firmly anchored within the interstices of the fabric, which made the outer surface smooth. The graft was then invaginated to bring the smooth surface into the luminal side.

RESULTS

No blood leakage was observed in an extracorporeal in vivo shunt load test with heparin (total 1400 IU/kg, actinomycin > 1500), whereas a continuous bleeding was seen in a preclotted control graft (400 IU/kg, actinomycin 657 +/- 341). The sealed in a preclotted control graft (400 IU/kg, actinomycin 657 +/- 341). The sealed grafts were implanted in the descending thoracic aorta of 40 dogs, and an equal number of control grafts was used. The grafts were removed at selected time intervals up to 738 days. No bleeding was observed with the sealed grafts, and a thin layer of neointima was observed at 30 postoperative days. Eight (20%) of the control dogs bled to death within 24 hours of implantation. The neointima in the control animals extended from the anastomotic sites slowly with complete healing observed at 217 postoperative days.

CONCLUSIONS

The autologous adipose tissue fragments could reliably seal the highly porous fabric prosthesis while allowing rapid and complete neointima healing in dogs.

Unusual inflammatory responses around a collagen-impregnated vascular prosthesis

A collagen-impregnated graft, called Hemashield, has been used clinically; however, some complications such as pyrexia, fluid accumulation, and unusual scar formation around the graft have been reported. To understand the cause of these problems, the graft was examined both in vivo and in vitro. Endotoxin and (1-3)beta-D-glucan were detected in the extract from Hemashield by special quantitative methods called Toxicolor and Endospecy. In an animal study, the grafts were implanted in the thoracic descending aorta of 9 dogs and were designed to explant at 2 weeks. Macroscopic evaluation of the explants showed that the graft had no infection, but fluid accumulation was found in the pleural cavity and around the graft-like seroma. Microscopical observations revealed that neither fibroblasts nor capillary blood vessels had infiltrated in the adventitial side of the graft, but numerous plasma cells, lymphocytes, and macrophages were noticed. The impregnated collagen was partially absorbed. These results indicate that the graft had some contaminants which contained a certain amount of endotoxin and (1-3)beta-D-glucan, resulting in noninfective inflammatory responses around the graft.