ePTFE Grafts Research Articles

Heparin-bonded expanded polytetrafluoroethylene vascular graft for femoropopliteal and femorocrural bypass grafting: 1-year results

Several prosthetic materials have been used for femoropopliteal bypass grafting in patients with peripheral vascular disease in whom a venous bypass is not possible. Expanded polytetrafluoroethylene (ePTFE) is the most commonly used, but patency results have not always equaled those achieved with vein, especially in below-knee reconstructions. This study assessed the performance of a new heparin-bonded ePTFE vascular graft that was designed to provide resistance to thrombosis and thereby decrease early graft failures and possibly prolong patency. From June 2002 to June 2003, 86 patients (62 men and 24 women; mean age, 70 years; 99 diseased limbs) were enrolled prospectively in a nonrandomized, multicenter study of the heparin-bonded ePTFE graft. Fifty-five above-knee and 44 below-knee (including 21 femorocrural) procedures were performed. Follow-up evaluations consisted of clinical examinations, ultrasonographic studies, and distal pulse assessments. Patency and limb salvage rates were assessed by using life-table analyses. All grafts were patent immediately after implantation. There were no graft infections or episodes of prolonged anastomotic bleeding. During the 1-year follow-up, 10 patients died, 15 grafts occluded, and 5 major amputations were performed. The overall primary and secondary 1-year patency rates were 82% and 97%, respectively. The limb salvage rate in patients with critical limb ischemia (n = 41) was 87%. Primary patency rates according to bypass type were 84%, 81%, and 74% for above-knee femoropopliteal, below-knee femoropopliteal, and femorocrural bypasses, respectively; the corresponding secondary patency rates were 96%, 100%, and 100%. In this study, the heparin-bonded ePTFE graft provided promising early patency and limb salvage results, with no device-related complications, in patients with occlusive vascular disease. Longer-term and randomized studies are warranted to determine whether this graft provides results superior to those achieved with other prostheses, especially in patients at increased risk of early graft failure, such as those undergoing below-knee bypass and those with poor run-off or advanced vascular disease.

A single center, retrospective study on a cuffed expanded polutetrafluoroethylene graft for hemodialysis vascular access

Background: Development of venous outflow stenosis has been a major obstacle in maintaining the patency of dialysis vascular grafts. In the current study, we retrospectively analyzed the long-term results (>1 year) of cuffed ePTFE and non-cuffed (standard) ePTFE grafts placed for hemodialysis access. Methods: A total of 42 patients who underwent placement of either cuffed (n=23) or non-cuffed (n=19) ePTFE grafts were retrospectively analyzed. There were no significant differences between the two groups in their age, gender, cause of ESRD and the number of previous vascular access surgeries.

Letter Regarding Article by Rotmans et al, “In Vivo Cell Seeding With Anti-CD34 Antibodies Successfully Accelerates Endothelialization but Stimulates Intimal Hyperplasia in Porcine Arteriovenous Expanded Polytetrafluoroethylene Grafts”

To the Editor: Rapid (re)endothelialization of autologous and synthetic vascular grafts is regarded as a key element in reducing the risk of acute thrombosis and, by limiting adverse vessel wall remodeling, which includes intimal hyperplasia, preserving long-term patency. Rotmans et al1 (and the accompanying editorial2) challenge this tenet of vascular biology in their report of human anti-CD34 antibody–coated polytetrafluoroethylene (PTFE) grafts in a porcine AV fistula model. Rapid “endothelialization” of grafts is described, which, rather than improving functional outcome, was associated with significantly increased intimal hyperplasia at the venous anastomosis. The authors conclude that future studies will need to address a putative deficiency in the functional capability of captured endothelial progenitor cells (EPCs), highlighting approaches based on the use of regulatory proteins or alternative cell combinations. In our opinion, the data do not support these conclusions. The graft endoluminal cells were inadequately characterized with lectin (a surface antigen shared by several blood-borne …

The Prophylactic Efficacy of Rifampicin-Soaked Graft in Combination with Systemic Vancomycin in the Prevention of Prosthetic Vascular Graft Infection: An Experimental Study

To investigate the prophylactic efficacy of systemic, topical, or combined antibiotic usage in the prevention of late prosthetic vascular graft infection caused by methicillin-resistant Staphylococcus epidermidis (MRSE) and the differential adherence of S. epidermidis to Dacron and ePTFE grafts in a rat model. Graft infections were established in the back subcutaneous tissue of 120 adult male Wistar rats by implantation of 1-cm(2) Dacron/ePTFE prosthesis followed by topical inoculation with 2 x 10(7) CFU of clinical isolate of MRSE. Each of the series included one group with no graft contamination and no antibiotic prophylaxis (uncontaminated control), one contaminated group that did not receive any antibiotic prophylaxis (untreated control), one contaminated group in which perioperative intraperitoneal prophylaxis with vancomycin (10 mg/kg) was administered, two contaminated groups that received rifampicin-soaked (5 mg/1 ml) or vancomycin-soaked (1 mg/1 ml) grafts, and one contaminated group that received a combination of rifampicin-soaked (5 mg/1 ml) graft with perioperative intraperitoneal vancomycin prophylaxis (10 mg/kg). The grafts were removed sterilely 7 days after implantation and evaluated by using sonication and quantitative blood agar culture. MRSE had significantly greater adherence to Dacron than ePTFE grafts in the untreated contaminated groups (P < 0.001). Rifampicin had better efficacy than vancomycin in topical application, but the difference was not statistically significant (P > 0.05). Intraperitoneal vancomycin showed a significantly higher efficacy than topical vancomycin or rifampicin (P < 0.001). The best results were provided by a combination of intraperitoneal vancomycin in rifampicin-soaked graft groups (P < 0.001). The combination of rifampicin and intraperitoneal vancomycin seems to be the best choice for the prophylaxis of late prosthetic vascular graft infections caused by MRSE.

How to perform an arteriovenous fistula

Endogenous arteriovenous fistula (AVF), first described in 1966, remains the optimal vascular access for chronic dialysis. An internal AVF avoids the disadvantages of an external appliance, such as frequent septic and clotting problems. In spite of surgical innovations, such as autogenous vein interpositional grafts, bovine heterografts, expanded polytetrafluoroethylene (ePTFE) grafts and permanent indwelling silastic central venous catheters, the Brescia–Cimino fistula has remained the best access for maintenance haemodialysis because of its low incidence of complications and high long-term patency rate. The 1- and 3-year cumulative patency rates are 85–90% and 60–85% respectively.

Mechanical properties of bacterial cellulose and interactions with smooth muscle cells

Tissue engineered blood vessels (TEBV) represent an attractive approach for overcoming reconstructive problems associated with vascular diseases by providing small calibre vascular grafts. The aim of this study has been to evaluate a novel biomaterial, bacterial cellulose (BC), as a potential scaffold for TEBV. The morphology of the BC pellicle grown in static culture was investigated with SEM. Mechanical properties of BC were measured in Krebs solution and compared with the properties of porcine carotid arteries and ePTFE grafts. Attachment, proliferation and ingrowth of human smooth muscle cells (SMC) on the BC were analysed in vitro. The BC pellicle had an asymmetric structure composed of a fine network of nanofibrils similar to a collagen network. The shape of the stress–strain response of BC is reminiscent of the stress-strain response of the carotid artery, most probably due to the similarity in architecture of the nanofibrill networks. SMC adhered to and proliferated on the BC pellicle; an ingrowth of up to 40 μm was seen after 2 weeks of culture. BC exhibit attractive properties for use in future TEBV.

An in vitro study of cryopreserved and fresh human arteries: a comparison with ePTFE prostheses and human arteries studied non-invasively in vivo

The surgical options in arterial reconstruction are: the use of autologous arteries; autologous veins; or expanded polytetrafluoroethylene (ePTFE) grafts. However, the development of intimal hyperplasia when using veins or ePTFE grafts has been associated with graft failure. Since autologous arteries are not always available, the use of cryopreserved arteries has to be considered. The aims of this study were: (a) to compare the viscoelastic properties of stored cryopreserved arteries and fresh arteries by in vitro analysis; and (b) to compare the viscoelastic properties of arteries measured non-invasively in normotensive patients, with fresh arteries, cryopreserved arteries, and ePTFE segments. The viscoelastic studies were performed in normotensive patients using stress–strain analysis with non-invasive measurement of pressure and diameter in the common carotid artery, and in vitro measurements of pressure and diameter in arteries and prostheses. The in vitro studies showed that the elastic modulus (E), viscous modulus ( η), Stiffness Index (SI), Peterson modulus (Ep), and the pulse wave velocity (PWV) values for human cryopreserved carotid arteries were similar to the values obtained non-invasively in normotensive subjects ( P > 0.05) and to human fresh vessels ( P > 0.05). In vitro, the SI, Ep, PWV, and E values of ePTFE were significantly higher than the observed values in subjects and with fresh and cryopreserved arteries ( P < 0.05); on the other hand the ePTFE η values were the lowest ( P < 0.05). We concluded that cryopreserved arteries have similar viscoelastic properties to those obtained in vivo in the arteries of normotensive subjects and in vitro in fresh arteries. Consequently, we conclude that the cryopreservation procedure does not modify the mechanical properties of the arterial wall.

Rapamycin-coated expanded polytetrafluoroethylene bypass grafts exhibit decreased anastomotic neointimal hyperplasia in a porcine model

We tested the hypothesis that rapamycin coated onto, and eluted from, expanded polytetrafluoroethylene (ePTFE) grafts would diminish neointimal hyperplasia in a porcine model. Rapamycin (also called sirolimus) was coated onto the luminal surface of 6-mm-internal-diameter thin-walled ePTFE grafts by using an adhesive polymer that allows timed release of the drug. An adhesive polymer that allows timed release of rapamycin from ePTFE was developed with commercially available chemicals and applied on 6-mm ePTFE grafts. Graft integrity was characterized by scanning electron microscopy, and rapamycin levels were quantified by using high-performance liquid chromatography. Twenty-two mongrel pigs were randomized into three groups: untreated ePTFE (n = 6), adhesive-only coated ePTFE (n = 6), or adhesive- and rapamycin-coated ePTFE (n = 10). End-to-side unilateral aortoiliac bypasses were performed by using 6-mm-internal-diameter ePTFE grafts and standardized anastomotic lengths. Unilateral end-to-side aortoiliac ePTFE grafts (6-mm internal diameter) were inserted by using polypropylene sutures, 6-0 proximally and 7-0 distally; all anastomoses were 12 mm long. All animals received aspirin (325 mg orally) daily. All animals were given oral aspirin (325 mg) daily beginning on the day before surgery. At 28 days, the animals were killed, and the grafts were explanted in continuity with the adjacent aortic cuff and the outflow iliac artery. Variables compared between groups included graft patency, distal anastomotic length and cross-sectional narrowing, and intimal thickness at the arterial-graft junction indexed to the adjacent graft thickness. Microscopic analysis was performed with hematoxylin and eosin and Masson trichrome stains on paraffin sections. A pathologist blinded to experimental groups graded sections for collagen deposition, neointima formation, inflammatory cellular infiltrates, medial necrosis, and aneurysmal degeneration. All animals survived until they were killed without clinical evidence of limb ischemia or graft infection. Preplanned t tests in the context of one-way analysis of variance showed no difference in outcome measures between the untreated ePTFE and adhesive-only coated ePTFE groups; therefore, they were combined in further comparisons with the adhesive- and rapamycin-coated ePTFE group. The Rapamycine eluting expanded polytetrafluoroethylene group had longer anastomoses (85.6% vs 60.6% of the initial anastomotic length maintained; P < .0001) and less cross-sectional narrowing in the outflow graft (16.2% vs 28.5%; P = .0007) when compared with the other two groups by using two-tailed Student t tests. There was no evidence of medial necrosis or aneurysmal degeneration. All patent grafts had complete endothelialization on hematoxylin and eosin sections. Rapamycin was detectable and quantifiable in the arterial wall at 28 days after implantation. Rapamycin can be coated onto and eluted from ePTFE by using a nonionic polymer and a simple coating technique. At 4 weeks after implantation, the rapamycin-eluting ePTFE grafts demonstrate gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with non-drug-eluting ePTFE. Four weeks after implantation in a porcine model, rapamycin-eluting ePTFE grafts demonstrated gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with untreated and adhesive-only coated ePTFE grafts. Rapamycin-eluting ePTFE grafts decrease neointimal hyperplasia in a porcine model. Further studies are needed to evaluate whether patency will be improved. Rapamycin-eluting ePTFE grafts may allow the use of prosthetic grafts in situations in which autologous vein is unavailable and in which neointimal hyperplasia is pronounced, such as in small-diameter (<6-mm) vessels typical of infrapopliteal interventions.

Systemic and local antibiotic prophylaxis in the prevention of Staphylococcus epidermidisgraft infection

BackgroundThe aim of the study was to investigate the in vivo efficacy of local and systemic antibiotic prophylaxis in the prevention of Staphylococcus (S.) epidermidis graft infection in a rat model and to evaluate the bacterial adherence to frequently used prosthetic graft materials.MethodsGraft infections were established in the subcutaneous tissue of 120 male Wistar rats by implantation of Dacron/ePTFE grafts followed by topical inoculation with 2 × 107 CFUs of clinical isolate of methicillin-resistant S. epidermidis. Each of the graft series included a control group, one contaminated group that did not receive any antibiotic prophylaxis, two contaminated groups that received systemic prophylaxis with teicoplanin or levofloxacin and two contaminated groups that received teicoplanin-soaked or levofloxacin-soaked grafts. The grafts were removed 7 days after implantation and evaluated by quantitative culture.ResultsThere was significant bacterial growth inhibition in the groups given systemic or local prophylaxis (P < 0.05). Methicillin-resistant S. epidermidis had greater affinity to Dacron graft when compared with ePTFE graft in the untreated contaminated groups (P < 0.05).ConclusionThe study demonstrated that the usage of systemic or local prophylaxis and preference of ePTFE graft can be useful in reducing the risk of vascular graft infections caused by staphylococcal strains with high levels of resistance.

Carotid Artery Pseudoaneurysm Treated with an ePTFE-prosthesis

We report a case with a pseudoaneurysm of the common carotid artery treated by carotid aneurysmectomy. A 34-year-old male was admitted with a swelling on the left side of his neck. A duplex ultrasound showed a 2.5×1.5×1.5 cm pseudoaneurysm of the left common carotid artery, 1 cm caudal to the bifurcation. Twelve hours later the pseudoaneurysm had increased and an acute aneurysmectomy was performed. An 8 mm externally supported expanded polytetrafluoroethylene (ePTFE) graft was interpositioned. The patient was discharged 1 week after the surgery and 6 months after the operation he had recovered completely from a paresis of the left vocal cord. The reason for the pseudoaneurysm formation remains unclear as no bacterial, iatrogenic or traumatically aetiology was found.

Carotid Artery Pseudoaneurysm Treated with an ePTFE-prosthesis

We report a case with a pseudoaneurysm of the common carotid artery treated by carotid aneurysmectomy.A 34-year-old male was admitted with a swelling on the left side of his neck. A duplex ultrasound showed a 2.5×1.5×1.5cm pseudoaneurysm of the left common carotid artery, 1cm caudal to the bifurcation. Twelve hours later the pseudoaneurysm had increased and an acute aneurysmectomy was performed. An 8mm externally supported expanded polytetrafluoroethylene (ePTFE) graft was interpositioned. The patient was discharged 1 week after the surgery and 6 months after the operation he had recovered completely from a paresis of the left vocal cord. The reason for the pseudoaneurysm formation remains unclear as no bacterial, iatrogenic or traumatically aetiology was found.

PPS-PEG Surface Coating to Reduce Thrombogenicity of Small Diameter ePTFE Vascular Grafts

Patency failure of small vascular synthetic grafts is still a major problem for coronary and peripheral revascularization. Thus, three new surface coatings of small synthetic grafts were tested in an acute pig model to evaluate their thrombogenicity (extracorporeal arterio-venous shunt) and in a chronic rat model to evaluate the tissue reaction they induced (subcutaneous implantation). In five domestic pigs (25-30 kg) an extracorporeal femoro-femoral arterio-venous shunt model was used. The study protocol included first a non-heparinized perfusion sequence followed by graft perfusion after 10,000 UI iv heparin. Grafts were perfused for 3 and 9 minutes. The following coatings were tested on ePTFE grafts: poly-propylene sulphide (PPS)--poly-ethylene glycol (PEG) (wet and dry applications) as well as carbon. Two sets of control were used, one dry and one wet (vehicle only). After perfusion grafts were examined by scanning electron microscopy for semi-quantitative assessment (score 0-3) of cellular and microthrombi deposition. To assess tissue compatibility, pieces of each material were implanted subcutaneously in 16 Wistar rats. At 2, 4, 8, 12 weeks four animals each were sacrificed for semi-quantitative (score 0-3) histologic evaluation of tissue reaction. In the pig model, cellular deposition and microthrombi formation increased over time. In non- heparinized animals, the coatings did not improve the surface characteristics, since they did not prevent microthrombi formation and cellular deposition. In heparinized animals, thrombogenicity was lowest in coated grafts,especially in PPS -PEG dry (p<0.05), and highest in controls. Cell deposition was lowest in PPS-PEG dry, but this difference was not statistically significant vs.controls. In the rat model,no significant differences of the tissue reaction could be shown between materials. While all coatings failed to add any benefit for lowering tissue reaction, surface coating with PPS -PEG (dry application) reduced thrombogenicity significantly (in heparinized animals) and thus appears to be promising for improving graft patency of small synthetic vascular prostheses.

Carotid graft replacement: A durable option

Carotid artery bifurcation reconstruction after endarterectomy has been refined over the years. Methods including primary closure, patch closure, and eversion endarterectomy have been proven to be durable. However, there are patients who require more complicated reconstructions in primary or recurrent disease management. Carotid replacement with a prosthetic interposition graft is potentially a durable option to reconstruct an artery that is technically unsuitable for primary or patch closure. The charts of all carotid endarterectomies (n = 482) performed by the authors at our institution between January 1999 and December 2003 were retrospectively reviewed. Follow-up was performed in an Intersocietal Commission for the Accreditation of Vascular Laboratories-accredited vascular laboratory. Patients were divided into two main groups: carotid replacement with 6-mm expanded polytetrafluoroethylene (ePTFE) (REP) or standard endarterectomy (CEA) with or without patch closure. The decision for REP vs CEA (as well as the type of closure) was at the discretion of the surgeon according to an assessment of the end point, the distal internal carotid artery, and the quality and length of the endarterectomy segment. Interposition grafting with a 6-mm stretch of ePTFE from the transected common carotid to the transected internal carotid artery was performed in replacement reconstruction. The external carotid was ligated. Follow-up statistical analyses were performed with the Fisher exact test and analysis of variance for nominal values and t tests for continuous variables. Life table analyses were performed for patency and survival. Complete perioperative data were available for 478 of the 482 operations performed (including all REP cases) during the study. At least one duplex ultrasound scan in follow-up was documented in 84% (n = 402) of the patients. A total of 51 were in the REP group, and 427 received CEA (95.3% with patch closure). Preoperative demographics, preoperative symptoms, and degree of stenosis did not vary within the study groups. Three 30-day surgical deaths occurred. The perioperative stroke rate between groups was not statistically different (REP, 1/51 [1.9%]; CEA, 3/427 [0.70%]; P = .35). Long-term patency and stroke-free survival rates at 3 years exceeded 96% and did not vary significantly between groups. The presence of a patch in the CEA group had no influence on outcomes. Duplex follow-up scan averaged two studies for at least 14 months in each group. Significantly more REP cases were reoperative procedures. Carotid interposition reconstruction with an ePTFE graft is an acceptable alternative in cases in which the standard technique would be technically difficult or compromising to the endarterectomy closure. Carotid ePTFE interposition graft replacement seems to be safe and durable and to have no increased perioperative risk or altered intermediate-term outcomes.

In Vivo Cell Seeding With Anti-CD34 Antibodies Successfully Accelerates Endothelialization but Stimulates Intimal Hyperplasia in Porcine Arteriovenous Expanded Polytetrafluoroethylene Grafts

The patency of AV expanded polytetrafluoroethylene (ePTFE) grafts for hemodialysis is impaired by intimal hyperplasia (IH) at the venous outflow tract. The absence of a functional endothelial monolayer on the prosthetic grafts is an important stimulus for IH. In the present study, we evaluated the feasibility of capturing endothelial progenitor cells in vivo using anti-CD34 antibodies on ePTFE grafts to inhibit IH in porcine AV ePTFE grafts. In 11 pigs, anti-CD34-coated ePTFE grafts were implanted between the carotid artery and internal jugular vein. Bare ePTFE grafts were implanted at the contralateral side. After 3 (n=2) or 28 (n=9) days, the pigs were terminated, and the AV grafts were excised for histological analysis and SEM. At 3 and 28 days after implantation, 95% and 85% of the coated graft surface was covered by endothelial cells. In contrast, no cell coverage was observed in the bare graft at 3 days, whereas at 28 days, bare grafts were partly covered with endothelial cells (32%; P=0.04). Twenty-eight days after implantation, IH at the venous anastomosis was strongly increased in anti-CD34-coated grafts (5.96+/-1.9 mm2) compared with bare grafts (1.70+/-0.4 mm2; P=0.03). This increase in IH coincided with enhanced cellular proliferation at the venous anastomosis. Autoseeding with anti-CD34 antibodies results in rapid endothelialization within 72 hours. Despite persistent endothelial graft coverage, IH at the outflow tract is increased profoundly at 4 weeks after implantation. Further modifications are required to stimulate the protective effects of trapped endothelial cells.

The Threat of Adhesive Embolization: BioGlue Leaks Through Needle Holes in Aortic Tissue and Prosthetic Grafts

BioGlue Surgical Adhesive (CryoLife, Inc, Kennesaw, GA) is used to reinforce anastomoses during cardiovascular operations. Previous reports have raised concerns that adhesives may leak through suture-line needle holes and that resulting intraluminal glue may embolize. The purpose of this study was to determine if BioGlue leaks through anastomotic needle holes in aortic tissue and two common prosthetic graft materials. Polypropylene suture was used to create end-to-end anastomoses in gelatin-sealed woven polyester grafts (n = 45), expanded polytetrafluoroethylene (ePTFE) grafts (n = 45), and fresh porcine aortas (n = 45). An additional 45 anastomoses were created in ePTFE grafts using ePTFE sutures. The outer surface of each anastomosis was covered with BioGlue. Anastomoses underwent inspection with direct magnification or histology. BioGlue leaked through needle holes and into the lumen in 10% of anastomoses (18 of 180). Leaks were significantly more common in fresh aorta (10 of 45, 22%) than in prosthetic grafts (8 of 135, 6%; p = 0.003). Suture size did not significantly affect the incidence of leak. The use of ePTFE sutures did not eliminate BioGlue leakage. Prosthetic graft leaks created discreet round adhesive particles. In contrast, aortic tissue leaks resulted in thin, friable flakes of glue extending along the intimal surface. Aortic histology confirmed that BioGlue reached the vessel lumen via the suture channels. BioGlue leaked through the needle holes in fresh aortic tissue and prosthetic grafts. Intraluminal adhesive particles were easily dislodged, supporting concerns regarding embolization. The potential for adhesive embolization should be a factor when considering the relative risks and benefits of using BioGlue.

Comparison of Small-Intestinal Submucosa and Expanded Polytetrafluoroethylene as a Vascular Conduit in the Presence of Gram-Positive Contamination

As a vascular conduit, expanded polytetrafluoroethylene (ePTFE) is susceptible to graft infection with Gram-positive organisms. Biomaterials, such as porcine small-intestinal submucosa (SIS), have been successfully used clinically as tissue substitutes outside the vascular arena. In the present study, we compared a small-diameter conduit of SIS to ePTFE in the presence of Gram-positive contamination to evaluate infection resistance, incorporation and remodeling, morphometry, graft patency, and neointimal hyperplasia (NH) development. Adult male mongrel pigs were randomized to receive either SIS or ePTFE (3-cm length, 6-mm diameter) and further randomized to 1 of 3 groups: Control (no graft inoculation), Staphylococcus aureus, or mucin-producing S epidermidis (each graft inoculation with 10 colonies/mL). Pressure measurements were obtained proximal and distal to the graft to create the iliac/aorta pressure ratio. Morphometric analysis of the neointima and histopathologic examinations was performed. Other outcomes included weekly WBC counts, graft incorporation, and quantitative culture of explanted grafts. Eighteen animals were randomized. All grafts were patent throughout the 6-week study period. Infected SIS grafts had less NH and little change in their iliac/aorta indices compared with infected ePTFE grafts. Quantitative cultures at euthanasia demonstrated no growth in either SIS group compared with 1.7 x 10(4) colonies for ePTFE S aureus and 6 x 10(2) for ePTFE S epi (each P < 0.001). All SIS grafts were incorporated. Histology demonstrated remodeling into host artery with smooth muscle and capillary ingrowth in all SIS groups. Scanning electron micrography illustrated smooth and complete endothelialization of all SIS grafts. Compared with ePTFE, SIS induces host tissue remodeling, exhibits a decreased neointimal response to infection, and is resistant to bacterial colonization. SIS may provide a superior alternative to ePTFE as a vascular conduit for peripheral vascular surgery.

Vascular Tissue Regeneration of the Hybrid ePTFE Graft for Adult Patients

Vascular Tissue engineering has drawn high interest due to its high demand in its vascular graft applications. We tissue-engineered a hybrid vascular graft consisting of tissues layers and non-biodegradable ePTFE by in vitro cell culture. Tissue formation was obtained by culturing vascular smooth muscle cells on the biodegradable polylactide scaffolds on the ePTFE surfaces. The fabricated hybrid ePTFE graft consisted of three layers, i.e. two biodegradable polylactide layers and a non-biodegradable ePTFE layer. The biodegradable layer was fabricated to have a porous structure with 30-60 µm pore sizes. Connection of biodegradable layers and ePTFE was obtained by filtering the polylactide solution through the porous ePTFE wall. For a better tissue formation coating of gelatin was performed on the luminal polylactide scaffolds. The generated tissues replaced the biodegradable layers on both inside and outside surfaces of the ePTFE.

Study of Bone Marrow Derived Stem Cells and Gene Therapy for Engineering of Cardiovascular Grafts

Recent study shows that endothelial progenitor cells (EPCs) and gene therapy technologies are effective strategies in the inhibition of stenosis and thrombus formation and improving the patency rate of the vascular graft in vivo. In this study, rat EPCs were cultured from bone marrow, and plated in fibronectin-coated plates with EBM-2 medium. Bone marrow mesenchymal stem cells (MSCs) were cultured with alpha minimum essential medium ( -MEM). After two weeks, EPCs were immunohistochemically characterized using antibodies specific for endothelial cells. Retroviral vectors pMSCV-eNOS, pMSCV-tPA, pMSCV-LacZ and pMCSV-GFP were constructed. Retroviral particles were produced using packaging cell line 293T cells. Gene transfer was carried out by exposing cells to virus solution for 6 hours in the presence of 8µg/ml polybrene. For constructing vessels, MSCs and EPCs were seeded on fibronectin coated ePTFE graft in tissue culture condition for 2-4 weeks. The attachment and growth of cells were analyzed with scanning electron microscopy (SEM). Our data showed that the EPCs expressed VEGF, Lectin BS-1, RECA-1, indicating they are endothelial lineage. The concentrated retroviral particles showed many folds higher transduction efficiency to NIH 3T3 cells than the commercial reagent Fugene. SEM data showed dense attachment of MSCs on the graft surface. MSCs/EPCs co-culture gave much better cell coverage on the graft than culture of EPCs alone.

Dual Role of VEGF in Pretreated Experimental ePTFE Arterial Grafts

Lack of endothelialization and abnormal smooth muscle cell (SMC) growth adversely affect the outcome of vascular synthetic grafts. The aims of our study were to investigate how a coating of extracellular matrix (ECM) and vascular endothelial growth factor (VEGF) might affect the endothelialization rate, smooth muscle cells (SMC) proliferation, and myointimal hyperplasia in experimental arterial ePTFE grafts. In each of 30 male Lewis rats, a 1-cm-long ePTFE graft was inserted at the level of the abdominal aorta. Animals were randomized in five groups (six animals each): groups A and A1 received ePTFE grafts coated with a synthetic extracellular matrix (growth factor-reduced matrigel) containing VEGF; groups B and B1 received ePTFE grafts coated with synthetic ECM; and group C received ePTFE grafts alone. The grafts were explanted at 30 days from surgery for immunohistochemical analysis. Both endothelialization rate and myointimal hyperplasia were augmented in group A versus groups B and C, and these findings were statistically significant. SMC density resulted significantly higher in group A versus groups B and C, and this was associated with an altered expression of bFGF and TGFbeta. Pretreating ePTFE grafts with synthetic ECM and VEGF results in better endothelialization, but also in undesired higher SMC density and myointimal hyperplasia.

Swirling flow pattern in a non-planar model of an interposition vein cuff anastomosis

One of the main causes of long-term failure of ePTFE grafts is the development of anastomotic intimal hyperplasia which leads to graft thrombosis. Experimental studies with bypass grafts have shown an inverse relationship between mean wall shear stress and intimal hyperplasia. The geometry of the anastomosis has a strong influence on the flow pattern and wall shear stress distribution. The aim of this in vitro study was to investigate the influence of non-planarity in a model of a distal anastomosis with interposition vein cuff, an anastomosis configuration that is increasingly being used because of improved clinical results. Laser Doppler anemometer measurements were carried out in silicone rubber models of interposition vein cuff anastomoses with planar and non-planar inflow. The pulsatile flow waveforms were typical of those found in femoro-infrapopliteal bypass. Axial and radial velocities were measured in the proximal and distal outflow segments. As expected a symmetrical helical flow pattern (Dean flow) was evident in the planar model. The model with non-planar inflow, however, gave rise to swirling flow in both the distal and proximal artery outflow segments for during the systolic phase. In patients, the anastomosis is usually non-planar. Since the configuration depends in part upon the tunnelling of the graft, this may be altered to some extent. Non-planar anastomotic configurations induce a swirling flow pattern, which may normalise wall shear stress, thereby potentially reducing intimal hyperplasia.