Expanded Polytetrafluorethylene Research Articles

Autologous Costal Cartilage With Expanded Polytetrafluorethylene (ePTFE) Implants for the Treatment of Nasal Deformity After Unilateral Cleft Lip Repair

To repair and reconstruct the secondary nasal deformity after unilateral cleft lip repair, we used autologous costal cartilage and expanded polytetrafluorethylene (ePTFE) to get a better nasal shape. Nineteen patients with nasal deformity after unilateral cleft lip repair were treated from July 2018 to July 2021. During the operation, autologous costal cartilage was carved and formed and then implanted into the nasal tip and nasal columella, while the back of the nose was raised with ePTFE. Nineteen cases were followed up for 6 to 30 months. No transplanted cartilage and swelling were exposed or discharged. The appearance was good, and the patients were satisfied. Autologous costal cartilage combined with ePTFE is an ideal treatment for nasal deformity after cleft lip repair.

EPTFE reinforced, sulfonated aromatic polymer membranes enable durable, high-temperature operable PEMFCs

SummarySulfonated polyphenylene (SPP)-based ionomers have been developed for electrochemical applications in recent years due to their inherent thermal and chemical stability. However, the difficult synthesis, limited solubility, and rigid backbone obstructs their progress. Herein, a new monomer, 3,3″-dichloro-2′,3′,5′,6′-tetrafluoro-1,1':4′,1″-terphenyl (TP-f) with high polymerization reactivity was designed and polymerized with sulfonated phenylene monomer to prepare SPP-based ionomers (SPP-TP-f) with high ion exchange capacity up to 4.5 mequiv g−1. The resulting flexible membranes were more proton conductive than Nafion (state-of-the-art proton exchange membrane) even at 120°C and 20% RH. Unlike typical SPP ionomers, SPP-TP-f 5.1 was soluble in ethanol and thus, could be reinforced with double expanded polytetrafluorethylene thin layers to obtain SPP-TP-f 5.1/DPTFE membrane. SPP-TP-f 5.1/DPTFE showed superior fuel cell performance to that of Nafion, in particular, at low humidity (30% RH, > 100°C) and reasonable durability under the severe accelerated conditions combining OCV hold and humidity cycling tests.

Surgical Results of the Use of Expanded Polytetrafluor Ethylene as an Adhesion Inhibitory Membrane in Anastomosis Surgery for Total Peripheral Nerve Cut

The fibrotic tissue that appears following nerve damage can prevent axonal regeneration. Expanded polytetrafluor ethylene (ePTFE) is a synthetic polymer with antiadhesive properties and a safe history of use in neurosurgery. The aim of this study was to use ePTFE to prevent postsurgical adhesions in patients undergoing anastomosis surgery and report the results. Between January 2014 and May 2018, six patients with primary and secondary peripheral nerve cuts underwent anastomosis (one with allograft and five with autografts). The anastomotic region was wrapped with ePTFE to form a barrier. The mean follow-up period was 28 months (minimum 3 months, maximum 4 years). In three of six patients whose nerve integrity was lost due to various reasons, there was an improvement in electrophysiological recordings. The allograft was used in a patient with peroneal nerve injury; the sural nerve was used as a graft in other patients. In three patients, the defect was more than 4 cm. Early surgery and defect size are important factors to consider when treating peripheral nerve anastomosis. Development of intraneural and perineural adhesions postsurgery can be problematic. ePTFE is an inert polymer that prevents adhesions from forming after anastomosis surgery.

Heparin-bonded expanded polytetrafluorethylene grafts in hemodialysis access.

When options for autologous arteriovenous (AV) fistulas have been fully exhausted, AV grafts continue to play an important role in access creation for hemodialysis, offering long-term hemodialysis access that is a better alternative to central vein catheters. The drawbacks of AV grafts are their poor patency, infection and higher cost. Their main advantages are that they are widely available, are easy to create, and mature early. In the context of the "Fistula First" initiative, many patients with low quality veins suffer from fistula failure and non-maturation resulting in prolonged catheter days that would otherwise be prevented by initial creation of an AV graft. Endeavors to improve graft patency include administration of pharmacological agents, changing graft configuration, altering graft biology, and altering the graft surface. In this review, the current status of heparin-bonded AV grafts for hemodialysis is discussed.

A Comparison of Femorocrural Bypasses Performed with Modified Heparin-Bonded Expanded Polytetrafluorethylene Grafts and Those with Great Saphenous Vein Grafts to Treat Critical Limb Ischemia

The purpose of this study was to evaluate our results involving femorocrural bypasses by comparing heparin-bonded expanded polytetrafluoroethylene (HePTFE) graft (Propaten) modified with handmade distal compliant HePTFE cuffs (mHePTFE graft) to great saphenous vein (GSV) graft. A retrospective study involving 74 femorocrural bypasses performed from January 2010 to May 2013 at a single institution was carried out. The indication for revascularization was critical limb ischemia (Rutherford stages 4-6. Forty-one femorocrural bypasses were created in 37 patients with unavailable GSVs using modified ringed HePTFE grafts with a handmade distal radial stretch HePTFE cuff to reduce the mismatch compliance between the graft and the artery wall. Thirty-three femorocrural bypasses were created using a reversed GSV graft. The results were analyzed in terms of primary graft patency, limb salvage, and patient survival using univariate (Kaplan-Meier curves and log-rank test) and multivariate (Cox regression) analyses. The 2 groups were statistically comparable for main risk factors, Rutherford stage, and target artery for distal anastomoses. The run-off anatomy did not significantly differ between the prosthetic and the vein bypass group. The cumulative 30-day operative mortality rate was 2.9%. At 1, 2, and 3 years, the 2 groups were equivalent in primary graft patency (the mHePTFE group: 84%, 80%, and 70%, respectively; the GSV group: 84%,71%, and 71%, respectively; P = 0.93) and were also equivalent in terms of limb salvage (the mHePTFE group: 87%, 87%, and 76%, respectively; the GSV group: 84%, 75%, and 75%, respectively; P = 0.78) and patient survival (the mHePTFE group: 87%, 75%, and 75%, respectively; the GSV group: 87%, 73%, and 65%, respectively; P = 0.86). At Cox regression analysis, only postoperative treatment with warfarin therapy compared with double antiplatelet therapy was independently associated with poorer primary patency (P = 0.003; 95% confidence interval, 1.80-18.00; hazard ratio, 5.7). In this retrospective study regarding femorocrural bypasses, the mHePTFE grafts had 1-, 2-, and 3-year primary patency and limb salvage results which were not significantly different from those in the GSV grafts. Additional randomized data and larger studies are needed to confirm these results.

A Retrospective Cohort Comparison of Expanded Polytetrafluorethylene to Autologous Vein for Vascular Reconstruction in Modern Combat Casualty Care

Reconstruction of vascular injury often requires use of a conduit, either autologous vein (AV) or expanded polytetrafluorethylene (ePTFE). The most common anatomic locations for and durability of ePTFE as an adjunct to vascular repair in the combat setting are unknown. The objectives of this study were to characterize the anatomic locations of use of ePTFE during the wars in Afghanistan and Iraq and to compare its effectiveness to AV. US service personnel undergoing vascular repair (2002-2012) were identified. Patients in whom ePTFE was used as an interposition conduit (n=25) were matched with similar patients who received AV (n=24) reconstruction. Injury and operative factors were assessed, and freedom from graft-related complication was quantified using Kaplan-Meier log-rank test. There was no difference between ePTFE and AV with regard to age, injury severity, or mangled extremity severity score. Follow-up for the ePTFE and AV groups was 71 and 62months, respectively. In the cohort there was an apparent but not significantly greater freedom from graft-related complication for AV compared with ePTFE (65% vs. 17%; P=0.13). In the carotid, subclavian, and axillary artery positions, ePTFE performed equal to AV with no apparent difference in freedom from graft-related complications (P=0.90). However, in the periphery, AV demonstrated greater 8-year freedom from graft-related complication than ePTFE (77% vs. 31%, P=0.044). AV is a more durable conduit than ePTFE in repair of wartime extremity vascular injury, whereas ePTFE is effective and durable in the carotid, subclavian, and axillary locations.

A Fractal Model for Heat Transfer Through Expanded Polytetrafluorethylene Membrane

Heat transfer through an expanded polytetrafluorethylene (ePTFE) membrane used in functional clothing is a key process in the design of membrane-based clothing. A fractal model for the thermal conductivity of an ePTFE membrane is demonstrated by considering the specific microstructure within the ePTFE membrane with the “nodes-fibrils” model. The prediction results from the proposed model are compared with calculated values from another theoretical model and are also validated by experimental data. The present model is more suitable for evaluating the effective thermal conductivity of a biaxial stretching PTFE membrane.

Preliminary comparative study of small amplitude helical and conventional ePTFE arteriovenous shunts in pigs.

Intimal hyperplasia (IH), which causes occlusion of arterial bypass grafts and arteriovenous (A-V) shunts, develops preferentially in low wall shear, or stagnation, regions. Arterial geometry is commonly three-dimensional, generating swirling flows, the characteristics of which include in-plane mixing and inhibition of stagnation. Clinical arterial bypass grafts are commonly two-dimensional, favouring extremes of wall shear. We have developed small amplitude helical technology (SwirlGraft) devices and shown them to generate physiological-type swirling flows. Expanded polytetrafluorethylene (ePTFE) grafts, although widely used as A-V shunts for renal dialysis access, are prone to thrombosis and IH. In a small preliminary study in pigs, we have implanted SwirlGraft ePTFE carotid artery-to-jugular vein shunts on one side and conventional ePTFE carotid artery-to-jugular vein shunts contralaterally. There was consistently less thrombosis and IH in the SwirlGraft than conventional shunts. At eight weeks (two animals), the differences were marked, with virtually no disease in the SwirlGraft devices and occlusion of the conventional grafts by thrombosis and IH. The study had limitations, but the lesser pathology in the SwirlGraft devices is likely to have resulted from their geometry and the associated swirling flow. The results could have implications for vascular biology and prolongation of the patency of arterial bypass grafts and A-V shunts.

Epithelialization model of non-biological tissue replacement materials in vitro

Successful use of non-biologic implants in reconstructive head and neck surgery is dependent on tissue compatibility and epithelization. This is true not only for epithelial cells, but also for mesenchymatic cells. Therefore we tested several substrates with human fibroblasts or keratinocytes from the oral mucosa in cell culture. In tissue culture keratinocyte outgrowth from small mucosal flaps onto the surface was observed. Preparations were evaluated by histology and scanning electron microscopy. Cellulose-ester, polyvinylidene-difluoride and polyglactin developed monolayers of fibroblasts and keratinocytes in cell cultures. In tissue culture mucosal flaps showed good adherence to the surface of these materials and a fine outgrowth of keratinocytes. Expanded polytetrafluor-ethylene (ePTFE) was partially covered by a layer of fibroblasts and keratinocytes in cell culture, but cell adherence was not sufficient. In tissue culture the mucosal flaps failed to attach on ePTFE. These results illustrate that the mesenchymatic and epithelial component of cell and tissue cultures show different qualities of cellular adherence and growth on the surface of non-biologic implants. We propose our method for the development of an in-vitro model for the epithelization of non-biologic implantation materials.

Thrombomodulin Activity of Fat-Derived Microvascular Endothelial Cells Seeded on Expanded Polytetrafluorethylene

Lining the luminal surface of prosthetic vascular grafts with endothelial cells (cell seeding) will lower its thrombogenicity. Commonly used macrovascular human adult endothelial cells (HAEC) require in vitro cultivation before large enough numbers are obtained to cover grafts confluently. Fat-derived microvascular endothelial cells (MVEC) prove to be a good alternative as they can be harvested in much larger numbers while showing similar antithrombotic and fibrinolytic characteristics. An important anticoagulant function of macrovascular endothelial cells is due to the activity of thrombomodulin (TM) on their surface. In this study, the presence and functional activity of TM on fat-derived microvascular cells used in cell seeding was investigated. The expression and localization of TM on MVEC was studied using immunohistochemistry. Functional activity of TM on MVEC was measured by the generation of activated protein C (APC) and was compared to human umbilical vein endothelial cells (HUVEC). TM activity was studied in MVEC seeded on expanded polytetrafluorethylene (ePTFE) vascular prostheses and compared to blank prostheses. We found that TM was expressed on the surface of MVEC, both in vivo and vitro. TM-dependent generation of APC differed significantly between MVEC and HUVEC (3.98 ± 1.2 vs. 3.0 ± 0.7 nM, respectively). After seeding MVEC on vascular prostheses, TM activity did not change. APC generation was significantly higher on MVEC-seeded vascular grafts compared to blank grafts (4.0 ± 0.7 vs. 1.7 ± 0.5 nM, respectively). We conclude that TM is present and highly active on cultured MVEC. When seeded on ePTFE, MVEC retain the possibility to inhibit thrombin coagulant activity and to activate protein C. Therefore, since MVEC are readily available, the anticoagulant properties demonstrated here indicate that this cell type is suitable for cell seeding of vascular prostheses.

Characterization of biomedical polymer-adherent macrophages: interleukin 1 generation and scanning electron microscopy studies

Macrophage activation following attachment to biomedical polymers was studied using two systems of analysis. Supematants generated by human peripheral blood monocytes cultured on the surface of several different biomedical polymers were evaluated for the presence of the secreted regulatory protein interleukin 1(IL1). In addition, each cell-polymer culture surface was subjected to scanning electron microscopy for gross morphological evaluation. Results indicate that, although all materials were efficient in the attachment and activation of cells, the panel of polymers showed a differential capacity in attachment and activation of monocytes. Dacron® and polyethylene surfaces had a greater density of cells showing morphology indicative of activation, corresponding to elevated levels of IL1 in these cultures. Biomer and polydimethylsiloxane surfaces showed fewer activated cells and had lower IL1 levels in culture. Expanded polytetrafluorethylene resulted in intermediate levels of IL1 and attached cells showing activated morphology.

The use of long synthetic microvascular grafts in dogs with a view to clinical application.

Five centimetres long segments of 3 mm internal diameter synthetic expanded polytetrafluorethylene (E-PTFE) vascular graft (Gore-Tex) were implanted into the femoral arteries, proximal to the origin of the saphenous artery, of 10 mongrel dogs. In five cases saphenous island flaps were raised and the femoral artery was ligated distal to the saphenous origin so that a low flow system was created through the graft. In 10 femoral vessels the Gore-Tex graft was inserted without raising a flap and the distal femoral artery not ligated so that the graft acted purely as a conduit for blood flow to the distal limb. This created a high flow rate model compared to the reduced flow in the former group. In the first group flap survival was evaluated daily by direct observation of the flaps and graft patency was assessed every 48 h by means of Doppler ultrasound. None of these flaps survived longer then 48 h. In the second group, graft patency was monitored every 48 h with Doppler ultrasound and exploration of Gore-Tex grafts at 3 weeks showed that all had thrombosed.

Significance of the inner-surface structure of small-caliber prosthetic blood vessels in relation to the development, presence, and fate of a neo-intima. A morphological evaluation.

Microvascular prostheses with three different inner surface structures were examined morphologically 1-18 months after implantation to evaluate the presence and structure of the neo-intima. Fibrous polyurethane tubes (length: 5-10 mm, inner diameter: 1.5 mm) were implanted in the rat abdominal aorta in group A with a fibrillar inner structure (pore sizes 20-50 microns), and in group B the inner fibrillar structure was coated with an impermeable continuous silicon sheet. Expanded polytetrafluorethylene vascular prostheses (length: 40 mm, inner diameter: 4 mm) were implanted in the dog carotid artery (group C). The specimens were examined by light microscopy and scanning electron microscopy. A continuous and permanent neointima was only found in the prostheses with the porous fibrillar inner structure (group A). The thin new lining sheet was well attached to the prosthetic wall by cellular protrusions. In the silicon-coated prostheses (group B) also a continuous neo-intima had developed which, however, was irregular, thicker, and not anchored to the prosthetic wall. The expanded polytetrafluorethylene prostheses (group C) showed also after 1 year only incomplete lining with a neo-intima. Fresh blood cell deposits could be observed in the unlined prosthetic wall. It is concluded that a continuous lining of vascular grafts with a thin neo-intima is only achieved if the cells invading the prostheses from the anastomotic areas can anchor their cytoplasmic protrusions onto an appropriately structured inner surface. If these anchoring facilities are not provided, the unattached neo-intima will thicken, interfering with the patency of these microvascular prostheses, or fragments of the neo-intima or alternatively mural thrombi may constantly strip off and embolize.