Heparin coating of vascular prostheses reduces thromboemboli

Sustained Thromboresistant Bioactivity with Reduced Intimal Hyperplasia of Heparin-Bonded Polytetrafluoroethylene Propaten Graft in a Chronic Canine Femoral Artery Bypass Model

BACKGROUND

Bypass graft thrombosis remains a significant mode of failure in prosthetic graft revascularization. The purpose of this investigation was to evaluate the long-term thromboresistant effect of heparin-bonded expanded polytetrafluoroethylene (ePTFE) graft using Carmeda BioActive Surface technology in a canine model.

METHODS

Bilateral femorofemoral artery bypass grafts with ePTFE grafts were performed in 25 adult grayhound dogs. In each animal, a heparin-bonded ePTFE graft (Propaten, WL Gore) was placed on one side, whereas a control nonheparin graft was placed on the contralateral side. The graft patency was assessed at 1, 6, 12, 18, and 24 months (n = 5 per group) following the bypass. Heparin bioactivity of the graft material was analyzed. The effect of intimal hyperplasia was also assessed.

RESULTS

All bypass grafts were patent at 1 month. Significantly greater patency rates were noted in the Propaten group compared to the control group at 12, 18, and 24 months, which were 84%, 80%, and 80% vs. 55%, 35%, and 20%, respectively (P < 0.02). There was a significant reduction in the anastomotic neointimal area and neointimal cell proliferation in Propaten grafts compared with control grafts at all groups between 6 and 24 months (P < 0.05). Heparin bioactivity as measured by antithrombin binding assay was demonstrated in the Propaten graft between 1 and 24 months. Mean heparin activities on Propaten grafts ranged from 26.3 ± 6.4 pmol/cm² to 18.4 ± 8.7 pmol/cm² between 1 and 24 months, which were significantly greater than the control group (P < 0.001). Differences between mean heparin activities of explanted Propaten graft samples at the various time points were nonsignificant (P > 0.05).

CONCLUSIONS

Heparin-bonded ePTFE graft provides a thromboresistant surface and reduced anastomotic intimal hyperplasia at 2 years. The stable heparin bioactivity of the Propaten graft confers an advantage in long-term graft patency.

Comparison of propaten heparin-bonded vascular graft with distal anastomotic patch versus autogenous saphenous vein graft in tibial artery bypass

Introduction

Heparin-bonded expanded polytetrafluoroethylene grafts (Propaten, WL Gore, Flagstaff, AZ, USA) have been shown to have superior patency compared to standard prosthetic grafts in leg bypass. This study analyzed the outcomes of Propaten grafts with distal anastomotic patch versus autogenous saphenous vein grafts in tibial artery bypass.

Methods

A retrospective analysis of prospective collected data was performed during a recent 15-year period. Sixty-two Propaten bypass grafts with distal anastomotic patch (Propaten group) were compared with 46 saphenous vein graft (vein group). Pertinent clinical variables including graft patency and limb salvage were analyzed.

Results

Both groups had similar clinical risk factors, bypass indications, and target vessel for tibial artery anastomoses. Decreased trends of operative time (196 ± 34 min vs. 287 ± 65 min, p = 0.07) and length of hospital stay (5.2 ± 2.3 days vs. 7.5 ± 3.6, p = 0.08) were noted in the Propaten group compared to the vein group. Similar primary patency rates were noted at four years between the Propaten and vein groups (85%, 71%, 64%, and 57%, vs. 87%, 78%, 67%, and 61% respectively; p = 0.97). Both groups had comparable secondary patency rates yearly in four years (the Propaten group: 84%, 76%, 74%, and 67%, respectively; the vein group: 88%, 79%, 76%, and 72%, respectively; p = 0.94). The limb salvage rates were equivalent between the Propaten and vein group at four years (84% vs. 92%, p = 0.89). Multivariate analysis showed active tobacco usage and poor run-off score as predictors for graft occlusion.

Conclusions

Propaten grafts with distal anastomotic patch have similar clinical outcomes compared to the saphenous vein graft in tibial artery bypass. Our data support the use of Propaten graft with distal anastomotic patch as a viable conduit of choice in patients undergoing tibial artery bypass.

Surface modification of poly(ether sulfone) membrane with a synthesized negatively charged copolymer

In this study, we provide a new method to modify poly(ether sulfone) (PES) membrane with good biocompatibility, for which diazotized PES (PES-N2(+)) membrane is covalently coated by a negatively charged copolymer of sodium sulfonated poly(styrene-alt-maleic anhydride) (NaSPS-MA). First, aminated PES (PES-NH2) is synthesized by nitro reduction reaction of nitro-PES (PES-NO2), and then blends with pristine PES to prepare PES/PES-NH2 membrane; then the membrane is treated with NaNO2 aqueous solution at acid condition; after surface diazo reaction, surface positively charged PES/PES-N2(+) membrane is prepared. Second, poly(styrene-alt-maleic anhydride) (PS-alt-MA) is synthesized, then sulfonated and treated by sodium hydroxide solution to obtain sodium sulfonated (PS-alt-MA) (NaSPS-MA). Finally, the negatively charged NaSPS-MA copolymer is coated onto the surface positively charged PES/PES-N2(+) membrane via electrostatic interaction; after UV-cross-linking, the linkage between the PES-N2(+) and NaSPS-MA changes to a covalent bond. The surface-modified PES membrane is characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) analyses, and surface zeta potential analyses. The modified membrane exhibits good hemocompatibility and cytocompatibility, and the improved biocompatibility might have resulted from the existence of the hydrophilic groups (sodium carboxylate (-COONa) and sodium sulfonate (-SO3Na)). Moreover, the stability of the modified membrane is also investigated. The results indicated that the modified PES membrane using negatively charged copolymers had a lot of potential in blood purification fields and bioartificial liver supports for a long time.

Toward High-Performance Coatings for Biomedical Devices: Study on Plasma-Deposited Fluorocarbon Films and Ageing in PBS

High performance coatings tailored to medical devices represent a recognised approach to modulate surface properties. Plasma-deposited fluorocarbon films have been proposed as a potential stent coating. Previous studies have shown promising adhesion properties: the 35 nm-thick film sustained plastic deformation up to 25% such as induced during the clinical implantation. In this study, the compositional and morphological changes of plasma-deposited fluorocarbon films were examined during ageing in a pseudo-physiological medium, a phosphate buffer solution (PBS), by angle-resolved XPS, FT-IR data and AFM images. The evolution of the ageing process is discussed: defluorination and crosslinking yielded an oxidized protective top layer onto the films, which showed further degradation.

Interventional Atrial Septal Defect Closure Using a Totally Bioresorbable Occluder Matrix

OBJECTIVES

We sought to test the hypothesis that interventional atrial septal defect (ASD) closure can be performed safely and effectively using a bioresorbable occluder matrix.

BACKGROUND

The ideal septal occluder scaffold should promote the healthiest and most complete healing response while eventually facilitating the full resorption of the material and leaving "native" tissue behind, thus minimizing the potential for future complications from chronic foreign body and maintaining the possibility for later unobstructed transseptal access to the left atrium.

METHODS

The STARFlex occluders (NMT Medical Inc., Boston, Massachusetts) were modified by substituting the conventional polyester fabric for a bioengineered, acellular type-I collagen matrix derived from porcine submucosa with a heparin-coated surface (BioSTAR occluder, NMT Medical Inc.). Comparative transcatheter closure of ASDs was performed in young sheep (n = 36). Gross pathology and histopathology were obtained after follow-up periods ranging from 7 days to 2 years.

RESULTS

The STARFlex (control) devices were encapsulated time-dependently by ingrown fibrous tissue. Histology showed a mild but chronically persisting foreign body reaction. By contrast, BioSTAR devices exhibited a mild-to-moderate transient cellular immune response. Heparin coating of the BioSTAR surface improved the biocompatibility of the device by reducing surface thrombogencity. A remodeling process of the collagen scaffold, starting after 30 days in vivo, resulted in the full replacement of the matrix by host tissue after 2 years of follow-up.

CONCLUSIONS

The BioSTAR device is the first septal occluder with a totally bioresorbable matrix that is fully replaced by host tissue during the healing process. The promising results of this study support testing of the BioSTAR device in clinical trials.

Immobilization of polysaccharides on a fluorinated silicon surface

A self-assembled monolayer (SAM) of fluoroalkyl silane (FAS) was deposited on a silicon surface by chemical vapor deposition (CVD) at room temperature under 1.01x10(5)Pa nitrogen. Using this new approach, the quality and reproducibility of the SAM are better than those prepared either in solution or by vapor phase deposition, and the deposition process is simpler. In this modified CVD process, the silane monomers, instead of the oligomeric species, are the primary reactants. Full coverage of the silicon surface by FAS molecules was achieved within 5 min. Heparin and hyaluronan, two naturally occurring biocompatible polysaccharides, were successfully covalently attached on the FAS SAM/Si surface by photo-immobilization. Atomic force microscopy (AFM) revealed the morphologic changes after the immobilization of heparin and hyaluronan, and X-ray photoelectron spectroscopy (XPS) confirmed the change in chemical compositions. Such combination of coatings is expected to enhance the stability and biocompatibility of the base material.

In vitro biological performances of phosphorylcholine-grafted ePTFE prostheses through RFGD plasma techniques

Arterial prostheses made of microporous Teflon (ePTFE) are currently used in vascular surgery as bypasses for small and medium vessels. However, several clinical complications, such as thrombosis, frequently occur in these prostheses when implanted in humans. In this work, an original strategy was developed to improve the hemocompatibility of ePTFE prostheses, based on glow-discharge surface modification followed by chemical grafting of phosphorylcholine, known for its hemocompatible properties. This procedure leads to a covalent attachment of the molecules, therefore preventing their removal by shear stress induced by blood flow at the implant wall. The improvement of the blood compatibility properties of the modified ePTFE arterial prostheses have been investigated by in vitro tests such as thromboelastography, neutrophil adsorption, platelet aggregation, and cell cultures. These in vitro tests put in evidence that thrombogenicity index, platelet aggregation, and neutrophil adhesion were decreased by the molecule grafted on the prostheses. Moreover, the cell growth on the surface of the PRC-grafted prostheses was greatly enhanced in comparison to the virgin prosthesis. Based on these results, it could be concluded that PRC grafting on ePTFE prostheses permit to improve in vitro hemocompatibility and biocompatibility in comparison with their virgin counterpart.

In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 degrees C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.

Improvements in GORE-TEX vascular graft performance by Carmeda BioActive surface heparin immobilization

OBJECTIVES

a performance improvement in small-diameter bypass grafts remains a clinical objective. The purpose of the present investigation was to evaluate the potential of enhancing the thromboresistance of ePTFE grafts using a bioactive heparinized graft luminal surface in a canine model.

MATERIAL AND METHODS

this study investigated the utility of heparin immobilization onto expanded polytetrafluoroethylene using Carmeda BioActive Surface technology (CBAS-ePTFE) as a means of improving vascular graft thromboresistance. Graft luminal surfaces were covered uniformly with the stably bound, end-point immobilized heparin.

RESULTS

acute canine (5 greyhounds) interposition experiments comparing CBAS-ePTFE grafts to control ePTFE grafts showed that CBAS-ePTFE grafts remained patent and had significantly greater thrombus-free luminal surface (p<0.05). In a chronic canine (16 greyhounds) interposition experiment, significantly improved patency (p<0.05) was observed with CBAS-ePTFE grafts compared to controls. Long-term in vivo heparin bioactivity was demonstrated on CBAS-ePTFE grafts explanted between 1 and 12 weeks. On all CBAS-ePTFE grafts, heparin activity levels ranged from 15-25pmol/cm(2) and did not differ significantly (p>0.05).

DISCUSSION

these results support the conclusion that a stable, CBAS-ePTFE surface provides improved thromboresistance and improved patency in canine interposition models. Maintenance of heparin catalytic activity on the graft surface in vivo likely contributes to this outcome and holds promise for the utility of this graft surface for clinical applications.

An assessment of covalent grafting of RGD peptides to the surface of a compliant poly(carbonate-urea)urethane vascular conduit versus conventional biological coatings: its role in enhancing cellular retention

The aim of sodding prosthetic grafts with endothelial cells (EC) is to establish a functioning antithrombogenic monolayer of EC. Application of basement membrane proteins improves EC adherence on ePTFE grafts. Their addition to a biodurable compliant poly(carbonate-urea)urethane graft (CPU) was studied with respect to EC adherence. Preclot, fibronectin, gelatin, and collagen were coated onto CPU. RGD peptide, heparin, and both RGD and heparin were chemically bonded to CPU. Human umbilical vein EC (HUVEC) labeled with 111-Indium oxine were sodded (1.8 x 10(6) EC/cm(2)) onto native and the modified CPU. The grafts were washed after 90 min and EC retention determined. The experiments were repeated six times. EC retention on native CPU was 1.0 +/- 0.2 x 10(5) EC/cm(2). The application of preclot, fibronectin, gelatin, and collagen did not improve EC retention, which was 0.8 +/- 0.1, 0.4 +/- 0.1, 0.3 +/- 0.08, and 0.5 +/- 0.2 x 10(5) EC/cm(2), respectively. Bonding RGD, heparin, and both RGD and heparin significantly improved EC retention to 1.9 +/- 0.6, 1.7 +/- 0.5, and 2.6 +/- 0.6 x 10(5) EC/cm(2), respectively (p < 0.01). Bonding of RGD, heparin, and both RGD and heparin accelerates and enhances EC retention onto CPU. Simple coating of basement membrane proteins confers no advantage over native CPU.

Immobilization of human thrombomodulin to expanded polytetrafluoroethylene

BACKGROUND

The success of synthetic grafts for vascular reconstruction remains limited by thrombosis and intimal hyperplasia. In addition to the well-described antithrombotic effects of thrombomodulin, we have demonstrated that recombinant human thrombomodulin (rTM) inhibits arterial smooth muscle cell proliferation induced by thrombin. This study investigated the binding of functional rTM to expanded polytetrafluoroethylene (ePTFE).

METHODS

Immobilization of rTM was achieved by either (1) a direct coating or (2) a two-step binding process using a water-soluble condensing cross-reaction agent EDAC to modify the ePTFE surface followed by binding of rTM. The samples were then subjected to a tangential shaken wash. The evidence of bound rTM was evaluated by both morphologic and functional studies.

RESULTS

SEM, BSI, and X-ray microanalysis identified that the two-step binding method resulted in significantly greater binding of rTM molecules to ePTFE pre- and post a 7-h wash than the direct coating method. With the two-step binding method rTM ranging from 0.25 to 12.5 microg immobilized to ePTFE-activated protein C (APC) in a concentration-dependent manner by more than 6000-fold compared to the buffer control (P < 0.04) and 50-85% more than direct coating (P < 0.004). With direct coating, the level of APC dropped significantly to near 40% of the preshaken level at 2 h and diminished to 26% at 7 h. Whereas, the level of APC with the two-step binding stabilized at 51 and 49% after being shaken 2 and 7 h, respectively.

CONCLUSION

Functional rTM binding to ePTFE was significantly improved with a new two-step binding method.