The initial blood retention properties of arterial prostheses

Stent-Graft Fabrics Incorporating a Specific Corona Ready to Fenestrate

In situ fenestration of endovascular stent-grafts has become a mainstream bailout technique to treat complex emergent aneurysms while maintaining native anatomical visceral and aortic arch blood supplies. Fabric tearing from creating the in situ fenestration using balloon angioplasty may extend beyond the intended diameter over time. Further tearing may result from the physiologic pulsatile motion at the branching site. A resultant endoleak at the fenestrated sites in stent-grafts could ultimately lead to re-pressurization of the aortic sac and, eventually, rupture. In an attempt to address this challenge, plain woven fabrics were designed. They hold a specific corona surrounding a square-shaped cluster with a plain weave fabric structure, a 2/2 twill, or a honeycomb. The corona was designed to stop potential further tearing of the fabric caused by the initial balloon angioplasty and stent or later post-implantation motion. The cluster within the corona was designed with relatively loose fabric structures (plain weave, 2/2 twill weave, and honeycomb) to facilitate the laser fenestration. Two commercial devices, Anaconda (Vascutek, Terumo Aortic) and Zenith TX2 (Cook), were selected as controls for comparison against this new design. All the specimens were characterized by morphology, thickness, and water permeability. The results demonstrated that all specimens with a low thickness and water permeability satisfied the requirements for a stent graft material that would be low profile and resistant to endoleaks. The in situ fenestrations were performed on all fabrics utilizing an Excimer laser followed by balloon angioplasty. The fabrics were further observed by light microscopy and scanning electron microscopy. The dimension of the fenestrated apertures was smaller than the balloon's diameter. The tearing was effectively confined within the corona. The clinical acceptability of this concept deserves additional bench testing and animal experimentation.

A comparative study of bovine and porcine pericardium to highlight their potential advantages to manufacture percutaneous cardiovascular implants

Rationale:

Prosthetic heart valves designed to be implanted percutaneously must be loaded within delivery catheters whose diameter can be as low as 18 F (6 mm). This mandatory crimping of the devices may result in deleterious damages to the tissues used for valve manufacturing. As bovine and porcine pericardial tissue are currently given preference because of their excellent availability and traceability, a preliminary comparative study was undertaken to highlight their potential advantages.

Materials and methods:

Bovine and pericardium patches were compared morphologically (light microscopy, scanning electron microscopy and transmission electron microscopy). The acute thrombogenicity of both materials was measured in term of platelet uptake and observed by scanning electron microscopy, porcine intact and injured arteries being used as controls. The pericardium specimens were also subjected to uniaxial tensile tests to compare their respective mechanical characteristics.

Results:

Both pericardiums showed a layered architecture of collagen bundles presenting some interstitial cells. They displayed wavy crimps typical of an unloaded collagenous tissue. The collagen bundles were not bound together and the fibrils were parallel with characteristic periodicity patterns of cross striations. The mesothelial cells found in vivo on the serous surface were no longer present due to tissue processing, but the adjacent structure was far more compacted when compared to the fibrous side. The fibrinocollagenous surfaces were found to be more thrombogenic for both bovine and porcine tissues and the serous side of the porcine pericardium retained more platelets when compared to the bovine samples, making the acute thrombogenicity more important in the porcine pericardium.

Conclusion:

Both bovine and porcine pericardium used in cardiovascular implantology can be selected to manufacture percutaneous heart valves. The selection of one pericardium preferably to the other should deserve additional testing regarding the innocuousness of crimping when loaded in delivery catheters and the long-term durability after percutaneous deployment.

Fluoropassivation and gelatin sealing of polyester arterial prostheses to skip preclotting and constrain the chronic inflammatory response

Fluoropassivation and gelatin coating have been applied to polyethylene terephthalate (PET) vascular prosthesis to combine the advantages of both polytetrafluoroethylene (PTFE) and PET materials, and to eliminate the preclotting procedure. The morphological, chemical, physical, and mechanical properties of such prostheses were investigated and compared with its original model. Fluoropassivation introduced -OCF(3), -CF(3), and -CFCF(2)- structures onto the surface of the polyester fibers. However, the surface fluorine content was only 28-32% compared to the 66% in expanded PTFE (ePTFE) grafts. The fluoropassivation decreased the hydrophilicity, slightly increased the water permeability, and marginally lowered the melting point and the crystallinity of the PET fibers. After gelatin coating, the fluoropassivated and nonfluoropassivated prostheses showed similar surface morphology and chemistry. While gelatin coating eliminated preclotting, it also renders the prostheses slightly stiffer. The original prosthesis had the highest bursting strength (275 N), with the fluoropassivated and gelatin-sealed devices showing similar bursting strength between 210 and 230 N. Fluoropassivation and gelatin coating lowered the retention strength by 23 and 30% on average, respectively. In vitro enzymatic incubation had only marginal effect on the surface fluorine content of the nongelatin-sealed prostheses. However, the gelatin-sealed ones significantly lost their surface fluorine after in vitro enzymatic incubation (by 69-85%) or in vivo 6-month implantation (by 51-60%), showing the lability of the fluoropolymer layer under the hostile biological environment.

Impregnated polyester arterial prostheses: performance and prospects

Impregnated polyester arterial prostheses have gained wide acceptance by most vascular surgery teams, probably because these prostheses are easy to use, without any preclotting. We offer here a synthesis of the main studies that have appraised the experimental and clinical performance of these prostheses, and we delineate their major prospects.

Acute thrombogenicity of intact and injured natural blood conduits versus synthetic conduits: neutrophil, platelet, and fibrin(ogen) adsorption under various shear-rate conditions

We investigated the acute thrombogenicity of synthetic arterial prostheses compared to biological arterial surfaces in contact with flowing nonanticoagulated blood. The acute events following blood/surface interactions were quantified using 51Cr-platelet deposition, 111In-neutrophil adhesion, and 125I-fibrin(ogen) adsorption on expanded polytetrafluoroethylene (ePTFE) synthetic arterial surfaces (Goretex and Impra) and on intact and injured biological arterial surfaces in ex vivo superfusion flow chambers at low (424/sec) and high (3397/sec) shear rates for 5 min at 37 degrees C. The hematological parameters were determined, and surface analysis was assessed by scanning electron microscopy. At low shear rate, the retention on intact arterial surfaces averaged 3.7 +/- 0.7 x 10(6) platelets/cm2, 26.5 +/- 4.2 x 10(3) neutrophils/cm2, and 10.7 +/- 2.2 cpm of fibrin(ogen)/cm2; retention remained statistically similar at the high shear rate on both Goretex and Impra ePTFE surfaces. In contrast, the deposition of platelets and neutrophils on injured arterial surfaces was significantly higher and increased with shear rate, although the significant increase in fibrin(ogen) adsorption was not influenced by the shear rate. At shear rates characterized by patent and stenosed arteries, ePTFE arterial prostheses demonstrated a low level of thrombogenicity compared to injured arteries. This favorable comparison can be considered as the first requirement for their successful use in arterial substitution.

In vitro characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair

The surgical management of abdominal hernias requires prosthetic grafting in situations where the defect is too large or the surrounding tissue is not available for repair. Flat patches made of different biomaterials have been used in textile or microporous forms. The present work describes the results of an in vitro study comparing the morphological, mechanical, and chemical characteristics of a new textile prototype, Fluoropassiv, made of polyester fibers treated with a fluoropolymer and impregnated with gelatin to those of seven existing commercial meshes and patches made from polypropylene, polyester, polytetrafluoroethylene (PTFE) yarns, and expanded microporous PTFE graft. The morphological study revealed a diversity of structures having a minimal relative porosity of 70%, high bursting, and suture retention strengths in comparison with natural muscular tissue. Elasticmoduli proved to depend more on the direction of the textile the rigidity was higher for those materials having tight structure, like the Fluoropassiv and the Surgipro meshes (> 30 MPa), whereas those with more open structures, such as the Marlex, Trelex, Lars, Bard Teflon, and GoreTex structures, showed lower elastic modulus (10 mPa). In addition, chemical analyses confirmed no irregularities in the polymers used in all prostheses and demonstrated that the fluoropolymer coating of the Fluoropassiv was uniformly distributed. The innovative aspects in the construction of the knitted fabric Fluoropassiv appears to make it suitable for repairing hernias, and the inclusion of both continuous fluoropolymer surface treatment of polyester fibers and gelatin impregnation appears to improve the 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.