Vascular cell attachment and procoagulant activity on metal alloys

Improved Neo-Endothelialization of Small Diameter ePTFE Grafts with Titanium Coating

Background

Patency of small synthetic bypass grafts is inferior compared to autologous grafts for revascularization procedures. Titanium coating of foreign surfaces has shown to decrease thrombogenicity, enhance biocompatibility and promote adhesion of endothelial cells. The aim of this study was to test the effect of titanium coating of small diameter ePTFE grafts on short term patency, neo-endothelialization and neointimal proliferation.

Methods

Bilateral carotid graft interposition was performed in 5 pigs with uncoated (n=5) and titanium-coated (n=5) ePTFE grafts (internal diameter=4 mm, length=5 cm), thus each pig served as its own control. At the end of the study (30 ± 3 days), patency and stenosis severity was assessed by carotid angiography. Animals were sacrificed and grafts were excised for histology and scanning electron microscopy. Morphometry of histologic sections was carried out to determine neointimal proliferation and percentage of neo-endothelial coverage.

Results

Patency rate was 80% for uncoated and titanium-coated grafts. Quantitative angiography did not show any significant difference in lumen size between two groups. Morphometry revealed a significantly higher cellular coverage with CD 31 positive endothelial cells for titanium-coated (84 ± 19%) than uncoated grafts (48 ± 26%, p<0.001). There was a non significant trend (p=0.112) towards increased neointimal proliferation in titanium-coated (94 ± 61 μm2/μm) compared to uncoated grafts (60 ± 57 μm2/μm).

Conclusions

Patency rate in uncoated and titanium-coated ePTFE grafts is similar at one month. However, titanium coated grafts show a significant improvement in neo-endothelialization compared to uncoated grafts.

The Engineering of Endovascular Stent Technology: A Review

The evolution of minimally invasive endovascular technology has initiated a significant paradigm shift in the treatment of vascular disease. A fundamental understanding of the science and engineering behind the technology of endovascular stents is a key to their appropriate implementation in practice. Furthermore, the rapid influx of new devices into the field requires practitioners to make their decisions on a foundation of the relative strengths and weaknesses of the various products. Although the principles of their use are not complex, the device design can have a profound effect on the device's functionality. Shape, thickness, coating, material selection, and imaging are just a few of the factors to consider in stent design. Subtle differences may have profound results. This review is designed to provide the reader with an overview of fundamental concepts that will aide the assessment of new technology.

Improvement in endothelial cell adhesion and retention under physiological shear stress using a laminin-apatite composite layer on titanium

Apatite (Ap), laminin-apatite composite (L5Ap, L10Ap, L20Ap and L40Ap) and albumin-apatite (AlbAp) composite layers were prepared on titanium (Ti) using a supersaturated calcium phosphate solution supplemented with laminin (0, 5, 10, 20 and 40 μg ml(-1)) or albumin (800 μg ml(-1)). With an increase in the concentrations of laminin in the supersaturated calcium phosphate solutions, the amounts of laminin immobilized on the Ti increased. The number of human umbilical vein endothelial cells (HUVECs) adhered to the laminin-apatite composite layers were remarkably higher than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells adhered to the L40Ap was 4.3 times the untreated Ti. Moreover, cells adhered to the laminin-apatite composite layers showed significantly higher cell retention under the physiological shear stress for 1 h and 2 h than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells remaining on the L40Ap under the physiological shear stress for 2 h was 9.5 times that of the untreated Ti. The laminin-apatite composite layer is a promising interfacial layer for endothelialization of blood-contacting materials.

CD41 Western blotting: a new method to detect platelet adhesion to artificial surfaces used in extracorporeal circulation procedures

Cardiopulmonary bypass (CPB) surgery is associated with platelet activation and reduced platelet counts due to artificial surface activation of blood elements and non-physiological flow-patterns. As shown in former studies, coating of medical devices can improve hemocompatibility in extracorporeal circulation systems. In this study, we demonstrate a new method to determine platelet adhesion on 18 coated and non-coated membrane oxygenators in a simulated CPB model with CD41 Western blot. Platelet loss and the release of beta-TG (platelet activation marker) were determined during a 120 min recirculation phase. At the end of the run the membrane oxygenators (with tubing system) were rinsed and the amount of adsorbed proteins on the surface was analyzed by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting technique. Uncoated devices showed significantly higher concentrations of CD41 and of fibrinogen adsorption compared to the coated membrane oxygenators. These results correspond with the release of beta-TG and platelet loss indicating less platelet adhesion on the coated oxygenators compared with the uncoated group. This new method may be useful in choosing less platelet activating materials for all kind of blood contacting devices to improve thrombogenicity including platelet functionality.

Characteristics of titanium-coated polyester prostheses in the animal model

Commercially available polyester vascular prostheses (n = 6) in the control group (CG) and titanium-coated vascular prostheses (TP; n = 7) were interposed within the infrarenal aorta of pigs. The respective healing characteristics and patency rates were compared after 3 months. For evaluation purposes, macroscopic, histological, and immunohistochemical criteria were applied. The macroscopic evaluation revealed complete healing of the TP in comparison with the CG. Extraluminal inspection revealed prominent firm cicatricial tissue in the prosthesis bed of the TP group. All TP were occluded. In the CG, occlusion of the prostheses occurred in n = 1 (16 %). On average, neointimal hyperplasia (NIH) in the proximal part of the anastomosis was not significantly different to the CG. The extraluminal proliferation index (Ki67) was reduced in the TP group (p = 0.002). The immunohistochemical analysis of intraluminal changes revealed no significant differences between CG and TP. All of the titanium-coated polyester vascular prostheses were found to be occluded. The additional coating of polyester prostheses with titanium would not appear to be of any particular benefit.

Gene monitoring of surface-activated monocytes in circulating whole blood using duplex RT-PCR

Previous studies have shown that blood-contacting materials activate blood monocytes. The aim of this study is to evaluate a highly sensitive technique for detecting changes at the mRNA level in circulating monocytes and to find suitable "gene markers" for assessing the hemocompatibility of biomaterials. Human blood was recirculated in a modified Chandler Loop formed of test tubes. Five groups of biomaterials were compared. Monocytes were separated by using magnetic beads, and gene expression analyses were performed using RT-PCR. We investigated the mRNA expression of stress proteins (hsp70) and inflammatory markers (IL-1alpha, IL-1beta, IL-6, TNF-alpha). mRNAs for cytokines were highly upregulated in LPS-stimulated monocytes. Hsp70 transcripts were upregulated after heat shock but were not influenced by treatment with LPS. The gene expression of the cytokines was affected by various biomaterials. The intensity of the inflammatory response increased in the following order: heparin coatings (PVC) < uncoated PVC < silicone, polypeptide-coated PVC. No change was seen in the expression of the hsp70 genes. An inhibitory effect of systemic heparin on surface-activated monocytes was observed for the mRNA expression of the cytokines. The recirculation of human blood in an in vitro model in combination with the immunomagnetic separation of monocytes and the Duplex RT-PCR method is a powerful tool for getting reliable results. Our data demonstrate that hsp70 genes cannot be recommended for short-term, biomaterial-induced mRNA expression studies. Conversely, mRNAs for IL-1alpha, IL-1beta, IL-6, and TNF-alpha were expressed in a material-dependent manner. Thus our model provides an effective tool for assessing the hemocompatibility of biomaterials before their clinical application and it also can serve as a safety control during the industrial manufacturing process. This method can be applied to various blood cell populations and numerous gene expression studies and may enable a more fundamental understanding of the biologic processes involved in blood-material interactions.

Evaluation of tissue-factor production by human endothelial cells incubated with three acrylic bone cements

The effect of three methacrylate-based cements used for the fixation of joint prostheses on tissue-factor production by human umbilical vein endothelial cells was evaluated in vitro. The extracts in the culture medium of the cements were tested after 1-h and 7-day curing. The endothelial cells were incubated with the cement extracts for 4 h, and then the tissue factor was determined in cell lysates with both the recalcification time and enzyme immuno assay. The cements did not induce significant production of tissue factor and, therefore, did not activate the extrinsic pathway of coagulation within the limits of the mechanism considered.