Improving Bioactive Characteristics of Small Diameter Polytetrafluoroethylene Stent Grafts by Electrospinning: A Comparative Hemocompatibility Study

Abstract

Polytetrafluoroethylene (PTFE) is a commonly used biomaterial for the manufacturing of vascular grafts and several strategies, such as coatings, have been explored to improve the hemocompatibility of small-diameter prostheses. In this study, the hemocompatibility properties of novel stent grafts covered with electrospun PTFE (LimFlow Gen-1 and LimFlow Gen-2) were compared with uncoated and heparin-coated PTFE grafts (Gore Viabahn^®) using fresh human blood in a Chandler closed-loop system. After 60 min of incubation, the blood samples were examined hematologically and activation of coagulation, platelets, and the complement system were analyzed. In addition, the adsorbed fibrinogen on the stent grafts was measured and the thrombogenicity was assessed by SEM. Significantly lower adsorption of fibrinogen was measured on the surface of heparin-coated Viabahn than on the surface of the uncoated Viabahn. Furthermore, LimFlow Gen-1 stent grafts showed lower fibrinogen adsorption than the uncoated Viabahn^®, and the LimFlow Gen-2 stent grafts showed comparable fibrinogen adsorption as the heparin-coated Viabahn^®. SEM analysis revealed no sign of thrombus formation on any of the stent surfaces. LimFlow Gen-2 stent grafts covered with electrospun PTFE exhibited bioactive characteristics and revealed improved hemocompatibility in terms of reduced adhesion of fibrinogen, activation of platelets, and coagulation (assessed by β-TG and TAT levels) similar to heparin-coated ePTFE prostheses. Thus, this study demonstrated improved hemocompatibility of electrospun PTFE. The next step is to conduct in vivo studies to confirm whether electrospinning-induced changes to the PTFE surface can reduce the risk of thrombus formation and provide clinical benefits.

Keywords: electrospinning; hemocompatibility; polytetrafluoroethylene stent graft.

Figure 1

Images of LimFlow stent grafts. Photographic images showing LimFlow Gen-1 and Gen-2 stent grafts (left), and SEM images showing the surface of the LimFlow Gen-2 stent grafts (right).

Figure 2

Analysis of fibrinogen adsorption to the graft surfaces. Detection of adsorbed fibrinogen in (A) experiment series B and (B) experiment series C. The data are shown as mean + SD. Statistical analysis was performed using the Friedman test followed by Dunn’s multiple comparison test. n = 8, (* p < 0.05, **** p < 0.0001).

Figure 3

Analysis of TAT concentrations in plasma after the incubation of stent grafts with fresh human blood. (A) Pilot study (n = 3), (B) Experiment series B (n = 8), (C) Experiment series C (n = 7). The data are shown as mean + SD. Statistical analysis was performed using the Friedman test followed by Dunn´s multiple comparison test. N = 8, (* p < 0.05, ** p < 0.01).

Figure 4

Analysis of platelet counts after the incubation of fresh human blood with test items for 60 min at 37 °C. (A) Pilot study (n = 3), (B) Experiment series B (n = 8), (C) Experiment series C (n = 8). Whole human blood without incubation and contact to test material served as baseline, and blood without test material but incubation as negative control. The data are shown as mean + SD. Statistical differences were determined using one-way ANOVA for repeated measurements followed by Bonferroni’s multiple comparison test. (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 5

Analysis of platelet activation by measuring β-TG concentration after the incubation of fresh human blood with test items for 60 min at 37 °C. (A) Pilot study (n = 3), Statistical differences were determined using one-way ANOVA for repeated measurements followed by Bonferroni’s multiple comparison test. (B) Study B (n = 8), (C) Study C (n = 8). Statistical analysis was performed using the Friedman test followed by Dunn´s multiple comparison test. Whole human blood without incubation and contact to test material served as baseline and blood without test material, but with incubation as the negative control. The data are shown as mean + SD. (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 6

Analysis of white and red blood cell counts after the incubation of fresh human blood with test items for 60 min at 37 °C. (A) Pilot study (n = 3), (B) Study B (n = 8), (C) Study C (n = 8). Whole human blood without incubation and contact to test material served as baseline and blood without test material, but with incubation as the negative control. The data are shown as mean + SD.

Figure 7

Analysis of hemolysis, hemoglobin, and hematocrit levels after the incubation of fresh human blood with test items for 60 min at 37 °C. (A) Pilot study (n = 3), (B) Study B (n = 8), (C) Study C (n = 8). Whole human blood without incubation and contact to test material served as baseline, and blood without test material, but with incubation as the negative control. The data are shown as mean + SD. Statistical differences were determined using one-way ANOVA for repeated measurements followed by Bonferroni’s multiple comparison test. (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 8

Analysis of complement activation by detection of SC5b-9 concentration. Detection of SC5b-9 in (A) experiment series B and (B) experiment series C. The data are shown as mean + SD. Statistical analysis was performed using the Friedman test followed by Dunn´s multiple comparison test. n = 8, (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 9

Analysis of the blood-contacting surface of stent grafts using SEM. Detection of the thrombogenicity in experiment series A. Representative images from one donor are shown after the blood contact (n = 3).

Figure 10

Analysis of the blood-contacting surface of stent grafts using SEM. Detection of the thrombogenicity in experiment series C. Representative images from one donor are shown after the blood contact (n = 8).

Figure 11

Clinical example of a patient treated at University Hospital Tuebingen with percutaneous deep venous arterialization (pDVA). The aim of this intervention is the redistribution of arterial blood to the foot via the tibial veins as a conduit. (A) Implantation of a dedicated tapered LimFlow endograft for crossing from the posterior tibial artery to a tibial vein (white arrows). (B) Straight LimFlow endografts in the tibial vein covering side branches until the foot (dotted arrow). (C) Angiographic of the proximal lower leg image after implantation of the LimFlow endografts. (D) Final angiographic result of the arterialized venous foot arch after successful pDVA.