Quantifying Physical Thrombus Characteristics on Cardiovascular Biomaterials Using MicroCT

Abstract

Hemocompatibility is a critical consideration when designing cardiovascular devices. Methods of assessing hemocompatibility range from in vitro protein adsorption and static platelet attachment to in vivo implantation. A standard preclinical assessment of biomaterial hemocompatibility is ex vivo quantification of thrombosis in a chronic arteriovenous shunt. This technique utilizes flowing blood and quantifies platelet accumulation and fibrin deposition. However, the physical parameters of the thrombus have remained unknown. This study presents the development of a novel method to quantify the 3D physical properties of the thrombus on different biomaterials: expanded polytetrafluoroethylene and a preclinical hydrogel, poly(vinyl alcohol). Tubes of 4–5 mm inner diameter were exposed to non-anticoagulated blood flow for 1 hour and fixed. Due to differences in biomaterial water absorption properties, unique methods, requiring either the thrombus or the lumen to be radiopaque, were developed to quantify average thrombus volume within a graft. The samples were imaged using X-ray microcomputed tomography (microCT). The methodologies were strongly and significantly correlated to caliper-measured graft dimensions (R2 = 0.994, p < 0.0001). The physical characteristics of the thrombi were well correlated to platelet and fibrin deposition. MicroCT scanning and advanced image analyses were successfully applied to quantitatively measure 3D physical parameters of thrombi on cardiovascular biomaterials under flow.

Hemocompatibility of micropatterned biomaterial surfaces is dependent on topographical feature size

“…Additional controls were unpatterned, planar PVA tubes (4 mm ID, n = 2), clinical ePTFE grafts (4 mm ID, n = 2), and collagen-coated ePTFE grafts (4 mm ID, n = 2), which served as negative, clinical, and positive controls, respectively. These samples were not compared to the micropatterned grafts statistically, but results were comparable with prior historical controls ( Cutiongco et al, 2015 ; Anderson et al, 2019 ; Bates et al, 2020 ; Gupta et al, 2020 ; Yao et al, 2020 ).…”

“…After 24–72 h of fixation, samples were rinsed and processed for micro-computed tomography (microCT) imaging. Tube lumens were filled with Microfil ® (Flow Tech, Inc.) and cured for 2 h at room temperature to render the tube lumens radiopaque, as described previously ( Gupta et al, 2020 ). Positive and clinical control ePTFE grafts were soaked in Lugol’s solution (Sigma) for 16 h to render the thrombus radiopaque.…”

Bioconjugation of a Collagen-Mimicking Peptide Onto Poly(vinyl alcohol) Encourages Endothelialization While Minimizing Thrombosis

“…Some of the samples used in the shunt studies were examined with micro-computed tomography (MicroCT). The samples were prepared as described previously (Gupta et al, 2020). Briefly, PVA samples were filled with Microfil R polymer to render the lumens radiopaque.…”

“…Micro-computed tomography (Inveon, Siemens) imaging was used to analyze thrombus area over the length of the samples (volume) in the small-diameter vascular grafts formed under flow by whole blood in ex vivo shunts, as described previously (Gupta et al, 2020). Imaging was performed with 2 × 2 binning, 220 projections, at an exposure of 660 ms/projection.…”

“…The software-calculated volumes and lengths of each sample were used for subsequent analysis. Amira R was utilized, as previously described (Gupta et al, 2020), to segment specific regions of interest (ROIs) in each cross-sectional image. For PVA samples, the ROI was the luminal area of the graft.…”