One-year performance of biorestorative polymeric coronary bypass grafts in an ovine model: correlation between early biomechanics and late serial Quantitative Flow Ratio

Synthetic vascular graft that heals and regenerates

Millions of synthetic vascular grafts (sVG) are needed annually to address vascular diseases (a leading cause of death in humans) and kidney failure (as vascular access). However, in 70+ years since the first sVG in humans, we still do not have sVGs that fully endothelialize (the "holy grail" for truly successful grafts). The lack of healthy endothelium is believed to be a main cause for thrombosis, stenosis, and infection (the major reasons for graft failure). The immune-mediated foreign body response to traditional sVG materials encapsulates the materials in fibrotic scar suppressing vascularized healing. Here, we describe the first sVG optimized for vessel wall vascularization via uniform, spherical 40 μm pores. This sVG induced unprecedented rapid healing of luminal endothelium in a demanding and clinically relevant sheep model, probably by attracting and modulating macrophages and foreign body giant cells towards diverse, pro-healing phenotypes. Both this sVG and the control (PTFE grafts) remained 100 % patent during the implantation period. This advancement has broad implications beyond sVGs in tissue engineering and biocompatibility.

Histological assessment of a novel restorative coronary artery bypass graft in a chronic ovine model

Background

Although prosthetic conduits for coronary artery bypass grafting (CABG) are increasingly needed because of the limited availability and patency of autologous conduits, no alternatives have succeeded.

Methods

Sixteen sheep underwent CABG. Thirteen received a bioabsorbable polymer graft with an incorporated nitinol microskeleton (Xeltis coronary artery bypass graft [XABG]), and three received autologous saphenous vein grafts (SVG). Pathological evaluation was conducted at 12 months.

Results

In the XABG group, two sheep died perioperatively; two were sacrificed at 3 months (1 occluded, 1 patent) and two at 6 months (both patent). Two more died from occlusion at 9-10 months, and five survived with patent grafts at 12 months. All SVGs remained patent for 12 months. Histology demonstrated near-complete luminal endothelialization in XABG, with increased polymer adsorption and matrix deposition. The cross-sectional area of the SVG lumen was significantly larger than XABGs (48.2 mm2 vs 12.9 mm2, p = 0.0018), consistent with a reduced angiographic flow velocity in SVG. The neointimal area was greater in SVGs than XABGs (19.6 vs. 6.7 mm2, p = 0.0005), especially at the distal ends of SVGs due to thrombus formation.

Conclusion

XABG demonstrated 1-year feasibility with consistent endothelialization and polymer absorption. While SVGs had better patency, they showed greater diametrical irregularity and subsequent neointimal proliferation.

An optical coherence tomography and endothelial shear stress study of a novel bioresorbable bypass graft

Endothelial shear stress (ESS) plays a key role in the clinical outcomes in native and stented segments; however, their implications in bypass grafts and especially in a synthetic biorestorative coronary artery bypass graft are yet unclear. This report aims to examine the interplay between ESS and the morphological alterations of a biorestorative coronary bypass graft in an animal model. Computational fluid dynamics (CFD) simulation derived from the fusion of angiography and optical coherence tomography (OCT) imaging was used to reconstruct data on the luminal anatomy of a bioresorbable coronary bypass graft with an endoluminal "flap" identified during OCT acquisition. The "flap" compromised the smooth lumen surface and considerably disturbed the local flow, leading to abnormally low ESS and high oscillatory shear stress (OSI) in the vicinity of the "flap". In the presence of the catheter, the flow is more stable (median OSI 0.02384 versus 0.02635, p < 0.0001; maximum OSI 0.4612 versus 0.4837). Conversely, OSI increased as the catheter was withdrawn which can potentially cause back-and-forth motions of the "flap", triggering tissue fatigue failure. CFD analysis in this report provided sophisticated physiological information that complements the anatomic assessment from imaging enabling a complete understanding of biorestorative graft pathophysiology.

1-Year Patency of Biorestorative Polymeric Coronary Artery Bypass Grafts in an Ovine Model

Many attempts have been made to inhibit or counteract saphenous vein graft (SVG) failure modes; however, only external support for SVGs has gained momentum in clinical utility. This study revealed the feasibility of implantation, and showed good patency out to 12 months of the novel biorestorative graft, in a challenging ovine coronary artery bypass graft model. This finding could trigger the first-in-man trial of using the novel material instead of SVG. We believe that, eventually, this novel biorestorative bypass graft can be one of the options for coronary artery bypass graft patients who have difficulty harvesting SVG.