Experimental Non-Inferiority Trial of Synthetic Small-calibre Biodegradable

vs. Stable Vascular Grafts

Departments of 1Cardiovascular Surgery, 3Pathology and 4Radiology University Hospital of Geneva;

Dept. of 2Pharmaceutics & Biopharmaceutics EPGL, University of Geneva; Switzerland.

1Beat H. WALPOTH, MD FAHA

Damiano Mugnai1, Sarra de Valence2, Wojciech Mrowczynski1, Jean-Christophe Tille3, Xavier Montet4, Robert Gurny2, Michael Moeller2, Afksendiyos Kalangos1

OBJECTIVES: There is a big need for shelf-ready, synthetic, small calibre prostheses for cardiovascular revascularisation procedures. Biodegradable scaffolds resistant to degradation-induced aneurysm formation in the systemic arterial circulation have been developed for :

“in vivo vascular tissue-engineering”

Our aim is to assess the long-term results of synthetic, biodegradable, electrospun, small-calibre vascular grafts compared to ePTFE for aortic replacement in the rat model.

Vascular Tissue Engineering:Manufacturing of scaffolds

Biodegradable grafts (polycaprolactone = PCL) were produced by random nano-fibre electro-spinning (porosity 80%)

Modern “BARBAPAPA” technique to create novel vascular grafts

METHODS - I: 14 anaesthetised Sprague Dawley rats (male, 275g), received an infrarenal aortic graft (8 biodegradable; 6 ePTFE) replacement (end-to-end; 2mm ID; 20mm long) and 6 rats (same age) served as sham (controls)

PCL graft

Quality and patency control after surgery

with transit time flowmeter

2 mm

ePTFE graft

METHODS - II: After 15 months survival in vivo high resolution ultra-sonography (Visualsonics) and angiography were performed to assess patency, stenosis, aneurysm formation, intimal hyperplasia and compliance. After explantation micro CT calcification quantification, histology, immuno-histology, scanning electron microscopy (SEM) and morphometry were carried out.

Rat 24 3 weeks afteroperation

Rat 24 3 weeks afteroperation

PCL ( n=8)

ePTFE (n=6)

P<

Patency (%) 100 67 nsEndothelialization (%) 98 93 nsCompliance (%) 8.2 5.7 0.01Calcification (%) 7.0 15.8 0.04Intimal Hyperplasia (µm) 47.2 62.2 0.09Cellular Ingrowth (%) 31.4 11.3 0.001

RESULTS:PCL vs. ePTFE grafts at 15 months

Angiography after 15 months implantation

A & B =ePTFE

C = PCL

D = NativeAorta

Vascular Compliance

HISTOLOGIC ASSESSMENTAFTER 15 MO

IMPLANTATION

PCLMorphological analysis of PLC grafts. (A) SEM image of the lumen of the PCL graft after explantation showing complete endothelialization. (B) Longitudinal section of the graft wall showing homogenous cellular infiltration giant cells on the periphery (arrows; HE staining, 100x magnification). (C) Neo-intima with spindle shape cells above a calcified area, indicated by the arrow. An endothelium is present on the luminal side. (HE staining, 200x magnification). (D) Immunohistochemistry anti CD31 labeling endothelial cells on the luminal side (200x magnification) (E) Elastin deposition in the neo-intimal layers is revealed in blue and collagen deposition is revealed in green by a Miller-Masson staining (200x magnification). (F) Immunohistochemistry anti Smooth Mucle Actin demonstrating positivity in spindle shape cells forming the neo-intima (200x magnification).

HISTOLOGIC ASSESSMENTAFTER 15 MO

IMPLANTATION

ePTFEMorphological analysis of ePTFE grafts. (A) Longitudinal section of the graft wall with neointima formation, limited cellular infiltration in the graft body and no giant cell reaction (HE staining, 100x magnification). (B) Neointima formation under the endothelium (indicated by an arrow) with no signs of calcification (HE staining, 200x magnification). (C) Miller-Masson staining revealing elastin fibers in bleu in the neointima and collagen depositions in green in the inner part of the graft (200x magnification). (D) Von Kossa staining showing in black the calcifications in the graft body (100x magnification). (E) SEM image of the lumen of the graft showing incomplete endothelialization (see insert) and microthrombi.

SUMMARY

PCL vs. ePTFE grafts at 15 months :

•100% patency vs. 67% for ePTFE•No aneurysms, no stenosis•Rapid and complete endothelialisation•Similar neo-intima formation to ePTFE•Better compliance than ePTFE, but•Worse compliance than native aorta•Less micro-calcifications than ePTFE (PET)•Better cellular ingrowth in PCL grafts•Vascular remodelling with live cells and ECM formation (collagen and elastin) with PCL degradation (65% MW reduction)

CONCLUSIONS

•Synthetic biodegradable small calibre nano-fibre polycaprolactone grafts show excellent results after 15 months of aortic replacement and compare favourably with the clinically used ePTFE grafts.

•Thus, such novel in situ tissue engineered grafts could become a future option for clinical applications such as coronary artery bypass grafting or endografting.

PCL vs. ePTFE grafts at 15 months :