Interspecies differences with in vitro and in vivo models of vascular tissue engineering

Additive manufacturing of the core template for the fabrication of an artificial blood vessel: the relationship between the extruded deposition diameter and the filament/nozzle transition ratio

An artificial blood vessel with a tubular structure was additively manufactured via fused deposition modeling (FDM) starting from a single strand of polyvinyl alcohol (PVA) filament coated with a specific thickness of biocompatible polydimethylsiloxane (PDMS), followed by removal of the inner core via hydrogen peroxide leaching under sonication. In particular, we examined the relationship between the extruded deposition diameter and the filament migration speed/nozzle control speed (referred to as the filament/nozzle transition ratio), which is almost independent of the extruded deposition flow rate due to the weak die-swelling and memory effects of the extruded PVA arising from its intrinsically low viscoelasticity. The chemical stability of the PDMS during sonication in the hydrogen peroxide solution was then determined by spectroscopic techniques. The PDMS displayed no mechanical degradation in the hydrogen peroxide solution, resulting in similar fracture elongation and yield strength to those of the pristine specimen without the leaching treatment. As a further advantage, the inside surface of the PDMS was smooth regardless of the hydrogen peroxide leaching under sonication. The potential application of the as-developed scaffold in soft tissue engineering (particularly that involving vascular tissue regeneration) was demonstrated by the successful transplantation of the artificial blood vessel in a right-hand surgical replica used in a clinical simulation.

In situ evolution of the mechanical properties of stretchable and non-stretchable ePTFE vascular grafts and adjacent native vessels

INTRODUCTION

The purpose of this study was to evaluate the evolution of the mechanical properties of stretchable and non-stretchable ePTFE vascular grafts over time following implantation, as well as those of the adjacent native vessels.

METHODS

One stretchable and one non-stretchable graft were implanted in either carotid position of six sheep. After twelve weeks, the samples, as well as the distal adjacent native vessel, were explanted and evaluated mechanically by means of uniaxial tensile tests. These tests were performed in the axial as well as in the circumferential direction. Also, patches of these grafts were implanted subcutaneously in the abdominal wall of the same animals. At 2, 4, 6, and 8 weeks, patches were explanted and evaluated mechanically. Baseline mechanical tensile tests were also performed on non-implanted grafts and on native sheep carotid arteries.

RESULTS

Statistical analysis shows a significant effect of implantation time on the tensile mechanical properties of ePTFE vascular grafts. This effect is present for stretchable as well as non-stretchable grafts, in axial as well as in circumferential direction of the material. Also the adjacent native vessels have a tendency to lose mechanical stiffness and strength in the circumferential direction, an effect which is most pronounced for stretchable grafts.

CONCLUSIONS

The mechanical properties of ePTFE vascular grafts and the adjacent native vessels significantly change as a function of implantation time. Compared to the native vessels, the grafts are still significantly stronger and stiffer, though longer term experiments are needed to evaluate whether and how much the decline would continue in time.