Mechanical Characterization and Torsional Buckling Effects of Pediatric Vascular Patches

Abstract

The selection of cardiovascular conduits during reconstructive surgical operations presents a significant challenge due to the potential complications that may arise post-operatively, depending on various parameters, including patient-to-patient variation. One particularly common mechanical complication is torsional buckling and conduit surface deformation, which occurs at the anastomosis site due to the mechanical instability of the composite material structure. This study investigates the torsional buckling characteristics of commonly used pediatric surgical materials. A practical method for estimating the critical buckling rotation angle at any physiological intramural pressure is derived utilizing experimental data on actual surgical conduits and uniaxial and biaxial tensile tests. While the proposed technique successfully predicted the critical rotation angle values of artificial conduits, Polytetrafluoroethylene (PTFE) and Dacron, at all lumen pressures, its accuracy for biological materials, such as porcine pericardium, is lower. Applicable to all surgical materials, this formulation enables surgeons to assess and analyze the torsional buckling potential of vascular conduits without the need for invasive procedures. This predictive capability is critical as new surgical materials steadily emerge. Among the three common materials studied, Dacron has been found to exhibit the highest stability against torsional buckling, while porcine pericardium has been identified as the least stable material. This conclusion is drawn based on the observed direct correlation between the resistance to torsional buckling under lumen pressure and the shear modulus of the materials. PTFE exhibited highly nonlinear behavior, with three different Young's modulus values reported to correspond to distinct mechanical characteristics. Dacron demonstrated a logarithmic behavior in the stress-strain relationship. The mechanical response of porcine pericardium was found to be highly anisotropic, with the Young's modulus in the circumferential direction being 12 times greater than the Young’s modulus in the axial direction. The stress-like material parameter in Fung's pseudo 2D strain energy function for porcine pericardium was found to be approximately 8 times greater than the literature value for human intracranial blood vessels. This significant difference indicates that porcine pericardium, unless preconditioned before implantation, may not be suitable for use as a vascular conduit due to its unsuitability in replicating the mechanical behavior of human blood vessels.