Comprehensive Ex Vivo Comparison of 5 Clinically Used Conduit Configurations for Valve-Sparing Aortic Root Replacement Using a 3-Dimensional–Printed Heart Simulator

Background: Many graft configurations are clinically used for valve-sparing aortic root replacement, some specifically focused on recapitulating neosinus geometry. However, the specific impact of such neosinuses on valvular and root biomechanics and the potential influence on long-term durability are unknown. Methods: Using a custom 3-dimenstional–printed heart simulator with porcine aortic roots (n=5), the anticommissural plication, Stanford modification, straight graft (SG), Uni-Graft, and Valsalva graft configurations were tested in series using an incomplete counterbalanced measures design, with the native root as a control, to mitigate ordering effects. Hemodynamic and videometric data were analyzed using linear models with conduit as the fixed effect of interest and valve as a fixed nuisance effect with post hoc pairwise testing using Tukey’s correction. Results: Hemodynamics were clinically similar between grafts and control aortic roots. Regurgitant fraction varied between grafts, with SG and Uni-Graft groups having the lowest regurgitant fractions and anticommissural plication having the highest. Root distensibility was significantly lower in SG versus both control roots and all other grafts aside from the Stanford modification ( P ≤0.01 for each). All grafts except SG had significantly higher cusp opening velocities versus native roots ( P <0.01 for each). Relative cusp opening forces were similar between SG, Uni-Graft, and control groups, whereas anticommissural plication, Stanford modification, and Valsalva grafts had significantly higher opening forces versus controls ( P <0.01). Cusp closing velocities were similar between native roots and the SG group, and were significantly lower than observed in the other conduits ( P ≤0.01 for each). Only SG and Uni-Graft groups experienced relative cusp closing forces approaching that of the native root, whereas relative forces were >5-fold higher in the anticommissural plication, Stanford modification, and Valsalva graft groups. Conclusions: In this ex vivo modeling system, clinically used valve-sparing aortic root replacement conduit configurations have comparable hemodynamics but differ in biomechanical performance, with the straight graft most closely recapitulating native aortic root biomechanics.

Maize brace root biomechanics are determined by geometry within a genotype and material properties between genotypes

ABSTRACTCrop plants are susceptible to yield loss by mechanical failure, which is called lodging. In maize (Zea mays), aerial nodal brace roots impart mechanical stability to plants, with previous studies showing that the lowest whorl of brace roots contributes the most. The features of brace roots that determine their contribution to mechanical stability are poorly defined. Here we tested the hypothesis that brace root mechanical properties vary between whorls, which may influence their contribution to mechanical stability. 3-point bending tests were used to determine that brace roots from the lowest whorl have the highest structural mechanical properties regardless of growth stage, and that these differences are largely due to brace root geometry within a genotype. Analysis of the brace root bending modulus determined that differences between genotypes are attributable to both geometry and material properties. These results support the role of brace root biomechanics to determine the brace root contribution to mechanical stability.HIGHLIGHTBrace root biomechanics vary within and between genotypes. These results support the importance of biomechanics to define the contribution of brace roots to mechanical stability.