Revealing The True Mechanical Behavior Of Porous Tendon Scaffolds Via In Situ Morphometry

Abstract

This study examines how strain-driven changes in volume fraction and geometry influence the mechanics of porous scaffolds, aiming to improve the accuracy of their stress-strain description. Single bundles and hierarchical structures (8 bundles surrounded by a membrane), made of poly(L-lactic) acid and collagen type I, were electrospun as tendon/ligament scaffolds and examined via In Situ tensile tests in micro-CT. This enabled the development of a framework to compare stress metrics with increasing complexity. Apparent and net stress were obtained from the initial samples' cross-sections and material volume fractions. Micro-CT revealed strain-dependent morphological changes, allowing computation of actual stress-strain behavior. Scaffolds' nanofibers orientation/cross-section were quantified via SEM. The mechanical interpretation changed significantly when using strain-dependent morphometry (actual stress-strain) rather than the initial, static geometry (apparent stress-strain). Bundles' actual elastic modulus was statistically higher than hierarchical structures' one due to membrane-bundle and inter-bundle interactions. The different stress definitions yield varying levels of accuracy depending on the experimental complexity. Stress models are provided, allowing a compromise between characterization reliability and experimental complexity. Morphological evolution during deformation strongly affects mechanical response: at the tissue scale, it improves comparison between scaffold and native tissue behavior; at the cellular scale, it predicts the substrate stiffness sensed by cells.