Relationship Between Actual Stress And In Situ Morphological Changes In The Mechanical Behavior Of Biomimetic Porous Hierarchical Scaffolds

This study investigates the evolution with strain of the material volume fraction (i.e., porosity) and geometry in porous scaffolds to obtain a more accurate description of their stress-strain behavior. Single bundles and hierarchical structures (8 bundles enveloped by a membrane) were produced by electrospinning as tendon/ligament scaffolds. They underwent a micro-tomography in situ tensile test. Apparent and net stress were obtained using the initial sample cross-section and material volume fraction to normalize axial force. Micro-tomography revealed sample morphology change with strain to calculate the actual stress-strain. Moreover, nanofibers arrangement was revealed by scanning electron microscopy on both bundles and membranes. The description of the mechanical response significantly changed using evolving morphometry (actual stress-strain) instead of initial static one (apparent stress-strain), for both single bundle and hierarchical structure. The actual elastic modulus of the single bundles (583{+/-}97 MPa) was statistically higher than that of the hierarchical structures (163{+/-}107 MPa). This is related to the membrane, membrane-bundle and inter-bundle interactions. In the hierarchical structure, portions of the material resisting traction are constituted by nanofibers not aligned with the load. The different definitions for the stress-strain behavior allow different accuracy levels depending on the experimental complexity. The evolution of morphology with deformation can significantly affect the description of the mechanical response of porous scaffolds. This has a double impact in practical applications: at the body scale, it allows a better comparison between the scaffold behavior and the target tissue; at the cellular scale, it predicts the actual substrate stiffness that cells will face. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/630537v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@5d5337org.highwire.dtl.DTLVardef@1027047org.highwire.dtl.DTLVardef@11966a9org.highwire.dtl.DTLVardef@a2e4e3_HPS_FORMAT_FIGEXP M_FIG C_FIG