Numerical validation of an in-situ test method to quantify the microscale kinematics of nanofibrous membranes based on continuum mechanics
Year: 2025
Type: article
Abstract: Introduction: Nanofibrous materials, such as electrospun membranes (ESM), are widely used in tissue engineering and soft tissue repair, due to their beneficial microstructure, closely resembling extracellular matrix. Their mechanical characteristics at the microscale are known to determine the response of ingrowing cells. To describe the inhomogeneous and, in general, non-affine deformations at the length scale of the cells, in-situ tests, i.e. mechanical tests accompanied by imaging techniques are performed. However, due to the multi-scale character of the materials, the derivation of robust quantitative measures for deformation, representative for the material and at the same time relevant for cells is challenging. Methods: In this study, we develop and validate a methodology to quantify the microscale kinematics of ESMs using in-situ uniaxial tensile testing in combination with scanning electron microscopy (SEM) and deformation analysis by digital image correlation (DIC). To this end, we apply a numerical discrete fiber model, to dimension the following aspects: (i) The kinematic quantities need to address the length scale of cells (e.g. fibroblasts 50-150 μm). (ii) The field of view must contain at least one representative surface element (RSE) of the ESM. (iii) Strain evaluation using DIC assumes affine deformations within a facet, which determines the minimum applicable facet size. Using the numerical model, different subsets of nodes, analog to facets in DIC, are defined to evaluate local, homogenized microscale deformation quantities based on continuum mechanics. Their means and variances are used to derive the size of an RSE by convergence studies. The relative frequency distributions of these local kinematic quantities on the RSE are representative for the material, why we call them the kinematic fingerprint. It represents the ground truth for the validation of the results using a commercial DIC software (Istra4D, Dantec Dynamics). For this purpose, the simulated configurations of the ESM are used as input for the deformation analysis using Istra4D. A variation of facet sizes according to different nodal subset sizes allows for an assessment of the validity range of DIC. Results: Convergence analyses using the kinematic fingerprint revealed a material specific RSE of 120x120 μm2 (thickness: 4 μm), exceeding the size of a representative volume element. Comparing the kinematic fingerprint based on DIC with the one derived purely numerically led to a minimum facet size of 5x5 μm2, one order of magnitude smaller compared to the size of fibroblasts. Discussion and conclusion: Thus, the numerical approach, allows for a rigorous justification of applied length scales for an experimental in-situ test using SEM imaging in combination with DIC on ESMs. By addressing the cellular length scale, this study will serve future quantitative investigations in mechanobiology, correlating the cell response to a specific microstructure of ESMs.
Language: English
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7154656776