Mechanical and Rheological Characterisation of 3D Fibronectin-Collagen Fibrillar Scaffolds
Creators: name: Sadeghi, Parisa
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2021
Subjects: Mechanical properties
Collagen-fibronectin scaffolds
Rheological properties

description: The extracellular matrix (ECM) is a complex fibrillar network that couples a cell with its environment and directly regulates the cell’s fate via structural, mechanical, and biochemical signals. The goal of this thesis was to engineer and characterize ECM-mimicking protein platforms with material properties covering both physiological and pathological tissues. First, we fabricated three-dimensional (3D) fibrillar scaffolds comprising the two major components of the ECM, namely collagen (COL) and fibronectin (FN), using a temperature-controlled casting technique to regulate the rate of protein gelation and consequently scaffold fibres’ density. Second, we assessed the material properties of the COL-FN scaffolds, in the presence (cell-laden) and absence (ECM only) of cells, to establish a correlation between their structural and mechanical characteristics. As structural scaffold characterization was the object of a previous thesis in our laboratory (in brief the higher the casting temperature, the denser the scaffolds result), the present work focused on exhaustive mechanical characterization. Here we report the quantification of both elastic and viscous properties of all scaffolds, when subjected either to compression or shear, using two different tools and protocols. In our first approach, we used a Dynamic Mechanical Analyzer (DMA) to compress the scaffolds and record consecutive force-indentation profiles, from which we extracted overall stiffness through the slope of the converted stress-strain profiles. The scaffolds were immersed in PBS and after 24hr, were compressed up to 25% strain, at a velocity of 25 µm/s. Although our numerous experiments suggested that denser scaffolds tended to have higher Young’s moduli than their sparse counterparts, the DMA technique did not allow us to establish a significant difference in stiffness between them. In our second approach, we used a Rheometer to subject the scaffolds to oscillatory shear stresses and assess their viscoelasticity by measuring their storage modulus (G’) and loss modulus (G”), characteristics of their elastic and viscous behaviours, respectively. After performing initial amplitude sweeps to determine the linear viscoelastic regime and set a desirable amplitude of deformation for further analysis (here 0.25%), various frequency sweeps were performed with strain rate ranging from 0.1 to 10 (1/s) at 0.25% amplitude of deformation. Our results clearly indicate that, in the absence of cells, dense scaffolds (composed of short and thin fibres) were both stiffer and more viscous than sparse scaffolds (composed of long and thick fibres). Our data also show that, unexpectedly, the presence of cells significantly decreases both stiffness and viscosity of dense scaffolds, while it increases them when scaffolds are less dense. Finally, all scaffolds exhibited a dominating elastic response. Collectively, our study shows that we were able to generate both ECM and cell-ECM scaffolds with controlled volume, density, elasticity, and viscous characteristics. These tunable platforms enable a better understanding of the critical link between ECM structure and mechanics, with the ultimate goal of controlling cellular functions. As such they represent a valuable tool for biomaterials and biophysics research, with many potential applications in basic research, medical diagnosis and tissue engineering.