(358a) Estimation of Mechanical Properties and Studies On Structural Deformation of Scaffolds in Tissue Engineering

Use of biodegradable porous scaffolds in tissue engineering have proved to be an attractive solution for creating functionally replaceable tissue parts, developing new drugs, and producing synthetic surrogates to test diseases propagation. The scaffolds help in guiding and supporting in-growth of cells during tissue development. Moreover, the extracellular matrix elements such as collagen, proteoglycans secreted by the cells undergo enzymatic processes and aggregate into the native fibers. To grow a tissue, a porous scaffold is seeded with cells, a bioreactor is used to provide nutrients and regulate culture conditions such as pH and temperature to mimic the native environment of the cells. In addition, several tissues in the body are exposed to stress based on their function. Therefore, it is vital to grow these cells in vitroby exposing them to the same physiological conditions. Uses of bioreactors and scaffolds have been explored extensively to improve the tissue growth process. Several bioreactor designs have been developed and advance biomaterials have been formulated. However, most studies have failed to account for structural mechanics of the scaffold in the bioreactor during its operation. The focus of this study was to estimate mechanical properties of the scaffold, such as Poisson’s ratio, density and Young’s Modulus. In addition, studies were performed to understand the effect of mechanical properties and bioreactor configuration on structural mechanics of the scaffold.

Two scaffolds were prepared: i) Chitosan-gelatin scaffold by freeze drying technique and ii) Polycaprolactone (PCL) scaffold using salt leaching technique. The scaffolds were characterized using scanning electron microscopy (SEM) for pore size and void fraction. Experiments were performed to estimate their Poisson’s ratio, density and Young’s modulus under physiological conditions. The Poisson’s ratio of chitosan-gelatin scaffold was 1.2 suggesting a non-linear behavior whereas PCL scaffold had a Poisson’s ratio of 0.3. To perform structural mechanics studies, a computational fluid dynamics (CFD) tool, COMSOL Multiphysics v4.2a was used. Two bioreactor configurations that can hold 100 mm diameter and 2 mm thick scaffold were selected: flow-through and parallel flow.  Our previous study involved creating a 2D geometry of these bioreactors to understand structural mechanics of the scaffold in these bioreactor configurations (AIChE annual meeting, 2010). This study involved extending that work to 3D geometry of the bioreactor configurations and to PCL scaffolds. The flow-through configuration involves positioning the scaffold in the path of the fluid flow; hence, this configuration was apt for studying structural deformation of the scaffold. The fluid flow in the porous scaffold was described by Darcy’s law and other domains were described by Navier-Stokes equation. Simulations were performed at different flowrates ranging from 1 mL/min to 25 mL/min. The results showed higher deformation at the beginning and around the periphery of the scaffold. Experimental studies were also performed to analyze the effect of fluid flow on the scaffold structure. The experimental results showed significant deformation of chitosan-gelatin scaffold at the beginning and around the periphery of the scaffold at flowrates 10 mL/min or above. To analyze the effect mechanical properties on scaffold deformation, simulations were performed at different set of Young’s modulus, Poisson’s ration and density values. A scaffold with Higher Young’s modulus and Poisson’s ratio was found to be more favorable in minimizing the deformation. The density of the scaffold did not show significant effect on scaffold deformation. For parallel-flow configuration, as the fluid flows over the scaffold, the effects of flow rate and mechanical properties were significantly less compared to the flow-through configuration. Hence, to improve the tissue quality, it is vital to understand and account for variations in the scaffold structure during the tissue growth process at given conditions.