(11d) Influence of Fluid Flow On Porous Scaffold Structural Deformation

Tissue engineering provides means to replace, restore tissue functions by growing cells on three-dimensional (3D) matrices. Porous structures are molded into the desired shape of the tissue and are used to support cells to colonize, organize and produce their own extracellular matrix elements. Regenerating the tissue outside the body is necessary when tissue functionality is critical to the survival of a patient. Bioreactors are utilized in tissue regeneration to ensure complete nutrient distribution and apply defined hydrodynamic stresses. Moreover, tissue regeneration is a dynamic process where the porous characteristics of the scaffolds change due to proliferation of cells, de novo deposition of matrix components, degradation of the porous architecture, and flow of nutrients through the reactor. These changes affect the transport characteristics and there is an imminent need to understand the influence of these factors. Previously, our group has evaluated the influence of various factors including reactor shape, inlet location and inlet shape on nutrient distribution, changes in pore size and void fraction in reactors suitable for regenerating large tissues [1, 2]. However, the effect of fluid flow on the dimensionality is not understood. Fluid flow could compress the scaffold which could alter the pore architecture and the nutrient distribution.

This study focused on the influence of fluid flow on the integrity of scaffolds and changes in structural dimension along with nutrient distribution. For this purpose, evaluating changes in dimensionality under applied stress is necessary. Poison's ratio was selected as criteria for analysis. Scaffolds made from different compositions viz. 0.5% chitoson- 0.5% gelatin, 1% chitoson- 1% gelatin, and 2% chitoson- 2% gelatin were selected for investigating poisons ratio with porosity and pore size. Experiments were performed under hydrated conditions using Phosphate buffered saline solution at a temperature of 37 degree centigrade. Instron's mechanical testing system is employed for applying desired stress. Digital photographs were taken in regular intervals and analyzed using Sigma Scan Pro software. Porosity of the samples is experimentally determined by evaluating weight, volume and density of a dry sample and when it is completely hydrated.

The results from the experiments were used in simulating the bioreactor at various flow rates and scaffold compositions. COMSOL multiphysics software was used along with appropriate modules to simulate structure deformation and nutrient distribution with consumption by smooth muscle cells. Accounting for the variation in scaffold structure during reactor operation will help understand its suitability at given conditions, and hence improve tissue quality.

References [1] Lawrence BJ, Devarapalli M, Madihally SV. Flow Dynamics in Bioreactors Containing Tissue Engineering Scaffolds. Biotechnology/Bioengineering. 102(3): 935-947, 2009. [2] Devarapalli M, Lawrence BJ, Madihally SV. Modeling Nutrient Consumptions in Large Flow-Through Bioreactors for Tissue Engineering. Biotechnology/ Bioengineering. 103(5):1003-1015, 2009.