(745f) Structure of Porous Nonwoven Fiber Mesh and Salt Leached Foam Bone Tissue Engineering Scaffolds Via Dispersion Simulations
Uniform tissue development requires satisfactory delivery of oxygen and nutrients, as well as removal of metabolic waste from bone tissue engineering constructs during the culturing process. Molecular oxygen is essential to cell survival, but can be readily depleted in high-density tissue cultures. Moreover, cell differentiation can be influenced by applying different ranges of oxygen concentration during culture. Therefore, a thorough understanding of oxygen, nutrient and waste transport within bone tissue engineering scaffolds can be used in order to increase the quality of cultured tissue and possibly to direct the fate of cell differentiation.
Several types of bone tissue engineering scaffold geometries are available, yet it is not apparent which one is the optimal manufacturing choice for efficient mass transfer. Tortuosity is a characteristic of the scaffold geometry that describes how twisted the paths are throughout the pores of a scaffold relative to the shortest distance between the entrance and the exit of the scaffold. It can be defined as the ratio of the nominal (bulk) diffusion coefficient to the effective diffusion coefficient (where the effective diffusion coefficient takes into account the effects of the presence of the porous medium walls).
In order to compare the tortuosity of the two common bone tissue engineering scaffold types (salt leached foams and nonwoven fiber meshes), the effective diffusion coefficient of various solutes in cell culture media perfused through the scaffolds are calculated via simulation. Lagrangian scalar tracking (LST) is used, which is a numerical technique for simulating mass transport in a flow field produced by a fluid dynamics solver. The fundamental hypothesis of LST is that solute transport behavior can be determined by tracking the movement of mass markers in the flow field. The movement of the markers is the combination of convection (obtained from a pre-solved velocity field) and diffusion (obtained from a mesoscopic Monte-Carlo approach that simulates Brownian motion). A custom-written, in-house lattice Boltzmann method (LBM) code that has been developed by Voronov et al.  for a previous study is used as the fluid dynamics solver. The LBM results provide the detailed velocity field within the scaffolds that is utilized be the LST algorithm. The structure of the scaffolds is obtained using high resolution micro-computed tomography imaging at 10 micrometers. The trajectories of 100,000 mass markers with different nominal diffusion coefficients are calculated, and the effective diffusion is calculated based on Taylor-Aris type of calculations, in order to eventually determine the porous medium tortuosity as a function of the scaffold structure (porosity, specific surface area, pore size).
Knowledge of the mechanism of mass transfer of nutrients to osteoblast cells growing within the porous scaffold obtained from LST simulations can enable for manufacturing optimization of the 3D scaffold structure for enhanced tissue growth.