Vassilios I. Sikavitsas

Distribution of flow-induced stresses in highly porous media

Simulation results for the distribution of flow-induced wall stresses within 36 different porous scaffolds with porosity larger than 80% indicate that the normalized wall stress follows a single gamma distribution. Experimental and computational results for scaffolds prepared via different techniques from different materials and by other laboratories follow the same distribution. The form of this universal distribution is offered, as well as the methodology to obtain it for laminar flow through high porosity materials.

Predicting multicomponent diffusivities for diffusion on surfaces and in molecular sieves with energy heterogeneity

A simple theory is derived for predicting multicomponent diffusion on solid surfaces and in molecular sieves with energetic heterogeneity. The energetic heterogeneity is represented by the uniform energy distribution and the equilibrium adsorption is assumed to follow the Langmuirian behavior. Multicomponent Fickian diffusivities can be predicted from pure-component Fickian diffusivities. The required information for the calculation includes the concentration-dependent pure-component diffusivities and the pure-component adsorption isotherms. The effects of the energetic heterogeneity can be significant, depending on the mutual direction of diffusion (co-diffusion or counter-diffusion), the initial and final surface coverages, and the relative diffusivities of the components. The effects of heterogeneity are stronger on the faster diffusing component. The effect of heterogeneity becomes stronger as the total surface coverage increases. The theory compares favorably with the available experimental data.

Predicting the stress distribution within scaffolds with ordered architecture

Current tissue engineering technologies involve the seeding of cells on porous scaffolds, within which the cells can proliferate and differentiate, when cultured in bioreactors. The flow of culture media through the scaffolds generates stresses that are important for both cell differentiation and cell growth. A recent study [Appl. Phys. Lett. 97 (2010), 024101] showed that flow-induced stresses inside highly porous and randomly structured scaffolds follow a three-point gamma probability density function (p.d.f.). The goal of the present study is to further investigate whether the same p.d.f. can also describe the distribution of stresses in structured porous scaffolds, what is the range of scaffold porosity for which the distribution is valid, and what is the physical reason for such behavior. To do that, the p.d.f. of flow-induced stresses in different scaffold geometries were calculated via flow dynamics simulations. It was found that the direction of flow relative to the internal architecture of the scaffolds is important for stress distributions. The stress distributions follow a common distribution within statistically acceptable accuracy, when the flow direction does not coincide with the direction of internal structural elements of the scaffold.

Image-based modeling: A novel tool for realistic simulations of artificial bone cultures

Computational modeling has been promulgated as a means of optimizing artificial bone tissue culturing ex vivo. In the present report, we show, as a proof-of-concept, that it is possible to model the exact microenvironment within the scaffolds while accounting for their architectural complexities and the presence of cells/tissues in their pores. Our results clearly indicate that image-based modeling has the potential to be a powerful tool for computer-assisted tissue engineering.