Hirarchical Design and Simulation of Tissue Engineering Scaffold Mechanical, Mass Transport, and Degradation Properties.

Abstract

In this study, a computational design framework was developed and demonstrated for hierarchical scaffold mechanical, mass transport and degradation properties. As a composite, multiscale structure, the tissue engineering scaffold should be designed to match tissue specific requirements such as tissue elastic modulus and diffusivity/permeability, for better tissue regeneration. In addition to these functional properties, the design of the tissue engineering scaffolds should include the time dependent change of the functions along with material degradation and erosion. With the aid of multiscale homogenization method and topology optimization technique, scaffold microstructures were designed and applied to the design of biodegradable spinal fusion cages. The degradation characteristics by the presence of microstructures were addressed using multiscale homogenization model of diffusion reaction system. The mechanical properties (bulk modulus) of the topology optimized microstructures range from 10% to 37% of base material property, whereas the mass transport properties (diffusivity) range from 12% to 41% of free diffusivity. The designed properties were optimal within known cross-property bounds connecting diffusivity and bulk modulus. Mechanical compression test confirmed the good correlation between the designed and experimentally measured Young’s moduli. As a clinical application, the topology optimization technique was adapted to the design of biodegradable fusion cages with the integrated global-local topology optimization. The mechanical strength of the fusion cage made of PCL was demonstrated to support physiological loads at human lumbar spine. Degradation of the porous scaffolds was characterized using a multiscale homogenization technique, demonstrating the effect of the release profiles of acidic products from polymer hydrolysis at local microstructure scale on the release at the global scaffold scale. The precise characterization and controlled design and fabrication within same theoretical framework will provide the basis of a consistent knowledge regarding the correlation between scaffold design parameters and the tissue regeneration.