Ice-templating of anisotropic structures with high permeability

Abstract

Nutrient diffusion and cellular infiltration are important factors for tissue engineering scaffolds. Maximizing both, by optimizing permeability and scaffold architecture, is important to achieve functional recovery. The relationship between scaffold permeability and structure was explored in anisotropic scaffolds from a human collagen I based recombinant peptide (RCP). Using ice-templating, scaffold pore size was controlled (80–600μm) via the freezing protocol and solution composition. The transverse pore size, at each location in the scaffold, was related to the freezing front velocity, via a power law, independent of the freezing protocol. Additives which interact with ice growth, in this case 1wt% ethanol, altered ice crystallization and increased the pore size. Variations in composition which did not affect the freezing, such as 40wt% hydroxyapatite (HA), did not change the scaffold structure, demonstrating the versatility of the technique. By controlling the pore size, scaffold permeability could be tuned from 0.17×10−8 to 7.1×10−8m2, parallel to the aligned pores; this is several orders of magnitude greater than literature values for isotropic scaffolds: 10−9–10−12m2. In addition, permeability was shown to affect the migration of osteoblast-like cells, suggesting that by making permeability a design parameter, tissue engineering scaffolds can promote better tissue integration.