Microcellular injection molding of thermoplastic polyurethane (TPU) scaffolds using carbon dioxide and water as co-blowing agents

In this study, a novel microcellular injection foaming method employing supercritical CO₂ (scCO₂) and water as co-blowing agents was developed to produce thermoplastic polyurethane (TPU) tissue engineering scaffolds with a uniform porous structure and no solid skin layer. Various characterization techniques were applied to investigate the cell morphology, crystallization behavior, and static and dynamic mechanical properties of solid molded samples, foamed samples using CO₂ or water as a single blowing agent, and foamed samples using both CO₂ and water as co-blowing agents. Compared with CO₂ foamed scaffolds, scaffolds produced by the co-blowing method exhibit much more uniform cell morphologies without a noticeable reduction in mechanical properties. Moreover, these TPU scaffolds have almost no skin layer, which permits free transport of nutrients and waste throughout the samples, which is highly desirable in tissue engineering. The effect of these blowing agents on the shear viscosity of various samples is also reported.