Evaluating changes in structure and cytotoxicity during in vitro degradation of three-dimensional printed scaffolds

This study evaluated the structural, mechanical, and cytocompatibility changes of three-dimensional (3D) printed porous polymer scaffolds during degradation. Three porous scaffold designs were fabricated from a poly(propylene fumarate) (PPF) resin. PPF is a hydrolytically degradable polymer that has been well characterized for applications in bone tissue engineering. Over a 224 day period, scaffolds were hydrolytically degraded and changes in scaffold parameters, such as porosity and pore size, were measured nondestructively using micro-computed tomography. In addition, changes in scaffold mechanical properties were also measured during degradation. Scaffold degradation was verified through decreasing pH and increasing mass loss as well as the formation of micropores and surface channels. Current methods to evaluate polymer cytotoxicity have been well established; however, the ability to evaluate toxicity of an absorbable polymer as it degrades has not been well explored. This study, therefore, also proposes a novel method to evaluate the cytotoxicity of the absorbable scaffolds using a combination of degradation extract, phosphate-buffered saline, and cell culture media. Fibroblasts were incubated with this combination media, and cytotoxicity was evaluated using XTT assay and fluorescence imaging. Cell culture testing demonstrated that the 3D-printed scaffold extracts did not induce significant cell death. In addition, results showed that over a 224 day time period, porous PPF scaffolds provided mechanical stability while degrading. Overall, these results show that degradable, 3D-printed PPF scaffolds are suitable for bone tissue engineering through the use of a novel toxicity during degradation assay.