ISO2-PU Honeycomb Porous Films with a Peculiar Crystalline Structure by the Breath Figure Method Promote Osteogenic Differentiation of Stem Cells

The breath figure (BF) method is a handy strategy to prepare porous films. Linear shape memory polyurethanes (SMPUs) are among the most promising polymers for bone repair or regeneration. However, little attention has been paid to the fabrication of SMPU films by using the BF method. In this work, an amorphous SMPU containing isosorbide (ISO) in the long-chain hard segments (ISO2-PU) is fabricated into honeycomb porous films. Strikingly, a peculiar crystalline structure with a "Z" configuration and highly regional orientation is formed on the hexagonal holes of the porous films, which results in significantly enhanced mechanical properties. Moreover, the ISO2-PU honeycomb porous films can markedly accelerate the osteogenic differentiation of rat mesenchymal stem cells, indicating that the porous films have great potentials as bone repair materials. It is further speculated that the Marangoni effect in the condensed water droplets and the molecular assembly of ISO2-PU due to the strong hydrogen bonds and the chiral center effect of ISO are key contributors. This work, to the best of authors' knowledge, is the first time that this special crystalline structure on BF-based porous films is observed and also the first speculation that combines Marangoni effect with the microstructure of BF-based porous films.