Hierarchical microchanneled scaffolds modulate multiple tissue-regenerative processes of immune-responses, angiogenesis, and stem cell homing.

Recapitulating the in vivo microenvironments of damaged tissues through modulation of the physicochemical properties of scaffolds can boost endogenous regenerative capacity. A series of critical events in tissue healing including immune-responses, angiogenesis, and stem cell homing and differentiation orchestrate to relay the regeneration process. Herein, we report hierarchically structured ('microchanneled') 3D printed scaffolds (named 'µCh'), in contrast to conventional 3D printed scaffolds, induce such cellular responses in a unique way that contributes to accelerated tissue repair and remodeling. The µCh reduced the extracellular trap formation of anchored neutrophils at the very beginning (24 h) of implantation while increasing the number of live cells. Among the macrophages covered the surface of µCh over 7 days a major population polarized toward alternativelly activated phase (M2) which contrasted with control scaffolds where classically activated phase (M1) being dominant. The mesenchymal stem cells (MSCs) recruited to the µCh were significantly more than those to the control, and the event was correlated with the increased level of stem cell homing cytokine, stromal derived factor 1 (SDF1) sequestered to the µCh. Furthermore, the neo-blood vessel formation was more pronounced in the µCh, which was in line with the piling up of angiogenic factor, vascular endothelial growth factor (VEGF) in the µCh. Further assays on the protein sequestration to the µCh revealed that a set of chemokines involved in early pro-inflammatory responses were less found whereas representative adhesive proteins engaged in the cell-matrix interactions were significantly more captured. Ultimately, the fibrous capsule formation on the µCh was reduced with respect to the control, when assessed for up to 21 days, indicating less severe foreign body reaction. The tissue healing and regenerative capacity of the µCh was then confirmed in a critically sized bone model, where those series of events observed are essential to relay bone regeneration. The results over 6 weeks showed that the µCh significantly enhanced the early bone matrix deposition and accelerated bone regeneration. While more in-depth studies remain as to elucidate the underlying mechanisms for each biological event, the molecular, cellular and tissue reactions to the µCh were coherently favorable for the regeneration process of tissues, supporting the engineered scaffolds as potential therapeutic 3D platforms.