Balancing topographical guidance and spatial capacity: Optimized spatial density of micropatterned filaments for...

Nerve guidance conduits (NGCs) require intraluminal fillers to bridge critical-sized peripheral nerve defects, yet balancing topographical guidance with adequate regenerative space remains a fundamental "spatial paradox". Herein, a hierarchical composite nerve support conduit is engineered, comprising a micropatterned poly(L-lactide-co-caprolactone) (PLCL) outer membrane and double-sided micropatterned intraluminal filaments. To decode spatial design rules, the intraluminal volumetric filling ratio (0% to 50%) was systematically modulated in a 10-mm rat sciatic nerve transection model. Results demonstrate that an optimal 5%-10% filling ratio resolves the spatial paradox by maximizing anisotropic contact guidance while preserving crucial luminal capacity. This highly permissive 3D immunovascular microenvironment synergistically directed Schwann cell alignment, and facilitated robust endothelial vascularization, yielding functional recovery and remyelination comparable to autologous nerve grafts. Conversely, excessive dense fillings (>20%) physically obstructed tissue infiltration. Furthermore, comprehensive multi-level transcriptomic sequencing elucidated that these structural and spatial cues might be associated with focal adhesion and PI3K-Akt signaling pathways, highlighting Ccn1 as a key mechanosensitive gene driving extracellular matrix remodeling. This study defines the precise spatial thresholds in conduit design, establishing a paradigm for optimizing biomechanical microenvironments in neural tissue engineering.