Giving It a Twist: One-Step Fabrication of Aligned Biomimetic Yarn Scaffolds via Rotational Melt Electrofibrillation.

Topographical mimicry of the extracellular matrix, particularly the hierarchical fibrillar structure of collagen, has emerged as an essential factor in guiding cellular phenotype and function. In many tissues, collagen fibrils are not only organized in hierarchical bundles but are also twisted, imparting crucial tensile strength to these structures. Here, we present a fabrication method that enables the generation of such twisted structures by introducing controlled rotation of polymer melt-loaded syringes during Melt Electrofibrillation. By adjusting the rotational speed, higher twist angles in braid-like structures can be generated, replicating the full range of twist angles observed in vivo. Moreover, this advancement not only facilitates the formation of twisted fibrillar bundles with enhanced mechanical properties that resist delamination but also allows their direct printing into stable scaffolds. Experimental evaluation with three mesenchymal cell types on the scaffolds demonstrated cellular alignment and elongation along the fibril angles, as well as expression of lineage-specific transcription factors and matrix genes. This creation of three levels of hierarchy in a single step-fibrillation, twisting, and scaffold generation-thus paves the way to replicate the ultrastructure and mechanical properties of twisted collagen structures in a biomimetic manner, providing a structurally faithful scaffold platform for various tissue types.