Patterned ELR-Gelatin Hydrogels Enable Rapid Endothelial Monolayer Formation via Bioactive Matrix Chemistry and Surface Topography

The endothelialization of organ-on-chip platforms and vascular implants is often limited by slow cell attachment and unstable monolayer formation. This work presents a scalable workflow that imprints micro- and nano-gratings into elastin-like recombinamer (ELR)-based hydrogels, enabling rapid endothelial cell capture and accelerating monolayer formation within 14 days. Three gelatin-ELR formulations are engineered, with {superscript 1}H-NMR confirming incorporation of sequences designed to modulate bioactivity (ELR1: inert; ELR2: uPA-responsive; ELR3: RGD-adhesive). ELR incorporation generates fibrillar microstructures and enhances mechanical performance, yielding elastic-dominant networks suitable for high-fidelity pattern transfer and stable culture. Using this library, the combined effects of ELR bioactivity and groove geometry on human iPSC-derived endothelial cells (iPSC-ECs) are systematically evaluated. In a 15-minute attachment assay, patterned ELR composites markedly improve cell retention compared to gelatin, with ELR2 on [~]350 nm and [~]4 {micro}m grooves performing best, consistent with controlled, cell-mediated interfacial remodeling. This early advantage persists, as ELR2 and ELR3 hydrogels support rapid alignment and reach confluence by day 14, whereas gelatin remains sub-confluent. Cytoskeletal analysis confirms F-actin alignment. By combining enhanced early capture with protease-regulated remodeling, ELR2 identifies a favorable design window. These results establish a materials design framework linking programmable ELR chemistry with surface topography to engineer endothelial interfaces, providing a versatile platform for vascular biomaterials and microphysiological systems.