A combinative approach for the selective cellularization of human capillary-sized microchannels

The controlled cellularization of enclosed microchannels with true capillary dimensions remains a major technical limitation in in vitro vascular models. While endothelial cell seeding is routinely achieved in microchannels with dimensions above several tens of micrometers, reliable and spatially selective endothelialization of capillary-sized geometries remains challenging. Here, we report a combined microfabrication and surface-patterning strategy that overcomes this barrier, enabling selective endothelial cell seeding in microchannels as small as 20 µm. The method introduces micrometric chemical selectivity in the microfabricated environment, allowing for precise control over cell-adhesive regions while preserving channel integrity and accessibility. The approach integrates soft lithography, thin metal film deposition, and gas-phase surface modification to define 15-µm-wide adhesive paths precisely aligned with SU-8 microchannels. This alignment enables selective inner-surface functionalization without the need for post-bonding treatments or complex flow-based patterning steps. SEM and AFM analyses confirm a clear physicochemical contrast between patterned and non-patterned regions throughout the fabrication process. After seeding, phase-contrast and fluorescence imaging demonstrate exclusive endothelial adhesion within the targeted microchannels. By enabling robust, reproducible, and selective cellularization at capillary dimensions, this approach allows to overcome a key technical barrier in microvascular fabrication and provides a versatile platform for capillary-scale in vitro models. .