Interfacial Pressure Gradient-Driven Protein Assembly Mediates Stem Cell Adhesion on Wettability-Patterned Microstructures

The interfacial mechanisms governing stem cell adhesion on wettability-patterned microstructures remain insufficiently understood, particularly regarding how initial fluid dynamics dictate subsequent protein distribution and cellular organization. Herein, we fabricate three distinct laser-textured surface architectures on Ti6Al4V─periodic microgrooves, microdimple arrays, and disordered porous structures─and investigate their physicochemical properties, protein adsorption behavior, and mesenchymal stem cell responses. Surface characterization reveals that laser texturing induces complete surface oxidation and generates pronounced time-dependent, anisotropic wettability, driven by capillary infiltration and plastron destabilization. Notably, cell adhesion exhibits strong topographical dependency: on deep microgrooves (depth > 20 μm), mesenchymal stem cells predominantly anchor at groove-ridge junctions rather than spreading within grooves, displaying either "spanning" or "guided" cytoskeletal architectures. Protein adsorption experiments demonstrate a consistent "high-seeking, low-avoiding" distribution pattern, where fetal bovine serum preferentially enriches on ridges and planar regions while being virtually excluded from pits and porous interiors. Using phase-field simulations of droplet dynamics on topology-mimetic models, we reveal that hydrophilic ridges generate moderate, positive interfacial pressure, serving as fluid-anchoring points, whereas grooves produce repulsive, high-pressure zones. This interfacial pressure gradient provides a physical rationale for the spatially selective fluid retention that precedes and likely directs protein patterning and subsequent cell adhesion.