Human In Vitro Model Mimicking Material-Driven Vascular Regeneration Reveals How Cyclic Stretch and Shear Stress Differentially Modulate Inflammation and Matrix Deposition

This study developed a human in vitro vascular-regeneration model to disentangle how physiological hemodynamic loads—cyclic circumferential stretch and flow-driven shear stress—shape the coupled immune response, (myo)fibroblast behavior, and matrix deposition/remodeling that govern early outcomes in in situ vascular tissue engineering. Electrospun supramolecular PCL-bis-urea (PCL-BU) tubular scaffolds (3 mm inner diameter; ~200 µm wall thickness) were seeded with a 2:1 coculture of human primary monocytes and human vena saphena-derived (myo)fibroblasts using fibrin as a carrier and cultured for 20 days in a bioreactor that applied either cyclic stretch (~1.06 at 0.5 Hz), shear stress (~1 Pa), both loads, or static control. Cyclic stretch drove the strongest tissue mass increase and significantly elevated DNA content by day 20, with Ki67 staining indicating proliferation predominantly in vimentin-positive (myo)fibroblasts. At the inflammatory level, cyclic stretch reduced proinflammatory cytokines (notably MCP-1 and IL-6) and, especially when combined with shear stress, increased anti-inflammatory IL-10, indicating a stretch-driven shift toward a less inflammatory environment. Functionally, cyclic stretch stimulated upregulation of matrix-growth genes and increased collagen deposition (favoring thicker/more mature collagen type I), producing the stiffest constructs at day 20. In contrast, shear stress attenuated stretch-induced matrix growth while increasing remodeling signals (MMP-1/TIMP-1), promoting collagen remodeling and stabilizing construct growth. Biaxial mechanics confirmed these divergent outcomes: stretch-only constructs stiffened substantially, whereas adding shear stress largely abrogated this stiffening, yielding stiffness close to the bare scaffold. Overall, the work positions shear stress as a stabilizing regulator of stretch-driven tissue formation and highlights the need to account for both loads when designing resorbable vascular grafts to avoid maladaptive inflammation and remodeling.