Instability of vascular bilayer reveals the protective role of connective tissue

Biological vessels are often enveloped by connective tissues that exhibit markedly different mechanical properties from the vessel wall, including high compressibility and nonlinear strain stiffening. While these composite structures are ubiquitous in soft tissue systems, the role of surrounding connective tissue in modulating vascular buckling behavior remains poorly understood. In this study, we develop a theoretical framework to investigate how connective tissue regulate mechanical stability in bilayer vessel–tissue systems. Moving beyond conventional models that assume homogeneous and incompressible materials, we introduce a more physiologically representative structure composed of a compliant, compressible outer tissue layer enclosing a stiff, incompressible vascular core. A bifurcation analysis based on incremental theory is performed to predict critical buckling performance, with results validated by both experiments and finite element simulations. The results reveal that connective tissue's compressibility substantially increases the buckling threshold by redistributing stress across the interface and mitigating stress concentration within the vessel layer. Furthermore, comparison with actual aortic tissue reveals a stress-deconcentrating mechanism that enhances the structural resistance to buckling, a behavior not captured by idealized neoHookean models. These findings might provide mechanistic insights into tissue-mediated buckling suppression and offer design guidelines in soft biological interfaces and vascular-mimetic materials.