Aging is a major risk factor in microvascular dysfunction and disease development, but the underlying mechanism remains largely unknown. As a result, age‐mediated changes in the mechanical properties of tissue collagen have gained interest as drivers of endothelial cell (EC) dysfunction. 3D culture models that mimic age‐mediated changes in the microvasculature can facilitate mechanistic understanding. A fibrillar hydrogel capable of changing its stiffness after forming microvascular networks is established. This hydrogel model is used to form vascular networks from induced pluripotent stem cells under soft conditions that mimic young tissue mechanics. Then matrix stiffness is gradually increased, thus exposing the vascular networks to the aging‐mimicry process in vitro. It is found that upon dynamic matrix stiffening, EC contractility is increased, resulting in the activation of focal adhesion kinase and subsequent dissociation of β ‐catenin from VE‐Cadherin mediated adherens junctions, leading to the abruption of the vascular networks. Inhibiting cell contractility impedes the dissociation of β ‐catenin, thereby preventing the deconstruction of adherens junctions, thus partially rescuing the age‐mediated vascular phenotype. The findings provide the first direct evidence of matrix's dynamic mechano‐changes in compromising microvasculature with aging and highlight the importance of hydrogel systems to study tissue‐level changes with aging in basic and translational studies.

With the increased realization of the effect of oxygen (O 2 ) deprivation (hypoxia) on cellular processes, recent efforts have focused on the development of engineered systems to control O 2 concentrations and establish biomimetic O 2 gradients to study and manipulate cellular behavior. Nonetheless, O 2 gradients present in 3D engineered platforms result in diverse cell behavior across the O 2 gradient, making it difficult to identify and study O 2 sensitive signaling pathways. Using a layer-by-layer assembled O 2 -controllable hydrogel, the authors precisely control O 2 concentrations and study uniform cell behavior in discretized O 2 gradients, then recapitulate the dynamics of cluster-based vasculogenesis, one mechanism for neovessel formation, and show distinctive gene expression patterns remarkably correlate to O 2 concentrations. Using RNA sequencing, it is found that time-dependent regulation of cyclic adenosine monophosphate signaling enables cell survival and clustering in the high stress microenvironments. Various extracellular matrix modulators orchestrate hypoxia-driven endothelial cell clustering. Finally, clustering is facilitated by regulators of cell-cell interactions, mainly vascular cell adhesion molecule 1. Taken together, novel regulators of hypoxic cluster-based vasculogenesis are identified, and evidence for the utility of a unique platform is provided to study dynamic cellular responses to 3D hypoxic environments, with broad applicability in development, regeneration, and disease.

Endothelial cell dysfunction plays a central role in many pathologies, rendering it crucial to understand the underlying mechanism for potential therapeutics. Tissue engineering offers opportunities for in vitro studies of endothelial dysfunction in pathological mimicry environments. Here, we begin by analyzing hydrogel biomaterials as a platform for understanding the roles of the extracellular matrix and hypoxia in vascular formation. We next examine how three-dimensional bioprinting has been applied to recapitulate healthy and diseased tissue constructs in a highly controllable and patient-specific manner. Similarly, studies have utilized organs-on-a-chip technology to understand endothelial dysfunction’s contribution to pathologies in tissue-specific cellular components under well-controlled physicochemical cues. Finally, we consider studies using the in vitro construction of multicellular blood vessels, termed tissue-engineered blood vessels, and the spontaneous assembly of microvascular networks in organoids to delineate pathological endothelial dysfunction.