The blood-brain barrier (BBB) regulates molecular trafficking, protects against pathogens, and prevents efficient drug delivery to the brain. Models to date failed to reproduce the human anatomical ...complexity of brain barriers, contributing to misleading results in clinical trials. To overcome these limitations, a novel 3-dimensional BBB microvascular network model was developed via vasculogenesis to accurately replicate the in vivo neurovascular organization. This microfluidic system includes human induced pluripotent stem cell-derived endothelial cells, brain pericytes, and astrocytes as self-assembled vascular networks in fibrin gel. Gene expression of membrane transporters, tight junction and extracellular matrix proteins, was consistent with computational analysis of geometrical structures and quantitative immunocytochemistry, indicating BBB maturation and microenvironment remodelling. Confocal microscopy validated microvessel-pericyte/astrocyte dynamic contact-interactions. The BBB model exhibited perfusable and selective microvasculature, with permeability lower than conventional in vitro models, and similar to in vivo measurements in rat brain. This robust and physiologically relevant BBB microvascular model offers an innovative and valuable platform for drug discovery to predict neuro-therapeutic transport efficacy in pre-clinical applications as well as recapitulate patient-specific and pathological neurovascular functions in neurodegenerative disease.
Animal cells in tissues are supported by biopolymer matrices, which typically exhibit highly nonlinear mechanical properties. While the linear elasticity of the matrix can significantly impact cell ...mechanics and functionality, it remains largely unknown how cells, in turn, affect the nonlinear mechanics of their surrounding matrix. Here, we show that living contractile cells are able to generate a massive stiffness gradient in three distinct 3D extracellular matrix model systems: collagen, fibrin, and Matrigel. We decipher this remarkable behavior by introducing nonlinear stress inference microscopy (NSIM), a technique to infer stress fields in a 3D matrix from nonlinear microrheology measurements with optical tweezers. Using NSIM and simulations, we reveal large long-ranged cell-generated stresses capable of buckling filaments in the matrix. These stresses give rise to the large spatial extent of the observed cell-induced matrix stiffness gradient, which can provide a mechanism for mechanical communication between cells.
The mechanical properties of the extracellular matrix (ECM)-a complex, 3D, fibrillar scaffold of cells in physiological environments-modulate cell behavior and can drive tissue morphogenesis, ...regeneration, and disease progression. For simplicity, it is often convenient to assume these properties to be time-invariant. In living systems, however, cells dynamically remodel the ECM and create time-dependent local microenvironments. Here, we show how cell-generated contractile forces produce substantial irreversible changes to the density and architecture of physiologically relevant ECMs-collagen I and fibrin-in a matter of minutes. We measure the 3D deformation profiles of the ECM surrounding cancer and endothelial cells during stages when force generation is active or inactive. We further correlate these ECM measurements to both discrete fiber simulations that incorporate fiber crosslink unbinding kinetics and continuum-scale simulations that account for viscoplastic and damage features. Our findings further confirm that plasticity, as a mechanical law to capture remodeling in these networks, is fundamentally tied to material damage via force-driven unbinding of fiber crosslinks. These results characterize in a multiscale manner the dynamic nature of the mechanical environment of physiologically mimicking cell-in-gel systems.
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•Several viable methods currently exist to create vascularized in vitro tissues.•Progress has been made in developing systems that mimic specific organs or tissues.•New technologies ...such as 3D printing have great potential to advance the field.•A major challenge is to vascularize organoids grown from human cells.•Applications include drug screening or growing human implants.
Vascularization of micro-tissues in vitro has enabled formation of tissues larger than those limited by diffusion with appropriate nutrient/gas exchange as well as waste elimination. Furthermore, angiocrine signaling from the vasculature may be essential in mimicking organ-level functions in these micro-tissues. In drug screening applications, the presence of an appropriate blood–organ barrier in the form of a vasculature and its supporting cells (pericytes, appropriate stromal cells) may be essential to reproducing organ-scale drug delivery pharmacokinetics. Cutting-edge techniques including 3D bioprinting and in vitro angiogenesis and vasculogenesis could be applied to vascularize a range of tissues and organoids. Herein, we describe the latest developments in vascularization and prevascularization of micro-tissues and provide an outlook on potential future strategies.
Neurovascular coupling plays a key role in the pathogenesis of neurodegenerative disorders including motor neuron disease (MND). In vitro models provide an opportunity to understand the pathogenesis ...of MND, and offer the potential for drug screening. Here, we describe a new 3D microvascular and neuronal network model in a microfluidic platform to investigate interactions between these two systems. Both 3D networks were established by co-culturing human embryonic stem (ES)-derived MN spheroids and endothelial cells (ECs) in microfluidic devices. Co-culture with ECs improves neurite elongation and neuronal connectivity as measured by Ca
oscillation. This improvement was regulated not only by paracrine signals such as brain-derived neurotrophic factor secreted by ECs but also through direct cell-cell interactions via the delta-notch pathway, promoting neuron differentiation and neuroprotection. Bi-directional signaling was observed in that the neural networks also affected vascular network formation under perfusion culture. This in vitro model could enable investigations of neuro-vascular coupling, essential to understanding the pathogenesis of neurodegenerative diseases including MNDs such as amyotrophic lateral sclerosis.
Significance The cancer biology seed-and-soil paradigm recognizes the existence of organ-specific patterns of metastasization that drive the spread of selected primary tumors toward specific ...secondary loci. However, despite efforts to model the organotypic microenvironment, the organ specificity of cancer metastases needs to be elucidated. The relevance of this study lies in the generation of a human vascularized organ-specific microenvironment, which can be used to investigate and tune the extravasation process of metastatic tumor cells. Furthermore, beyond mimicking the pro- or antimetastatic signatures of different microenvironments, our microfluidic model provides insights into different properties of organ-specific endothelia. This study paves the way toward advanced in vitro models to screen for highly tailored organ-specific therapeutics and investigate key molecular pathways involved in organ-specific metastases.
A key aspect of cancer metastases is the tendency for specific cancer cells to home to defined subsets of secondary organs. Despite these known tendencies, the underlying mechanisms remain poorly understood. Here we develop a microfluidic 3D in vitro model to analyze organ-specific human breast cancer cell extravasation into bone- and muscle-mimicking microenvironments through a microvascular network concentrically wrapped with mural cells. Extravasation rates and microvasculature permeabilities were significantly different in the bone-mimicking microenvironment compared with unconditioned or myoblast containing matrices. Blocking breast cancer cell A ₃ adenosine receptors resulted in higher extravasation rates of cancer cells into the myoblast-containing matrices compared with untreated cells, suggesting a role for adenosine in reducing extravasation. These results demonstrate the efficacy of our model as a drug screening platform and a promising tool to investigate specific molecular pathways involved in cancer biology, with potential applications to personalized medicine.
Microfluidics is invaluable for studying microvasculature, development of organ-on-chip models and engineering microtissues. Microfluidic design can cleverly control geometry, biochemical gradients ...and mechanical stimuli, such as shear and interstitial flow, to more closely mimic in vivo conditions. In vitro vascular networks are generated by two distinct approaches: via endothelial-lined patterned channels, or by self-assembled networks. Each system has its own benefits and is amenable to the study of angiogenesis, vasculogenesis and cancer metastasis. Various techniques are employed in order to generate rapid perfusion of these networks within a variety of tissue and organ-mimicking models, some of which have shown recent success following implantation in vivo. Combined with tuneable hydrogels, microfluidics holds great promise for drug screening as well as in the development of prevascularized tissues for regenerative medicine.
Biology and Models of the Blood-Brain Barrier Hajal, Cynthia; Le Roi, Baptiste; Kamm, Roger D ...
Annual review of biomedical engineering,
07/2021, Volume:
23, Issue:
1
Journal Article
Peer reviewed
Open access
The blood-brain barrier (BBB) is one of the most selective endothelial barriers. An understanding of its cellular, morphological, and biological properties in health and disease is necessary to ...develop therapeutics that can be transported from blood to brain. In vivo models have provided some insight into these features and transport mechanisms adopted at the brain, yet they have failed as a robust platform for the translation of results into clinical outcomes. In this article, we provide a general overview of major BBB features and describe various models that have been designed to replicate this barrier and neurological pathologies linked with the BBB. We propose several key parameters and design characteristics that can be employed to engineer physiologically relevant models of the blood-brain interface and highlight the need for a consensus in the measurement of fundamental properties of this barrier.
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