Blood and Lymphatic Vasculatures On-Chip Platforms and Their Applications for Organ-Specific In Vitro Modeling

Abstract

The human circulatory system is divided into two complementary and different systems, the cardiovascular and the lymphatic system. The cardiovascular system is mainly concerned with providing nutrients to the body via blood and transporting wastes away from the tissues to be released from the body. The lymphatic system focuses on the transport of fluid, cells, and lipid from interstitial tissue spaces to lymph nodes and, ultimately, to the cardiovascular system, as well as helps coordinate interstitial fluid and lipid homeostasis and immune responses. In addition to having distinct structures from each other, each system also has organ-specific variations throughout the body and both systems play important roles in maintaining homeostasis. Dysfunction of either system leads to devastating and potentially fatal diseases, warranting accurate models of both blood and lymphatic vessels for better studies. As these models also require physiological flow (luminal and interstitial), extracellular matrix conditions, dimensionality, chemotactic biochemical gradient, and stiffness, to better reflect in vivo, three dimensional (3D) microfluidic (on-a-chip) devices are promising platforms to model human physiology and pathology. In this review, we discuss the heterogeneity of both blood and lymphatic vessels, as well as current in vitro models. We, then, explore the organ-specific features of each system with examples in the gut and the brain and the implications of dysfunction of either vasculature in these organs. We close the review with discussions on current in vitro models for specific diseases with an emphasis on on-chip techniques.

Keywords: blood vessels; brains; disease models-on-a-chip platforms; in vitro models; intestines; lymphatic vessels; micro-physiological systems; organ specificity; vasculatures-on-a-chip platforms.

Figure 1

(a) The distinct structures and general functions of the three main types of blood vessels: arteries/arterioles, capillaries, and veins/venules; (b) The differentiation pathway of the major cell types in the cardiovascular system as well as lymphatic endothelial cells (ECs). The mesoderm is the source of the precursor vessel cells and hematopoietic progenitor cells. From there, precursor vessel cells differentiate into either arterial-fated or venous-fated ECs. In the lymphatic vasculature, venous-fated ECs further differentiate into lymphatic ECs (LECs).

Figure 2

A collection of blood vasculature on-chip in vitro models that recreate different aspects of blood vessel anatomy and physiology. (a) The multiwell tissue flow chambers of Hughes lab’s on-chip model illustrate (i) the EC (mCherry) vascular networks formed after 7 days and the flow of 70 kDa FITC-dextran 30 min after perfusion, (ii) the distribution of Claudin-5 (Alexa Flour 488) and nuclei (4× and 20× magnification), and (iii) the expression of VE-cadherin junctions (Alexa Flour 488) and nuclei (DAPI) (4× and 20× magnification). Scale bar = 50 µm [17]. (b) The iPSC-EC microvessels display complete lumens with laminin deposition in the basement membrane, Scale bar = 100 µm, in (i) and 25 µm in (ii) [18]. (c) A double vessel chip (i) with separate channels for blood vessel (BV) and lymphatic vessel (LV) shows the effect of different VEGF-C concentrations on angiogenesis and lymphangiogenesis [19]. (d) A multichannel chip (i) overview schematic and (ii) cross-sectional schematic illustrating the layering of the pericytes (stromal cells) with the endothelial cells and fluid media channels. (iii) Immunostaining with confocal microscopy reveals the architecture of the microvessel including complete lumen formation and pericyte incorporation through Hoechst 33,342 staining of the nuclei (blue), CD31 as an EC marker to illustrate angiogenesis (red), and α-SMA (smooth muscle actin alpha) as a marker of pericytes (green) following fixation 8 days after seeding. Scale bars = 40 µm [20]. (e) Immunostaining for VE-cadherin (magenta), labelled with DAPI (blue), and the actin stain phalloidin (green) as compared with the structure of human engineering microvessels (hEMVs) in static conditions and exposed to flow containing either dimethyl sulfoxide (DMSO) or DAPT (a Notch signaling inhibitor). Scale bar = 50 µm [21]. Figure republished with permission from each indicated reference as follows: [17] for part (a), [18] for part (b), [19] for part (c), [20] for part (d), and [21] for part (e).

Figure 3

Lymphatics-on-a-chip: (a) A single lymphatic vessel in a microfluidic system [55], (b) bioprinted perfusable blood vessel and one-end-blinded lymphatic vessel on a microfluidic chip [56], (c) Generation of interstitial flow using pressure gradient created by the volume difference between the two fluidic channels around the central channel [57]. Figure republished with permission from each indicated reference as follows: [55] for part (a), [56] for part (b), and [57] for part (c).

Figure 4

Vasculatures in a villus of the small intestine.

Figure 5

Microfluidic chip designs for a potential intestinal-vasculature-on-a-chip: (a) The “cut and assemble” method can be used to independently design the channel of each layer [132], (b) the 3D cylindrical system can be used for more physiologically relevant model of the intestinal vasculatures for 3D analyses [133], (c) blood and lymphatic vessels can be formed on a single chip [134], and (d) vacuum chambers generate cyclic mechanical strain [124].

Figure 6

A simplified cross-sectional diagram showing the structure of a neurovascular unit in the brain and illustrating the cell–cell interactions. The innermost layer consists of the mircovessel endothelial cells surrounded by the basement membrane. Pericytes attach to and incompletely cover the basement membrane. The endfeet of astrocytes act as the outermost layer of the vascular structure and interact directly with the other cells of the neurovascular unit (NVU). Neurons can interact with the other cells either directly through their dendrites and subsequent synaptic space or through the astrocytes.