Microvasculature on a chip: study of the Endothelial Surface Layer and the flow structure of Red Blood Cells

Abstract

Microvasculatures-on-a-chip, i.e. in vitro models that mimic important features of microvessel networks, have gained increasing interest in recent years. Such devices have allowed investigating pathophysiological situations involving abnormal biophysical interactions between blood cells and vessel walls. Still, a central question remains regarding the presence, in such biomimetic systems, of the endothelial glycocalyx. The latter is a glycosaminoglycans-rich surface layer exposed to blood flow, which plays a crucial role in regulating the interactions between circulating cells and the endothelium. Here, we use confocal microscopy to characterize the layer expressed by endothelial cells cultured in microfluidic channels. We show that, under our culture conditions, endothelial cells form a confluent layer on all the walls of the circuit and display a glycocalyx that fully lines the lumen of the microchannels. Moreover, the thickness of this surface layer is found to be on the order of 600 nm, which compares well with measurements performed ex or in vivo on microcapillaries. Furthermore, we investigate how the presence of endothelial cells in the microchannels affects their hydrodynamic resistance and the near-wall motion of red blood cells. Our study thus provides an important insight into the physiological relevance of in vitro microvasculatures.

An integrated assay to probe endothelial glycocalyx-blood cell interactions under flow in mechanically and biochemically well-defined environments

“…In addition, this example illustrates how biomimetic surfaces can be interfaced with living cells. This approach has the potential to be extended further, to observe circulating cellmimetic beads on real glycocalyces on cultured endothelial monolayers [46], and even to live circulating cells on real glycocalyces. In this way, our integrated assay can encompass a large range of complexity, from fully reconstituted models that are well-defined and capture selected aspects of the cell-glycocalyx interaction in their pure form (thus facilitating mechanistic studies and the identification of new phenomena), to fully cellular systems that reproduce the complexity of the real endothelial glycocalyx-blood cell interactions more closely (thus facilitating tests of biological relevance).…”

Endothelial glycocalyx regulates cytoadherence inPlasmodium falciparummalaria

“…Nevertheless, the application of such models has been hindered by the experimental difficulty to obtain a mature glycocalyx in vitro. Protocols to observe endothelial glycocalyx in vitro by confocal microscopy under static [37] and flow conditions [38] have been recently published. However, to the best of our knowledge, no reports describing models of microcirculation to study the effect of glycocalyx on malaria in vitro are available in the literature.…”

Vascularized Microfluidics and the Blood–Endothelium Interface

“…Furthermore, damage to the endothelial glycocalyx can lead to shedding of the red blood cells' own glycocalyx layer [93], which itself has been implicated in various disease processes such as hemodialysis dependent end-stage renal disease [94]. In an effort to better understand this integral component of RBC-endothelial communication, Tsvirkun et al [95] developed an endothelialized microvascular model with channels 30 µm in diameter that allowed for measurement of the glycocalyx (600 nm), recapitulating the thickness of its in vivo counterpart, as seen in Figure 3 [96]. Furthermore, they confirmed the existence of a near-wall layer of approximately 4.5 µm away from the apical membrane of the ECs, depleted of RBC and consistent with the cell-free layer (CFL) which has been observed in vivo [97].…”