Lung Development in a Dish: Models to Interrogate the Cellular Niche and the Role of Mechanical Forces in Development

Abstract

Over the past decade, emphasis has been placed on recapitulating in vitro the architecture and multicellular interactions found in organs in vivo [1, 2]. Whereas traditional reductionist approaches to in vitro models enable teasing apart the precise signaling pathways, cellular interactions, and response to biochemical and biophysical cues, model systems that incorporate higher complexity are needed to ask questions about physiology and morphogenesis at the tissue scale. Significant advancements have been made in establishing in vitro models of lung development to understand cell-fate specification, gene regulatory networks, sexual dimorphism, three-dimensional organization, and how mechanical forces interact to drive lung organogenesis [3–5]. In this chapter, we highlight recent advances in the rapid development of various lung organoids, organ-on-a-chip models, and whole lung ex vivo explant models currently used to dissect the roles of these cellular signals and mechanical cues in lung development and potential avenues for future investigation (Fig. 3.1).

Stochastic to Deterministic: A straightforward approach to create serially perfusable multiscale capillary beds

“…The vasculature develops through a complex series of coordinated events to generate a mature, hierarchically organized vascular network (63). The two main mechanisms for the establishment and growth of the vasculature are vasculogenesis, the formation of new vessels from endothelial cell aggregates to generate an initial primitive stochastic vascular network (64), and different modes of angiogenesis, the formation of new vessels from existing vessels (25, 65, 66). The formation of a mature tissue vasculature during development requires extensive use and coordination of the dynamic processes of growth, remodeling, and pruning.…”

“…Methods to create large vessels often rely on "top-down" deterministic approaches, including micromolding via casts and needles, direct 3D printing of cellular biomaterials to create vessel channels, or 3D printing of multi-ink systems including sacrificial biomaterials to form a vessel lumen (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). However, due to fabrication resolution limitations, these methods cannot be used to generate small vessels, so microvasculature is often created via endothelial self-assembly (19)(20)(21)(22)(23)(24)(25)(26)(27) which generates a vascular network called a plexus. Perfusable plexuses are most often fabricated as small regions within microfluidic devices; however, recent work has demonstrated the capability to create large perfusable self-assembled plexuses with tunable vessel sizes within arbitrarily shaped collagen gels (28).…”

A straightforward cell culture insert model to incorporate biochemical and biophysical stromal properties into transplacental transport studies

“…of the placental ECM change over gestation and in disease (8)(9)(10)(11)(12). Inclusion of these parameters is limited primarily to three-dimensional cell culture models or "organ-on-a-chip" models (13)(14)(15)(16)(17), which significantly increase the complexity and decrease the throughput of the number of individual samples that can be tested simultaneously. To date, independent control of the biophysical and biochemical properties of tissue stroma has not been introduced to cell culture insert systems in a straightforward and reproducible manner that would make them suitable for transport studies.…”

Zonal Patterning of Extracellular Matrix and Stromal Cell Populations Along a Perfusable Cellular Microchannel

“…In vitro models created with morphogen or mechanical gradients within a bulk hydrogel traditionally used to investigate their role in development or disease are often 2D, which lack architectural cues relevant to many tissues, including the kidney. Microphysiological systems (MPSs), while reductionist, offer a platform to recapitulate and precisely control key biochemical, biophysical, and cellular components of the microenvironment with well defined geometries (10)(11)(12). However, current techniques to regionally pattern the ECM around a microchannel within an MPS only have control radially/circumferentially and not longitudinally along the microchannel length.…”