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

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.

Generation of in vitro tissue models with serially perfused hierarchical vasculature would allow greater control of fluid perfusion throughout the network and enable direct mechanistic investigation of vasculogenesis, angiogenesis, and vascular remodeling. In this work, we have developed a method to produce a closed, serially perfused, multiscale vessel network embedded within an acellular hydrogel. We confirmed that the acellular and cellular gel-gel interface was functionally annealed without preventing or biasing cell migration and endothelial self-assembly. Multiscale connectivity of the vessel network was validated via high-resolution microscopy techniques to confirm anastomosis between self-assembled and patterned vessels. Lastly, using fluorescently labeled microspheres, the multiscale network was serially perfused to confirm patency and barrier function. Directional flow from inlet to outlet man-dated flow through the capillary bed. This method for producing closed, multiscale vascular networks was developed with the intention of straightforward fabrication and engineering techniques so as to be a low barrier to entry for researchers who wish to investigate mechanistic questions in vascular biology. This ease of use offers a facile extension of these methods for incorporation into organoid culture, organ-on-a-chip (OOC) models, and bioprinted tissues.