In vitro biomimetic modeling of physio­logical structures bridges the gap between 2D in vitro culture and animal models. Lumens (tubular structures) are ubiquitous in vivo, being present in blood vessels, mammary ducts, and the lymphatic system. A method ‘LumeNEXT' is presented here that allows the fabrication of 3D embedded lumens where size, structure, distance, and configuration can be controlled using standard poly­dimethylsiloxane micromolding methods.

We inhale respiratory pathogens continuously, and the subsequent signaling events between host and microbe are complex, ultimately resulting in clearance of the microbe, stable colonization of the host, or active disease. Traditional in vitro methods are ill-equipped to study these critical events in the context of the lung microenvironment. Here we introduce a microscale organotypic model of the human bronchiole for studying pulmonary infection. By leveraging microscale techniques, the model is designed to approximate the structure of the human bronchiole, containing airway, vascular, and extracellular matrix compartments. To complement direct infection of the organotypic bronchiole, we present a clickable extension that facilitates volatile compound communication between microbial populations and the host model. Using Aspergillus fumigatus, a respiratory pathogen, we characterize the inflammatory response of the organotypic bronchiole to infection. Finally, we demonstrate multikingdom, volatile-mediated communication between the organotypic bronchiole and cultures of Aspergillus fumigatus and Pseudomonas aeruginosa.

Advances in tissue engineering and microtechnology have enabled researchers to more easily generate in vitro tissue models that mimic the tissue geometry and spatial organization found in vivo (e.g., vessel or mammary duct models with tubular structures). However, the widespread adoption of these models for biological studies has been slow, in part due to the lack of direct comparisons between existing 2-dimensional and 3-dimensional cell culture models and new organotypic models that better replicate tissue structure. Using previously developed vessel and mammary duct models with 3-dimensional lumen structures, we have begun to explore this question. In a direct comparison between these next generation organotypic models and more traditional methods, we observed differences in the levels of several secreted growth factors and cytokines. In addition, endothelial vessel geometry profoundly affects the phenotypic behavior of carcinoma cells, suggesting that more traditional in vitro assays may not capture in vivo events. Here, we seek to review and add to the increasing evidence supporting the hypothesis that using cell culture models with more relevant tissue structure influences cell fate and behavior, potentially increasing the relevance of biological findings.-Bischel, L. L., Sung, K. E., Jiménez-Torres, J. A., Mader, B., Keely, P. J., Beebe, D. J. The importance of being a lumen. FASEB J. 28, 4583-4590 (2014). www.fasebj.org Key Words: tissue engineering ⅐ cell culture ⅐ tissue geometry ⅐ microtechnology ⅐ microfluidics Current research tools for the study of cell-or tissue-level biological processes can be classified along a continuum of increasingly more complex models, ranging from 2-dimensional (2D) cell culture to in vivo animal models (Fig. 1). In vivo models involve the use of whole organisms, usually mice, which inherently account for many important complexities in the body (1-3). However, it is difficult to investigate the role of the many microenvironmental factors individually using in vivo models, due to challenges associated with isolating specific interactions. In addition, in vivo models tend to be time consuming and costly, limiting their use in routine assays. Moreover, the use of animal models comes with ethical issues, and, in many cases, animal biology is significantly different from humans. At the other end of the spectrum, in vitro 2D cell culture is commonly used to study specific cell behavior and interactions. While these assays have provided much scientific knowledge and insight, they typically lack numerous factors associated with complex microenvironments, including tissue structure, cell-cell interactions, or cell-extracellular matrix (ECM) interactions, raising questions regarding the relevance of 2D cell culture for modeling in vivo responses.To bridge this gap between in vivo and in vitro models and augment the tools available to biologists, there has been an increasing interest in the development of biomimetic tissue models with improved representation of in vivo condi...