Assistant professor SUNY Binghamton Binghamton, New York, United States
Introduction:: The lung is arguably the most dynamic organ in the human body that continually undergoes dynamic tissue deformation and fluid flow throughout life. The dynamic environment generates various types of mechanical forces that are essential to the homeostasis and physiological functions of the respiratory system. Studies suggest that abnormal alterations in the lung mechanics (Fig. 1a) may play a causative role in the development and progression of many respiratory diseases [1]. Despite this evidence, research efforts to gain a better understanding of the pathological implications of physical abnormalities have been significantly hampered by the technical challenges associated with modeling complex changes in the structure and mechanical microenvironment of the respiratory tract during disease progression.
Here we describe a novel microengineering strategy to tackle this long-standing, critical challenge in respiratory biology and medicine. This approach is based on microphysiological three-dimensional (3D) cell culture integrated with programmable actuation of soft elastomeric microstructures to emulate i) cellular heterogeneity and complex microarchitecture of native lung tissue and ii) disease-induced mechanical forces and resultant pathophysiological tissue distortion in the lung (Fig. 1b and c). Specifically, we created a microengineered disease model that reconstitutes the constriction of conducting airways in the distal lung, which is a hallmark of obstructive lung diseases such as asthma. Using this engineering approach, we suggest the pathophysiological association of the mechanical abnormalities with the asthmatic airway tissue remodeling by showing that compressive forces promote extracellular matrix (ECM) deposition and vascular abnormality.
Materials and Methods:: As the first step to establish the mechanically active airway on a chip, we constructed a compartmentalized microfluidic device that enabled co-culture of primary human small airway epithelial cells (SAECS), lung fibroblasts (LFs), and pulmonary microvascular endothelial cells (PMVECs) in a physiologically relevant spatial arrangement. Fabrication of this device was achieved by utilizing removable templates and surface tension-induced pinning effects to form an airway compartment enclosed by an ECM hydrogel scaffold that contained a perfusable feeding channel. Cell culture in this system produced multilayered tissue constructs consisting of the small airway epithelium supported by the underlying vascularized stroma laden established through the vasculogenic self-organization of blood vessels during the coculture of LFs and PMVECs (Fig. 1b).
To mimic pathophysiological obstruction of small airways during asthma, we integrated our cell culture platform with a microfabricated soft elastomeric actuator capable of converting pneumatic pressure into precisely controlled inflation of microchannel walls. Actuation of this component exerted compressive forces on the cell culture chamber and induced the microfluidic airway tissue to undergo 3D structural distortion reminiscent of airway constriction in vivo (Fig. 1c). Using this microengineered model, we investigated how compressive mechanical forces contribute to disease processes such as ECM remodeling and vascular abnormalities which are defining features of asthmatic airways.
Results, Conclusions, and Discussions:: We successfully constructed a vascularized airway asthma model by integrating primary culture of human asthmatic airway cells with a pneumatically regulated elastomeric actuator (Fig. 1d and e). This disease model is capable of converting actuation of the micromechanical component to 3D structural compaction of engineered airway tissue reminiscent of the pathological constriction of in vivo small airways in asthma.
Using this engineering approach, we suggested that tissue-compression induced mechanical forces can contribute to ECM and vascular remodeling as metrics of pathophysiological association of the mechanical abnormalities with the airway tissue remodeling processes in asthma (Fig. 2a and b). Specifically, our study demonstrated that compressive forces can enhance LFs’ production of ECM proteins such as fibronectin and type III collagen, indicative of ECM remodeling process in asthmatic airways (Fig. 2a). Our observation also raised the possibility that compressive forces may serve as an angiogenic factor capable of causing structural changes in blood vessels known as one of remarkable features in asthmatic airways (Fig. 2b). Our proteomic analysis confirmed the pathological effect of microengineered tissue compression in our model, which further demonstrated the potential of our engineering approach to investigate how mechanical abnormalities contribute to disease processes in the respiratory system.
As clinical evidence has suggested that airway constrictions in asthmatics can lead to fibrotic remodeling of lung tissues in a manner independent of inflammation [2], pathophysiological effect of mechanical abnormalities have garnered great attention to gain better understanding of complex processes of the obstructive lung disease. Our work represents an important contribution to the collective research effort in that it introduces a novel microengineering approach to recapitulate the pathological deformation of diseased airways and interrogate its influence in the progression of tissue remodeling in asthma. By combining primary culture of human airway cells with pneumatic actuation of functional micro-cavity, we developed a mechanically compressible airway tissue model that can be used for emulating 3D tissue distortions during bronchoconstriction. As demonstrated in this study, the unique capability makes our airway model an attractive platform to examine mechanoresponsive contribution of airway cells to the ECM and vascular remodeling in asthmatic lungs.
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Ingber, D.E. Mechanobiology and diseases of mechanotransduction. Ann Med 35, 564-577 (2003).
Grainge, C.L. et al. Effect of bronchoconstriction on airway remodeling in asthma. N Engl J Med 364, 2006-2015 (2011).