Suitability of Bronchoscopic Spraying for Fluid Deposition in Lower Airway Regions: Fluorescence Analysis on a Transparent In Vitro Airway Model.

Introduction: Bronchoscopic spraying has potential for the application of therapeutic drugs in distal regions of the lung by bypassing the upper airways. However, there is a lack of understanding about the underlying fluid transport phenomena that are responsible for the intrapulmonary propagation of applied liquid. Methods: By using a transparent airway model, this study provides first experimental insights into relevant transport phenomena of bronchoscopic spraying. Furthermore, the penetration depth of the application is quantitatively evaluated. Laser-induced fluorescence is used to analyze fluid propagation in the transparent channels. Potential influencing factors such as the positioning in different airways, application number, breathing pattern, and lung obstructions are varied within this study to determine their influence on liquid deposition. Findings: This study shows that the method of bronchoscopic spraying allows the application of liquid in distal regions of the airway model. The position of the bronchoscope is a key influencing factor in increasing the penetration depth. We found that fluid transport along the distal airways essentially occurs by the film and plug flow phenomenon during application, which is similar to the transport mechanisms during instillation. Liquid plugs in lower airways are responsible for the reorganization of liquid during proximal movements and thereby influence the penetration depth in subsequent applications.

Combination of vascularization and cilia formation for three-dimensional airway tissue engineering.

Tissue engineering is a promising approach to treat massive airway dysfunctions such as tracheomalacia or tumors. Currently, there is no adequate solution for patients requiring the resection of more than half of the length of their trachea. In this study, the best conditions for combination of three different cell types from the respiratory airway system were investigated to develop a functional ciliated and pre-vascularized mucosal substitute in vitro. Primary human fibroblasts were combined with respiratory epithelial cells and endothelial cells. As scaffolds, fibrin gel and agarose-type I collagen blends were used and cultured with different medium compositions to optimize both vascularization and differentiation of the respiratory epithelium. A mixture of endothelial growth medium and epithelial differentiation medium was shown to optimize both vascularization and epithelial growth and differentiation. After 28 days of co-culture, significantly increased formation of capillary-like structures was observed in fibrin gels with more than three times higher structure volumes compared to agarose-collagen gels. After 35 days, epithelial differentiation into a pseudostratified epithelium with typical marker expression was improved on fibrin gels. While cilia formation was shown on both scaffolds, a higher number of ciliated cells and longer cilia were observed on fibrin gels. The data elucidate the important interplay of co-culture parameters and their impact on vascularization as well as epithelium development and provide a basis for development of functional three-dimensional airway constructs.