Microfabrication of In Vitro Alveolar-Capillary Barrier Model by Inkjet-based Bioprinting

Abstract

An in vitro alveolar-capillary barrier is one of the essential model systems for pulmonary drug and particle tests in disease studies, drug discovery and toxicology. An alveolar-capillary barrier in the gas exchanging region of the lung consists of epithelial and endothelial layers with a thickness of 2 μm. This thin structure is critical to sustain pulmonary function such as gas diffusion. There has been efforts to fabricate the biomimetic human alveolar-capillary barrier model, using microfluidic devices and bioprinting technology. However, none of the works has achieved to mimic this thin membrane, a key feature for the model. Here, we present a human alveolar-capillary model with a sub-10 mm-thick membrane, containing multi-type alveolar cells. We fabricated the alveolar-capillary barrier model with four types of human alveolar cell lines, including type 1 alveolar cell (NCI-H1703), type 2 alveolar cell (A549), lung fibroblast (MRC5), and lung microvascular endothelial cell (HULEC5a). High-resolution drop-on-demand inkjet printing enabled the fabrication of the thin alveolar-capillary barrier model under sub-10 μm thickness for the optimal structure by drop-on-demand deposition of multi-type alveolar cells as a thin layer. We evaluated the functions of the fabricated models by histology, barrier integrity test, and barrier permeability test to demonstrate the level of biomimicry. Inkjet-based bioprinting enabled the fabrication of reproducible in vitro alveolar-capillary models, which have biomimetic microstructures with customized and functionally designed micro-patterns. The inkjet-bioprinted alveolar-capillary models have a potential to replace animal testing as expecting to be applied in disease models for pathology, drug discovery, and toxicology.