DEVELOPMENT OF TECHNOLOGIES TO ENABLE EXTRUSION 3D BIOPRINTING FOR LUNG TISSUE MODELS

Abstract

The lung structure, composition and properties create a balanced combination that allows the breathing process to occur, generating a dynamic environment that is challenging to model in vitro. Extrusion is a popular 3D bioprinting technology that can address some challenges in the design and development of in vitro models that mimic the lung tissue’s architecture and properties. We designed bioinks printable via extrusion that yield tunable crosslinked materials with biochemical and mechanical properties suitable to develop in vitro lung models. Two main components were identified that could mimic the properties of the lung: a) poly(ethylene glycol) diacrylate (PEGDA), a polymer capable of generating tunable stretchable hydrogels, b) lung tissue-derived extracellular matrix (ECM) that present the biochemical cues found in natural tissue microenvironments. However, these materials, as many other biomaterials available, are not printable via extrusion. The introduction of polyacrylic acid particles as rheology modifiers resulted in a versatile strategy that enabled the design of highly printable bioinks based on non-extrudable natural and synthetic polymers with different crosslinking mechanisms. PEGDA bioinks resulted in tunable non-cytotoxic hydrogels that can be engineered to mimic the mechanical properties of different tissues and allowed cell survival. The main drawback of the PEGDA based bioinks is the lack of cell adhesion points, which we addressed by introducing ECM proteins into the hydrogels. To work in that direction, a robust protocol to decellularize human and porcine lung tissue was developed and validated, allowing consistent cell removal while retaining important components like collagen, elastin, and GAGs. The following ECM digestion process was also optimized, and the influence of different conditions on cell behaviour was evaluated. Finally, ECM proteins were added to the bioink and printed, yielding materials that can be engineered to resemble the lung mechanical properties (by changing PEGDA concentration) and the desired biochemical cues (introduced by ECM proteins). The work developed in the present thesis will contribute to get closer to create a dynamic 3D lung model using extrusion bioprinting. The flexibility of this technology, and the tunability of the mechanical and biochemical properties that the methods being developed offer, can open the door to creating better in vitro models to study cell behaviour and disease evolution.