Microfluidic systems for artificial biological barriers

The concept of biological barriers, albeit intuitive, implies a certain extent of complexity, related to the diversity of their structure, organisation and size throughout the living organisms. For this reason, reliable experimental models are necessary to reproduce and characterise these biological structures in a relatively simple and isolated environment. In this PhD project, microfluidics has been employed for the realisation of experimental models resembling two different biological barriers: the endothelial barrier and the cell plasma membrane. In the first case, endothelial cells (ECs) were grown in the microchannels of a microfluidic device under physiological levels of shear stress, obtained by perfusing the system with a continuous constant flow. This allowed cells to form a mature physiological-like barrier, whose integrity is guaranteed by the formation of adherens junctions, containing the adhesion protein vascular endothelial (VE )-cadherin. This model was exploited for enhanced drug delivery studies, with the aim of increasing endothelial permeability through microbubble-enhanced ultrasound-induced (USMB) cavitation. Particular attention was paid to characterise the dynamics of permeabilisation events, with the employment of genetically engineered ECs expressing constitutively fluorescent VE-cadherin. Another microfluidic platform was developed and realised for the high-throughput and reproducible production of giant unilamellar vesicles (GUVs), a vesicular model of phospholipid bilayer that reproduces some of the features of cell plasma membrane. The produced GUVs were exploited for the measurement of important biomechanical parameters, such as the bending rigidity modulus, playing a role in cell membrane response to mechanical stimuli, like cavitation. The geometry of the device was designed to produce GUVs through the double emulsion method, including in the protocol the removal of the oil phase residues from the bilayer, to prevent them from affecting the bilayer biomechanical properties. The collected GUVs are intended for biomechanical studies through thermal fluctuation analysis.