Study, development and realisation of microfluidic devices able to generate nonlinear concentration gradients

Biomolecular gradients are an important, evolutionarily-conserved signalling mechanism for guiding growth, migration, and differentia- tion of cells within dynamic, three-dimensional environments of living tissues. Gradients play essential roles in many phenomena including development, inflammation, wound healing, and cancer. Interest in elucidating these phenomena has led to the development of numerous in vitro methods for exposing cells to chemical gradients. The core of this research was to develop and to realise engineered devices able to generate nonlinear concentration gradients of soluble species in cell culture chambers, in order to study cell response. During this PhD the 2D concentration gradient generator paradigm was first analysed in all its aspect, from theory (using fluid-electrical analogies) to simulation (CFD simulation showing accurately the species distribution within the device), ending with the realisation and experimental validation of the developed device. While advancing with the work, practical issues proper of those systems were faced, critically analysed and finally engineered solutions were proposed and applied, in order to make possible a reliable cell perfusion within the device. Concentration gradient concept was extended from common 2D to 3D, because soluble gradients in-vivo act in a 3D environment, thus stimulating a 3D scaffold with a 3D concentration gradient could lead in mimicking a more physiological environment. Gradients of me- chanical properties could lead cell migration and differentiation, and also them are in 3D in living tissues, i.e in the cartilage-subchondral bone system. For this reason a novel 3D concentration gradient maker, able to generate steady three-dimensional concentration gradients, was developed and realised.The device was applied as an hydrogel maker, fabricating hydrogel matrixes with a 3D gradient of mechanical properties. Those construct could be used as smart scaffolds. It is also important to guarantee the possibility to monitor environmental variables such as pH either into microfluidic devices and smart scaffolds, with not invasive/destructive methods. For this reason we developed 2D pH sensitive surfaces, with the perspective to be integrated into micro devices. To create a biocompatible 2D pH sensor, sensitive nanoparticles could be immobilised inside a hydrogel matrix, in order to guarantee a proper fluorescence Signal to Noise Ratio. Using extended range pH sensitive nanoparticles developed by the University of Nottingham, we developed sensitive surfaces. The idea of sensitive surfaces was then extended using inkjet printing coupled with Sol-gel method, using as polymeric ma- trix a Gelatine/Glycidoxypropyltrimethoxysilane (GPTMS) system, because the picoliter-size ink droplets evaporate quickly, thus allow- ing quick sol-gel transitions on the printed surface. An Ink with the pH sensitive nanoparticles was successfully printed with a modified Inkjet printer.Thanks to inkjet printing is also possible to think at 3D smart scaffolds of Gelatine/GPTMS, which inner behaviour could be investigated by optical fluorescence techniques, such as confocal microscopy, in order to have in-situ measurements. Devices and techniques developed during this PhD could have applications in biological research, as integrated tools for simultaneously stimulating and monitoring live cells, in order to gain knowledge about their behaviour. Also pharmacological profiling with ”one-shot” experiments, so drawing the dose-response curve of a compound in a single experimental run, could be an application of interest.