A novel method to produce immobilised biomolecular concentration gradients to study cell activities: design and modelling.

It is well known that many cell functions are activated by chemical signals with a time and space-dependent profile. To mimic these profiles in vitro, it is necessary to develop a system that is able to generate concentration gradients with a resolution similar to that perceived by cells, which is around nanomolar with a spatial resolution of a few tens of microns. Many devices capable of generating steady-state concentration gradients have been developed using continuous flow micro-fluidic techniques. However, these systems cannot reproduce the immobilised concentration gradients that are present in the extracellular matrix. For this reason, we have developed a new gradient generator to enable precise and reproducible studies on the effects of immobilised concentration gradients on cell behaviour. A well-known gradient of a desired molecule was generated on the bottom surface of a hydrogel, which was then used as a stamp to immobilise the molecule on a functionalised substrate. A concentration gradient was thus obtained using a simple silane-based chemical reaction. To validate the method, image analysis was performed on glass slides printed with fluorescein isothiocyanate (FITC)- collagen and FITC-poly-lysine concentration gradients. Preliminary cell adhesion tests were also carried out by seeding NIH-3T3 and mesencephalic cells on lab-glass slides printed with concentration profiles of collagen and poly-lysine, respectively.