The new gradient wave: soluble compound screening using microfluidic gradients for regenerative medicine research

The aim of regenerative medicine (RM) is to restore normal function of damaged tissues or organs, using cell therapy, tissue engineered constructs and synthetic graft substitutes. Since the population of the western world is ageing, there is an increasing need for RM therapies, which are readily available in large quantities. In general, the search for such strategies is based on the candidate approach in which a limited number of candidates (e.g. biomaterials, growth factors and cells) are selected, based on a rationale. As a result, a limited number of candidates is investigated, and therefore development and clinical implementation of novel, significantly improved strategies is relatively slow. This thesis presents a novel method for screening effects of soluble factors on the behaviour of mammalian cells, which has been developed as an alternative to the classical candidate approach in RM research, with the goal to speed up the search for such candidates. The method covers the entire route from the development of a cell culture platform, to biological assay optimisation and data analysis. The method is based on a microfluidic multi-gradient platform that is capable of temporal screening, combination and concentration screening, single per-cell in situ assay and analysis, and mimicking of the biological microenvironment. Therefore, combining different experimental conditions into a single experiment. First, a microtiter plate-sized standalone chip holder was developed that allows for precise control of physiological conditions inside closed microfluidic cell culture systems, made from gas-impermeable materials. Next, a microfluidic multi-gradient microfluidic platform was developed, which can generate four orthogonal and overlapping concentration gradients of soluble compounds. Finally, a complete screening method was developed to observe single per-cell behaviour upon exposure to soluble compounds, using automated and in situ image analysis. As a proof-of-concept, the platform was applied to assess the concentration-dependent response of an osteoblast (bone) cells exposed to a hypoxia (low-oxygen) mimicking molecule phenanthroline, using an in situ fluorescent staining assay in combination with image analysis, applicable to closed microfluidic devices. In the future this method is intended to complement or replace current research approaches in screening soluble compounds for RM.