Dynamic in vitro microfluidic system for standardised osteoimmunological evaluation of implant materials

In the last few decades, ceramics have entered the field of dental and bone implants and have been subject to extensive implant-related research. Yet there is a variety of suitable ceramic compositions available which remain to be tested for implant research. Furthermore, few studies have investigated the impact of surface conditions such as roughness, surface chemistry, or polarity, and their impact on protein adsorption and cell adhesion and differentiation. At the implant site, the general assumption is that at first blood proteins are being adsorbed by the implant and subsequently immune cells adhere to the surface. Macrophages, as major protagonists in inflammatory responses, are well known to polarize and either promote pro- or anti-inflammatory actions at the wound site. Macrophages signal the surrounding cell types, e.g. other immune cells or mesenchymal stem cells (MSCs), via cytokine release and thereby also have a strong effect on bone forming processes. However, studies focusing on macrophage polarization and their effects to other cells, like MSCs, directly on the biomaterial are still elusive due to varying experimental setups and approaches. With emerging materials and surface functionalizations intended for implant purposes, there is a strong need for a standardized procedure in immunological and osteoimmunological evaluation. In this work, we are implementing a modular microfluidic approach that will allow investigation of various materials of interest, co-culturing experiments, and simple and rapid secretome analysis. Our interest is particularly vested in the influence of various solid biomaterials on the polarization of macrophages, and cellular communication between them and osteogenic differentiating MSCs. In a novel approach, we incorporate biomaterials in a circular microfluidic system allowing cytokine signalling of immune cells and MSCs that are spatially separated. Cytokine release and concentrations are being monitored by sampling of circulating supernatant and instant analysis via a homogeneous immunoassay in a separate microfluidic module.