69 Dipl.-Biol. Claudia Kleinhans Phone +49 711 970-4073 claudia.kleinhans@igb.fraunhofer.de Prof. Dr. Petra Kluger Phone +49 711 970-4072 petra.kluger@igb.fraunhofer.de Funding We would like to thank the Fraunhofer-Gesellschaft for funding the “DegraLast” project under the program market-driven prospective research (MAVO). Project partners Fraunhofer IFAM, Bremen and Dresden | Fraunhofer ILT, Aachen | Fraunhofer IBMT, St. Ingbert Advanced model by the co-culture of osteoblasts and osteoclasts The recapitulation of the physiological process of bone re- modeling is an effective method to obtain the desired proper- ties for bone replacement materials. While osteoclasts resorb the material, osteoblasts form new bone. Current in vitro studies focus only on one type of cell and investigate either bone resorption or bone formation. Therefore, we aimed to establish a co-culture of both cell types to simulate the bone remodeling process and to extend current test systems. In the development of in vitro co-culture systems, we first identified optimal culture conditions for the two cell types. Then we developed a method that leads to osteoclast differentiation without addition of differentiation factors, which allowed for the co-culture of both cell types (Fig. 3). Outlook A decisive advantage of our in vitro test system is the ability to work with human cells in the testing of new materials or coat- ings. The results generate the initial evidence on the suitability of newly developed implant material. 1 Actin cytoskeleton (red) and cell nuclei (blue) of undifferentiated (A) and differentiated (B) monocytes. 2 Scanning electron microscopic image of resorption lacunae after removal of osteoclasts cultured on bovine bone substitute material. 3 Histological staining of the vitronectin receptor and the cell nuclei of human mesenchymal stem cells and monocytes. In co-culture, the cells develop an osteoclast phenotype. 32 100 μm10 μm Contacts