There is an increasing demand for bone graft substitutes that are used as osteoconductive scaffolds in the treatment of bone defects and fractures. Achieving optimal bone regeneration requires initial cell seeding of the scaffolds prior to implantation. The cell seeding chamber is a closed assembly. It works like a sandglass. The position of the scaffold is between two reservoirs containing the fluid (e. g. blood). The fluid at the upper reservoir flows through the scaffold driven by gravity. Fluid is collected at the lower reservoir. If the upper reservoir is empty the whole assembly turned and the process starts again. A new compact cell seeding chamber for initial cell seeding has been developed that can be used in the operating theater.