AbstractCost effective and safely to apply tissue engineered constructs of big volume bone transplants for the reconstruction of critical sized defects (CSD) are still not available. Key problems with synthetic scaffold materials are shrinkage and fast degradation of the scaffolds, a lack of blood supply and nutrition in the central scaffold volume and the absent or the scarce development of bone tissue along the scaffold to bridge the bone defect. The use of composite scaffolds made of biopolymers like polylactidglycolid acid (PLGA) coated and loaded with calcium phosphates (CaP) revealed promising therapeutical options for the regeneration of critical sized bone defects. In this study interconnectively macroporous PLGA scaffolds loaded with microporous and coated with nanoporous calcium phosphates were either seeded in fixed bed bioreactors with allogenic osteogenically induced mesenchymal stem cells and implanted or implanted unseeded into critical sized femoral bone defects. As CSD a 12 mm long segment of the chinchilla femur was excised where the proximal and distal parts of the femur were fixed and stabilized by the use of an eight-hole linear reconstruction plate and secured with three bicortical screws (2.7 mm diameter) on every side of the osteotomy. Aim of the study was if we could find a way to load and coat PLGA scaffolds with CaP so that shrinkage of scaffolds could be avoided, which would favour angiogenesis, blood supply and nutrition in the construct and thus avoid central necroses regularly observed so far in transplants not vascularized and which would be inhabited by cells of he bone lineage forming new bone and healing the defect. Four weeks, at least, a notable shrinkage of the scaffolds was avoided and scaffolds were practically not degraded. Both scaffolds, loaded and loaded and coated, revealed blood vessels in all parts of the implants after 4 weeks. Only in scaffolds seeded with allogenic mesenchymal stem cells the development of bridging bone constructs between proximal and distal edges of the femur was observed after four weeks without further supplementation of growth factors. In case of the implantation of non-seeded scaffolds no obvious scaffold bound bone development could be shown.