Novel standardized massive bone defect model in rats employing an internal eight‐hole stainless steel plate for bone tissue engineering

Massive bone defects are a challenge in orthopaedic research. Defective regeneration leads to bone atrophy, non-union of bone, and physical morbidity. Large animals are important models, however, production costs are high, nursing is complex, and evaluation methods are limited. A suitable laboratory animal model is required to explore the underlying molecular mechanism and cellular process of bone tissue engineering. We designed a stainless steel plate with 8 holes; the middle 2 holes were used as a guide to create a standardized critical size defect in the femur of anaesthetized rats. The plate was fixed to the bone using 6 screws, serving as an inner fixed bracket to secure a tricalcium phosphate implant seeded with green fluorescent protein-positive rat bone marrow mesenchymal stem cells within the defect. In some animals, we also grafted a vessel bundle into the lateral side of the implant, to promote vascularized bone tissue engineering. X-ray, microcomputed tomography, and histological analyses demonstrated the stainless steel plate resulted in a stable large segmental defect model in the rat femur. Vascularization significantly increased bone formation and implant degradation. Moreover, survival and expansion of green fluorescent protein-positive seeded cells could be clearly monitored in vivo at 1, 4, and 8 weeks postoperation via fluorescent microscopy. This standardized large segmental defect model in a small animal may help to advance the study of bone tissue engineering. Furthermore, availability of antibodies and genetically modified rats could help to dissect the precise cellular and molecular mechanisms of bone repair.