Establishment of Femoral Bone Defect Model in Sprague-Dawley Rat for Engineered Scaffold Implantation: A Pilot Study

Animal models undeniably offer advantages for studying bone regeneration in bone tissue engineering. Currently, a lack of documented and standardized critical size defects (CSD) protocol exists for femoral bone. This study established a femoral bone rat model to evaluate engineered scaffold and its effect on bone regeneration. Eight Sprague-Dawley rats were divided into four groups, each induced with specific sizes of circular femoral defects: 1.5 mm diameter; 4.0 mm depth (Groups A and B), and 2.4 mm diameter; 7.0 mm depth (Groups C and D). Rats were euthanized at 4- and 8-weeks post-induction. Observations revealed that the 4-week period was insufficient for initiating the bone healing process. Notable signs of bone healing and remodelling become apparent only after 8 weeks with normal morbidity scoring at week 5 onwards. Gross examination indicated that rat models with a defect size of 1.5 mm diameter; and 4.0 mm depth healed at a faster rate suggesting inadequate defect size. In contrast, the rat model 2.4 mm diameter; and 7.0 mm depth defect emerged as the suitable model with evidence of newly formed bone signifying the process of mineralization at the defect site. The Hematoxylin and Eosin (H&E) staining of bone tissue demonstrates substantial formation of bone tissues (osteoid) and vascularized areas, consequently supporting the efficacy of this model. Therefore, this study finds that the 8-week timepoint with a 2.4 mm diameter and 7.0 mm circular defect is ideal for assessing bone regeneration of an engineered scaffold in rat bone model.