Background: Bone grafts are in high demand due to the increase in the cases of bone defects mainly caused by trauma, old age, and disease-related bone damages. Tissue-engineered calcium phosphate (CaP) biomaterials match the major inorganic contents of bone, thereby could be the potential bone graft substitute. However, CaP-bone grafts lack the osteoinductivity that is vital for effective bone regeneration. In this study, we aimed to test the bone defect healing potential of biomimetically fabricated low dose BMP2-doped CaP (BMP2.BioCaP) grafts in a large animal model.

Methods: Low dose BMP2 was doped internally (BMP2-int.BioCaP) or on the surface of CaP (BMP2-sur.BioCaP) grafts during the fabrication process. Our previous study showed the robust bone regenerative potential of BMP2-int.BioCaP and BMP2-sur.BioCaP grafts in the rat ectopic model. In this study, we investigated the bone defect healing potential of BMP2.BioCaP grafts in sheep humerus/femoral defects, as well as compared with that of autologous bone graft and clinically used deproteinized bovine bone (DBB) xenograft.

Results: Different ways of BMP2 doping did not affect the surface morphology and degradation properties of the graft materials. Micro-CT and histology results showed robustly higher bone defect-healing potential of the BMP2.BioCaP grafts compared to clinically used DBB grafts. The bone defect healing potential of BMP2.BioCaP grafts was as effective as that of the autologous bone graft. Although, BMP2-int.BioCaP doped half the amount of BMP2 compared to BMP2-sur.BioCaP, its' bone defect healing potential was even robust. The BMP2.BioCaP grafts showed less immunogenicity compared to BioCaP or DBB grafts. The volume density of blood vessel-like and bone marrow-like structures in both BMP2.BioCaP graft groups were in a similar extent to the autologous group. Meticulous observation of higher magnification histological images showed active bone regeneration and remodeling during bone defect healing in BMP2.BioCaP graft groups.

Conclusion: The robust bone regenerative potential of BMP2.BioCaP grafts in the ectopic model and in-situ bone defects in small and large animals warrant the pre-clinical studies on large animal critical-sized segmental bone defects.

背景：由于主要由创伤，老年和与疾病相关的骨损伤引起的骨缺损病例的增加，对骨移植物的需求很高。组织工程磷酸钙（CaP）生物材料与骨骼的主要无机含量相匹配，因此可能是潜在的骨移植替代物。但是，CaP骨移植物缺乏对有效骨再生至关重要的骨诱导能力。在这项研究中，我们旨在在大型动物模型中测试仿制的低剂量BMP2掺杂CaP（BMP2.BioCaP）移植物的骨缺损愈合潜力。

方法：在制造过程中，将低剂量的BMP2掺杂在内部（BMP2-int.BioCaP）或CaP（BMP2-sur.BioCaP）移植物的表面上。我们先前的研究显示了BMP2-int.BioCaP和BMP2-sur.BioCaP移植物在大鼠异位模型中具有强大的骨再生潜力。在这项研究中，我们研究了BMP2.BioCaP移植物在绵羊肱骨/股骨缺损中的骨缺损愈合潜力，并与自体骨移植物和临床使用的脱蛋白牛骨（DBB）异种移植物进行了比较。

结果：BMP2掺杂的不同方式不会影响接枝材料的表面形态和降解性能。显微CT和组织学结果显示，与临床使用的DBB移植相比，BMP2.BioCaP移植具有更高的骨缺损修复潜力。BMP2.BioCaP移植物的骨缺损愈合潜力与自体骨移植物一样。尽管与BMP2-sur.BioCaP相比，BMP2-int.BioCaP掺杂的BMP2量是其一半，但其骨缺损愈合潜力甚至很强。与BioCaP或DBB移植物相比，BMP2.BioCaP移植物显示出较低的免疫原性。BMP2.BioCaP移植物组的血管样和骨髓样结构的体积密度与自体组相似。

结论： BMP2.BioCaP移植物在异位模型和 原位 大型和大型动物的骨缺损值得对大型动物的关键尺寸节段性骨缺损进行临床前研究。