Biomimetic Hematoma Promotes Superior Bone Regeneration With Ultra-low-Dose rhBMP-2 in a Goat Large-Defect Model

The aim of this study was to evaluate whether an ultra-low dose of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered within a biomimetic hematoma (BH) scaffold could regenerate a large bone defect in goats more efficiently than a high dose of rhBMP-2 delivered on an absorbable collagen sponge (ACS). The BH is an autologous scaffold, created from whole blood and defined concentrations of coagulants, and is designed to closely mimic the structural and biological properties of a naturally healing fracture hematoma. It initiates the body's intrinsic healing cascade, thereby recapitulating the sequential phases of bone repair.

A 2.5-cm defect was created in goat tibias and treated with either a BH scaffold containing ultra-low doses of rhBMP-2 (210 and 42 μg) or ACS with 2.1 mg of rhBMP-2. Empty defects and contralateral tibias served as controls. Bone regeneration was evaluated biweekly using radiographs and further assessed with micro-CT and histology at 8 weeks.

A total of 12 specimens, three per group, were used for radiographic, micro-CT, and histological evaluations. By 8 weeks, radiographic scores showed complete regeneration in the BH+210 µg (5.0 ± 0.0) and BH+42 µg (4.7 ± 0.2) groups. The ACS+2.1 mg group scored 4.3 ± 0.4 with some unmineralized regions while the ED group showed limited healing (2.6 ± 0.2; P < 0.001 vs. all other groups). Micro-CT analysis demonstrated significant differences in TV and BV between the BH group treated with 210 μg of rhBMP-2 and that treated with 42 μg of rhBMP-2 (TV: P = 0.02; BV: P = 0.009), and between the ACS+2.1 mg rhBMP-2 group and the BH+42 μg rhBMP-2 group (BV: P = 0.05), with the higher dose BH group showing significantly lower values than the other rhBMP-2 groups. Notably, the BH+42 µg group showed superior bone structural quality, with the highest predicted torsional strength ( P < 0.0001 vs. all groups). Histological observations revealed that BH+210 µg rhBMP-2 generated the most mature and organized bone architecture, closely resembling native tissue. By contrast, BH+42 µg showed ongoing remodeling with residual cartilage, while in the ACS+2.1 mg group, the marrow space remained filled with dense bone. The ED group predominantly contained fibrocartilage and collapsed muscle within the defect.

This study demonstrated that the BH scaffold, an autologous biodegradable matrix, enabled delivery of ultra-low rhBMP-2 doses that achieved rapid and consistent bone regeneration and outperformed the clinically used ACS. This has significant clinical implications, as the BH scaffold offers a promising biomaterial-free solution for precise rhBMP-2 delivery, enhancing rapid bone regeneration while minimizing dosage, reducing adverse effects, and lowering treatment costs, making it an effective intervention for complex bone injuries.