Alginate Beads Encapsulating Hydroxyapatite Microparticle and BMP-2 for Long Bone Defect Regeneration: A Pilot Study

Large bone defects caused by trauma, infection, tumor excision, and non-union fractures are challenging to treat. Mechanical stability, appropriate osteoconductive bone grafts, and osteoinductive growth factors are necessary for bone regeneration in long bone diaphyseal defects. This study aimed to investigate the efficiency of a hybrid bone scaffold formed using hydroxyapatite (HAp) and bone morphogenetic protein (BMP)-2-containing alginate beads, combined with a barrier membrane, in promoting new bone formation in a rabbit radial segmental defect model.

Nine rabbits were divided into two groups depending on the type of implant: Alginate beads containing HAp microparticles in phosphate-buffered saline (n=5) or BMP-2 (n=4). A 10-mm radial segmental defect was stabilized using a bone plate and screws, wrapped with an absorbable collagen membrane, and filled with alginate beads. Bone healing at the defect site was assessed via radiography, micro-computed tomography, and histological analysis after 12 weeks.

The BMP-2/HAp alginate bead group showed significantly increased bone volume, polar moment of inertia, and periosteal callus ossification, along with a decreased fibrous infiltration at the defect site. Conversely, the BMP-2-unloaded HAp bead group exhibited membrane degradation, with no hard callus formation at the defect site. Therefore, HAp- and BMP-2-encapsulating alginate beads provided sufficient osteoconductive and osteoinductive support for long bone defect repair.

BMP-2/HAp alginate beads, combined with an appropriate collagen membrane and proper internal fixation, may be an effective treatment strategy for long bone segmental defects.