β-TCP/Collagen Composite Scaffolds Facilitate Bone Remodeling in Vertebral Plate Fusion

β-tricalcium phosphate (β-TCP) is widely used as a bone substitute because of its biocompatibility, osteoconductivity, and biodegradability; however, its brittleness and limited adaptability to irregular bone surfaces may restrict its performance in spinal fusion. This study aimed to evaluate whether a β-TCP/collagen composite scaffold could enhance osteogenesis and promote sustained bone remodeling in a sheep lumbar interlaminar fusion model. β-TCP/collagen composite scaffolds and β-TCP scaffolds were compared in vitro using MC3T3-E1 osteogenic precursor cells. Cell adhesion, proliferation, apoptosis, extracellular matrix mineralization, and osteogenic differentiation were assessed by scanning electron microscopy, CCK-8 assay, flow cytometry, alizarin red staining, alkaline phosphatase staining, RT-qPCR, and western blotting. In vivo, β-TCP and β-TCP/collagen scaffolds were implanted into the L3-L4 and L4-L5 interlaminar spaces, respectively, in a self-controlled sheep model. Bone formation and remodeling were evaluated by X-ray, micro-CT, and Van Gieson staining at 3, 5, and 8 months after surgery. The β-TCP/collagen scaffold showed a porous collagen-containing structure that supported greater MC3T3-E1 cell spreading and pseudopod extension than β-TCP alone. Cell proliferation on the β-TCP/collagen scaffold was significantly increased from day 3, whereas apoptosis remained low in all groups, with apoptotic cells accounting for less than 5%. Alizarin red and alkaline phosphatase staining showed more pronounced extracellular matrix mineralization in the β-TCP/collagen group. RT-qPCR and western blotting further demonstrated enhanced expression of osteogenic markers in the β-TCP/collagen group compared with β-TCP alone. In the sheep lumbar interlaminar fusion model, radiological, and histological analyses showed more sustained new bone formation and more organized trabecular remodeling in the β-TCP/collagen group. The β-TCP/collagen composite scaffold enhanced osteogenic activity in vitro and promoted more sustained bone remodeling in a sheep lumbar interlaminar fusion model compared with β-TCP alone. These findings suggest that β-TCP/collagen scaffolds may provide a clinically relevant biomaterial strategy for posterior spinal fusion, although further studies are needed to clarify the mechanisms underlying scaffold-mediated vascularized bone remodeling.