Bone fusion materials: past, present, and future

Bone fusion is one of the mainstay managements for degenerative spinal diseases and critical-sized bone defects resulting from trauma, tumors, infection, and nonunion. Bone graft materials are required for promoting bone healing, with autografts historically considered the gold standard due to their osteogenic, osteoinductive, and osteoconductive properties. However, donor site morbidities have led to the development of alternative bone graft substitutes. Currently available alternative options for bone fusion include allografts, ceramics, demineralized bone matrix (DBM), and bone morphogenetic proteins (BMPs). Each material has its advantages and disadvantages. Allografts avoid donor site morbidities but lack osteogenic properties and pose disease transmission risks. DBMs are acid-extracted allografts that have osteoconductive and osteoinductive properties but require combination with autografts because of the lack of evidence for their stand-alone use. BMP-2 has potent osteoinductive properties and is considered an ideal fusion material, but faces unresolved challenges related to optimal dosage and carrier. Synthetic peptides, mimicking the cell-binding domain of type I collagen, facilitate the attachment of osteogenic cells (such as osteoblasts) to the graft material and the production of extracellular matrix, leading to improved bone growth at the fusion site. The development of materials with ideal properties is a research hotspot. Recent advancements in biomaterials, such as hydrogels, nanomaterials, and three-dimensional-printed biomaterials, offer promising future options for bone fusion. This review provides an overview of available bone fusion materials, their advantages and disadvantages, and introduces emerging candidate options for bone fusion.