Effect of an injectable 3D scaffold for osteoblast differentiation depends on bead size

The objective of this study was to evaluate the effect of beta-tricalcium phosphate (beta-TCP) bead size on the behavior of KUSA/A1 mouse osteoblasts when the beta-TCP beads are used as the solid phase of a scaffold in which alginate was used as the gel phase. KUSA/A1 cells were loaded onto a three-dimensional (3D) scaffold fabricated from beta-TCP beads with diameters ranging from 300 to 500 mu m (small beads), 500-700 mu m (medium beads) and 700-850 mu m (large beads); cells were cultured for 3, 7 and 14 days. Scanning electron microscope observations showed that each bead was connected in a network consisting of the alginate gel and KUSA/A1 cellular matrix that was tightly bonded to form a 3D structure. After 3 days, cells in the 3D scaffold with medium beads had a significantly higher alkaline phosphatase activity (ALP) than cells in the other scaffolds. However, by 7 and 14 days in culture there was no significant difference in DNA levels, ALP activity or osteocalcin expression. At 8 weeks, only the composite containing small beads and KUSA/A1 cells had turned completely into bone in vivo. Thus, bead size may influence the success of bone formation in this context.