Introduction Distraction osteogenesis is widely used in surgical correction of craniofacial skeleton abnormalities, however, its underlying cellular mechanisms are poorly understood. We used a new in vitro model, the microdistractor, to study changes in morphology, proliferation and differentiation of preosteoblasts under mechanical strain.
Methods Mouse calvarial immortalized cell line, MC3T3 cells were suspended in a polymerized three-dimensional collagen gel and subjected to either a distraction (tension stress), oscillation (alternating tension/compression stress), or no stress schedule for 14 days. Cell aspect ratio (largest/smallest diameter), deviation from axis of stress, proliferation (cell number), and expression of osteogenic lineage markers were monitored for all groups.
Results Cell morphology changed differently depending on stress schedule, but consistently within experimental groups and throughout the gels. Aspect ratio increased for all cells, but was greatest for the distracted group. The orientation of cells with respect to the linear axis of stress was either arbitrary (control), parallel (during distraction), or perpendicular (during compression). Proliferation and differentiation into osteogenic lineage occurred in all groups, with greatest cell count and protein concentration in the distraction group, and earliest osteogenic marker expression in the oscillation group.
Conclusions The microdistractor is an effective in vitro model of distraction osteogenesis, yielding uniform stress distribution throughout the gel and consistent changes in two cell morphologic parameters. Distraction is more effective than oscillation in stimulating proliferation of preosteoblastic cells, however, oscillation induces differentiation into osteogenic lineage earlier than distraction does. Studies using adipose derived stem cells in the microdistractor system are ongoing.