Favorable morphologic change of preosteoblasts in a three-dimensional matrix with in vitro microdistraction

Background: Distraction osteogenesis has been used to correct hypoplastic and asymmetric bony deformities in the growing patient, yet its underlying cellular mechanisms are poorly understood. Using a new in Vitro model, the microdistractor, morphologic properties of preosteoblasts under mechanical strain were studied. Methods: Mouse calvarial MC3T3 cells were suspended in a polymerized three-dimensional collagen gel and stressed for 14 days as one of three groups (n = 30): (1) distraction (0.5 min/day); (2) oscillation (1 min/day for 2 days alternated with 1 mm/day for 2 days); and (3) control (no force). A computer modeling system, KS-300, was used to record cell shape (aspect ratio) and orientation (deviance from axis of stress). Results: In part I of the study, morphologic cellular changes were found to be even throughout different regions of the gel (central versus peripheral, versus different vertical layers), suggesting the force was evenly applied to all cells in the gel. In addition, when linear distraction forces were applied, morphologic change occurred over time, suggesting a morphologic response to the applied stress. In part II of the study, with different forces applied, morphologic changes occurred over time such that linear distraction forces caused cells to elongate and align in a parallel direction to the force, whereas oscillation caused cells to switch from parallel (with distraction) to perpendicular ( with compression) orientation relative to the force applied. Conclusion: The authors' data suggest that the microdistractor device is an effective in vitro model for studying the cellular response to distraction stresses. It may be used in future studies to optimize clinical methods of distraction.