Adaptive responses of murine osteoblasts subjected to coupled mechanical stimuli

Restitution of the natural organization and orientation of cells is imperative for the construction of functional tissue scaffolds. While numerous studies have exploited mechanical methods to engineer tissues with the desired cellular architecture, fundamental knowledge is still lacking in understanding the manner in which morphological features can be modulated through coupled mechanical cues. To address this knowledge gap, the adhesion and alignment response of murine osteoblast cells under the synergistic effects of matrix rigidity and cyclic mechanical loading was investigated. This was accomplished by applying cyclic mechanical strain (1% at 0.05 Hz) to MC3T3-E1 cells seeded on PDMS substrates of different elastic moduli (1.22, 1.70 and 2.04 MPa). Results demonstrate that the overall cell density and expression of inactive vinculin increased on substrates subjected to cyclic stimulus in comparison to substrates under static loading. Conversely, in terms of the adhesion response, osteoblasts exhibited an increased growth of focal adhesion complexes under static substrates. Interestingly, results also elucidate that substrates of a stiffer matrix exposed to cyclic stimulus, had a significantly higher percentage of osteoblasts aligned parallel to the direction of the applied strain, as well as a higher degree of internal order with respect to the strain axis, in comparison to both cells seeded on substrates of lower stiffness under cyclic loading or under static conditions. These findings suggest the role of cyclic mechanical strain coupled with matrix rigidity in eliciting mechanosensitive adaptations in cell functions that allow for the reconstitution of the spatial and orientational assembly of cells in vivo for tissue engineering.