Improving linear stiffness of the cell-seeded collagen sponge constructs by varying the components of the mechanical stimulus.

In vitro mechanical stimulation has been reported to induce cell alignment and increase cellular proliferation and collagen synthesis. Our group has previously reported that in vitro mechanical stimulation of tissue-engineered tendon constructs significantly increases construct stiffness and repair biomechanics after surgery. However, these studies used a single mechanical stimulation profile, the latter composed of multiple components whose individual and combined effects on construct properties remain unknown. Thus, the purpose of this study was to understand the relative importance of a subset of these components on construct stiffness. To try to optimize the resulting mechanical stimulus, we used an iterative process to vary peak strain, cycle number, and cycle repetition while controlling cycle frequency (1 Hz), rise and fall times (25% and 17% of the period, respectively), hours of stimulation/ day (8 h/day), and total time of stimulation (12 days). Two levels of peak strain (1.2 % and 2.4%), cycle number (100 and 3000 cycles/day), and cycle repetition (1 and 20) were first examined. Higher levels of peak strain and cycle number were then examined to optimize the stimulus using response surface methodology. Our results indicate that constructs stimulated with 2.4% strain, 3000 cycles/day, and one cycle repetition produced the stiffest constructs. Given the significant positive correlations we have previously found between construct stiffness and repair biomechanics at 12 weeks post-surgery, these in vitro enhancements offer the prospect of further improving repair biomechanics.