The effects of varying frequency and duration of mechanical stimulation on a tissue-engineered tendon construct

Decellularized, discarded human tissues, such as the human umbilical vein, have been widely utilized for tissue engineering applications, including tendon grafts. When recellularized, such natural scaffolds are cultured in 3D dynamic culture environments (bioreactor systems). For tendon tissue-engineered grafts, such systems often employ oscillatory mechanical stimulation in the form uniaxial tensile strain. The three main parameters of such stimulation are frequency, duration, and force. In this study we investigated the effects of changing the duration (0.5, 1, and 2 h/day) and frequency (0.5, 1, 2 cycles/min) of stimulation of a human umbilical vein seeded with mesenchymal stem cells cultured for up to 7 days. Strain of the construct was held constant at 2%. The highest proliferation rates were observed in the 0.5 h/day duration and 1 cycle/min frequency (203% increase) with a close second being 1 h/day and 1 cycle/min frequency (170% increase). Static cultures along with a 2 cycles/min frequency and a 2 h/day duration of stretching did not increase cellular proliferation significantly. Extracellular matrix quality and alignment of the construct fibers had a direct relation to cellularity and those groups with the highest cellularity improved the most. Gene expression indicated cellular activity consistent with tendon-like tissue remodeling. In addition, scleraxis, tenascin-C, and tenomodulin were upregulated in certain groups after 7 days, with osteoblast, chondrocyte, and adipocyte phenotypes depressed. The stimulation parameters investigated in this study indicated that slower frequencies and shorter durations were best for construct quality in early stage cultures.