Sequential Biochemical and Mechanical Stimulation in the Development of Tissue-Engineered Ligaments

Application of stimuli in sequence to developing cultures in vitro offers the potential to intricately direct cell development and differentiation by following the template of native tissue behavior. We hypothesize that administration of mechanical stimulation at the peak of growth factor-induced cell activity will differentiate bone marrow stromal cells (BMSCs) along a fibroblast lineage and enhance in vitro ligament development through enhanced matrix ingrowth, matrix metalloproteinase-2 (MMP-2) production, collagen type I production, and extracellular matrix (ECM) alignment. BMSC-seeded silk matrices were cultured in a static growth-factor-free environment for 5 days prior to loading into bioreactor vessels to first establish an appropriate dynamic rotational regime, as determined through assessment of cell activity, histology, and surface topography. Once the regime was determined, seeded matrices initially cultured in basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), or growth-factor-free control medium for 5 days were loaded into the bioreactor for 9 days of mechanical stimulation. Our findings indicated that the sequential application of mechanical stimulation following growth factor supplemented static culture-induced cell differentiation toward a fibroblast lineage, enhancing matrix ingrowth, cell and ECM alignment, and total collagen type I produced compared to respective static cultures. The current results suggest a dynamic culturing regime in the development of engineered tissues.