Purpose Rupture of the anterior cruciate ligament (ACL) is among the most common musculoskeletal injuries. Surgery utilizes ligament autografts or allografts, both of which have significant limitations. Tissue engineering overcomes the current limitations by in vitro growth of reparative cells on a biomaterial scaffold for implantation. The ACL's high tensile strength results from cellular production and organization of extracellular matrix (ECM). Mechanical stimulation may increase ECM production and organization. We have previously demonstrated that fibroblasts on a polymer scaffold showed increased cell spreading, a sign of adaptation to the local environment and a precursor to ECM production, when subjected to cyclic mechanical stimulation for 24 hours. In this study we investigated the effects of isometric stress on spreading of fibroblast on a poly(“-caprolactone) (PCL) scaffold.
Methods Nine 95% porous PCL scaffolds were fabricated and seeded with NIH 3T3 fibroblasts. After 48 hours in static culture, three scaffolds were place in each experimental group and isometric stress was applied by stretching the scaffolds 0%, 6%, or 15%. After 8 days in culture, the cell-seeded scaffolds were sectioned and stained with H&E. Cell length and area were measured, from which cell aspect ratio, a measure of cell spreading, was calculated.
Results For the 0%, 6%, and 15% stretch groups, the average cellular aspect ratios were 0.172 (0.249-0.146) (95% C.I.), 0.177 (0.247-0.158), and 0.168 (0.208-0.145) respectively. There were no significant differences in aspect ratio between groups. Qualitatively, morphology was consistent between groups, with most cells forming aggregates through extensive cytoplasmic processes.
Conclusion Although mechanical stimulation is necessary for fibroblast spreading during a short culture period, for a longer culture period, isometric stress is not necessary for fibroblast spreading. Another explanation is that perhaps isometric stretch is not the ideal form of mechanical stimulation and another form (ie, cyclic stretch) could induce changes in cellular morphology.
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