Engineering human neo-tendon tissue in vitro with human dermal fibroblasts under static mechanical strain

Proper cell source is one of the key issues for tendon engineering. Our previous study showed that dermal fibroblasts could be used to successfully engineer tendon in vivo and tenocytes could engineer neo-tendon in vitro with static strain. This study further investigated the possibility of engineering human neo-tendon tissue in vitro using dermal fibroblasts. Human dermal fibroblasts were seeded on polyglycolic acid (PGA) fibers pre-fixed on a U-shape as a mechanical loading group, or simply cultured in a dish as a tension-free group. In addition, human tenocytes were also seeded on PGA fibers with tension as a comparison to human dermal fibroblasts. The results showed that human neo-tendon tissue could be generated using dermal fibroblasts during in vitro culture under static strain and the tissue structure became more mature with the increase of culture time. Longitudinally aligned collagen fibers and spindle shape cells were observed histologically and collagen fibril diameter and tensile strength increased with time and reached a peak at 14 weeks. In contrast, the dermal fibroblast-PGA constructs failed to form neo-tendon, but formed disorganized fibrous tissue in tension-free condition with significantly weaker strength and poor collagen fiber formation. Interestingly, neo-tendon tissues generated with human dermal fibroblasts were indistinguishable from the counterpart engineered with human tenocytes, which supports the viewpoint that human dermal fibroblasts is likely to replace tenocytes for future tendon graft development in vitro with dynamic mechanical loading in a bioreactor system.