Mechanical Stimulation by Ultrasound Enhances Chondrogenic Differentiation of Mesenchymal Stem Cells in a Fibrin‐Hyaluronic Acid Hydrogel

Chondrogenic differentiation and cartilage tissue formation derived from stem cells are highly dependent on both biological and mechanical factors. This study investigated whether or not fibrin‐hyaluronic acid ( HA ) coupled with low‐intensity ultrasound ( LIUS ), a mechanical stimulation, produces an additive or synergistic effect on the chondrogenesis of rabbit mesenchymal stem cells ( MSC s) derived from bone marrow. For the purpose of comparison, rabbit MSC s were first cultured in fibrin‐ HA or alginate hydrogels, and then subjected to chondrogenic differentiation in chondrogenic‐defined medium for 4 weeks in the presence of either transforming growth factor‐beta3 ( TGF ‐β3) (10 ng/mL) or LIUS treatment (1.0  MHz and 200 mW/cm 2 ). The resulting samples were evaluated at 1 and 4 weeks by histological observation, chemical assays, and mechanical analysis. The fibrin‐ HA hydrogel was found to be more efficient than alginate in promoting chondrogenesis of the MSC s by producing a larger amount of sulfated glycosaminoglycans ( GAG s) and collagen, and engineered constructs made with the hydrogel demonstrated higher mechanical strength. At 4 weeks of tissue culture, the chondrogenesis of the MSC s in fibrin‐ HA were shown to be further enhanced by treatment with LIUS , as observed by analyses for the amounts of GAG s and collagen, and mechanical strength testing. In contrast, TGF ‐β3, a well‐known chondrogenic inducer, showed a marginal additive effect in the amount of collagen only. These results revealed that LIUS further enhanced chondrogenesis of the MSC s cultured in fibrin‐ HA , in vitro , and suggested that the combination of fibrin‐ HA and LIUS is a useful tool in constructing high‐quality cartilage tissues from MSC s.