This study investigated the effect of mechanical load on human mesenchymal stem cell (hMSC) differentiation under different exogenous transforming growth factor‐β1 (TGF‐β₁) concentrations (0, 1 or 10 ng/ml).The role of the TGF‐β signalling pathway in this process was also studied. Human MSCs were seeded into fibrin‐biodegradable polyurethane scaffolds at a cell density of 5 × 10⁶ cells per scaffold and stimulated using our bioreactor. One hour of surface motion superimposed on cyclic compression was applied once a day over seven consecutive days. Scaffolds were analysed for gene expression, DNA content and glycosaminoglycan amount. Addition of TGF‐β₁ in the culture medium was sufficient to induce chondrogenesis of hMSCs. Depending on the TGF‐β₁ concentration of the culture medium, mechanical load stimulated chondrogenesis of hMSCs compared to the unloaded scaffolds, with a much stronger effect on gene expression at lower TGF‐β₁ concentrations. With TGF‐β₁ absent in the culture medium, mechanical load stimulated gene transcripts and protein synthesis of TGF‐β₁ and TGF‐β₃. TGF‐β type I receptor inhibitor LY364947 blocked the up‐regulation on TGF‐β₁ and TGF‐β₃ production stimulated by mechanical load, and also blocked the chondrogenesis of hMSCs. Taken together, these findings suggest that mechanical load promotes chondrogenesis of hMSCs through TGF‐β pathway by up‐regulating TGF‐β gene expression and protein synthesis.

In this study, human bone marrow mesenchymal stem cell (hMSC)–seeded fibrin–polyurethane composite scaffolds were subjected to various mechanical load protocols to determine the effect of compression and surface rotation frequency and axial compression magnitude on the induction of chondrocyte-specific gene expression and protein synthesis. After 7 days of preculture and 7 days of load, application of dynamic compression and surface shear 1 h daily enhanced chondrogenesis of hMSCs compared with the nonloaded control samples. Higher load frequency and higher compression amplitude induced higher glycosaminoglycan synthesis, higher chondrocytic gene expression, higher chondrocytic:fibroblastic, chondrocytic:hypertrophic, and chondrocytic:osteoblastic gene expression ratios, as well as higher transforming growth factor β1 ( TGFB1 ) and TGFB3 gene expression. The chondrogenesis level of hMSCs was positively related to the TGFB1 and TGFB3 gene expression level, which was determined by various load regimes. In conclusion, chondrogenesis of human MSCs induced by mechanical stimulation can be further enhanced by modifying frequency and compression.

Objective: To determine whether engineered cartilage generated by nasal chondrocytes (ECN) is responsive to different regimens of loading associated with joint kinematics and previously shown to be stimulatory of engineered cartilage generated by articular chondrocytes (ECA).Methods: Human nasal and articular chondrocytes, harvested from 5 individuals, were expanded and cultured for 2 weeks into porous polymeric scaffolds. The resulting ECN and ECA were then maintained under static conditions or exposed to the following loading regimens: regimen 1, single application of cyclic deformation for 30 minutes; regimen 2, intermittent application of cyclic deformation for a total of 10 days, followed by static culture for 2 weeks; regimen 3, application of surface motion for a total of 10 days.Results: Prior to loading, ECN constructs contained significantly higher amounts of glycosaminoglycan (GAG) and type II collagen compared with ECA constructs. ECN responded to regimen 1 by increasing collagen and proteoglycan synthesis, to regimen 2 by increasing the accumulation of GAG and type II collagen as well as the dynamic modulus, and to regimen 3 by increasing the expression of superficial zone protein, at the messenger RNA level and the protein level, as well as the release of hyaluronan. ECA constructs were overall less responsive to all loading regimens, likely due to the lower extracellular matrix content.Conclusion: Human ECN is responsive to physical forces resembling joint loading and can up‐regulate molecules typically involved in joint lubrication. These findings should prompt future in vivo studies exploring the possibility of using nasal chondrocytes as a cell source for articular cartilage repair.

Articular cartilage injuries and degeneration affect a large proportion of the population in developed countries world wide. Stem cells can be differentiated into chondrocytes by adding transforming growth factor-β1 and dexamethasone to a pellet culture, which are unfeasible for tissue engineering purposes. We attempted to achieve stable chondrogenesis without any requirement for exogenous growth factors. Human mesenchymal stem cells were transduced with an adenoviral vector containing the SRY-related HMG-box gene 9 ( SOX9 ), and were cultured in a three-dimensional (3D) hydrogel scaffold composite. As an additional treatment, mechanical stimulation was applied in a custom-made bioreactor. SOX9 increased the expression level of its known target genes, as well as its cofactors: the long form of SOX5 and SOX6 . However, it was unable to increase the synthesis of sulfated glycosaminoglycans (GAGs). Mechanical stimulation slightly enhanced collagen type X and increased lubricin expression. The combination of SOX9 and mechanical load boosted GAG synthesis as shown by ³⁵ S incorporation. GAG production rate corresponded well with the amount of (endogenous) transforming growth factor-β1. Finally, cartilage oligomeric matrix protein expression was increased by both treatments. These findings provide insight into the mechanotransduction of mesenchymal stem cells and demonstrate the potential of a transcription factor in stem cell therapy.