For the therapy of cartilage lesions, cell-based approaches may be associated with the formation of fibrocartilage tissue, resulting in a lower resistance to mechanical loading. The aim of the present in vitro study was to characterize the influence of hydrodynamic shear stress on human chondrocytes with regard to chondrogenic differentiation.
A standard 6-well cell culture plate combined with a linear piezo positioning system (Ziebart et al. 2018) was used for the application of hydrodynamic shear stress on human chondrocytes. For the experiments, 50,000 cells were seeded on collagen type I based scaffolds (Ø 10 mm). The sinusoidal micro motion with amplitudes of 25 µm, 50 µm and 100 µm were applied six hours per day over a period of seven days. After mechanical stimulation, metabolic activity of cells was identified. Additionally, analyses of important differentiation marker on gene expression and protein levels were performed.
Compared to non-stimulated cells, metabolic activity increased with increasing amplitude, statistically significant for 100 µm (p = 0.0083). Furthermore, stimulation with 100 µm amplitude led to increased release of glycosaminoglycans and ACAN gene expression (p = 0.0071). Also increased Sox9 mRNA (p = 0.0129; 25 µm vs. 100 µm) and collagen 2 protein levels were observed. In contrast, collagen 1 content decreased with increasing amplitude. In addition, the underlying pathway appears to be triggered by PIEZO1 (p = 0.0082 non-stimulated control vs. 100 µm) rather than PIEZO2.
Through the targeted use of mechanical stimulation, physiological signaling pathways can be triggered and used for the directed differentiation of de-differentiated human chondrocytes. The combination with other types of biophysical stimulation, such as electrical stimulation, could further enhance the chondrogenic effects. Nevertheless, further investigations are needed to elucidate in detail the signaling pathways and biological effects of mechanical stimulation of hyaline cartilage by hydrodynamic shear stress.