An integrated microfluidic device for characterizing chondrocyte metabolism in response to distinct levels of fluid flow stimulus

In this work, we presented a novel integrated microfluidic perfusion system to generate multiple parameter fluid flow-induced shear stresses simultaneously and investigated the effects of distinct levels of fluid flow stimulus on the responses of chondrocytes, including the changes of morphology and metabolism. Based on the electric circuit analogy, two devices were fabricated, each with four chambers to enable eight different shear stresses spanning over four orders of magnitude from 0.007 to 15.4 dyne/cm 2 with computational fluid dynamics analysis. Chondrocytes subjected to shear stresses (7.5 and 15.4 dyne/cm 2 ) for 24 h reoriented their cytoskeleton to align with the direction of flow. Meanwhile, the collagen I, collagen II and aggrecan expression of chondrocytes increased in different ranges, respectively. Furthermore, interleukin-6 as a proinflammatory cytokine can be detected at shear stress of 7.5 and 15.4 dyne/cm 2 in mRNA level. These results indicated that fluid flow was beneficial for chondrocyte metabolism at interstitial levels (0.007 and 0.046 dyne/cm 2 ), but induced an increase in fibrocartilage phenotype with increasing magnitude of stimulation. Moreover, a moderate level of flow stimulus (7.5 dyne/cm 2 ) could also result in detrimental cytokine release. This work described a simple and versatile way to rapidly screen cell responses to fluid flow stimulus from interstitial shear stress level to pathological level, providing multi-condition fluid flow-induced microenvironment in vitro for understanding deeply chondrocyte metabolism, cartilage reconstruction and osteoarthritis etiology.