Cell migration is highly sensitive to fluid shear stress (FSS) in blood flow or interstitial fluid flow. However, whether the FSS gradient can regulate the migration of cells remains unclear. In this work, we constructed a parallel-plate flow chamber with different FSS gradients and verified the gradient flow field by particle image velocimetry measurements and finite element analyses. We then investigated the effect of FSS magnitudes and gradients on the migration of osteoclast precursor RAW264.7 cells. Results showed that the cells sensed the FSS gradient and migrated toward the low-FSS region. This FSS gradient-induced migration tended to occur in low-FSS magnitudes and high gradients, e.g., the migration angle relative to flow direction was approximately 90° for 0.1 Pa FSS and 0.2 Pa mm −1 FSS gradient. When chemically inhibiting the calcium signaling pathways of the mechanosensitive cation channel, endoplasmic reticulum, phospholipase C, and extracellular calcium, the cell migration toward the low-FSS region was significantly reduced. This study may provide insights into the mechanism of the recruitment of osteoclast precursors at the site of bone resorption and of mechanical stimulation-induced bone remodeling.

The skeleton is able to adapt to mechanical loading through bone remodeling, i.e. bone resorption followed by bone formation. The osteoclasts close to microdamages are believed to initiate bone resorption, but whether local mechanical loading such as fluid flow regulates recruitment and differentiation of osteoclast precursors at the site of bone resorption has yet to be investigated. In the present study, finite element analysis first revealed that there exists low fluid shear stress (FSS) field inside microdamage. Basing on a custom-made device of cone-and-plate fluid chamber, finite element analysis and particle image velocimetry measurement were performed to verify the formation of gradient FSS flow field. Furthermore, the effects of gradient FSS on the migration, aggregation, and fusion of osteoclast precursors were observed.Results showed that osteoclast precursor RAW264.7 cells migrate along radial direction toward the region with lower FSS during exposure to gradient FSS stimulation for 40 min, obviously deviating from the direction of actual fluid flow indicated by fluorescent particles. When inhibiting calcium signaling pathway with gadolinium and thapsigargin, cell migration toward low-FSS region was significantly reduced. For other cell lines, MC3T3-E1, PDLF, rMSC and MDCK, gradient FSS stimulation did not lead to the low-FSS-inclined migration. After being cultured under gradient FSS stimulation for 6 days, the density of RAW264.7 cells and the ratio of TRAP-positive multinucleated osteoclasts in low-FSS region were significantly higher than those in high-FSS region. Therefore, osteoclast precursor cells may have special ability to sense FSS gradient and tend to actively migrate toward low-FSS region, which is regulated by calcium signaling pathway.

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The skeleton is able to adapt to mechanical loading through bone 22 remodeling, i.e. bone resorption followed by bone formation. The osteoclasts close to 23 microdamages are believed to initiate bone resorption, but whether local mechanical 24 loading such as fluid flow regulates recruitment and differentiation of osteoclast 25 precursors at the site of bone resorption has yet to be investigated. In the present study, 26 finite element analysis first revealed that there exists low fluid shear stress (FSS) field 27 inside microdamage. Basing on a custom-made device of cone-and-plate fluid chamber, 28 finite element analysis and particle image velocimetry measurement were performed to 29 verify the formation of gradient FSS flow field. Furthermore, the effects of gradient 30 FSS on the migration, aggregation, and fusion of osteoclast precursors were observed. 31Results showed that osteoclast precursor RAW264.7 cells migrate along radial 32 direction toward the region with lower FSS during exposure to gradient FSS 33 stimulation for 40 min, obviously deviating from the direction of actual fluid flow 34 indicated by fluorescent particles. When inhibiting calcium signaling pathway with 35 gadolinium and thapsigargin, cell migration toward low-FSS region was significantly 36 reduced. For other cell lines, MC3T3-E1, PDLF, rMSC and MDCK, gradient FSS 37 stimulation did not lead to the low-FSS-inclined migration. After being cultured under 38 gradient FSS stimulation for 6 days, the density of RAW264.7 cells and the ratio of 39 TRAP-positive multinucleated osteoclasts in low-FSS region were significantly 40 higher than those in high-FSS region. Therefore, osteoclast precursor cells may have 41 special ability to sense FSS gradient and tend to actively migrate toward low-FSS 42 region, which is regulated by calcium signaling pathway. 43

Traditional course teaching evaluation models face increasing challenges in higher education due to their limitations in measuring qualitative indicators. To address this issue, this study constructs a classroom teaching quality evaluation system based on YOLOv5 object detection technology and the five major processes of course teaching management. Here, Fermatean fuzzy set (FFS) is introduced to express the uncertainty in the evaluation process. The core of this study is to establish a scientifically effective comprehensive evaluation model for university classroom teaching quality. Specifically, this model utilizes the minimum discriminative information principle and combines the order relation analysis method (G1 method) and the FFS entropy weighting method to determine attribute weights for weighted attribution. Thereafter, the proposed generalized distance measurement formula is utilized to enhance the technique for order preference by similarity to ideal solution (TOPSIS) for assessing similarity, thereby achieving the objective of evaluating classroom teaching. Eventually, the effectiveness and practicality of the evaluation model are validated through case studies and comparisons with other methods.