ON THE TRACTION BEHAVIOR OF 4109 CHINESE AVIATION LUBRICANT

Based on improved test rig with cooling system, the traction experiments for 4109 Chinese aviation lubricant are tested under various simulated working conditions. Both the experimental data thanks to their accuracy and stability and the better cooling effect of the electric shafts has given the rationality of the experimental rig a strong support. An empirical equation for calculating the traction coefficient of 4109 lubricant, which may be conveniently used for engineering application,is obtained. Furthermore, the rheological properties of the lubricant are investigated.

OPTICALLY TRACKING THE MOTION OF MICROBEADS TO STUDY PHYSICAL BEHAVIORS OF THE LIVING CELL IN RESPONSE TO TRANSIENT STRETCH OR COMPRESSION

Optical magnetic twisting cytometry and traction force microscopy are two advanced cell mechanics research tools that employ optical methods to track the motion of microbeads that are either bound to the surface or embedded in the substrate underneath the cell.The former measures rheological properties of the cell such as cell stiffness,and the latter measures cell traction force dynamics.Here we describe the principles of these two cell mechanics research tools and an example of using them to study physical behaviors of the living cell in response to transient stretch or compression.We demonstrate that,when subjected to a stretch
unstretch manipulation,both the stiffness and traction force of adherent cells promptly reduced,and then gradually recover up to the level prior to the stretch.Immunofluorescent staining and Western blotting results indicate that the actin cytoskeleton of the cells underwent a corresponding disruption and reassembly process almost in step with the changes of cell mechanics.Interestingly,when subjected to compression,the cells did not show such particular behaviors.Taken together,we conclude that adherent cells are very sensitive to the transient stretch but not transient compression,and the stretch-induced cell response is due to the dynamics of actin polymerization.

THE DEVELOPMENT OF A LUBRICANT TRACTION MEASUREMENT SYSTEM

A ball-disc traction test rig is improved through the development of a lubricant traction measurement system, consisting of a resonance force sensitive quartz sensor, a circuit of the sensor and a rigid bracket jointed by a frictionless hinge. The traction coefficients of a kind of domestic lubricating oil were measured at various normal loads, rolling velocities, lubricant inlet temperatures and slide-to-roll ratios on a ball-disc traction test rig equipped with this traction measurement system. The results show that the traction test curve is smooth and the data enjoy a good accuracy, which indicates that the design of the lubricant traction measurement system is reasonable and the precision of the system is high, especially, at high temperature, high rolling speed and small slide-to-roll ratio.

Quantifying 3D cell-matrix interactions during mitosis and the effect of anticancer drugs on the interactions

The mechanical force between cells and the extracellular microenvironment is crucial to many physiological processes such as cancer metastasis and stem cell differentiation. Mitosis plays an essential role in all these processes and thus an in-depth understanding of forces during mitosis gains insight into disease diagnosis and disease treatment. Here, we develop a traction force microscope method based on monolayer fluorescent beads for measuring the weak traction force (tens of Pa) of mitotic cells in three dimensions. We quantify traction forces of human ovarian granulosa (KGN) cells exerted on the extracellular matrix throughout the entire cell cycle in three dimensions. Our measurements reveal how forces vary during the cell cycle, especially during cell division. Furthermore, we study the effect of paclitaxel (PTX) and nocodazole (NDZ) on mitotic KGN cells through the measurement of traction forces. Our results show that mitotic cells with high concentrations of PTX exert a larger force than those with high concentrations of NDZ, which proved to be caused by changes in the structure and number of microtubules. These findings reveal the key functions of microtubule in generating traction forces during cell mitosis and explain how dividing cells regulate themselves in response to anti-mitosis drugs. This work provides a powerful tool for investigating cell-matrix interactions during mitosis and may offer a potential way to new therapies for cancer.

Mechanical transmission enables EMT cancer cells to drive epithelial cancer cell migration to guide tumor spheroid disaggregation

Cell phenotype heterogeneity within tumor tissue,especially which due to the emergence of epithelial-mesenchymal transition(EMT) in cancer cells,is associated with cancer invasion and metastasis.However,our understanding of the cellular mechanism(s)underlying the cooperation between EMTcell and epithelial cancer cell migration remains incomplete.Herein,heterotypic tumor spheroids containing both epithelial and EMT cancer cells were generated in vitro.We observed that EMT cells dominated the peripheral region of the self-organized heterotypic tumor spheroid.Furthermore,our results demonstrated that EMT cells could serve as leader cells to improve the collective migration efficiency of epithelial cancer cells and promote dispersion and invasion of the tumor spheroids,which was regulated by the force transition between EMT cells and epithelial cancer cells.Mechanistically,our data further suggest that force transmission is mediated by heterophilic N-cadherin/E-cadherin adhesion complexes between EMT and epithelial cancer cells.Impairment of N-cadherin/E-cadherin adhesion complex formation abrogated the ability of EMT cells to guide epithelial cancer cell migration and blocked the dispersion of tumor spheroids.Together,our data provide new insight into the mechanical interaction between epithelial and EMT cancer cells through heterophilic cadherin adhesion,which enables cooperative tumor cell migration,highlighting the role of EMT cells in tumor invasion.

Deep learning for complex displacement field measurement

Traction force microscopy(TFM)is one of the most successful and broadly-used force probing technologies to quantify the mechanical forces in living cells.The displacement recovery of the fluorescent beads within the gel substrate,which serve as the fiducial markers,is one of the key processes.The traditional methods of extracting beads displacements,such as PTV,PIV,and DIC,persistently suffer from mismatching and loss of high-frequency information while dealing with the complex deformation around the focal adhesions.However,this information is crucial for the further analysis since the cells mainly transmit the force to the extracellular surroundings through focal adhesions.In this paper,we introduced convolutional neural network(CNN)to solve the problem.We have generated the fluorescent images of the non-deformable fluorescent beads and the displacement fields with different spatial complexity to form the training dataset.Considering the special image feature of the fluorescent images and the deformation with high complexity,we have designed a customized network architecture called U-DICNet for the feature extraction and displacement estimation.The numerical simulation and real experiment show that U-DICNet outperforms the traditional methods(PTV,PIV,and DIC).Particularly,the proposed U-DICNet obtains a more reliable result for the analysis of the local complex deformation around the focal adhesions.

A chemotaxis model to explain WHIM neutrophil accumulation in the bone marrow of WHIM mouse model

Neutrophils are essential immune cells that defend the host against pathogenic microbial agents.Neutrophils are produced in the bone marrow and are retained there through CXCR4–CXCL12 signaling.However,patients with the Warts,Hypogammaglobulinemia,Infections,and Myelokathexis(WHIM)syndrome are prone to infections due to increased accumulation of neutrophils in the bone marrow leading to low numbers of circulating neutrophils.How neutrophils accumulate in the bone marrow in this condition is poorly understood.To better understand factors involved in neutrophil accumulation in the bone marrow,neutrophils from wildtype and WHIM mouse models were characterized in their response to CXCL12 stimulation.WHIM neutrophils were found to exert stronger traction forces,formed significantly more lamellipodia-type protrusions and migrated with increased speed and displacement upon CXCL12 stimulation as compared to wildtype cells.Migration speed of WHIM neutrophils showed a larger initial increase upon CXCL12 stimulation,which decayed over a longer time period as compared to wildtype cells.We proposed a computational model based on the chemotactic behavior of neutrophils that indicated increased CXCL12 sensitivity and prolonged CXCR4 internalization adaptation time in WHIM neutrophils as being responsible for increased accumulation in the bone marrow.These findings provide a mechanistic understanding of bone marrow neutrophil accumulation in WHIM condition and novel insights into restoring neutrophil regulation in WHIM patients.

Benchmark of an intelligent fuzzy calculator for admissible estimation of drawbar pull supplied by mechanical front wheel drive tractor

This paper proposes a calculator for estimation of drawbar pull supplied bymechanical front wheel drive tractor based on nominal input variable of tractor drivingmode in two-wheel drive(2WD)and four-wheel drive(4WD),and numeral input variables of tractor weight(53.04–78.45 kN)and slip of driving wheels(1.4–15.1%)utilizing intelligent fuzzy systems.The systemswere developed bymeans of various input membership functions,output membership functions,defuzzification methods,and training cycles.The prominent developed system for estimation of the drawbar pull yielded a user-friendly intelligent fuzzy calculator with admissible accuracy(coefficient of determination=0.993).Data obtained from the calculator revealed increasing nonlinear trend of the drawbar pull in range of 12.9–57.5 kN as concurrent augment of slip of the wheels and tractor weight,for 2WD mode.In case of the 4WD mode,it nonlinearly raised from 12.8 to 77.7 kN.Therefore,effect of the slip and weight on the drawbar pull was found synergetic.Moreover,the drawbar pull ranges elucidated that the drawbar pull proliferated as the 4WD mode was employed rather than the 2WD mode.Generally,benchmark of the prominent developed intelligent fuzzy system,not only provide simple calculator with the widest applicability for different tractormodels,but also produces added values in enrichment of realization level in domain of tractor drawbar pull concepts.