ON THE MECHANICS OF INTEGRIN CLUSTERING DURING CELL-SUBSTRATE ADHESION

Recent numerical simulations have indicated that integrin clustering during cell- substrate adhesion can be driven by the presence of a repulsive layer between the cell membrane and the substrate （Paszek et al., PLoS Comput Biol 5：12, 2009）. Here we present a simple me- chanics model of this phenomenon in which the attraction between integrins is mediated by the long-range elastic deformation of the membrane and the repulsive layer. We obtain analytical solutions to the problem by employing the small deformation theory of an infinitely extended plate resting on an elastic foundation.

Computational Study of Collective Cell Migration By Meshfree Method

The collective cell migration behavior on a substrate was studied using RKPM meshfree method.The cells were modeled as nematic liquid crystal with hyperelastic cell nucleus.The cell-substrate and cell-cell interactions were modeled by coarse-grained potential forces.Through this study,the pulling and pushing phenomenon during collective cell migration process was observed and it was found that the individual cell mobility significantly influenced the collective cell migratory behavior.More self-propelled cells are in the system along the same direction,the faster the collective group migrates toward coordinated direction.The parametric study on cell-cell adhesion strength indicated that as the adhesion strength increases,the collective cell migration speed increases.It also showed that the mechanical stress in leader cell is higher than stress in follower cells.

Microcontroller-Based Sinusoidal Voltage Generation for Electrical Bio-Impedance Spectroscopy Applications

A sinusoidal voltage wave generator is proposed based on the use of micro-processor digital signals with programmable duty-cycles, with application to real-time Electrical Cell-substrate Impedance Spectroscopy (ECIS) assays in cell cultures. The working principle relies on the time convolution of the programmed microcontroller (μC) digital signals. The expected frequency is easily tuned on the bio-impedance spectroscopy range [100 Hz, 1 MHz] thanks to the μC clock frequency selection. This system has been simulated and tested on the 8 bits μC ArduinoTM Uno with ATmega328 version. Results obtained prove that only three digital signals are required to fit the general specification in ECIS experiments, below 1% THD accuracy, and show the appropriateness of the system for the real-time monitoring of this type of biological experiments.

Paxillin tunes the relationship between cell-matrix and cell-cell adhesions to regulate stiffness-dependent dentinogenesis

Mechanical stiffness is recognized as a key physical factor and directs cell function via a mechanotransduction process,from extracellular physical cues to intracellular signaling cascades that affect transcriptional activity.Cells continually receive mechanical signals from both the surrounding matrix and adjacent cells.However,how mechanical stiffness cue at cell-substrate interfaces coordinates cell-cell junctions in guiding mesenchymal stem cell behaviors is poorly understood.Here,polydimethylsiloxane substrates with different stiffnesses were used to study mechanosensation/transduction mechanisms in controlling odontogenic differentiation of dental papilla cells(DPCs).DPC phenotypes(morphology and differentiation)changed in response to the applied force derived from stiff substrates.Significantly,higher expression of paxillin on stiffer substrates promoted DPC dentinogenesis.Upon treatment with siRNA to knockdown paxillin,N-cadherin increased mainly in the cytomembrane at the area of cell-cell contacts,whereasβ-catenin decreased in the nuclei.The result of a double luciferase reporter assay showed that stiffness promotedβ-catenin binding to TCF,which could coactivate the target genes associated with odontogenic differentiation,as evidenced by bioinformatics analysis.Finally,we determined that the addition of aβ-catenin inhibitor suppressed DPC mineralization in all the stiffness groups.Thus,our results indicated that a mechanotransduction process from cell-substrate interactions to cell-cell adhesions was required for DPC odontogenic differentiation under the stimulation of substrate stiffness.This finding suggests that stem cell fate specification under the stimulus of stiffness at the substrates is based on crosstalk between substrate interactions and adherens junctions,which provides an essential mechanism for cell-based tissue engineering.

Response of MG63 Osteoblast Cells to Surface Modification of Ti-6Al-4V Implant Alloy by Laser Interference Lithography

The response of human osteoblast-like osteosarcoma cells （MG63） to surface modification of Ti-6Al-4V implant alloy was investigated by Laser Interference Lithography （LIL）. In this work, laser interference lithography was employed to fabricate the microstructures of grooves, dots and dimples onto the surfaces of Ti-6Al-4V samples. Two and three beam LIL systems were developed to carry out the experiments. The laser treatment resulted in the increases of the roughness and the contact angle of water on the implant alloy surfaces. The proliferation of osteoblasts was analyzed by MTT （3-（4,5-dirnethyl- 2-thiazolyl）-2,5-diphenyl-2-H-tetrazolium bromide） assay for the time periods of 4 hours, 2 days, 3 days, and 6 days. The MTT test results demonstrated that the laser treatment surfaces had a positive impact on the proliferation of os- teoblast cells after 24 hours. The alloy surface morphology and the morphological changes of MG63 cells cultured on the laser textured Ti-6Al-4V surface were observed by Scanning Electron Microscope （SEM）. The SEM results indicated that the os- teoblast cells were aligned on grooved surfaces and they were prolonged with the structures. Enzymatic detachment results showed that the 20 μm grooved structures provided the better cell adhesion to the textured Ti-6Al-4V surfaces.