Prescripted cellular course.

<p>(A) Desired cellular output; (B) Imposed externally controlled mechanotactic signal; (C) Measured cellular displacement in the direction for 3 distinct cells with a different color for each cell. The observed small differences in cellular response between the three cells are rooted in the biological variability of this sample. The initial positions of the 3 cells have been arbitrarily shifted to circumvent the overlapping of the plots; (D) Instantaneous snapshot of the 3 cells in the observation area at instant s. The double red arrow indicates the mechanostimulus direction. See SI <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0105406#pone.0105406.s008" target="_blank">Movie S1</a> for the complete migration of these 3 cells. The calcium concentration is 3 mM and the complete duration of the cellular course is 2600 seconds or 43 minutes. Cells are crawling over a plastic hydrophobic surface.</p

Influence of shear stress on shearotactic cell migration.

<p>(A) Influence on cell speed: probability density function (PDF) of the cell speed for five different magnitudes of the shearotactic signal with the associated average speed vs. shear stress in insert. For shear stress levels lower than 0.05 Pa, the average cell speed is of the order of the cell speed in the absence of any signal (insert). For values of in the range 0.18 to 0.5 Pa, the average cell speed is found to be almost constant. This conclusion, established on the sole basis of first-order statistics of cell speed, is readily generalized by noticing the similarities in the PDFs of cell speed for 0.05 Pa on the one hand, and for 0.18 Pa on the other hand. (B) Evolution of the shearotactic directionality with the shear stress. (C) Evolution of the with the shear stress. is a measure of the instantaneous ability of the cell to migrate in the signal's direction, while is an integrated measure of throughout the entire cell path. This subtle relationship between and is reflected in the above variations with the shear stress where a plateau about 0.9 is reached for 0.18 Pa. For all values of , only cells adhering to the substrate throughout the entire duration of the experiment were considered and analyzed. All experiments were conducted with a soluble concentration of calcium, [Ca²⁺]_ext, set and fixed at 3 mM and cells are crawling over a plastic hydrophobic surface.</p

Influence of the extracellular calcium concentration on the shearotactic cellular response.

<p>(A) . (B) . (C) Average cell speed , average -component (resp. -component) of the cell velocity (resp. ) for a shearotactic signal pointing toward the positive direction. At both ends of the calcium concentration range considered, the shearotactic efficiency is extremely poor as attested by the values of and . A high shearotactic efficiency is achieved for calcium concentrations in the 1–3 mM range. For the speed, a clear maximum is attained for a concentration of 3 mM. The optimal shear stress level of 0.18 Pa is considered for the seven different values of the external calcium concentration. A log-scale is used for the calcium concentration on the -axis and for each value of [Ca²⁺]_ext the averaging process is based on a population comprising between 60 to 135 individual tracked cells for a duration of 1,200 seconds and with a sampling time of 15 seconds. Cells are crawling over a plastic hydrophobic surface.</p

Cell Kinematics: Average displacement along the signal direction for different flow reversal frequencies.

<p>Note the difference in scales on the -axis for both graphs (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0105406#pone.0105406.s003" target="_blank">Fig. S3</a>). (A) For frequencies smaller than 0.01 Hz, on average the cells clearly undergo a uniform translational migration. When the flow direction is reversed, almost immediately the cells stop moving and it takes approximately 20 s before a motion in the opposite direction is measured. (B) For the frequencies Hz and Hz, the cells are still able to follow the faster reversals of signal directions but no longer in a uniform way (i.e. at constant speed). For the even higher frequency Hz, some changes in the cells' migration direction are discernible but the displacements with respect to the baseline are extremely small: cells are effectively trapped.</p

Revealing the Dual Functions of Graphene Oxide to Promote the Antibiofouling Property in Anaerobic Membrane Bioreactors

An anaerobic membrane bioreactor (AnMBR) is a promising technology with the potential for energy, water, and fertilizer recovery in wastewater treatment processes. However, serious biofouling remains to be the main obstacle to future development. In this study, we selected graphene oxide (GO) that owns both defensive (antiadhesive) and offensive (antibacterial) properties as a modification material to regulate the membrane surface. Instead of focusing on the signal property in the current studies, the role of antiadhesive and antibacterial properties’ cooperation in combating biofouling was comprehensively evaluated. Results showed that with better hydrophilicity and antibacterial properties (73% inhibition rate for Staphylococcus aureus), the GO-functionalized membrane significantly inhibited the development of biofilms, resulting in Stage 2 of membrane fouling being widely prolonged (∼2 times). The mechanism analysis of microbiology and thermodynamics has consistently revealed the significant effect and importance of dual-function cooperation: (1) the co-constructed adverse environment for microbes induced a looser biofilm on the membrane surface with a lower filtration resistance, and (2) the changes in the biofilm composition and membrane matrix weakened the adhesion strength between them and then slowed down the formation of biofilms. These findings proved the efficient and long-lasting ability of GO for biofouling mitigation and highlighted the potential of dual-functional materials in AnMBR

Effects of flow reversal frequency on cellular directionality.

<p>(A) Pack average speed as a function of the flow reversal frequency using a log-scale. Beyond the trapping frequency 1/17.5 Hz, the pack speed is still significant: which is to be compared to the average cell speed found for the uniform one-dimensional translation along the signal direction. (B): Average vs. flow reversal frequency. The average directionality does not follow the same trend as the pack speed: it decreases sensibly with . Even when cells are effectively trapped, they still exhibit a fairly high directionality, close to a value of .</p

Aggregation, Adsorption, and Morphological Transformation of Graphene Oxide in Aqueous Solutions Containing Different Metal Cations

The colloidal behavior of graphene oxide (GO) has been extensively studied in the presence of common environmental cations, but the aggregation, adsorption, and morphological transformation of GO under heavy metal ions have not been investigated. We observed that heavy metal cations (Cr³⁺, Pb²⁺, Cu²⁺, Cd²⁺, Ag⁺) destabilized GO suspension more aggressively than common cations (Ca²⁺, Mg²⁺, Na⁺, K⁺). In addition to electric double-layer (EDL) suppression, heavy metal cations can easily cross the EDL, bind to GO surface, and then change the surface potential, which is a more efficient pathway for GO aggregation. According to aggregation kinetics, the destabilizing ability of cations follows the order of Cr³⁺ ≫ Pb²⁺ > Cu²⁺ > Cd²⁺ > Ca²⁺ > Mg²⁺ ≫ Ag⁺ > K⁺ > Na⁺. The destabilizing capability of metal cations is consistent with their adsorption affinity with GO, which is determined by their electronegativity and hydration shell thickness. GO nanosheets can be transformed to 1D tube-like carbon material, 2D multiple overlapped GO plane, and 3D sphere-like particles during aggregation, thereby combined to form a sphere-like aggregated GO, which is for the first time observed by TEM and AFM images. Therefore, the aggregation of GO 2D nanosheets follows the Schulze-Hardy rule, which is usually used for spherical particles. An integrative process of adsorption-transformation-aggregation is proposed to better understand the nanomaterial (e.g., GO) colloidal behavior, environmental risk, self-assembly process, and application as a novel adsorbent

Porous PVdF/GO Nanofibrous Membranes for Selective Separation and Recycling of Charged Organic Dyes from Water

Graphene oxide (GO) membranes are robust and continue to attract great attention due to their fascinating properties, despite their potential issues regarding stability and selectivity in aqueous-phase processing. That being said, however, the functional moieties of GO could be used for membrane surface modification, while ensuring simultaneous removal and recycling of industrial organic dyes. Herein, we present a versatile porous structured polyvinylidene fluoride–graphene oxide (PVdF-GO) nanofibrous membranes (NFMs), prepared by using simple and straightforward electrospinning approach for selective separation and filtration. The GO nanosheets were distributed homogeneously throughout the PVdF nanofiber, regulating the surface morphology and performance of PVdF-GO NFM. The PVdF-GO NFMs possesses high mechanical strength and surface free energy (SFE), consequently resulting high permeation and filtration efficiency as compared to PVdF NFM. The selectivity (99%) toward positively charged dyes based on electrostatic attraction, while maintaining rejection (100%) for negatively charged dye from mixed solutions highlight the role of GO in PVdF-GO NFM, owing to uniform pores and negatively charged surface. In addition, the actual efficiency of NFMs could be recovered easily up to three consecutive filtration cycles by regeneration, thereby assuring high stability. The high permeation, purification and filtration efficiency, good stability and recycling of PVdF-GO NFMs are promising for use in practical water purification and applications, particularly for selective filtration and recycling of dyes

Lagrangian tracking of cells in the -plane of the microchannel.

<p>A sample of 205 cells crawling over a plastic hydrophobic surface were subjected to a shear stress 0.18 Pa in the positive -direction, with a soluble calcium concentration of 3 mM. Hundred time samples were collected every 3.5 seconds. (A) Odograph for the average cell position along the signal direction (blue dots). The red dashed line corresponds to a purely uniform translation with . (B) Odograph for the average cell position transversely to the signal direction. (C) Average cell trajectory . (D) Coefficient of variation vs. time for the motion along the signal direction.</p