scholarly journals Impact of surface charge on the motion of light-activated Janus micromotors

2021 ◽  
Vol 44 (3) ◽  
Author(s):  
Tao Huang ◽  
Bergoi Ibarlucea ◽  
Anja Caspari ◽  
Alla Synytska ◽  
Gianaurelio Cuniberti ◽  
...  
Keyword(s):  
Surface Charge ◽  
Biomedical Engineering ◽  
Surface Charge Density ◽  
Practical Application ◽  
Glass Substrates ◽  
Propulsion Mechanism ◽  
Qualitative Understanding ◽  
Encounter Complex ◽  
Negative Surface ◽  
Negative Surface Charge

Abstract Control over micromotors’ motion is of high relevance for lab-on-a-chip and biomedical engineering, wherein such particles encounter complex microenvironments. Here, we introduce an efficient way to influence Janus micromotors’ direction of motion and speed by modifying their surface properties and those of their immediate surroundings. We fabricated light-responsive Janus micromotors with positive and negative surface charge, both driven by ionic self-diffusiophoresis. These were used to observe direction-of-motion reversal in proximity to glass substrates for which we varied the surface charge. Quantitative analysis allowed us to extract the dependence of the particle velocity on the surface charge density of the substrate. This constitutes the first quantitative demonstration of the substrate’s surface charge on the motility of the light-activated diffusiophoretic motors in water. We provide qualitative understanding of these observations in terms of osmotic flow along the substrate generated through the ions released by the propulsion mechanism. Our results constitute a crucial step in moving toward practical application of self-phoretic artificial micromotors. Graphic abstract

scholarly journals Alteration of the Cell Periphery During Granulocyte Maturation: Relationship to Cell Function

Blood ◽  
1972 ◽  
Vol 39 (3) ◽  
pp. 301-316 ◽  
Author(s):  
Marshall A. Lichtman ◽  
Robert I. Weed
Keyword(s):  
Bone Marrow ◽  
Charge Density ◽  
Surface Charge ◽  
Functional Capacity ◽  
Surface Charge Density ◽  
Cell Spreading ◽  
Cell Periphery ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Immature Granulocyte

Abstract Physiologic characteristics of the surface of human granulocytes may be important determinants of functional capacity. Studies of immature granulocytes and polymorphonuclear neutrophils (PMN’s) from marrow and blood indicated that immature granulocytes are characterized by a high, neuraminidase-susceptible, negative surface charge density; a high degree of cellular rigidity, as measured by an elastimeter with a micropipette orifice size that approximated estimates of average bone marrow basement membrane pore size (3.5µ); low adhesiveness to glass and plastic; low propensity to aggregate; a slow rate of cell spreading, pseudopod extension, and motility; and a very low rate of phagocytosis. At the myelocyte stage, adhesiveness and phagocytosis, although not prominent, became evident. In contrast PMN’s had a lower negative surface charge density, a higher degree of surface deformability (the entire PMN readily deforming to enter a 3.5µ micropipette whereas the immature granulocyte would not so deform), higher adhesiveness (plastic > glass), a higher propensity to aggregate, a higher rate of cell spreading, pseudopod formation and motility, and a higher rate of phagocytosis. The increased deformability and adhesiveness of the PMN as compared to the immature granulocyte may be a reflection of an altered relationship between relaxing and contracting systems at the cell periphery during maturation and/or changes in the sol-gel state of macromolecules at the cell periphery. This concept is supported by the change in surface properties of the PMN toward those of the immature granulocyte at cold temperature (4°C). The increased deformability and reduced surface negative charge of the PMN could facilitate adhesiveness and pseudopod formation and, thereby, increase cell-surface and cell-particle contact with enhancement of motility and phagocytosis. Hence the exit of PMN from bone marrow and circulation and the functional capacity of the PMN may be determined by a process of cytoplasmic maturation during granulopoiesis that adapts the PMN for its essential cell-extracell interactions.

scholarly journals The negative surface charge density of plasmalemma vesicles from wheat and oat roots

FEBS Letters ◽  
1984 ◽  
Vol 167 (1) ◽  
pp. 181-185 ◽  
Author(s):  
Ian M. Møller ◽  
Tomas Lundborg ◽  
Alajos Bérczi
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Charge Density ◽  
Negative Surface ◽  
Negative Surface Charge

scholarly journals Negative surface charge density near heart calcium channels. Relevance to block by dihydropyridines.

1987 ◽  
Vol 89 (4) ◽  
pp. 629-644 ◽  
Author(s):  
R S Kass ◽  
D S Krafte
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Potential ◽  
Surface Charge Density ◽  
Ca Channel ◽  
Surface Charges ◽  
Purkinje Fibers ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Induced Changes

We have measured the density of negative surface charges near the voltage sensor for inactivation gating of (L-type) Ca channels in intact calf Purkinje fibers and in isolated myocytes from guinea pig and rat ventricles. Divalent cation-induced changes in the half-maximal voltage for inactivation were determined and were well described by curves predicted by surface potential theory. We measured shifts in inactivation induced by Ca, Sr, and Ba in the single cells, and by Sr in the Purkinje fibers. All of the data were consistent with an estimated negative surface charge density of 1 electronic charge per 250 A2. In addition, the data suggest that Ca, but neither Ba nor Sr, binds to the negative charges with an association constant on the order of 1 M-1. We find that divalent ion-induced changes in surface potential can account for most of the antagonism between these ions and Ca channel block by 1,4-dihydropyridines.

scholarly journals Improvement of Manganese Feroxyhyte’s Surface Charge with Exchangeable Ca Ions to Maximize Cd and Pb Uptake from Water

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1762 ◽  
Author(s):  
Evgenios Kokkinos ◽  
Chasan Chousein ◽  
Konstantinos Simeonidis ◽  
Sandra Coles ◽  
Anastasios Zouboulis ◽  
...  
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Charge Density ◽  
Small Scale ◽  
Adsorption Sites ◽  
Exchangeable Ca ◽  
Preparation Step ◽  
Negative Surface ◽  
Ca Ions ◽  
Negative Surface Charge

The surface configuration of tetravalent manganese feroxyhyte (TMFx) was appropriately modified to achieve higher negative surface charge density and, hence, to improve its efficiency for the removal of dissolved Cd and Pb mostly cationic species from water at pH values commonly found in surface or ground waters. This was succeeded by the favorable engagement of Ca2+ cations onto the surface of a mixed Mn-Fe oxy-hydroxide adsorbent during the preparation step, imitating an ion-exchange mechanism between H+ and Ca2+; therefore, the number of available negatively-charged adsorption sites was increased. Particularly, the calcium coverage can increase the deprotonated surface oxygen atoms, which can act as adsorption centers, as well as maintain them during the subsequent drying procedure. The developed Ca-modified adsorbent (denoted as TMFx-Ca) showed around 10% increase of negative surface charge density, reaching 2.0 mmol [H+]/g and enabling higher adsorption capacities for both Cd and Pb aquatic species, as was proved also by carrying out specific rapid small-scale column tests, and it complied with the corresponding strict drinking water regulation limits. The adsorption capacity values were found 6.8 μg·Cd/mg and 35.0 μg·Pb/mg, when the restructured TMFx-Ca adsorbent was used, i.e., higher than those recorded for the unmodified material.

Surface charge and extracellular polymer of sludge in the anaerobic degradation process

1996 ◽  
Vol 34 (5-6) ◽  
pp. 309-316 ◽  
Author(s):  
X. S. Jia ◽  
Herbert H. P. Fang ◽  
H. Furumai
Keyword(s):  
Surface Charge ◽  
Growth Phase ◽  
Anaerobic Degradation ◽  
Degradation Process ◽  
Anaerobic Sludge ◽  
Batch Experiments ◽  
High Substrate Concentration ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Extracellular Polymer

Changes of surface charge and extracellular polymer (ECP) content were investigated in batch experiments for three anaerobic sludges, each of which had been enriched at 35°C and pH 639-7.3 for more than 40 batches using propionate, butyrate and glucose, individually, as the sole substrate. Results showed that both ECP and the negative surface charge were dependent on the growth phase of microorganisms. They increased at the beginning of all batches when the microorganisms were in the prolific-growth phase, having high substrate concentration and food-to-microorganisms ratio. Both later gradually returned to their initial levels when the microorganisms were in the declined-growth phase, as the substrate became depleted. The negative surface charge increased linearly with the total-ECP content in all series with slopes of 0.0187, 0.0212 and 0.0157 meq/mg-total-ECP for sludge degrading propionate, butyrate and glucose, respectively. The change of surface charge for the first two sludges was mainly due to the increase of proteinaceous fraction of ECP; but, for glucose-degrading sludge, that could be due to the increases of both proteinaceous and carbohydrate fractions of ECP. The negative-charged nature of anaerobic sludge implies that cations should be able to promote granulation of anaerobic sludge.

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