Friction reduction by texturing of DLC coatings sliding against steel under oil lubrication

It has been demonstrated that tetrahedral amorphous carbon (ta-C) films provide excellent wear and friction properties in dry sliding. Recently the applications of ta-C coatings in lubricated conditions have become more important. The use of carbon coatings aims at reducing the wear and coefficient of friction under minimum lubrication and without hazardous lubricant additives. For optimum tribological performance, a modification of the ta-C coated surfaces is required. The present paper describes an innovative method of coated surface texturing, by which nanometer and micrometer size pores are processed by various methods. Particle masking was used for processing micrometer size pores and for controlling the coating growth conditions in order to produce nanometer size pores in the ta-C surface. The masking by particles yielded a pore geometry which varied from complex shaped channels to small individual pores. The texturing was performed by distributing metallic powder particles on the surface or by direct chemical deposition of metal particles on the substrate in prior to pulsed vacuum arc deposition. The tribological characterization was carried out by applying reciprocating friction tests with controlled lubricant replenishment, in order to simulate metal forming processes. The friction reducing effect, which was observed in the tribological tests, indicated a microlubrication effect of the textured coating surfaces.     

Fc receptor-triggered insertion of secretory granules into the plasma membrane of human neutrophils: selective retrieval during phagocytosis

We studied the kinetics of secretion in human neutrophils stimulated by IgG-opsonized zymosan. Secretion of azurophilic and specific granules was quantified measuring the appearance of the granule markers CD63 and CD66b, respectively, at the cell surface. The kinetics of secretion was compared with the course of phagocytosis, revealed by the trapping of the fluid phase marker, Lucifer Yellow, in vacuoles containing zymosan particles. We found that secretion of both azurophilic and specific granules precedes phagosome sealing. An initial rapid phase of secretion was followed by a decrease in the amount of CD63 and CD66b at the cell surface. This subsequent disappearance of surface CD63 and CD66b was inhibited by cytochalasin B and probably represents internalization of the granular markers into the forming phagosome. The decrease in the amount of CD63 and CD66b exposed at the cell surface was not accompanied by a commensurate reduction in cell surface area, measured with the amphiphilic fluorescent dye FM1-43. These findings imply that CD63 and CD66b are selectively retrieved from the plasma membrane following secretion. Evidence is also presented that calcium is not the sole mediator of the rapid secretion of azurophilic and specific granules triggered by IgG-opsonized particles and that cytochalasin does not impair signaling of the calcium transient elicited by Fc receptors. Instead, actin disassembly appears to reduce the efficiency of the interaction between opsonized particles and their receptors, an effect that can be overcome by increasing the concentration of the stimulating particles.