Differential Effect of Hypoxia in Human and Mouse Vascular Smooth Muscle Cell Migration through LRP1-pPyk2-MMP-9 Axis

LRP1-pPyk2 axis is essential for the upregulatory effect of hypoxia on MMP-9 activation and human VSMC (hVSMC) migration. Currently, there are not efficient models for the translational study of atherosclerosis. The morphological and physiological features of atherosclerosis are different between human and animal models, particularly in mouse models. Therefore, the aim of current investigation was to compare the effect of hypoxia on LRP1-Pyk2-MMP-9 axis in human and mouse vascular smooth muscle cells (mVSMC) and its consequences on VSMC migration. We demonstrated that hypoxic modulation of LRP1-pPyk2-MMP-9 axis is opposite between hVSMC and mVSMC. The modulation of LRP1/pPyk2 levels by hypoxia is positive in hVSMC but negative in mVSMC. We showed that the inverse effect of LRP1/pPyk2 axis is associated with a differential effect of hypoxia on MMP-9 expression and activation. Hypoxia-induced MMP-9 activation was concomitant with an increased hVSMC migratory capacity. Surprisingly, mVSMC migrate under hypoxic conditions despite the downregulatory effect of hypoxia on MMP-9 expression or activation. Our results highlight the crucial role of LRP1-pPyk2-MMP-9 axis in vascular cell migration. In addition, we propose that the extrapolation of results from animal models to humans is not suitable for this specific mechanism in hypoxia-related vascular conditions.

Local Angiotensin Pathways in Human Carotid Atheroma: Towards a Systems Biology Approach

We will summarize the data we have obtained in human carotid artery concerning the organization of an extended local renin angiotensin aldosterone system and its variations at different stages of atheroma. In a system view, we propose a model where concomitant increase in angiotensin and glucocorticoid signaling is induced and amplified in VSMC while vascular smooth muscle cells transdifferentiate toward a lipid storing phenotype.

Tribological Characteristics of the Magnesium Matrix-Glassy Carbon Particles Composite Manufactured by Different Casting Methods

A particulate composite with a magnesium matrix (Mg3Al) and glassy carbon particles (GCp) obtained under industrial conditions from a gravity cast and pressure die cast suspension was examined. The influence of the casting procedure on the microstructure and mechanical properties was revealed. Sliding friction tests by the pin-on-disc method for different loads (2.3, 5, and 9.3 N) and speeds (0.06, 0.09, and 0.14 m/s) were performed. Regardless of the technology, the sliding friction coefficient’s value strongly depended on the load and speed. Its value was changing (0.35–0.13) and was usually higher for the pressure die cast material, yet the wear resistance of the composite processed in that way was considerably better compared with the gravity cast. The results of the worn surface observation by SEM with EDS showed an influence of the initial Mg3Al-GCp composite’s microstructure on the processes of its wear.

On the Role of Oxidation in Tribological Contacts under Environmental Conditions

Oxidation processes in tribological steel contacts are investigated, which are treated in a dry sliding, linear reciprocating model tribometer, by EDX (energy dispersive X-ray spectroscopy), AES (Auger electron spectroscopy), and HREFTEM (high resolution energy filtered transmission electron microscopy). Typical for steel contacts under environmental conditions is the feature that the counterparts are separated by oxide layers, which influence the tribological properties. And vice versa the tribological load will influence and change the oxide layers. The interaction of this dynamically coupled system was resolved by focussing the postexperimental surface analysis to long time stable balance states. As special challenge for the analyst of the tribological experiment under environmental conditions a postexperimental grown oxide layer covers the tribological induced changes and has to be distinguished from the tribological induced changes. Thick oxide layers, formed during the tribological load, were observed, which start to grow in form of islands and at the end separate the metallic bulk materials of the counterparts completely and avoid direct metal-metal contact. Thicknesses up to some microns strength, exceeding native oxide layers by magnitudes, were reached. Ploughing under fresh surface oxide and compacting and embedding of fresh oxidized debris particles were identified as main mechanisms responsible for the growing of these thick oxide layers.

Surface Analysis of Chain Joint Components after Tribological Load and Usage of Antiwear Additives

Wear in chain joints leads to an increased clearance and thus an elongation of the entire chain which determines the lifetime of the chain. This particularly applies for chains that are used in timing chain drives. The aim of this study was to investigate especially the influences of lubricant additives and a contamination with carbon black on the tribological behavior of chain joint components and to correlate these influences to observable changes in topographical and chemical surface properties. A precisely defined contact and load situation is essential for generating a comparable series of samples for surface analyses. To meet this requirement, chain joint component samples from tests on a linear reciprocating model tribometer were used for the following analyses. But to connect the results to the realistic situation regarding the typical wear rates of the subjected chain types, suited experimental parameters were selected. Topographical, structural, and chemical characterization of the worn surface regions of the components were performed after the tribological loading. The results show the influence of the lubricant, the additive, and the contamination with carbon black especially on the chemical properties of the component surfaces.

Experimental Analysis of Microstructured Steel Surfaces for Wet Tribological Applications in the Low Velocity Regime

The surface topography plays an important role in the design of a function-optimised surface. Therefore, the influence of topography with microsized structures produced by laser surface texturing (LST) is experimentally examined under lubricated sliding conditions. The structured specimens were made of AISI 51200 (DIN 100Cr6) hardened to about 800 HV. Concerning the requirements of tribological testing without any debris caused by the preprocessing, the structuring was carried out using a picosecond laser system (Trumpf TruMicro) with 6 ps pulse duration. A laboratory pin-on-disc tribometer (Plint TE-92 HS) was used for the tests, which were run under wet conditions with counterbodies made of bronze and steel at a nominal contact pressure of up to 4 MPa and sliding speeds between 0.04 and 2.0 m/s. Furthermore, start-stop cycles with accelerating and decelerating shares were used to simulate an automotive start-stop system. In the tribological experiments, a significant reduction of the friction coefficient was observed compared to sliding pairs without microstructured pin surfaces. Whereas no measureable wear occurred on the steel pins and discs, the bronze discs showed a significant amount of wear and the microstructures on the pin surfaces mated against bronze discs were almost completely filled with wear debris.

A New Compression-Torsion-Tribometer with Scalable Contact Pressure for Characterization of Tool Wear during Plastic Deformation

A contact pressure which reaches up to ten times the yield stress of the workpiece material is characteristic for cold extrusion processes. Common tests for friction and wear are limited to rather low contact pressures. Thus, the aim of this paper is to present a new compression-torsion-tribometer which is able to scale the contact pressure to a multiple of the yield stress of the workpiece. In order to enable a contact pressure that greatly exceeds the yield stress of the workpiece material, the workpiece specimen is encapsulated laterally. As main parameters, contact pressure, glide length, and relative velocity can be adjusted independently, thus allowing for multiple load cycles. The resulting torque is measured continuously as an indicator for wear. Afterwards wear can be also quantified by examination of surfaces. Hence, the developed setup enables a comparison of tool surfaces and coatings and a characterization of wear behaviour under high contact pressure.

A Study of Correlation between Crack Initiation during Dynamic Wear Process and Fatigue Crack Growth of Reinforced Rubber Materials

The aim of this study is concentrated on the experimental investigation of crack initiation during dynamic wear process and its correlation with fatigue crack growth of reinforced rubber materials. The analyzed rubber compounds suitable for applications such as treads for truck tires were based on natural rubber (NR) and polybutadiene rubber (BR). The dynamic wear behavior has been studied using an own developed testing equipment based on gravimetric determination of mass loss of test specimen. Fatigue crack growth (FCG) analysis was performed under pulse loading in accordance with real dynamic loading conditions of rolling tires using the Tear Analyser (TA). We show the crack initiation process during dynamic wear with respect to different impact energies and correlate the liability of crack initiation with FCG data at given tearing energy as a function of the rubber compositions. We demonstrate the higher crack initiation resistance of rubber blends with increased content of BR, while a predominant influence of NR improves the resistance against crack propagation especially at higher strain levels due to strain induced crystallization.