Characterization of the role of integrin α5β1 in platelet function, hemostasis and experimental thrombosis

Objective: Integrins are key regulators of various platelet functions. The pathophysiological importance of most platelet integrins has been investigated, with the exception of α5β1, a receptor for fibronectin. The aim of this study was to characterize the role of α5β1 in megakaryopoiesis, platelet function, and to determine its importance in hemostasis and arterial thrombosis. Approach and results: We generated a mouse strain deficient for integrin α5β1 on megakaryocytes and platelets (PF4Cre-α5-/-). PF4Cre-α5-/- mice were viable, fertile and presented no apparent signs of abnormality. Megakaryopoiesis appears unaltered as evidence by a normal megakaryocytes morphology and development, which is in agreement with a normal platelet count. Expression of the main platelet receptors and the response of PF4Cre-α5-/- platelets to a series of agonists were all completely normal. Adhesion and aggregation of PF4Cre-α5-/- platelets under shear flow on fibrinogen, laminin or von Willebrand factor were unimpaired. In contrast, PF4Cre-α5-/- platelets displayed a marked decrease in adhesion, activation and aggregation on fibrillar cellular fibronectin and collagen. PF4Cre-α5-/- mice presented no defect in a tail-bleeding time assay and no increase in inflammatory bleeding in a reverse passive Arthus model and a lipopolysaccharide pulmonary inflammation model. Finally, no defects were observed in three distinct experimental models of arterial thrombosis based on ferric chloride-induced injury of the carotid artery, mechanical injury of the abdominal aorta or laser-induced injury of mesenteric vessels. Conclusion: In summary, this study shows that platelet integrin α5β1 is a key receptor for fibrillar cellular fibronectin but is dispensable in hemostasis and arterial thrombosis.

Compliant Detachment of Wall-Climbing Robot Unaffected by Adhesion State

Adhesion state is a key factor affecting the motion stability of a wall-climbing robot. According to different adhesion states, there is no universal method for compliant detachment. We propose an online impedance strategy for controlling peeling angle to realize compliant movement. Variable compliant motions are achieved by online tuning the stiffness and damping parameters of proportional-derivative control, which realizes compliant detachment with a peeling angle of π, the adhesion strength to adjust to a minimum and basically eliminated the instant change in normal adhesion strength at the detachment end state. The proposed controller was validated using a vertical climbing robot. The results showed that, with the proposed controller, the sudden change in the normal adhesion force during peeling was significantly reduced. Besides, there is no correlation between the sudden change in the normal adhesion force at the detachment end state and the adhesion state. Regardless of the adhesion states, the compliant detachment can be accomplished reliably.

PEDOT:PSS Coating Improves Gecko-Inspired Adhesive Performance

We report a surface treatment for an elastomeric dry adhesive that improves adhesion, especially on surfaces with microscopic roughness. The process involves coating wedge-shaped polydimethylsiloxane (PDMS) features of the adhesive with a 50 nm coating of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). As compared to the uncoated adhesive, performance is 1.25× better on smooth surfaces like glass, with a maximum shear stress of 70 kPa in shear and 25 kPa in normal adhesion under controlled loading conditions. On slightly rough surfaces such as paper and panels painted with flat paint, it provides between 2.5× and over 12× greater shear stress than the uncoated adhesive. Moreover, the coating, being much stiffer than the underlying wedges, does not increase the tendency to become dirty and does not tend to self-stick, or clump. Durability tests show that the performance remains substantially unchanged for 80,000 attachment/loading/detachment cycles. We describe the coating process, present the test results, and discuss the reasons for the enhanced performance on a variety of materials.

The Mechanism of Layer Stacked Clamping (LSC) for Polishing Ultra-Thin Sapphire Wafer

Double-sides polishing technology has the advantages of high flatness and parallelism, and high polishing efficiency. It is the preferred polishing method for the preparation of ultra-thin sapphire wafer. However, the clamping method is a fundamental problem which is currently difficult to solve. In this paper, a layer stacked clamping (LSC) method of ultra-thin sapphire wafer which was used on double-sides processing was proposed and the clamping mechanism of layer stacked clamping (LSC) was studied. Based on the rough surface contact model of fractal theory, combining the theory of van der Waals force and capillary force, the adhesion model of the rough surfaces was constructed, and the reliability of the model was verified through experiments. Research has found that after displacement between the two surfaces the main force of the adhesion force is capillary force. The capillary force decreases with the increasing of surface roughness, droplet volume, and contact angle. For an ultra-thin sapphire wafer with a diameter of 50.8 mm and a thickness of 0.17 mm, more than 1.4 N of normal adhesion force can be generated through the LSC method. Through the double-sides polishing experiment using the LSC method, an ultra-thin sapphire wafer with an average surface roughness (Ra) of 1.52 nm and a flatness (PV) of 0.968 μm was obtained.

Increasing the Monolithic Nature of Masonry Made of Cellular Concrete Blocks by Using Polyurethane Foam Glue as a Masonry Mortar

This study is a continuation of previously published work [1]. The results of experimental determination of the strength of normal adhesion (under axial tension) in masonry made of autoclave–hardened cellular concrete blocks of compressive strength classes B1,5-B3,5 on cement mortars and polyurethane foam adhesives are presented. The tests were carried out in the laboratory of the Department “Reinforced Concrete and Stone Structures” of the Moscow State University of Civil Engineering (National Research University). The experiment was carried out on samples-cubes with a size of 150x150x150 mm, which were cut out of cellular concrete blocks, fastened (glued) together using masonry (binding) compositions. In the course of the study, it was found that when using various polyurethane foam glue compositions in masonry made of cellular concrete blocks of compressive strength classes B1,5–B3,5, the resistance to axial stretching over an unbound section (normal adhesion) of the masonry increases by approximately 9–25%. It was also found that the nature of the destruction of samples made on polyurethane foam adhesives (destruction occurs along the body of concrete), indicates the monolithic nature of the masonry. The analysis of the results obtained makes it possible to conclude that the resistance to axial tension along the unbound section of the masonry depends on the strength of the material from which the block is made, and not on the compressive strength of the masonry (binder) mortar used, as indicated in table 11 of SP 15.13330.2012 “Stone and reinforced masonry structures”. This factor must be taken into account when calculating masonry from autoclave-hardened cellular concrete blocks on polyurethane foam compositions.

Development of a gecko-like robotic gripper using Scott–Russell mechanisms

SummaryThis paper describes the development of a gecko-inspired robotic gripper for grasping flat objects using Scott–Russell mechanisms. Compared to previously reported grippers that utilize gecko-like adhesives, the one presented here produces higher normal adhesion and has robustness and controllability advantages. To verify the applicability of proposed gripper, a mechanical model and experimental results on a variety of substrates are presented. The experimental results demonstrated a 19.6% and 50% increase in normal adhesion using a preload of <15 and <30 N, respectively, compared to previously reported results under similar testing parameters and conditions.

Adhesion and running speed of a tropical arboreal ant ( Cephalotes atratus ) on wet substrates

In the tropical forest canopy, wingless worker ants must cling to and run along diverse vegetative surfaces with little protection from sun, wind and rain. Ants rely in part on their tiny adhesive tarsal pads to maintain sufficient contact with substrates to prevent falls under these varied conditions. Here, we examined the effects of substrate wettability and surface water on the tarsal pad adhesive performance of a common tropical arboreal ant. Ant adhesion was consistently higher on an intermediately wetting substrate (static water contact angle ca 90°) when resisting both perpendicular (normal) force and parallel (shear) force. Normal adhesion was maintained on intermediately wetting and hydrophobic substrates following the addition of rain-mimicking water droplets, whereas shear adhesion declined on all substrate types tested after wetting. Ant running speed was slower on wet substrates. On wood substrates, normal and shear adhesion declined with increasing wetness from dry, to misted, to water-soaked. These differences probably contributed to lower ant running speed on wet wood. The results of this study provide the first quantitative assessment of tropical arboreal ant adhesive performance under substrate conditions that are commonly encountered in the rainforest canopy.