High Traction Forces Research Articles

β1- and αv-class integrins cooperate to regulate myosin II during rigidity sensing of fibronectin-based microenvironments

How different integrins that bind to the same type of extracellular matrix protein mediate specific functions is unclear. We report the functional analysis of β1- and αv-class integrins expressed in pan-integrin-null fibroblasts seeded on fibronectin. Reconstitution with β1-class integrins promotes myosin-II-independent formation of small peripheral adhesions and cell protrusions, whereas expression of αv-class integrins induces the formation of large focal adhesions. Co-expression of both integrin classes leads to full myosin activation and traction-force development on stiff fibronectin-coated substrates, with αv-class integrins accumulating in adhesion areas exposed to high traction forces. Quantitative proteomics linked αv-class integrins to a GEF-H1-RhoA pathway coupled to the formin mDia1 but not myosin II, and α5β1 integrins to a RhoA-Rock-myosin II pathway. Our study assigns specific functions to distinct fibronectin-binding integrins, demonstrating that α5β1integrins accomplish force generation, whereas αv-class integrins mediate the structural adaptations to forces, which cooperatively enable cells to sense the rigidity of fibronectin-based microenvironments.

High-Altitude Wind Energy for Sustainable Marine Transportation

This paper investigates the use of a controlled tethered wing, or kite, for naval transportation. Linked to a boat by light composite-fiber lines, the kite is able to fly between 200 and 600 m above the sea and to generate high traction forces. A mechatronic system named Kite Steering Unit (KSU) that is installed on the boat controls the kite and converts the line speed and force into electricity. Different from previous works, the boat is also equipped with electric propellers so that naval propulsion can be achieved both directly, i.e., through the towing forces exerted by the lines, and indirectly, i.e., through the electricity generated by the KSU that is fed to the electric propellers via a battery pack. The optimal system operating conditions that maximize the boat speed for the given wind characteristics are computed. Then, a model predictive controller is designed, and numerical simulations with a realistic model are carried out to assess the performance of the control system against the optimal operating conditions. The results indicate that, with this system, a completely green naval transportation system can be obtained, regardless of the wind direction.

Optimization and control of a hybrid kite boat1

AbstractThis paper investigates the use of a controlled tethered wing, or kite, for naval transportation. Linked to a boat by light composite-fibre cables, the kite is able to fly between 200 m and 600 m above the sea and to generate high traction forces. A mechatronic system installed on the boat, named Kite Steering Unit (KSU), controls the kite and converts the cable speed and force into electricity. Differently from previous works, the boat is also equipped with two electric propellers, so that naval propulsion can be achieved both directly, through the towing forces exerted by the cables, and indirectly, through the electricity generated by the KSU and fed to the electric propellers via a battery pack. The results indicate that, by properly choosing the operating conditions of the system, a completely green naval transportation system can be obtained regardless of the wind direction.

Alignment and Cell-Matrix Interactions of Human Corneal Endothelial Cells on Nanostructured Collagen Type I Matrices

To use nanoscopically defined, two-dimensional matrices assembled from aligned collagen type I fibrils as a sheet substratum for in vitro cultivation of human corneal endothelial cells (HCECs). To assess the effect of matrix architecture on HCEC morphology and to characterize integrin-mediated HCEC-matrix interaction. Cell alignment and cell-matrix interactions of primary HCECs and three different immortalized HCEC populations on native and UV-cross-linked collagen type I matrices were examined by time-lapse microscopy. Specific integrin α(2)β(1) binding to the collagen matrix was demonstrated using a function-blocking α(2) antibody. Integrin α(2) subunit expression levels of the four HCEC populations were analyzed by Western blot analysis. All HCEC populations aligned along the oriented collagen fibrils. Primary HCECs and, to a lesser extent, the other tested HCEC populations exerted high traction forces, leading to progressive matrix destruction. Cross-linking of the collagen matrices considerably increased matrix stability. Integrin subunit α(2) expression levels of the four cell types correlated with the degree of cell alignment and exertion of traction forces. In turn, blocking integrin subunit α(2) reduced cell alignment and prevented matrix destruction. HCECs align directionally along parallel arrays of collagen type I fibrils. The interactions of HCECs with collagen type I are primarily mediated by integrin α(2)β(1). Integrin subunit α(2) levels correlate with matrix contraction and subsequent destruction. Sustained cultivation of HCECs on ultrathin collagen matrices thus requires matrix cross-linking and moderate integrin α(2)β(1) expression levels.

PTA und Stent distal der AFS

Although angioplasty and stent applications in the iliac vessels and the superficial femoral artery have become routine procedures, their usefulness for the treatment of lesions of the popliteal artery and the lower leg arteries is still under discussion. For the popliteal artery, limitations are mainly due to the high mechanical stress in this area, causing high traction forces. Moreover, beyond the occlusive atherosclerotic changes, specific pathological entities such as aneurysms, emboli, entrapment syndromes, and cystic adventitial disease have to be differentiated. There is hope that the development of innovative stent designs with high flexibility might overcome the limitations. For lesions of the lower leg arteries treatment with percutaneous transluminal angioplasty (PTA) has become the method of choice. However, stent designs as used for cardiac interventions have been adapted for their application below the knee, and first encouraging results may help to justify their broad use in the future. Regarding PTA, innovative equipment and techniques for the treatment of arterial lesions below the knee include dedicated, long, and very flexible balloons, cutting balloon cryoplasty, and laser angioplasty. Regarding stents, bare metal stents, stents with passive or active coatings, and bioabsorbable stents have all been successfully used.

Simplified motion control of a two-axle compliant framed wheeled mobile robot

Kinematic models and motion control algorithms for a two-axle compliant frame mobile robot are examined. General kinematics describing the compliantly coupled nonholonomic kinematics are derived using velocity constraints that minimize traction forces and consider foreshortening of the frame. Given the complexity of these equations, the steering ratio a is defined to describe the relative heading angles of the front and rear axles. Simplified kinematic models are developed based upon a (Types I, II, and III) and the reference point used to guide the robot. Physical limitations and performance metrics (lateral mobility and maneuverability per unit of traction force) are derived to evaluate the models. Six groups of simulations and 24 experimental tests consisting of 120 trials evaluate the performance of the algorithms on carpet, sand, and sand with rocks. Results indicate that Type I (curvature-based steering) provides superior maneuverability and regulation accuracy, whereas Type II provides excellent lateral mobility at the cost of high traction forces, reduced accuracy, and potential singularities. Both models offer significant reductions in complexity for simplified control using standard curvature-based unicycle control algorithms. These results support expectations derived from performance metrics and physical limitations. Experimental results also demonstrate the efficacy of the robot to adapt to and maneuver over extremely rugged rocky terrain.

Integrin-dependent actomyosin contraction regulates epithelial cell scattering

The scattering of Madin-Darby canine kidney cells in vitro mimics key aspects of epithelial–mesenchymal transitions during development, carcinoma cell invasion, and metastasis. Scattering is induced by hepatocyte growth factor (HGF) and is thought to involve disruption of cadherin-dependent cell–cell junctions. Scattering is enhanced on collagen and fibronectin, as compared with laminin1, suggesting possible cross talk between integrins and cell–cell junctions. We show that HGF does not trigger any detectable decrease in E-cadherin function, but increases integrin-mediated adhesion. Time-lapse imaging suggests that tension on cell–cell junctions may disrupt cell–cell adhesion. Varying the density and type of extracellular matrix proteins shows that scattering correlates with stronger integrin adhesion and increased phosphorylation of the myosin regulatory light chain. To directly test the role of integrin-dependent traction forces, substrate compliance was varied. Rigid substrates that produce high traction forces promoted scattering, in comparison to more compliant substrates. We conclude that integrin-dependent actomyosin traction force mediates the disruption of cell–cell adhesion during epithelial cell scattering.

Effects of traction, distension, and joint position on distraction of the hip joint: An experimental study in cadavers

Purpose: To quantify the effects of traction alone and in combination with distension of air in different joint positions in order to find out the conditions for adequate distraction of the hip joint with minimal traction force. Type of Study: Experimental cadaver study. Methods: Eight cadaver hip joints were studied. The cadavers were placed supine on a fracture table and traction was applied in different joint positions for flexion and abduction with and without distension using air. For the measurement, the joint space between the acetabulum and femoral head was separated by 4 different lines characterizing the lateral margin of the acetabulum, the superior portions of the lunate cartilage, and the acetabular fossa. Results: At all measurement lines, distraction of the hip was significantly better when traction and distension were combined. At traction forces from 250 to 300 N, traction plus distension resulted in a 1.59- to 2.25-fold increase of joint distraction compared to traction alone. The maximum effect of distension was achieved between 200 and 250 N. Up to traction forces of 250 N, the joint vacuum force counted for more than half of the total resistance. The effects of flexion and abduction on distraction of the hip were smaller. A trend for better distraction was found for 20° of flexion and a significantly better distraction by avoiding abduction. Conclusions: High traction forces by breakage of the joint seal can be avoided by distension using air. The passive resistance of the soft tissues increases at higher traction forces. Slight flexion without abduction showed further increase of joint distraction. Reducing the amount of traction may possibly reduce the risk of soft tissue perineal and neurologic injuries.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 8 (October), 2002: pp 865–871

Forest operations and environmental protection

Increased mechanisation in forestry usually means increased traffic over the ground, which also is a substrate for growth. Soil compaction, rut formation, and damage to stems and roots may all result in growth reduction. To reduce soil disturbance and tree damage, smaller machines or machines with less ground pressure must be considered. Today the traffic may cover 10–30% of the site area. This is mainly due to skidding during clear-felling and thinning. If present trends of heavy mechanisation continue, in the future there could be as many as six machine entries onto the site by the time a stand has reached an age of 50 years. Rut formation from forwarders and skidders is a problem. Harvesters seem to cause minor problems. The engine torque powering the driving wheels adds considerably to the influence of the total weight of the vehicle on the ground. High traction forces and slipping may contribute twice as much to soil disturbance as the vehicle ground pressure. When designing forest machinery for transportation of timber the payload itself is the most complicated problem. During the XIX World Congress of the International Union of Forestry Research Organisations (IUFRO) in Montreal, Canada, 1990, a Project Group on Forest Operations and Environmental Protection was established within IUFRO Division 3. From the author's point of view, concern about biodiversity is not taken into account through single-track and profit-oriented forestry in some areas and total preservation in other areas. It is the manifold of different ways of forestry that is the answer to sustainable development and conservation of biodiversity.