Adhesion Traction Research Articles

Lipoabdominoplasty with Progressive Traction Sutures.

Proactively preserving Scarpa's fascia and thus its intrinsic lymphatic drainage and tensile strength for suture placement can eliminate the need for drains after lipoabdominoplasty and therefore reduce the rate of seroma development. In this article, we describe the effectiveness of a modified progressive traction suture (PTS) technique, which enables us to lessen the most common complications and avoid hospital readmission; these sutures take 3-5 minutes of additional surgery time. Two hundred seventy-six patients (mean age, 38 years; range, 19-67 years), with a mean body mass index of 25 were included in this study. All patients underwent complete lipoabdominoplasty with ultrasound-assisted liposuction (VASER) throughout the abdomen and flanks. Abdominal rectus plication was performed in 100% of cases. All patients were operated on under spinal anesthesia and stayed overnight in hospital. Of the 276 patients, 1.8% developed postoperative seromas. No patients developed hematomas. New wound closure was needed in 1.4% of patients, performed within 7-10 days of surgery, scar revision in 4.7%, residual liposuction under local anesthesia in 9.7%, and liposuction under sedation in 1%; deep vein thrombosis without thromboembolic phenomenon developed in 1%, none resulting in death. In addition, the use of a PTS technique is a time-saving procedure because it takes the surgeons between 3-5 minutes of operative time, unlike that of adhesion and/or separate traction, which takes between 30 and 45 minutes. The use of PTSs helped diminish complications such as seroma and hematoma and prevent additional cost involving hospital readmission and/or further surgery. Furthermore, use of these sutures required only 3-5 minutes of additional operative time.

Dynamic monitoring of the driving wheels’ pre-sliding of the railway transport

The proposed method of dynamic monitoring of the driving wheels’ state of the railway transport makes it possible to detect in a timely manner the processes accompanying the transition of the wheel from the adhesion to slipping mode. This in turn helps prevent a loss of adhesion traction that have a wide range of negative consequences. The method is based on the spectral analysis of the vibration processes of the driving wheels of the railway transport.

Cellular adhesome screen identifies critical modulators of focal adhesion dynamics, cellular traction forces and cell migration behaviour

Cancer cells migrate from the primary tumour into surrounding tissue in order to form metastasis. Cell migration is a highly complex process, which requires continuous remodelling and re-organization of the cytoskeleton and cell-matrix adhesions. Here, we aimed to identify genes controlling aspects of tumour cell migration, including the dynamic organization of cell-matrix adhesions and cellular traction forces. In a siRNA screen targeting most cell adhesion-related genes we identified 200+ genes that regulate size and/or dynamics of cell-matrix adhesions in MCF7 breast cancer cells. In a subsequent secondary screen, the 64 most effective genes were evaluated for growth factor-induced cell migration and validated by tertiary RNAi pool deconvolution experiments. Four validated hits showed significantly enlarged adhesions accompanied by reduced cell migration upon siRNA-mediated knockdown. Furthermore, loss of PPP1R12B, HIPK3 or RAC2 caused cells to exert higher traction forces, as determined by traction force microscopy with elastomeric micropillar post arrays, and led to considerably reduced force turnover. Altogether, we identified genes that co-regulate cell-matrix adhesion dynamics and traction force turnover, thereby modulating overall motility behaviour.

Measurement of the strength and range of adhesion using atomic force microscopy

Adhesion of nanoscale contacts is important in many applications, including microelectromechanical systems, fibrillar adhesives, and atomic force microscopy (AFM). Here, we quantify the properties of the adhesive traction–separation relation between ultrananocrystalline diamond (UNCD) AFM tips and polymethyl methacrylate (PMMA) surfaces using a novel AFM-based method that combines pull-off force measurements and characterization of the 3D geometry of the AFM tip. Three AFM tips with different nanoscale geometries were characterized and used to perform pull-off force measurements. Using the pull-off force data, the measured 3D tip geometries, and an assumed form of the traction–separation relation, specifically the Dugdale or 3-9 Lennard-Jones relations, the range, strength, and work of adhesion of the UNCD–PMMA contact were determined. The assumptions in the analyses were validated via finite element modeling. Both forms of the traction–separation laws result in a work of adhesion of approximately 50 mJ/m2 and the peak adhesive stress in the Lennard Jones relation is found to be about 50% higher than that obtained for the Dugdale law.

Macrophages Mediate the Repair of Brain Vascular Rupture through Direct Physical Adhesion and Mechanical Traction

Hemorrhagic stroke and brain microbleeds are caused by cerebrovascular ruptures. Fast repair ofsuch ruptures is the most promising therapeuticapproach. Due to a lack of high-resolution in vivoreal-time studies, the dynamic cellular events involved in cerebrovascular repair remain unknown. Here, we have developed a cerebrovascular rupture system in zebrafish by using multi-photon laser, which generates a lesion with two endothelial ends. Invivo time-lapse imaging showed that a macrophage arrived at the lesion and extended filopodia or lamellipodia to physically adhere to both endothelial ends. This macrophage generated mechanical traction forces to pull the endothelial ends and facilitate their ligation, thus mediating the repair of the rupture. Both depolymerization of microfilaments and inhibition of phosphatidylinositide 3-kinase or Rac1 activitydisrupted macrophage-endothelial adhesion and impaired cerebrovascular repair. Our study reveals ahitherto unexpected role for macrophages in mediating repair of cerebrovascular ruptures through direct physical adhesion and mechanical traction.

Management of Vitreomacular Traction

Vitreomacular adhesion (VMA) and vitreomacular traction (VMT) syndrome belong to a spectrum of macular diseases in which vision impairment is caused by posterior hyaloid traction at the vitreoretinal interface. In the past, the diagnosis of VMA and VMT depended upon the clinician’s ability to identify vitreomacular abnormalities on slit lamp biomicroscopy. Thus, often relatively advanced cases were visually identifiable biomicroscopically (Johnson in Trans Am Ophthalmol Soc 103:537–567, 2005; Sebag in Eye (Lond) 16(4):429–439, 2002; Schepens in Am J Ophthalmol 39(5):631–633, 1955; Johnson in Am J Ophthalmol 149(3):371–382.e1, 2010). With the advent of optical coherence tomography, more previously unrecognized cases have been identified and better understood. This review discusses the variable presentations of this condition with a focus on the current classification and the various treatment strategies.

Pharmacologic vitreolysis with ocriplasmin: rationale for use and therapeutic potential in vitreo-retinal disorders.

With increased knowledge about the origins and pathophysiology of vitreo-retinal disorders—and, in particular, the central role of anomalous posterior vitreous detachment in vitreo-maculopathies—a paradigm shift from surgery to pharmacotherapy is taking place with the development of pharmacologic vitreolysis. The first approved agent for pharmacologic vitreolysis therapy is ocriplasmin, a truncated form of the nonspecific serine protease plasmin. Twelve studies comprise the current ocriplasmin clinical trial program, demonstrating the efficacy and safety of a single intravitreal injection of ocriplasmin for the treatment of patients with symptomatic vitreo-macular adhesion or vitreo-macular traction, including patients with macular holes. Although post-approval implementation of ocriplamsin in clinical practice has shown success rates of up to 78%, there have been recent case reports of acute, transient visual dysfunction. There are thus new initiatives to further refine clinical indications for case selection and to identify possible untoward effects. Although more studies are warranted, it appears that ocriplasmin offers a good alternative to surgery. The future lies in pharmacologic vitreolysis, and the future of pharmacologic vitreolysis lies in prevention. Thus, long-term studies are needed to define a role for pharmacologic vitreolysis, in particular with ocriplasmin, in the prevention of progressive diabetic retinopathy and age-related macular degeneration.

Influence of vitrectomyon the progressionof wet age related macular degeneration

Purpose. To study the effects of vitrectomy on the course of wet age-related macular degeneration (AMD). Materials and methods. 99 patients (99 eyes) with wet AMD associated with vitreo-macular adhesion or posterior hyaloid traction were included in the study. During the first 6 months, all patients received anti-VEGF treatment according to a PRN regimen. Then, they were divided into two groups: in 45 patients vitrectomy was performed and 54 patients did not receive surgical treatment. The follow-up period duration was one year. Results. At the beginning of the study, visual acuity was 0.27 ± 0.17 in the control group, and 0.17 ± 0.15 in the treatment group. Most prominent differences in visual acuity between the two groups were observed during the first 6 months (visual acuity in the treatment group before surgery was 0.12 ± 0.1) (p 0.01 and p 0.001), at the same time during the following 6 follow-up months, this difference decreased (p 0.05 and p 0.01). 1 year from the study start, visual acuity in the control group was 0.24 ± 0.17, and 0.17 ± 0.13 in the treatment one. Conclusions. Vitrectomy surgery in patients with wet AMD in association with vitreo-macular adhesion or posterior hyaloid traction does not exacerbate the disease course, stabilizes visual functions and improves the quality of life.

Contributions of the integrin β1 tail to cell adhesive forces

Integrin receptors connect the extracellular matrix to the cell cytoskeleton to provide essential forces and signals. To examine the contributions of the β1 integrin cytoplasmic tail to adhesive forces, we generated cell lines expressing wild-type and tail mutant β1 integrins in β1-null fibroblasts. Deletion of β1 significantly reduced cell spreading, focal adhesion assembly, and adhesive forces, and expression of human β1 (hβ1) integrin in these cells restored adhesive functions. Cells expressing a truncated tail mutant had impaired spreading, fewer and smaller focal adhesions, reduced integrin binding to fibronectin, and lower adhesion strength and traction forces compared to hβ1-expressing cells. All these metrics were equivalent to those for β1-null cells, demonstrating that the β1 tail is essential to these adhesive functions. Expression of the constitutively-active D759A hβ1 mutant restored many of these adhesive functions in β1-null cells, although with important differences when compared to wild-type β1. Even though there were no differences in integrin-fibronectin binding and adhesion strength between hβ1- and hβ1-D759A-expressing cells, hβ1-D759A-expressing cells assembled more but smaller adhesions than hβ1-expressing cells. Importantly, hβ1-D759A-expressing cells generated lower traction forces compared to hβ1-expressing cells. These differences between hβ1- and hβ1-D759A-expressing cells suggest that regulation of integrin activation is important for fine-tuning cell spreading, focal adhesion assembly, and traction force generation.

Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization.

Polymerase-δ-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner.

Autolytic degradation of ocriplasmin: a complex mechanism unraveled by mutational analysis.

Ocriplasmin, a truncated form of plasmin, is commercialized in the USA and in Europe under the trade name Jetrea(®), and indicated for the treatment of symptomatic vitreomacular adhesion and vitreomacular traction including when associated with macular hole ≤400 µm, respectively. We have shown in a previous study that ocriplasmin undergoes autolytic degradation when injected in eye vitreous, which leads to its rapid inactivation. In order to investigate this process further, we have introduced in ocriplasmin a variety of amino acid substitutions within or in the immediate vicinity of the three major autolytic cleavage sites. We demonstrate here that autolytic inactivation of ocriplasmin is a sequential process where initial cleavage occurs primarily between residues 156 and 157. Reduction or even blocking of autolysis can be achieved by mutating a limited number of key residues. In this study, we also report the identification of a series of ocriplasmin variants with improved resistance to autolysis and unimpaired catalytic activity. Such variants represent useful tools for the exploration of therapeutic approaches aiming at non-surgical resolution of vitreomacular adhesion.

Both contractile axial and lateral traction force dynamics drive amoeboid cell motility

Chemotaxing Dictyostelium discoideum cells adapt their morphology and migration speed in response to intrinsic and extrinsic cues. Using Fourier traction force microscopy, we measured the spatiotemporal evolution of shape and traction stresses and constructed traction tension kymographs to analyze cell motility as a function of the dynamics of the cell's mechanically active traction adhesions. We show that wild-type cells migrate in a step-wise fashion, mainly forming stationary traction adhesions along their anterior-posterior axes and exerting strong contractile axial forces. We demonstrate that lateral forces are also important for motility, especially for migration on highly adhesive substrates. Analysis of two mutant strains lacking distinct actin cross-linkers (mhcA(-) and abp120(-) cells) on normal and highly adhesive substrates supports a key role for lateral contractions in amoeboid cell motility, whereas the differences in their traction adhesion dynamics suggest that these two strains use distinct mechanisms to achieve migration. Finally, we provide evidence that the above patterns of migration may be conserved in mammalian amoeboid cells.

Traction Stress Dynamics During Chemotactic Amoeboid Cell Migration

Chemotaxis is involved in a broad range of biological phenomena such as during cancer metastasis. It requires a tightly regulated, spatiotemporal coordination of underlying biochemical processes that impact the mechanics of cell migration. In response to intrinsic and environmental cues, motile cells can adapt their migration effectively. Yet both the mechanisms by which this adaptation occurs and the role of the interactions between biochemistry and mechanics of cell migration are largely unknown.We use Fourier Traction Force Microscopy to measure the spatiotemporal evolution of shape and traction stresses and construct traction tension kymographs to analyze cell motility as a function of the dynamics of the cells' mechanically active adhesions (traction adhesions). We show that wild-type cells migrate mainly by forming two stationary traction adhesion sites at their front and back halves, over which the cell body moves forward in a step-wise fashion through periodic axial and, to a lesser degree, lateral contractions. We demonstrate that lateral forces are critical in mediating cell motility and essential for migration on highly adhesive substrates where cells implement two alternate motility modes to achieve migration. Our analysis of two mutant strains that lack distinct F-actin crosslinkers (mhcA- and abp120- cells) also supports a key role for lateral contractions in amoeboid cell motility, while the differences in their traction adhesion dynamics suggest the two mutant strains use distinct mechanisms to achieve migration. The considerable differences we find in both the spatiotemporal organization of traction adhesions and contractility, when comparing to the control wild type, provide insight into the role of the extracellular environment and of key cytoskeletal proteins in cell migration. We propose that these are highly conserved mechanisms, which function in a range of amoeboid cells, including leukocytes, as well as other forms of cell motility.

Impact of Cell Shape on Cell Migration Behavior on Elastic Substrate

Cell shape is known to have profound effects on a number of cell behaviors. In this paper we have studied the role of cell shape in cell migration through modeling its effect on cell traction force distribution, traction force dependent stability of cell adhesion and matrix rigidity dependent traction force formation. To quantify the driving force of cell migration, a new parameter called the motility factor, that takes account of the effect of cell shape, matrix rigidity and dynamic stability of cell adhesion, is proposed. We found that the motility factor depends on the matrix rigidity in a biphasic manner, in consistence with the experimental observations of the biphasic dependence of cell migration speed on the matrix rigidity. We showed that the cell shape plays a pivotal role in the cell migration behavior by regulating the traction force at the cell front and rear. The larger the cell polarity, the larger the motility factor is. The keratocyte-like shape has a larger motility factor than the fibroblast-like shape, which explains why keratocyte has a much higher migration speed. The motility factor might be an appropriate parameter for a quantitative description of the driving force of cell migration.

Deformation Gradients Imprint the Direction and Speed of En Masse Fibroblast Migration for Fast Healing

En masse cell migration is more relevant than single cell migration in physiological processes of tissue formation, such as embryogenesis, morphogenesis and wound healing. In these situations, cells are influenced by the proximity of other cells including interactions facilitated by substrate mechanics. Here we found that when fibroblasts migrated en masse over a hydrogel, they established a well-defined deformation field by traction forces and migrated along a trajectory defined by field gradients. The mechanics of the hydrogel determined the magnitude of the gradient. For materials stiff enough to withstand deformation related to cellular traction forces, such patterns did not form. Furthermore, migration patterns functioned poorly on very soft matrices where only a minimal traction gradient could be established. The largest degree of alignment and migration velocity occurred on the gels with the largest gradients. Granulation tissue formation in punch wounds of juvenile pigs was correlated strongly with the modulus of the implanted gel in agreement with in vitro en masse cell migration studies. These findings provide basic insight into the biomechanical influences on fibroblast movement in early wounds and relevant design criteria for development of tissue-engineered constructs that aim to stimulate en masse cell recruitment for rapid wound healing.

Ocriplasmin: A Review of Its Use in Patients with Symptomatic Vitreomacular Adhesion

Ocriplasmin (JETREA(®)) is a recombinant human serine protease plasmin with proteolytic activity against the protein components (e.g. laminin, fibronectin and collagen) of the vitreous and vitreoretinal interface, thereby facilitating vitreous liquefaction and separation of vitreous from the retina. Intravitreal ocriplasmin is indicated for the treatment of symptomatic vitreomacular adhesion (USA) and vitreomacular traction including when associated with a macular hole of diameter ≤400μm in adult patients (EU). The efficacy of ocriplasmin at the recommended dose of a single 125μg intravitreal injection was demonstrated in two well-designed pivotal phase III trials of virtually identical design (TG-MV-006 and TG-MV-007) in patients with symptomatic vitreomacular adhesion. A significantly greater proportion of patients treated with ocriplasmin than those treated with placebo achieved nonsurgical resolution of vitreomacular adhesion at day 28 (primary endpoint), with the significant between-group difference sustained until study end (month 6). At day 28, the proportion of eyes achieving total posterior vitreous detachment or nonsurgical closure of macular holes was also significantly greater with ocriplasmin than with placebo. Ocriplasmin was generally well tolerated in these trials, with most ocular adverse events being mild in severity and transient in nature. Current evidence suggests that ocriplasmin is a useful treatment option for patients with symptomatic vitreomacular adhesion.

How vinculin regulates force transmission

Focal adhesions mediate force transfer between ECM-integrin complexes and the cytoskeleton. Although vinculin has been implicated in force transmission, few direct measurements have been made, and there is little mechanistic insight. Using vinculin-null cells expressing vinculin mutants, we demonstrate that vinculin is not required for transmission of adhesive and traction forces but is necessary for myosin contractility-dependent adhesion strength and traction force and for the coupling of cell area and traction force. Adhesion strength and traction forces depend differentially on vinculin head (V(H)) and tail domains. V(H) enhances adhesion strength by increasing ECM-bound integrin-talin complexes, independently from interactions with vinculin tail ligands and contractility. A full-length, autoinhibition-deficient mutant (T12) increases adhesion strength compared with VH, implying roles for both vinculin activation and the actin-binding tail. In contrast to adhesion strength, vinculin-dependent traction forces absolutely require a full-length and activated molecule; V(H) has no effect. Physical linkage of the head and tail domains is required for maximal force responses. Residence times of vinculin in focal adhesions, but not T12 or V(H), correlate with applied force, supporting a mechanosensitive model for vinculin activation in which forces stabilize vinculin's active conformation to promote force transfer.

High Resolution Mapping of Cytoskeletal Dynamics in Neurons via Combined Atomic Force Microscopy and Fluorescence Microscopy

ABSTRACTLiving neuronal cells present active mechanical structures which evolve with cellular growth and changes in the cell microenvironment. Detailed knowledge of various mechanical parameters such as cell stiffness or adhesion forces and traction stresses generated during axonal extension is essential for understanding the mechanisms that control neuronal growth, development and repair. Here we present a combined Atomic Force Microscopy (AFM)/Fluorescence Microscopy approach for obtaining systematic, high-resolution elasticity and fluorescent maps for live neuronal cells. This approach allows us to simultaneously image and apply controllable forces to neurons, and also to monitor the real time dynamics of the cell cytoskeleton. We measure how the stiffness of neurons changes both during axonal growth and upon chemical modification of the cell, and identify the cytoskeletal components most responsible for the changes in cellular elasticity. This is accomplished by identifying cellular components with unique elastic signatures, and tracking those components over time within healthy cells or within cells treated to disrupt selective components.

Influence of friction and adhesion on the onset of plasticity during normal loading of spherical contacts

Increasing contact loading causes early transformation from elastic to elastic–plastic deformations in many conventional systems as well as micro/nano-electro-mechanical systems. The load required for yielding and the location of the onset of plasticity is critical in the robustness of systems with contacts. For frictionless (such as fully-lubricated) contacts, inception of plastic yielding occurs beneath the contact surface. However, frictional slip (contact shear) and adhesion push the inception of plastic yielding toward the contact surface. The influence of elastic mismatch, shear tractions and adhesive normal tractions on the subsurface stress field is studied analytically by superposition of the Hertzian stress field and the stress field created by the shear and additional (due to adhesion) normal tractions. Specifically, three contact conditions have been studied in this work: (i) frictionless, (ii) finite friction, and (iii) infinite friction (full stick). Also, a finite-element model is developed to verify certain assumptions in the analytical solution for the contact with finite friction. The results obtained are applied to two sets of in situ nanoindentation experiments to explain the change in the yielding behavior of submicrometer polycrystalline aluminum grains.

Total Internal Reflection Fluorescence Microscopy, Cell Adhesion, and Cell Traction Force Measurements on Soft Silicone Gels

Substrate rigidity impacts cellular behaviors such as migration, gene expression, and cell fate. Total Internal Reflection Fluorescence (TIRF) microscopy enables selective visualization of the dynamics of substrate adhesions, vesicle trafficking, and biochemical signaling at the cell-substrate interface. Here we apply high-refractive-index silicone gels to perform TIRF microscopy on substrates with a wide range of physiological elastic moduli, measure traction forces exerted by cells on the substrate, and perform analysis of the cell spreading and the biochemical signaling that drives this process. We successfully implemented TIRF on mouse endothelial cells plated on ∼30 micron thick layers of silicone gels with a refractive index of 1.49 and obtained high quality images. We also functionalized gel surfaces and covalently bound to them 40nm far-red fluorescent beads that were distributed nearly evenly with a high surface density. Measurements of displacements of the beads under cell traction forces made it possible to obtain high-resolution substrate deformation maps that were converted to traction force maps. We show mouse embryonic fibroblasts (MEFs) spreading over a significantly larger area on silicone gels of moderate physiological stiffness, 30 kPa, versus those grown on softer substrates of 0.5 and 3.5 kPa, in agreement with cells grown on polyacrylamide substrates of similar stiffness. We developed a novel microfluidic technique to measure the elastic moduli of thin gel layers and applied it to characterizing gels made using Sylgard 184 silicone with elastic moduli from 0.4 to 300 kPa. We prepared gel substrates with elastic moduli covering nearly the entire physiological range in different wells of a 6-well plate. Western-blot analysis of harvested cells revealed varying levels of phosphorylated Focal Adhesion Kinase (FAK) in MEFs grown on silicone gels with different elastic moduli.