Simultaneous Force Measurements Research Articles

Adhesion of multilayered coatings by low load scratch test

A scratch test in the intermediate load range between the nanoscratch test and the microscratch test is used to determine the failure properties of thin coatings and their interface with the substrate on which the coating was deposited. The technique consists in drawing a stylus with a rounded conical tip along a coated material, while the stylus is simultaneously lowered into the material. A new piece of equipment is introduced for these experiments, that allows simultaneous measurement of forces and displacements in three orthogonal directions, with respectively micro-Newton and nanometre scale resolutions. It is shown that this equipment restrains the degrees of freedom of the moving system and the indenter, to suppress all moments in the system, thereby minimising the uncertainty of the measurement. A full description of the measurement system is given, together with its control electronics and calibration details. Among the many materials systems tested, three systems showed several interfacial failures in the load range considered, and are examined in detail. A simple model of the scratch test is used to derive the work of adhesion of these coatings, and it is further shown that: the first failure event is a combination of the coating and the interface failures, where the interface certainly fails in mixed-mode; and all subsequent failure events being characterised by similar values of the work of adhesion, they are attributed to a mode I failure of the interface. Works of adhesion of 3·06±0·41 J m−2 for the ZnO–Ag/glass system, and 2·36±0·12 J m−2 for the TiB2–Hf/steel system are determined. These values are well within the range of possible adhesion values for these systems, while the dispersion of the results is exceptionally low for this type of experiment, and found comparable to the experimental uncertainty.

Simultaneous measurement of normal force and electrical resistance during isothermal crystallization for carbon black filled high-density polyethylene

The kinetics of isothermal crystallization for high-density polyethylene (HDPE) containing different volume fraction (Φ) of carbon black (CB) have been evaluated by using differential scanning calorimetry (DSC) at 123, 124, and 125 °C where the rate of crystallization is moderate. Simultaneous measurement of normal force (FN) and electrical resistance (R) has been performed to probe the process of isothermal crystallization at strain zero. Results reveal that, at the early stage of crystallization, FN is almost independent of time (t) while relative resistance (R/R0) changes slightly with increasing time t. However, a significant increment in FN and a remarkable change in R/R0 can be observed at the same critical time (tc), and the value of tc is dependent on the crystallization temperature and CB content, which is available for describing the isothermal crystallization as a characteristic parameter. It is found that tc is greater than induction time of crystallization (t0) due to the less sensitivity of mechanical and electrical responses than enthalpy to the structural changes in the composites. It is suggested that mechanical and electrical simultaneous measurement endows us a novel approach to probing the formation of percolation network involving in crystallization of polymer matrix.

Functional Consequences of the Human Cardiac Troponin I Hypertrophic Cardiomyopathy Mutation R145G in Transgenic Mice

In this study, we addressed the functional consequences of the human cardiac troponin I (hcTnI) hypertrophic cardiomyopathy R145G mutation in transgenic mice. Simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145G transgenic mice (Tg-R145G) versus hcTnI wild type transgenic mice (Tg-WT) showed a significant decrease in the maximal Ca(2+)-activated force without changes in the maximal ATPase activity and an increase in the Ca(2+) sensitivity of both ATPase and force development. No difference in the cross-bridge turnover rate was observed at the same level of cross-bridge attachment (activation state), showing that changes in Ca(2+) sensitivity were not due to changes in cross-bridge kinetics. Energy cost calculations demonstrated higher energy consumption in Tg-R145G fibers compared with Tg-WT fibers. The addition of 3 mm 2,3-butanedione monoxime at pCa 9.0 showed that there was approximately 2-4% of force generating cross-bridges attached in Tg-R145G fibers compared with less than 1.0% in Tg-WT fibers, suggesting that the mutation impairs the ability of the cardiac troponin complex to fully inhibit cross-bridge attachment under relaxing conditions. Prolonged force and intracellular [Ca(2+)] transients in electrically stimulated intact papillary muscles were observed in Tg-R145G compared with Tg-WT. These results suggest that the phenotype of hypertrophic cardiomyopathy is most likely caused by the compensatory mechanisms in the cardiovascular system that are activated by 1) higher energy cost in the heart resulting from a significant decrease in average force per cross-bridge, 2) slowed relaxation (diastolic dysfunction) caused by prolonged [Ca(2+)] and force transients, and 3) an inability of the cardiac TnI to completely inhibit activation in the absence of Ca(2+) in Tg-R145G mice.

Interpreting muscle function from EMG: lessons learned from direct measurements of muscle force

Electromyography is often used to infer the pattern of production of force by skeletal muscles. The interpretation of muscle function from the electromyogram (EMG) is challenged by the fact that factors such as type of muscle fiber, muscle length, and muscle velocity can all influence the relationship between electrical and mechanical activity of a muscle. Simultaneous measurements of EMG, muscle force, and fascicle length in hindlimb muscles of wild turkeys allow us to probe the quantitative link between force and EMG. We examined two features of the force-EMG relationship. First, we measured the relaxation electromechanical delay (r-EMD) as the time from the end of the EMG signal to time of the end of force. This delay varied with locomotor speed in the lateral gastrocnemius (LG); it was longer at slow walking speeds than for running. This variation in r-EMD was not explained by differences in muscle length trajectory, as the magnitude of r-EMD was not correlated with the velocity of shortening of the muscle during relaxation. We speculate that the longer relaxation times at slow walking speeds compared with running may reflect the longer time course of relaxation in slower muscles fibers. We also examined the relationship between magnitude of force and EMG across a range of walking and running speeds. We analyzed the force-EMG relationship during the swing phase separately from the force-EMG relationship during stance phase. During stance, force amplitude (average force) was linearly related to mean EMG amplitude (average EMG). Forces during swing phase were lower than predicted from the stance phase force-EMG relationship. The different force-EMG relationships during the stance and swing phases may reflect the contribution of passive structures to the development of force, or a nonlinear force-EMG relationship at low levels of muscle activity. Together the results suggest that any inference of force from EMG must be done cautiously when a broad range of activities is considered.

Simultaneous measurement of temperature and force based on a special-strain-function-chirped FBG

A novel scheme for simultaneous measurement of temperature and force based on a special-strain-function-chirped fiber Bragg grating (FBG) is presented. A specifically designed cylinder tapered cantilever beam (CTCB) can provide special strain distribution function to modulated the FBG's reflection spectrum. The feasibility of the special-strain-function-chirped FBG as sensor for simultaneous measurement of temperature and force was validated. Experimental results match the theoretical results well. The force sensitivities to the bandwidth and central wavelength of the FBG are 0.344 nm/N and 0.408 nm/N, respectively, and the temperature sensitivity is 0.078 nm/°C.

Morphology, Calcium Signaling and Mechanical Activity in Human Ureter

We determined the mechanisms of calcium signaling in the human ureter, and the relationship to peristaltic contractions and bundular structure in living tissue, thereby advancing the understanding of ureteral function in health and obstruction and reflux. Confocal imaging of 31 ureters was performed and simultaneous force and calcium measurements were made. Immunohistochemistry and Western blotting were also performed. Confocal imaging showed a 3-dimensional network of smooth muscle bundles with no defined longitudinal or circular layers. Fast propagating Ca waves spread throughout the bundles, were closely associated with contraction and depended on L-type Ca channel entry. Immunohistochemistry and Western blotting demonstrated L-type Ca channels, Ca dependent K channels, sarcoplasmic reticulum Ca-adenosine triphosphatase isoforms 2 and 3, inositol triphosphate, and ryanodine receptors. Modulation of Ca and K channel activity was a potent mechanism for affecting Ca and force, whereas manipulation of the sarcoplasmic reticulum had little effect. To our knowledge this study represents the first measurements of Ca signals in the human ureter obtained during phasic contractions and in response to agonists. Results show that it is controlled by fast propagating Ca waves, which spread rapidly between the muscle bundles, producing regular contractions, and drugs that interfere with excitability or Ca entry through L-type Ca channels have profound effects on Ca signaling and contractility. These data are discussed in relation to the treatment of patients with suspected ureteral dysfunction using Ca entry blockers.

A two-dimensional force sensor in the millinewton range for measuring vibrissal contacts

The rat vibrissal (whisker) array is a common model system in neuroscience used to study sensorimotor integration. Recent work has suggested that during object contact, the forces and moments at the whisker base may serve as important perceptual cues to the rat. To date, however, the force/moment profile that results from a whisker sweeping against an object has yet to be characterized, because it requires the simultaneous measurement of two-dimensional forces on the order of millinewtons. Current technology for these measurements typically involves prohibitively bulky, expensive equipment with complicated fabrication techniques. We have developed a simple, yet effective two-dimensional force sensor with ±0.02mN resolution; it is extremely compact, has a highly linear static response with low-noise output, and is inexpensive to build. We demonstrate the advantages and limitations of the sensor in three different experimental protocols, ranging from the precise quantification of forces on isolated (plucked) whiskers, to the detection of whisker-contact times in the awake behaving animal. Given the high fidelity of the sensor, it could have utility in a broad range of applications in which measuring contact/detach occurrence and/or small magnitude forces are important.

TGF β‐1 mediated increase in Nox‐4 expression enhances hypoxic pulmonary vasoconstriction in bovine pulmonary arteries

Hypoxic pulmonary vasoconstriction (HPV) in de‐endothelialized bovine pulmonary arteries (BPA) is potentially mediated through lowering of superoxide derived peroxide and removal of its basal relaxing effect. Simultaneous force and peroxide measurements showed decreased peroxide levels preceding HPV. Peroxide scavenging with 0.1mM ebselen increased 25mM KCl force and attenuated HPV. BPA pretreated with copper chelator 10mM diethyldithiocarbamate (DETCA), for inactivating Cu Zn SOD, increased 5μM lucigenin‐detectable superoxide and decreased horseradish peroxidase‐luminol detectable peroxide. DETCA also increased 20mM KCl force and attenuated HPV. 48 hr culture of BPA with 10nM Transforming growth factor β‐1 (TGF β‐1) increased NAD(P)H oxidase‐4 (Nox‐4) expression along with superoxide and peroxide levels. 10μM plumbagin (Nox‐4 inhibitor) reversed the increase in superoxide and peroxide with TGF β‐1, however 100μM apocynin (Nox‐2 inhibitor) did not reverse the increased superoxide level. Also TGF β‐1 decreased 20mM KCl force and increased HPV in BPA. Thus, TGF β‐1 mediated increase in Nox‐4 resulted in higher levels of superoxide derived peroxide in BPA which increased HPV.NIH grants (HL31069/HL66331).

Integrated IPMC/PVDF sensory actuator and its validation in feedback control

Position and/or force feedback is critical in ensuring precise and safe operation of ionic polymer–metal composite (IPMC) actuators in bio/micromanipulation. In this paper the design of an integrated sensory actuator is presented, where polyvinylidene fluoride (PVDF) films are used to provide simultaneous feedback of bending and force outputs of the IPMC actuator. The design adopts differential configurations for sensing, which eliminates corruption of sensing signals by feedthrough of actuation signal or by thermal drift. Experimental results are presented to demonstrate closed-loop control of IPMC bending output based upon the integrated PVDF sensor, together with simultaneous tip force measurement with μ N resolution.

Friction of elastomer-on-glass system and direct observation of its frictional interface

We performed a study on the static friction of PDMS elastomers with well-defined surface topography sliding over glass. An experimental setup for simultaneous measurements of friction force and direct observations of frictional interface has been developed. The static friction force was nearly proportional to normal load. The static friction force was independent of stick time. The simultaneous measurements revealed that the static friction force was proportional to the total area of contact. The coefficient was nearly independent of the surface topography of PDMS elastomers.

Integrin-linked Kinase Regulates N-WASp-mediated Actin Polymerization and Tension Development in Tracheal Smooth Muscle

The contractile stimulation of smooth muscle tissues stimulates the recruitment of proteins to membrane adhesion complexes and the initiation of actin polymerization. We hypothesized that integrin-linked kinase (ILK), a beta-integrin-binding scaffolding protein and serine/threonine kinase, and its binding proteins, PINCH, and alpha-parvin may be recruited to membrane adhesion sites during contractile stimulation of tracheal smooth muscle to mediate cytoskeletal processes required for tension development. Immunoprecipitation analysis indicted that ILK, PINCH, and alpha-parvin form a stable cytosolic complex and that the ILK.PINCH.alpha-parvin complex is recruited to integrin adhesion complexes in response to acetylcholine (ACh) stimulation where it associates with paxillin and vinculin. Green fluorescent protein (GFP)-ILK and GFP-PINCH were expressed in tracheal muscle tissues and both endogenous and recombinant ILK and PINCH were recruited to the membrane in response to ACh stimulation. The N-terminal LIM1 domain of PINCH binds to ILK and is required for the targeting of the ILK-PINCH complex to focal adhesion sites in fibroblasts during cell adhesion. We expressed the GFP-PINCH LIM1-2 fragment, consisting only of LIM1-2 domains, in tracheal smooth muscle tissues to competitively inhibit the interaction of ILK with PINCH. The PINCH LIM1-2 fragment inhibited the recruitment of endogenous ILK and PINCH to integrin adhesion sites and prevented their association of ILK with beta-integrins, paxillin, and vinculin. The PINCH LIM1-2 fragment also inhibited tension development, actin polymerization, and activation of the actin nucleation initiator, N-WASp. We conclude that the recruitment of the ILK.PINCH.alpha-parvin complex to membrane adhesion complexes is required to initiate cytoskeletal processes required for tension development in smooth muscle.

Influence of cadence, power output and hypoxia on the joint moment distribution during cycling

The purpose of this study was to use a hypoxic stress as a mean to disrupt the normal coordinative pattern during cycling. Seven male cyclists pedalled at three cadence (60, 80, 100 rpm) and three power output (150, 250, 350 W) conditions in normoxia and hypoxia (15% O2). Simultaneous measurements of pedal force, joint kinematics, % oxyhaemoglobin saturation, and minute ventilation were made for each riding condition. A conventional inverse dynamics approach was used to compute the joint moments of force at the hip, knee, and ankle. The relative contribution of the joint moments of force with respect to the total moment was computed for each subject and trial condition. Overall, the ankle contributed on average 21%, the knee 29% and the hip 50% of the total moment. This was not affected by the relative inspired oxygen concentration. Results showed that the relative ankle moment of force remained at 21% regardless of manipulation. The relative hip moment was reduced on average by 4% with increased cadence and increased on average by 4% with increased power output whereas the knee moment responded in the opposite direction. These results suggest that the coordinative pattern in cycling is a dominant characteristic of cycling biomechanics and remains robust even in the face of arterial hypoxemia.

Simultaneous measurement of force and respiratory profiles during chest physiotherapy in ventilated children

There are currently no objective means of quantifying chest wall vibrations during manual physiotherapy. The aims of the study were to (i) develop a method to quantify physiotherapy-applied forces and simultaneous changes in respiratory flow and pressure, (ii) assess the feasibility of using this method in ventilated children and (iii) characterize treatment profiles delivered by physiotherapists in the paediatric intensive care unit. Customized sensing mats were designed and used in combination with a respiratory profile monitor. Software was developed to align force and flow data streams. Force and respiratory data were successfully collected in 55 children (median age 1.6 years (range 0.02–13.7 years)). Physiotherapists demonstrated distinctive variations in the pattern of force applied and manual lung inflations. The maximum applied force ranged from 15 to 172 N, and was correlated with the child's age (r = 0.76). Peak expiratory flow increased significantly during manual inflations both with and without chest wall vibrations (p < 0.05). This method provides the basis for objective assessments of the direct and independent effects of vibration forces and manual lung inflations as an essential precursor to developing evidence-based practice.

Structure of Nanometer-Sized Palladium Contacts and Their Mechanical and Electrical Properties

Structural evolution in the nanometer-sized contacts (NCs) of two palladium (Pd) tips during tensile deformation was observed in situ at room temperature by transmission electron microscopy with the simultaneous measurements of force and conductance. The constants concerning the mechanical properties of individual Pd NCs, i.e., elastic limit, Young's modulus, and strength, were analyzed on the basis of stress–strain curves on an atomic scale. It was found that, in contrast to those of coarse-grained Pd crystals, the strength and elastic limit of Pd NCs with a cross-sectional area of approximately 1 nm2 increase to 1.0±0.2 GPa and 0.04–0.16, respectively, whereas Young's modulus decreases to 3.4±0.9 GPa. The histogram of conductances showed a maximum peak at 1.6G0 (where G0=2e2/h, with e being the charge of an electron and h Planck's constant) and on almost constant distribution at other conductance levels.

A Biaxial Load Cell Design for Simultaneous Measurement of Horizontal and Vertical Spring Forces in Sinuous Spring-Supported Seating

Abstract Sinuous springs are the most commonly used method of seat support in upholstered furniture. The dynamics of load transference by these springs to the furniture frame members has not been thoroughly studied. Rational strength design of sinuous-type upholstered furniture frames, especially their seating support systems, requires information concerning the magnitudes and directions of spring loads on spring supporting rails. These values are important for frame designers to be able to adjust member sizes and materials and select appropriate fasteners. Presently, furniture design largely depends on trial and error. A load cell was conceived, designed, and verified which can determine horizontal and vertical components of a spring load. Preliminary results showed that the average initial spring tension on each load cell, with no external loading applied to the springs, was 46 lb. (205 N) horizontal. For some situations, the horizontal load components actually decrease when a person comes to rest on the seat. Vertical and horizontal loading is greatest on the center three springs of the seat which used five, equally spaced springs in this paper.

Solvation and squeeze out of hexadecane on graphite

We have performed simultaneous force and conductivity measurement of hexadecane liquid confined between a conducting atomic force microscope tip and a graphite surface. Both the current and the force data reveal discrete solvation layering of the hexadecane near the surface. We typically observe that the current does not vary with load in a simple way as the layer closest to the surface is compressed, but increases markedly prior to the expulsion of material from the tip-sample gap. We infer that even for a nanoscale asperity there is conformation change of the confined hexadecane under the tip apex prior to squeeze out of the molecules.

Direct Detection of the Solvent Molecules between Solid Surfaces with Simultaneous Adhesion Force Measurement

In this study, we applied the force curve mode confocal laser scanning/atomic force microscope (CLSM/AFM) to detect solvent properties in the contact area with the simultaneous force measurement. Two experimental approaches were carried out. First, we performed an adhesion force measurement between a carboxylated polystyrene microbead and the substrate surface that has the terminus group of −NH2 or −CF3 at various pH by the traditional AFM measurement. The results revealed that the hydrophobic interaction and hydrogen bonding force operates when the microbead is brought into contact with the −CF3 and −NH2 surface, respectively. Next, the solvent molecules between solid surfaces were detected with the simultaneous adhesion force measurement by the CLSM/AFM system. The results revealed that the fluorescence intensity of fluorescein was decreased only when the hydrophobic interaction worked. It was due to the removal of solvent molecules in the contact area, and the hydrophobic surfaces stabilize each other by making the contact area hydrophobic. On the other hand, when the hydrophilic interaction, such as hydrogen bonding, operates, the solvent molecules exist in the contact area.

Simultaneous measurement of structural and hydrodynamic forces between colloidal surfaces in complex fluids

An AFM study was performed to measure the effect of approach/retraction speed on the interaction force between a colloidal particle and a flat substrate in aqueous solutions containing silica nanospheres at concentrations of 4.5 and 6.5 vol.%. The total force consisted of contributions of electrostatic, depletion, structural and hydrodynamic forces. The hydrodynamic component of the force could be isolated by comparing the force profiles measured upon approach and retraction. It was found that when the hydrodynamic component was subtracted from the total force, the resulting force profiles measured at scan speeds of 80, 800, 2400, 4800 and 11,200 nm/s all overlaid, indicating that the surface forces (electrostatic, depletion and structural) were not affected by the scan speed. This result was further supported by an approximation of the rates of viscous and diffusive motion in the gap region. In addition, the variation of the hydrodynamic force with particle/plate separation distance agreed relatively well with a prediction made using the mobility correction factor developed for simple fluids, suggesting that the nanoparaticles do not alter the flow in the lubrication layer at these concentrations.

A study on the reduction of uncertainty in the measurement of power tool vibration

To increase accurateness and reliability of the evaluation of power tool vibration transmitted to an operator, it is necessary to measure the grip and feed forces during the measurement of hand-transmitted vibration. In the study a system was invented to measure the vibration and the grip and/or feed force, which consists of a measurement handle and a PC with a data acquisition system and the corresponding software. Strain gages and an accelerometer were mounted on the handle surface for the simultaneous measurement of the forces and the vibration. The program in the system makes it possible to monitor the grip and feed force during the tool operation so that the operator keeps the applying forces within the pre-determined range. Investigating the vibration total values, frequency-weighted root-mean-square accelerations at the handle, obtained in repetition for each power tool with control of the grip and feed force showed more consistency than those measured without force control. By using the system the experimenter can reduce uncertainty in measurement of hand-held power tool vibration.

Effects of knee injection on skeletal muscle metabolism and contractile force in rats

We tested the hypothesis that intrusion of the knee joint capsule alters quadriceps muscle metabolism and function independently from the damage induced to knee cartilage. Adult rats were separated into four groups: intraarticular injections of saline (SAL; n=9); intraarticular injections of papain, a model for osteoarthritis (PIA; n=7); sham injections (SHAM; n=8); and controls (CTL; n=5). 31P magnetic resonance spectroscopy (31P-MRS) was performed after 2 weeks. Spectra were obtained from the left quadriceps: two at baseline, eight during electrical stimulation with simultaneous measurement of contractile force, and 15 during recovery. 31P-MRS data were presented as the ratio of inorganic phosphate (Pi) to phosphocreatine (PCr), concentrations of PCr [PCr], intramuscular pH, and the rates and time constants of PCr breakdown during stimulation and PCr recovery. Intramuscular cytokine concentrations were measured within the quadriceps. Histologic slides of the knees were scored for severity of cartilage damage. The interventional groups produced values of Pi/PCr ratio, [PCr], contractile force and pH that were significantly different from CTL. These changes in muscle function were accompanied by higher concentrations of interleukin-1 observed with PIA and SAL. We did not observe any effect of cartilage damage on muscle function or metabolism. Knee joint intrusion alters quadriceps muscle metabolism with accelerated depletion of energy stores and fatigue during stimulation. This study demonstrates that needle intrusion into the knee joint results in muscle dysfunction, independently from the extent of cartilage damage.