Pressure-sensitive Film Research Articles

BIOMECHANICAL STUDY ON UPPER THORACIC SPINE BASED ON PRESSURE SENSITIVE FILM MATERIALS IN CHINESE MINI PIGS

To analyze the pressure change and distribution of the intervertebral disc of upper thoracic spine in vertical pressure and 5° flexion, extension, or lateral bending. Twelve thoracolumbar spinal specimens were harvested from mini pigs and were divided into 2 groups (n=6). T1, 2, T3, 4, T5, 6, and T7, 8 segments were included in one group, and T2, 3, T4, 5, T6, 7, and T8, 9 segments were included in the other group. The data from both groups represented the complete upper thoracic vertebra data. Biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns under loadings of 100, 150, and 200 N in vertical pressures and 5° flexion, extension, or lateral bending. The pressure change of each intervertebral disc under different loads and in different movement conditions was analyzed. In flexion, the anterior annulus pressure of the upper thoracic vertebra increased (P<0.05), whereas the posterior annulus pressure showed no significant change (P>0.05) or an increasing trend (P<0.05). In extension, the anterior annulus pressure of the upper thoracic vertebra decreased (P<0.05), whereas the posterior annulus pressure decreased (P<0.05) or had no obvious change (P>0.05). In lateral bending, the pressure on the concave side of the annulus increased significantly (P<0.05). The upper thoracic vertebra has unique biomechanical characteristics under different loadings; moreover, the posterior vertebral structure plays an important role in the movement of the upper thoracic vertebral segment and pressure distribution. In lateral bending of the upper thoracic vertebra, the concave side pressure will increase significantly, which suggests that asymmetrical force is an important cause of scoliosis progression. Gravity plays an important role in the progression of scoliosis.

Biomechanical Consequences of Excessive Patellar Distalization

Iatrogenic patellar baja can be a result of excessive tibial tubercle distalization or overtightented patellar tendon repair. Tubercle distalization is increasing in popularity for the treatment of recurrent patella instability. Clinically, patellar baja can present as a debilitating problem with motion loss, increased pain, and arthrosis progression. However, previous biomechanical studies have not shown an increase in patellofemoral joint contact pressures. The purpose of this study is to examine the patellofemoral contact pressure after a tibial tubercle distalization osteotomy. Ten matched pair fresh-frozen cadaveric knees were studied. Average Blackburne-Peel ratio of the native knees was 0.91. The knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. A straight tubercle distalization osteotomy of 1 cm was performed and fixed with screws, with and without a lateral release. Patellofemoral contact pressures were measured at 0°, 10°, 20°, 30°, 45°, 60°, and 90° of flexion using pressure-sensitive films on the medial and lateral trochlea. The contact force, area and pressure were measured at the following states: (1) native knee, (2) with distalization and (3) distalization with lateral release. Average Blackburne-Peel ratio after distalization was 0.64. Tibial tubercle distalization resulted in a six fold increase in mean contact pressures at 0° (0.15 versus 0.90 MPa, p<0.001), and a 55% increase at 10° of flexion (0.70 versus 1.09 MPa, p=0.02). After distalization, total contact area was significantly higher at 0° of flexion (17.7 mm2 versus 58.4 mm2, p=0.02). Lateral release after distalization did not significantly change contact pressure (p>0.21). Our results suggest that patellar baja, as a result of excessive patellar distalization, can cause increased patellofemoral contact pressures during early flexion.

Factors Affecting Gloss and Color of Decorative Pressure Sensitive Adhesive Films During Thermomechanical Deformation

Decorative polymer films are finding applications in processes that require forming at elevated temperatures and significant strain. In order to satisfy their function in these applications, the appearance of these films must remain unaltered or at least any changes must be predictable. This paper examines four different high gloss decorative films comprised of different materials in the layers of their construction. The films were uniaxially stretched up to failure (which was up to 75% strain) at isothermal conditions of 25, 40, or 75°C and then examined. Gloss (at 20°) was the most strongly altered parameter concerning the appearance of the films after thermomechanical deformation while color intensity was relatively unaffected. The change in gloss was higher for the two amorphous films compared to the two that exhibited crystallinity. The films were analyzed for their surface roughness using a white light interferometer, for their crystallinity by X‐ray diffraction and for their morphology by atomic force microscopy (AFM). Surface roughness increased with crystallinity for the two films that exhibited crystals but overall showed no correlation to the gloss measurements. Only evidence of altered domain morphology in the films as determined by AFM appeared to correlate with the changes in gloss reported. POLYM. ENG. SCI., 56:1357–1365, 2016. © 2016 Society of Plastics Engineers

Micro-pillars enhanced all vanadium redox flow batteries and the effect of assembly torque on the electrochemical performance

A uniformly distributed electrolyte system based on enhanced micro-pillars flow field design is proposed for a vanadium redox flow battery (VRFB). The uniformity experiments show that the flow uniformity can be effectively increased and normalized velocity variation for any channel is measured to be less than 18 %, demonstrating the effectiveness of micro-pillars for enhanced flow field. Experimental validation is carried out experimentally and the effect of different assembly torque is also investigated for VRB cell electrochemical performance via polarization and cyclic voltammograms (CV) test. The results show that an optimal assembly torque (11 N-m) can yield a significant improvement of 68.5 % current density when compared with the case of 10 N-m. Furthermore, the CV results clearly indicate that the optimal assembly torque with enhanced micro-pillars design can result in the 37.3 % improvement of electrochemical surface area. Moreover, the contact pressure contours from the pressure-sensitive films are measured to check the influence on the configuration of VRFB unit cell.

A Subscale Experimental Test Method to Characterize Extrusion-Based Elastomer Seals

Extrusion-based elastomer seals are used in many applications, such as the seal in a variable bore ram valve used in offshore oil and gas drilling. Performing full-scale closing pressure experiments of such valves to characterize the seal performance and material failure of elastomer, especially under various temperature conditions, are quite expensive and time consuming. Conversely, simple coupon tests to characterize the elastomer mechanical properties and failure do not capture the complex deformation associated with the extrusion and subsequent sealing type that these materials undergo in the valves. In view of this, a simple subscale experimental test method capable of simulating the extrusion and sealing type deformation is developed. The extrusion and sealing deformation are realized by bonding the rectangular elastomer sample to metal pieces on top and bottom surfaces, and then compressing the sample in the vertical direction, while the deformation of the three lateral surfaces is kept constrained. As a result, sample deforms and extrudes out of the front surface, eventually forming the seal against a flat rigid metal plate placed at an appropriate distance. Simple scaling rules to determine the appropriate sample size and initial sealing gap, equivalent to the full-scale valve in terms of similar strain conditions, are derived and then verified using finite element analysis (FEA). Finally, the experimental test method is demonstrated by characterizing the contact pressure of nitrile (NBR) samples under different operating temperatures, ranging from 21 °C to 160 °C using pressure-sensitive film sensor.

Patella tracking and patella contact pressure in modular patellofemoral arthroplasty: a biomechanical in vitro analysis.

In the recent years modular partial knee prosthesis with the opportunity to combine unicompartmental tibiofemoral (UKA) and patellofemoral prosthesis (PFJ) were introduced to the clinics. To date, little is known about the biomechanics of these bi-cruciate retaining prosthetic designs. Aim of this study was to evaluate the influence of a PFJ in bicompartmental arthroplasty (UKA+PFJ) on patella tracking and retropatella pressure distribution. A dynamic in vitro knee kinemator simulating an isokinetic extension cycle of the knee was used on eight knee specimen. Patella tracking and patellofemoral contact pressure were evaluated using pressure sensitive films after implantation of a medial UNI and after subsequent implantation of a PFJ. Whereas the area contact pressure remained the same after PFJ implantation, the contact area was reduced significantly and significantly elevated peak pressures were determined in deep flexion and close to extension. The patella tracking was not significantly altered, however, effects of edge loading could be shown. When using PFJ prosthesis, one must be aware of altered pressure introduction on the retropatella surface compared to the physiological situation. The elevated peak pressures and reduced contact area may be an argument for patella resurfacing and the problems of edge loading indicate that care must be taken on the correct implantation of the device with no implant overhang.

Comparison of Surfactant Distributions in Pressure-Sensitive Adhesive Films Dried from Dispersion under Lab-Scale and Industrial Drying Conditions.

Film-forming latex dispersions are an important class of material systems for a variety of applications, for example, pressure-sensitive adhesives, which are used for the manufacturing of adhesive tapes and labels. The mechanisms occurring during drying have been under intense investigations in a number of literature works. Of special interest is the distribution of surfactants during the film formation. However, most of the studies are performed at experimental conditions very different from those usually encountered in industrial processes. This leaves the impact of the drying conditions and the resulting influence on the film properties unclear. In this work, two different 2-ethylhexyl-acrylate (EHA)-based adhesives with varying characteristics regarding glass transition temperature, surfactants, and particle size distribution were investigated on two different substrates. The drying conditions, defined by film temperature and mass transfer in the gas phase, were varied to emulate typical conditions encountered in the laboratory and industrial processes. Extreme conditions equivalent to air temperatures up to 250 °C in a belt dryer and drying rates of 12 g/(m(2)·s) were realized. The surfactant distributions were measured by means of 3D confocal Raman spectroscopy in the dry film. The surfactant distributions were found to differ significantly with drying conditions at moderate film temperatures. At elevated film temperatures the surfactant distributions are independent of the investigated gas side transport coefficients: the heat and mass transfer coefficient. Coating on substrates with significantly different surface energies has a large impact on surfactant concentration gradients, as the equilibrium between surface and bulk concentration changes. Dispersions with higher colloidal stability showed more homogeneous lateral surfactant distributions. These results indicate that the choice of the drying conditions, colloidal stability, and substrates is crucial to control the surfactant distribution. Results obtained under lab-scale drying conditions cannot be transferred directly to the industrial application. The results were similar for both tested adhesive material systems, despite their different properties. This indicates that other properties, such as the particle size distribution and glass transition temperature, have surprisingly little effect on the development of the surfactant distribution.

Effect of Medial Patellofemoral Ligament Reconstruction Method on Patellofemoral Contact Pressures and Kinematics

Background: There remains a lack of evidence regarding the optimal method when reconstructing the medial patellofemoral ligament (MPFL) and whether some graft constructs can be more forgiving to surgical errors, such as overtensioning or tunnel malpositioning, than others. Hypothesis: The null hypothesis was that there would not be a significant difference between reconstruction methods (eg, graft type and fixation) in the adverse biomechanical effects (eg, patellar maltracking or elevated articular contact pressure) resulting from surgical errors such as tunnel malpositioning or graft overtensioning. Study Design: Controlled laboratory study. Methods: Nine fresh-frozen cadaveric knees were placed on a customized testing rig, where the femur was fixed but the tibia could be moved freely from 0° to 90° of flexion. Individual quadriceps heads and the iliotibial tract were separated and loaded to 205 N of tension using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film inserted between the patella and trochlea, in conjunction with an optical tracking system. The MPFL was transected and then reconstructed in a randomized order using a (1) double-strand gracilis tendon, (2) quadriceps tendon, and (3) tensor fasciae latae allograft. Pressure maps and tracking measurements were recorded for each reconstruction method in 2 N and 10 N of tension and with the graft positioned in the anatomic, proximal, and distal femoral tunnel positions. Statistical analysis was undertaken using repeated-measures analyses of variance, Bonferroni post hoc analyses, and paired t tests. Results: Anatomically placed grafts during MPFL reconstruction tensioned to 2 N resulted in the restoration of intact medial joint contact pressures and patellar tracking for all 3 graft types investigated (P > .050). However, femoral tunnels positioned proximal or distal to the anatomic origin resulted in significant increases in the mean medial joint contact pressure, medial patellar tilt, and medial patellar translation during knee flexion or extension, respectively (P < .050), regardless of graft type, as did tensioning to 10 N. Conclusion: The importance of the surgical technique, specifically correct femoral tunnel positioning and graft tensioning, in restoring normal patellofemoral joint (PFJ) kinematics and articular cartilage contact stresses is evident, and the type of MPFL graft appeared less important. Clinical Relevance: The correct femoral tunnel position and graft tension for restoring normal PFJ kinematics and articular cartilage contact stresses appear to be more important than graft selection during MPFL reconstruction. These findings emphasize the importance of the surgical technique when undertaking this procedure.

Femorotibial kinematics and load patterns after total knee arthroplasty: An in vitro comparison of posterior-stabilized versus medial-stabilized design

BackgroundFemorotibial kinematics and contact patterns vary greatly with different total knee arthroplasty (TKA) designs. Therefore, guided motion knee systems were developed to restore natural knee kinematics and make them more predictable. The medial stabilized TKA design is supposed to replicate physiological kinematics more than the posterior-stabilized TKA system. We conducted this study to compare a newly developed medial stabilized design with a conventional posterior-stabilized design in terms of femorotibial kinematics and contact patterns in vitro. MethodsTwelve fresh-frozen knee specimens were tested in a weight-bearing knee rig after implantation of a posterior stabilized and medial-stabilized total knee arthroplasty under a loaded squat from 20° to 120° of flexion. Femorotibial joint contact pressures in the medial and lateral compartments were measured by pressure sensitive films and knee kinematics were recorded by an ultrasonic 3-dimensional motion analysis system. FindingsThe medial stabilized design showed a reduction of medial femorotibial translation compared to posterior-stabilized design (mean 3.5mm compared to 15.7mm, P<0.01). In the lateral compartment, both designs showed a posterior translation of the femur with flexion, but less in the medial stabilized design (mean 14.7mm compared to 19.0mm, P<0.01). In the medial femorotibial compartment of medial stabilized design, we observed an enlarged contact area and lower peak pressure, in contrast in the lateral compartment there was a reduced contact area and an increased peak pressure. InterpretationWhile posterior-stabilized design enforces a medio-lateral posterior translation, the medial stabilized arthroplasty system enables a combination of a lateral translation with a medial pivot, which restores the physiological knee kinematics better.

Load distribution on abutment tooth, implant and residual ridge with distal-extension implant-supported removable partial denture

PurposeThe aim of this study was to evaluate the effect of implant location on load distribution in the abutment tooth, implant and residual ridge with a distal-extension implant-supported removable partial denture (ISRPD). MethodsA mandibular unilateral distal-extension edentulous simulation model was used. Implants were inserted at the second premolar (mesial implant) and second molar (distal implant) positions in the edentulous area. An experimental ISRPD was fabricated of acrylic resin with a cobalt-chromium alloy framework. Loads on the implants and abutment tooth were measured with piezoelectric force transducers. The load on the residual ridge was measured with pressure-sensitive film. A vertical load of 100N was applied at the first molar region. Measurements were made under the following three conditions: with conventional removable partial denture (CRPD), with mesial-implant-supported removable partial denture (MISRPD), and with distal-implant-supported removable partial denture (DISRPD). In each condition, the unused implants were made inactive by eliminating contact with the inner surface of the denture. ResultsThe load on the abutment tooth was greatest with DISRPD, followed by CRPD and MISRPD (P<0.01). The load on the implant was greater with DISRPD than with MISRPD (P<0.01). The load on the residual ridge was lowest with DISRPD, followed by MISRPD and CRPD (P<0.01). ConclusionsThis experimental study provided quantitative data regarding the effect of implant location on load distribution with ISRPDs. Further investigation regarding the effect of denture design on the load distribution is needed for determining the proper implant location of ISRPD.

Numerical and experimental study of contact for bodies of complex shape

This work delivers results of experimental studies performed in order to justify the validity of the developed version of the boundary element method that accounts for the compliance of the intermediate layer. Experimental investigation of contact interaction of complex shaped bodies in the presence of local compliance of conjugate surfaces has been conducted on a prototype of a hydrovolumetric drive, for which the contact area and the magnitude of the contact pressure were determined by means of pressure sensitive films. In order to capture the entire domain where contact pressure is applied and their maximal values and therefor for the sake of measurement error reduction each test is made using two types of contact films: MS and HS. It was demonstrated that the increased compliance of the intermediate layer results in contact over a larger area and leveling of the maximal contact pressure pike. With the increase of pressing force both the size of the contact zone and the values of contact pressure grow. Comparison of contact pressure distributions obtained experimentally and from numerical boundary element method solution confirmed full qualitative and quantitative correspondence of the experimental and numerical results. The discrepancy in contact area and maximal contact pressure was less then 10%. The results are summarised in a curve chart that contains correlation between the size of the contact area and the value of the maximal contact pressure for different local compliances of the contact layer.

Biomechanical evaluation of MPFL reconstructions: differences in dynamic contact pressure between gracilis and fascia lata graft.

To evaluate the knee kinematics of the intact, MPFL-ruptured and MPFL-reconstructed knee and, moreover, to compare dynamic patellofemoral contact pressure of the gracilis tendon and the fascia lata as an alternative graft option for reconstruction of the MPFL. Eight paired human cadaveric knees were fixed in a custom-made fixation device. Patellofemoral contact pressure was assessed during a dynamic flexion movement at 15°-30°-45°-60°-75° and 90° using a pressure-sensitive film (Tekscan). The medial patellofemoral ligament was cut, and measurements were repeated. Finally, reconstruction of the MPFL was performed using the gracilis tendon (group I) or a fascia lata graft (group II). Tunnel localization was performed under fluoroscopic control. Grafts were fixed at 30° of flexion, and pressure measurements were repeated. Incision of the medial patellofemoral ligament significantly reduced patellofemoral contact pressure at 15°, 30° and 45° of knee flexion compared to the intact knee (p<0.05), whereas reconstruction of the MPFL using either gracilis tendon of the fascia lata was able to restore pressure distributions at 15° and 30° of knee flexion. However, in the hamstring group, reconstruction of the MPFL revealed a significantly reduced contact pressure at 45° of flexion (p=0.038) compared to the intact knee. In the fascia lata group, a significant reduction in patellofemoral contact pressure was observed after MPFL reconstruction at 45°, 60°, 75° and 90° of knee flexion (p<0.05). Anatomic reconstruction of the MPFL with either a gracilis or a fascia lata graft showed comparable patellofemoral pressure distributions which were closely restored compared to the native knee. Therefore, the fascia lata has shown to be a viable alternative to the gracilis tendon for reconstruction of the MPFL. However, anatomic reconstruction of the MPFL may lead to persistently altered patellofemoral contact pressure during knee flexion compared to the native knee independent of the tested graft.

Autologous distal clavicle versus autologous coracoid bone grafts for restoration of anterior-inferior glenoid bone loss: a biomechanical comparison

Treating anterior glenoid bone loss in patients with recurrent shoulder instability is challenging. Coracoid transfer techniques are associated with neurologic complications and neuroanatomic alterations. The purpose of our study was to compare the contact area and pressures of a distal clavicle autograft with a coracoid bone graft for the restoration of anterior glenoid bone loss. We hypothesized that a distal clavicle autograft would be as effective as a coracoid graft. In 13 fresh-frozen cadaveric shoulder specimens, we harvested the distal 1.0 cm of each clavicle and the coracoid bone resection required for a Latarjet procedure. A compressive load of 440 N was applied across the glenohumeral joint at 30° and 60° of abduction, as well as 60° of abduction with 90° of external rotation. Pressure-sensitive film was used to determine normal glenohumeral contact area and pressures. In each specimen, we created a vertical, 25% anterior bone defect, reconstructed with distal clavicle (articular surface and undersurface) and coracoid bone grafts, and determined the glenohumeral contact area and pressures. We used analysis of variance for group comparisons and a Tukey post hoc test for individual comparisons (with P <.05 indicating a significant difference). The articular distal clavicle bone graft provided the lowest mean pressure in all testing positions. The coracoid bone graft provided the greatest contact area in all humeral positions, but the difference was not significant. An articular distal clavicle bone graft is comparable in glenohumeral contact area and pressures to an optimally placed coracoid bone graft for restoring glenoid bone loss. Basic Science Study; Biomechanics.

Effect of three remplissage techniques on tendon coverage and shoulder kinematics: a navigated robotic biomechanical study.

BackgroundIn addition to Bankart repair engaging Hill-Sachs defects in glenohumeral instability have been treated successfully with remplissage procedure. The purpose of this study was to compare three remplissage techniques regarding (I) ability of preventing Hill-Sachs defect from engaging, (II) influence on glenohumeral rotational torque, and (III) resulting tendon coverage over the Hill-Sachs defect.MethodsStandardized engaging Hill-Sachs defects and Bankart lesions were created in n = 7 fresh frozen human shoulder specimens. Besides Bankart repair three remplissage techniques (T) with double anchor position in the valley of the defect zone were studied: T1, knots tied over anchors; T2, knots tied between anchors (double-pulley); T3, knotless anchors with a suture tape.A parallel position-orientation and force-moment controlled navigated roboticsystem was used to compare prevention of Hill-Sachs defect engagement and torque [Nm]. Pressure sensitive film was used to study area of infraspinatus tendon coverage over Hill-Sachs defect [%].ResultsAll remplissage techniques prevented engagement of the Hill-Sachs defect without showing any construct failures. Regarding humeral torque there were significant impairments observed between intact conditions and the three investigated repair techniques in 60° abduction and ≥30° external rotation (p < .04). There was no significant difference in torque between intervention groups (n.s.). With a mean coverage of 26.8 % over the defect zone the knotless suture tape technique (T3) significantly improved area of soft tissue coverage compared to the other techniques (p = .03).ConclusionAll remplissage techniques prevented engagement of the Hill Sachs defect. With high abduction and external rotation ≥30° all techniques showed significant higher humeral torque compared to the intact specimens, while there was not one technique superior over the others. The suture tape technique conferred the largest and most effective area of tendon coverage over the Hill-Sachs defect zone. Long-term success of the remplissage procedure can possibly be enhanced by increasing the interface area of tendon coverage over the Hill-Sachs defect. Clinical studies will be necessary to proof potential benefits for clinical outcome.

Evaluation of Contact Pressure in Bending under Tension Test by a Pressure Sensitive Film

The contact pressure acting on the sheet/tools interface has been studied because of growing the concern about the wear of tools. Recent studies make use of numerical simulation software to evaluate and correlate this pressure with the friction and wear generated. Since there are many studies that determine the coefficient of friction in sheet metal forming by bending under tension (BUT) test, the contact pressure between the pin and the sheet was measured using a film that has the ability to record the applied pressure. The vertical force applied to pin was also measured. The results indicate that the vertical force is more accurate to set the contact pressure that using equations predetermined. It was also observed that the contact area between the sheet and the pin is always smaller than the area calculated geometrically. The friction coefficient was determined for the BUT test through several equations proposed by various authors in order to check if there is much variation between the results. It was observed that the friction coefficient showed little variation for each equation, and each one can be used. The material used was the commercially pure aluminum, alloy Al1100.

Investigation of contact pressure distribution over the active area of PEM fuel cell stack

Contact pressure distribution over the active area of proton exchange membrane fuel cell (PEMFC) has significant effects on the performance of PEMFCs. Even clamping pressure over the membrane electrode assembly (MEA) affects contact resistance, characteristics of porous media and sealing task. This paper develops a PEM fuel cell model to study the contact pressure distribution over the membrane electrode assembly using finite element model. At first, the three-dimensional model of a single cell was reduced to a two-dimensional model to decrease the calculation time. After validation of the obtained results via the pressure sensitive films, the effect of some parameters such as thickness and material of the end plates, sealant hardness, number of the stack's cells and position of the cell on the contact pressure distribution over the MEA were investigated. The results reveal that optimizing mentioned parameters leads to design PEM fuel cells with proper contact pressure distribution over the MEA.

Experimental investigation of oscillation of loads in ice high-pressure zones, part 1: Single indentor system

The paper commences with a review of ice-induced vibrations in full-scale structures in the field, in medium-scale tests, and particularly, in small-scale indentation tests. The mechanics of compressive ice failure is reviewed, with emphasis on the processes leading to the formation of a layer of microstructurally modified material under the indenter, as well as fracture. Previous tests in the present series using small-scale indentors are reviewed, and a recently conducted series of tests is introduced. This series involved confined ice specimens of cylindrical shape 154mm in diameter moving at various constant displacement rates against a 20-mm diameter indentor attached to an elastic-compliant structure. The displacement rates (ice speeds) were chosen so as to induce “sawtooth” vibrations. Two beam structures, one stiff and the other flexible, were used. In general, the desired sawtooth pattern was achieved, particularly with the more flexible system, but also with the stiffer one at higher ice speeds. Some results involving “lock-in” were obtained with the stiffer setup. Measurements were made of the distribution of pressure at the ice–indentor interface using pressure-sensitive film, and thin sections were taken from the indented samples. The thin sections in all cases showed the presence of a microstructurally modified layer of ice adjacent to the indentor. Pressure distributions showed that regular vibrations were associated mainly with activity in the layer, whereas the larger spall fractures generally caused irregular load patterns with significant loss of contact area under the indentor. The regular failure can be analysed as a self-sustained oscillation, which is common among dissipative systems. The system in this case comprises the moving ice field and the compliant structure with which the ice interacts, resulting in autonomous vibrations of the sawtooth variety. Regularity was interrupted by the larger spalling fractures.

Assessment of Competency During Orotracheal Intubation in Medical Simulation

Background Clinicians performing orotracheal intubation need to be competent to perform this technical skill safely. It is recognized that aggressive force applied during direct laryngoscopy may damage the oropharyngeal soft tissue; however, force is seldom considered in assessment of competency. The objective of this study was to explore the force applied during orotracheal intubation as a method of further discriminating between levels of competence. We sought evidence of construct validity in the form of discriminant, criterion, and concurrent validity. We hypothesized that the force generated during simulated intubation could serve to discriminate skill level among clinicians. Methods A convenience sample of 35 health-care professionals filled a self-reported questionnaire and were then divided into the following three groups: Group 1, experts (n=16); Group 2, intermediates (n=7); and Group 3, novices (n=12). They then intubated a part-task trainer (Laerdal Airway Management Trainer) after reviewing a procedural video and engaging in one practice session. Intubations were recorded. Outcome measures were as follows: (i) force applied to the epiglottis, calculated (in newtons) using two superimposed pressure-sensitive films (Prescale; Fujifilm, Madison, WI, USA) on the laryngoscope blade; (ii) number of attempts required to achieve successful intubation; (iii) time to intubation; and (iv) hand position. Results Of the four outcome measures, only force applied during orotracheal intubation was able to discriminate between groups. All data are reported as the mean (sd). There was a significant difference in force between groups during orotracheal intubation [one-way anova; experts, 102 (25) N; intermediates, 134 (28) N; and novices, 153 (43) N], with a significant difference (P Conclusions Force exerted during intubation provides meaningful information when attempting to discriminate intubation skill level. Force demonstrated criterion validity and could be used as a measure of competency during training.

Validation of a Finite Element Humeroradial Joint Model of Contact Pressure Using Fuji Pressure Sensitive Film.

A finite element (FE) elbow model was developed to predict the contact stress and contact area of the native humeroradial joint. The model was validated using Fuji pressure sensitive film with cadaveric elbows for which axial loads of 50, 100, and 200 N were applied through the radial head. Maximum contact stresses ranged from 1.7 to 4.32 MPa by FE predictions and from 1.34 to 3.84 MPa by pressure sensitive film measurement while contact areas extended from 39.33 to 77.86 mm2 and 29.73 to 83.34 mm2 by FE prediction and experimental measurement, respectively. Measurements from cadaveric testing and FE predictions showed the same patterns in both the maximum contact stress and contact area, as another demonstration of agreement. While measured contact pressures and contact areas validated the FE predictions, computed maximum stresses and contact area tended to overestimate the maximum contact stress and contact area.

Mapping the morphological changes of deposited gold nanoparticles across an imprinted groove

The gradient gold layer morphology below the percolation threshold along a channel groove imprinted into a pressure-sensitive adhesive polymer film is studied. In order to elucidate the complex nanostructure of the sputter-deposited gold nanoparticle layer, nanobeam grazing-incidence small-angle X-ray scattering and imaging ellipsometry are used. Thus, the complex nanostructure of this metal–polymer nanocomposite can be detected, distinguished and identified. The presence of macroscopically curved structures, as introduced by the imprinted ridges, can cause deviations from the mean metal nanoparticle morphology, probed on the `flat' sample area outside the ridges. The phase-separated morphology of the polymer film is rather unaffected by the imprint structure but leads, in addition, to a selective growth of gold on polystyrene-rich domains.