Contact Area Ratio Research Articles

Fusion rates of a morselized local bone graft in polyetheretherketone cages in posterior lumbar interbody fusion by quantitative analysis using consecutive three-dimensional computed tomography scans

Background context Posterior lumbar interbody fusion (PLIF) using harvested local bone inserted into a polyetheretherketone (PEEK) cage is a commonly used procedure, but the accurate fusion rate of a cage, cage to bone contact area ratio, and the changes in fusion rate with time after surgery are unknown. Purpose The aim was to conduct a quantitative analysis of the fusion rates and the cage to bone contact area ratios at each period of time using a PEEK cage in PLIF using a consecutive three-dimensional (3D) computed tomography (CT) scan. Study design This was a prospective study using a consecutive 3D thin-section CT scan. Patient sample Thirty patients aged between 37 and 73 years set to undergo elective PLIF with PEEK cages and pedicle screw fixation were included in the study. Outcome measures The assessments included the Korean Oswestry Disability Index (K-ODI), Short Form (SF)-36 questionnaire, Visual Analog Scale (VAS) pain score, and dynamic plane radiographs, preoperatively and at 6 and 12 months after surgery. Methods Three-dimensional CT scans were performed at 6 and 12 months after surgery. Three-dimensional CT assessments of the following were performed: fusion rate of the cage, cage to bone contact area ratio, and fusion rate of the interbody bone graft besides the cage. Results The 6-month fusion rate of the segment was 86.7%, which increased to 90.0% at 12 months. The fusion area ratio between the cage area and end plate showed a significant increase from 52.0% at 6 months to 58.5% at 12 months. Regarding the fusion area ratio between the cage and end plate, the ratio between the lower surface of the cage was significantly higher than that of the upper surface. In addition, the K-ODI, SF-36, and VAS values were similar at 6 and 12 months after surgery. Conclusions The fusion rate of the PEEK cage used in PLIF measured at 12 months was higher than that measured at 6 months. Therefore, an assessment on the complete fusion of local bone at 12 months after surgery is more accurate.

FEM analyses for influences of stress corrosion and pressure solution on THM coupling in dual-porosity rock mass

With the models of stress corrosion and pressure solution, by Yasuhara et al., two computation conditions were designed for a hypothetical nuclear waste repository in an unsaturated dual-porosity rock mass: (i) the fracture apertures are changed with the stress corrosion and pressure solution (the porosity of rock matrix is also a function of stress); (ii) the fracture apertures and the porosity of rock matrix are constants. Then the corresponding two-dimensional FEM analyses for the coupled thermo- hydro-mechanical processes were carried out, and the states of temperatures, rates and magnitudes of aperture closure, pore pressures, flow velocities and stresses in the rock mass were investigated. The results show the followings: The aperture closure rates caused by stress corrosion are almost six orders higher than those caused by pressure solution, and the two kinds of closure rates climb up, then decline, furthermore tend towards stability; the fracture apertures decrease from the original value and tend towards the residual value, and the contact-area ratios of asperities increase also from the original value and tend towards the nominal value; when the effects of stress corrosion and pressure solution are considered, the negative fracture pressures in near field rise very highly; the differences between the magnitudes and distributions of stresses within the rock mass in two calculation cases are very small.

Fabrication and characterization of e-beam photoresist array for biomimetic self-cleaning dry adhesives

Inspired from gecko foot-hairs, this paper presents the fabrication and characterization of e-beam photoresist nano-pillar array as biomimetic self-cleaning dry adhesives. Resist pillars of different widths and pitches were designed and fabricated using e-beam lithography. The pillar array of the negative e-beam resist (SAL 601) laterally collapsed after development, resulting from larger surface energy. The positive e-beam resist (ZEP 520A) is suitable for fabricating nano-pillar array. An AFM plateau tip was used to measure and characterize the adhesion force of the resist pillar array. The adhesion strengths significantly increase with the decreasing pillar width at the same pillar pitch and height. The contact angle measurement was used to evaluate the self-cleaning effect. Air trapped in the nano-gap between the pillars made the surface approach to the Cassie’s state of hydrophobicity. Since the contact angle and the adhesion strength have opposite trends with the contact area ratio, the result indicates that the dry adhesive needs to decrease to nanometer scale for obtaining the self-cleaning effect.

Observation of Real Contact Area Using Laser Microscope with Wide Field of View

In tribology, a contact condition between mating surfaces is very important to reduce friction and raise their lifetime. Direct observation of apparent contact area is necessary for a better understanding of the contact condition. We examined the distribution of real contact area between a platen rubber roller and a glass plate using a laser microscope with wide field of view. Based on these observations, the distribution of real contact area ratio, which is the ratio of real contact area to the apparent contact area at each point, was calculated. Micro-slips over the whole apparent contact area were measured with several torques applied to the platen roller. The relationship between real contact area ratio and micro-slips on the contact area are discussed.

Drag Reduction by Hydrophobic Microstructures

We studied the mechanism of drag reduction due to textured hydrophobic surfaces in Newtonian laminar flow through a rectangular channel. The test wall surfaces were fabricated with different fine groove patterns and groove area ratios, and were then coated with PTFE to produce hydrophobic surfaces. Drag reduction was estimated by pressure loss measurements in a 12 × 12 mm channel. Visualization of the gas-liquid interface was carried out using a 0.5 × 5 mm microchannel to investigate the mechanism of drag reduction. A series of experiments showed that the gas-liquid contact area ratio and the air layer thickness influence the drag reduction, the maximum drag reduction ratio is 3.7 %.

Estimation of wheel/rail adhesion coefficient under wet condition with measured boundary friction coefficient and real contact area

Abstract This paper describes how to improve the prediction method of the adhesion coefficient by means of the experimentally estimated boundary friction coefficient obtained by two kinds of twin-disc rolling contact machines and the ratio of real contact area to nominal contact area ( RCA / NCA ) obtained by ultrasonic measurement. The previous prediction method that the authors had already proposed in the last paper was based on Greenwood–Tripp's rough surface contact model; however, in this study, the authors adopted Lee & Ren's rough surfaces contact model and focused on the RCA / NCA measured by ultrasonic wave in order to predict the adhesion coefficient under wet conditions with the actual surface contact conditions. As a result, regarding the tendency of adhesion coefficient decreasing with an increase of running speed, a good agreement has been obtained between the results obtained by the prediction method proposed in this study and the measured results obtained by the field-test of Japanese Shinkansen vehicle (series 200).

Suggestion of new methodology for evaluation of osseointegration between implant and bone based on μ-CT images

Osseointegration has been used as an index for prediction of long-term success of implant. Osseointegration has been routinely evaluated by measuring bone contact ratio on histology based on two-dimensional (2D) sections or images. However, these both methodologies have been less informative analysis of results and have several disadvantages. The aim of this study is to introduce new methodology for evaluation of a degree of osseointegration between bone and implant based on micro computed tomography (μ-CT) images. Specimen was scanned at a voxel resolution of 35 μ by μ-CT. Three-dimensional (3D) models of bone and implant were reconstructed respectively. Bone contact area (BCA) and bone contact area ratio (BCAR) were measured and calculated. Here, osseointegrated BCA between bone and implant surfaces was determined by computing areas of all bone regions existed within 35μ distance from implant surface. Osseointegration of flapless implant surgery was evaluated by new methodology, compared with that of flap implant surgery. BCA and BCAR in flapless implant surgery was significantly bigger than that in flap implant surgery (p<0.05), suggesting that flapless implant surgery was more effective than flap implant surgery consistent with previous studies. In the conclusion, new methodology for evaluation osseointegration between bone and implant based on μ-CT images was likely to be reliable, useful and more informative analysis of results.

Optimization of Thermal Friction Drilling Using Grey Relational Analysis

The main purpose of this research is to study the optimal machining parameters for a novel process of thermal friction drilling on SUS 304 stainless steel. The experiments were conducted according to an L9 orthogonal array based on Taguchi experimental designs method, and the multiple performance characteristics correlated with surface roughness (SR) and bush length (BL) was investigated by grey relational analysis systematically and comprehensively. Moreover, the significant machining parameters that most intensively affected the multiple performance characteristic and the optimal combination levels of machining parameters associated with the thermal friction drilling on SUS 304 stainless steel were determined through the analysis of variance (ANOVA) and the response graph of grey relational grade. The main machining parameters of the thermal friction drilling such as friction angle, friction contact area ratio, feed rate, and drilling speed were selected to evaluate the effects on SR and BL. The experimental results show that the thermal friction drilling revealed beneficial effects on SR and BL for drilling processes. Moreover, the optimal machining parameters for multiple performance characteristics associated with SR and BL were attained. The developed thermal friction drilling avoids serious tool wears, enhances the surface quality of the machined hole, and prolongs the tool life significantly.

Effects of interfacial adhesion and crystallization on the thermoresistance of poly(lactic acid)/mica composites

Mechanical and thermal properties of poly(lactic acid) (PLA)/mica and poly(butylene terephthalate) (PBT)/mica composites were investigated when a coupling agent was added. When the PLA matrix was crystallized, it was observed that the interfacial adhesion between the PLA and the mica particles was improved. The result of dynamic mechanical analysis (DMA) showed that the thermoresistance of the crystallized PLA/mica composite was improved significantly. Influence of the interfacial adhesion was studied through finite element analysis (FEA) by inserting void elements between the polymers and the mineral particles. The FEA results were compared with the DMA results and predicted the contact area ratio between the PLA and the mica particles.

Optimization in thermal friction drilling for SUS 304 stainless steel

The main purpose of this research is to develop a new type of thermal friction drill made of sintered carbide. In addition, to optimize the machining process of the thermal friction drilling using Taguchi method is explored. The experiments were conducted on a 30 × 30 × 2 mm SUS 304 stainless steel plate. The effects of friction angles (FA), friction contact area ratio (FCAR), feed rate (FR), and spindle speed (SS) on the two quality characteristics, surface roughness (SR) and bushing length (BL), were also investigated. After conducting all the experimental trials, the analysis procedure followed. Firstly, the significance of the four parameters on the two quality characteristics was examined by ANOVA. Then the optimal combination levels of parameters for SR and BL were determined based on the S/N ratios. Finally, confirmation experiments were conducted to verify the experimental findings. Results showed that FA and SS were the significant machining parameters that most intensively affect SR while FCAR was the only significant parameter for BL. Specially, the SR and BL were greatly improved when used in the optimized parameters settings. More importantly, the performance of the friction drill was conducted 60 runs. The thermal friction drill demonstrated a smoother, mirror-like surface and showed less wear. This proved that thermal friction drilling provided the better machining performance and longer tool life.

Finite Element Modeling of the Nano-scale Adhesive Contact and the Geometry-based Pull-off Force

Nano-scale adhesive contact mediated by intermolecular van der Waals forces has become a typical fundamental problem in many areas. Interpretation and control of the strength and efficiency of the nano-scale adhesive contacts require a proper modeling considering the actual interfacial forces, the varying contact area, and clearance. In this article, the finite-element (FE) method is developed to model the nano-scale adhesive contact of elastic bodies with an adhesive pressure derived from the interatomic interaction Lennard-Jones potential, which permits numerical solutions for a variety of interface geometries. Compared with the analytical results from conventional Hertz, JKR, and DMT models, the validity of the FE model is verified. For nano-scale contact, the assumption of equivalent radius adopted in the Hertz model is initially investigated and proved to be improper for nano-scale adhesive contact due to the distribution variations of interfacial force caused by local contact geometry. Then adhesive contact behaviors of four typical nano-scale contact geometries inspired by tip shapes of bio-adhesive pads are investigated in detail, which are flat punch tip, sphere tip, mushroom tip, and empty cup tip. The simulation results indicate that the nano-scale tip geometry plays a dominant role on the pull-off strength. Within the investigated geometries, cup tip results in a highest adhesion efficiency followed by flat punch tip, sphere tip, and mushroom tip, respectively, which are highly geometry dependent and verified by former experimental results. The dominant effect is found coming from the contact area ratio of the adhesive area to the sticking area or the whole contact area. The FE modeling can serve a useful purpose in revealing the nano-scale geometry-based adhesion contact for surface topography design in MEMS to avoid stiction failure and for the artificial sticky feet in bionics to increase adhesion strength.

Evaluation of friction coefficient using simplified deformation model of plastic hemispherical contact with a rigid flat

This work evaluates the friction coefficient using the model of plastic hemispherical contact against a rigid flat. The fractional profile of an ellipsoid is utilized to describe the deformed hemispherical shape, and simultaneously define the contact area ratio. Particularly, an adhesion factor is defined to assess the junction ability of asperity adhesion under compressive loading. Additionally, the complex process of contact is assumed as a series of contact states changing from fracture to shearing. The friction coefficient, which obeys the constant friction law, is then derived as a function of interference and strain hardening exponent via adhesion theory. Finally, a comparison of friction coefficient is made with the published experiment, showing that the calculated value is larger than the experimental value. Some practical conclusions are presented and a conceptual understanding of contact friction is provided.

Fusion Rates and Subsidence of Morselized Local Bone Grafted in Titanium Cages in Posterior Lumbar Interbody Fusion Using Quantitative Three-Dimensional Computed Tomography Scans

Prospective, controlled study. To determine fusion rates, cage to bone contact area ratios, and subsidences using titanium cages filled with a local bone graft for posterior lumbar interbody fusion (PLIF). PLIF using decompressed local bone inserted in titanium cages combined with pedicle screw fixation is a popular procedure for treating lumbar spine degeneration. There is no report about cage to bone contact area ratios using titanium cages filled with a local bone graft for PLIF. PLIF using a titanium cage filled with excised laminar and facet joint bone with pedicle screw fixation was performed in 54 (78 levels) consecutive patients. Mean age at the time of surgery was 62.5 years. Radiographic assessments of posterior and anterior disc heights were performed. Three-dimensional thin-section computed tomography assessments of cage subsidences, fused area ratios of local bone inside cages, and overall fusion rates were analyzed. Mean values of anterior and posterior disc heights at 1 year after surgery were significantly greater than mean preoperative disc heights. The fusion rate of cages over both upper and lower segment endplates was 96.2%. The ratios of fused areas of local bone inside cages exposed to upper and lower segment endplates were 46.7% and 52.2% in the coronal plane and 46.4% and 49.9% in the sagittal 3-dimensional computed tomography plane, respectively. And, subsidences of titanium cages at upper and lower segment endplates were 1.26 mm and 0.72 mm in the coronal plane and 1.04 mm and 0.53 mm in the sagittal plane, respectively. The ratio of fused area of local bone inside cages at regions exposed to endplates was <50%, which is insufficient for physiologic load transmission. The authors recommend that additional bone should be grafted into the disc space or new bone bonding interbody spacer should be considered.

Development of a Model Based Method for Investigating Facet Articulation

Reported investigations of facet articulation in the human spine have often been conducted through the insertion of pressure sensitive film into the joint space, which requires incision of the facet capsule and may alter the characteristics of interaction between the facet surfaces. Load transmission through the facet has also been measured using strain gauges bonded to the articular processes. While this method allows for preservation of the facet capsule, it requires extensive instrumentation of the spine, as well as strain-gauge calibration, and is highly sensitive to placement and location of the strain gauges. The inherently invasive nature of these techniques makes it difficult to translate them into medical practice. A method has been developed to investigate facet articulation through the application of test kinematics to a specimen-specific rigid-body model of each vertebra within a lumbar spine segment. Rigid-body models of each vertebral body were developed from CT scans of each specimen. The distances between nearest-neighboring points on each facet surface were calculated for specific time frames of each specimen's flexion/extension test. A metric describing the proportion of each facet surface within a distance (2 mm) from the neighboring surface, the contact area ratio (CAR), was calculated at each of these time frames. A statistically significant difference (p<0.037) was found in the CAR between the time frames corresponding to full flexion and full extension in every level of the lumbar spine (L1-L5) using the data obtained from the seven specimens evaluated in this study. The finding that the contact area of the facet is greater in extension than flexion corresponds to other findings in the literature, as well as the generally accepted role of the facets in extension. Thus, a biomechanical method with a sufficiently sensitive metric is presented as a means to evaluate differences in facet articulation between intact and treated or between healthy and pathologic spines.

A friction model for dry contacts during metal-forming processes

In a metal-working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. This frictional behavior is often taken into account by using a constant coefficient of friction in the finite element simulations. However, friction coefficient varies in time and space with many parameters. This paper aims at modeling of friction in dry contacts which happens at metal-forming processes in the lack of lubricant. The coefficient of dry friction in this model is a function of contact area ratio (which is a function of surface contact characteristics) and strain hardening exponent (material property). The V-bending process of aluminum alloy 6061-T4 sheets was studied experimentally and numerically using ABAQUS/Standard with two kinds of friction models: Coulomb friction and newly developed dry friction models. The results clearly showed that the developed dry friction model has better results in predicting load-stroke curves and springback compared to traditional Coulomb friction model. The FE prediction error for 6061-T4 AA is 16.9% using Coulomb friction model and 9.2% using dry friction model.

Study of Polishing Characteristics of Monodisperse Ceria Abrasive in Chemical Mechanical Planarization

In this study, the monodisperse abrasive deposition (MDAD) system was developed to investigate the polishing mechanism of ceria abrasives for the chemical mechanical planarization of a wafer. Using the MDAD system, groups of ceria particles with a specific size were collected from slurry with various particle size distributions, and each group was deposited on a blanket silicon wafer to study the size effect of the ceria particle on polishing results. The effects of the ceria particle size on surface roughness, contact area ratio, and subsurface damages on the surface and subsurface crystallographic structure were investigated using atomic force microscopy, transmission electron microscopy, and a surface inspection system. A similar set of experiments was performed with types of ceria abrasive particles with the same diameter but different morphologies to investigate the effect of the ceria abrasive geometry on polishing results. In addition, the effect of the ceria particle size on the pattern loading was investigated by polishing the shallow trench isolation and high aspect ratio patterned wafers.

Investigation of the strain distribution with lubrication during the deep drawing process

A lubrication/friction model can be implemented in FEM codes to predict the contact area ratio, friction coefficient and strain distribution in lubricated deep drawing process. In the lubrication analysis, the surface roughness effect on lubrication flow is included by using Wilson and Marsault's average Reynolds equation that is appropriated for mixed lubrication with severe asperity contact. With regard to the asperity contact theory, the well-known flattening effect is considered. Friction is expressed in terms of variables such as lubricant film thickness, sheet roughness, lubricant viscosity, interface pressure, sliding speed, and strain rate. The proposed lubrication/friction model combined with a finite element code of deep drawing process to predict the contact area ratio, friction coefficient and strain distribution. Numerical results showed that the present analysis provides a good agreement with the measured strain distributions.

Influence of rigid base on damping of finite sand stratum

Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of a finite sand layer with different height-to-width ratios underlain by either a rigid concrete base or a natural red-earth base. Comparison of the results of the experimental study showed that the rigidity of the finite base has a significant influence on the damping ratio of the foundation–soil system. The damping ratio of the finite sand stratum underlain by the rigid concrete base is significantly lower than that obtained for the finite sand stratum underlain by the natural red-earth base. The damping ratio in both cases is less than 10%, suggesting that only material damping predominates. Comparison of the predicted damping ratio for a homogeneous sand stratum with the experimental damping ratio obtained corresponding to the height-to-width ratio of 3 of the finite sand stratum underlain by either the rigid concrete base or natural red-earth base indicated a significant reduction in damping ratio of the foundation–soil system, irrespective of the contact area and mass ratio of the model footing.

Daily chewing gum exercise for stabilizing the vertical occlusion

We investigated the effects of a chewing gum exercise program on occlusal conditions and evaluated compliance of subjects. Thirty-five healthy adult volunteers (26 males and nine females) were asked to chew gum for 10-15 min before or after three meals daily for four weeks. Occlusal conditions were recorded as occlusal parameters, such as occlusal contact area, occlusal contact force, and pressure using dental prescale films. These parameters were evaluated by an Occluzer before the exercise period commenced, after four weeks of exercise, and then one month after the end of the exercise period. These parameters were statistically compared using one-way ANOVA. We found that: (i) after four weeks of exercise, anterior and posterior occlusal contact areas and forces were significantly (P < 0.05) increased and the increments were significantly (P < 0.05) higher in the anterior occlusal contact area and force than in the posterior occlusal contact area and force, (ii) the anteroposterior ratio of occlusal contact area and force increased, but not markedly, (iii) increased parameters had significantly (P < 0.05) decreased within one month after the end of the four-week exercise period, (iv) most participants did not complain for discomfort or stress during the exercise. The chewing gum exercise program could increase occlusal contact area and force and also move the anteroposterior occlusal balance forward. Patient compliance with the exercise is likely high enough to keep them exercising.

Hybrid Atomistic/Continuum Study of Contact and Friction Between Rough Solids

A hybrid simulation method is used to study the effect of atomic structure and self-affine roughness on non-adhesive contact and friction between two-dimensional surfaces. Rough-on-flat and rough-on-rough contact are compared as a function of system size up to several micrometers. In order to contrast elastic and plastic behavior, interactions within the deformable substrate are either harmonic or Lennard-Jones. The ratio of lattice constants in the solids is varied to examine the effect of commensurability. In all cases the true area of contact rises linearly with load, but the slope is much larger than expected from continuum calculations. These calculations considered a continuous distribution of surface heights that is appropriate for large scales, rather than the discrete height distribution of the crystalline surfaces used here. The ratio of contact area to load depends on the ratio of lattice constants in the solids and varies with system size in small systems that deform plastically. While some dislocations are observed, plasticity is dominated by an asperity flattening mechanism where surface atoms are displaced into a lower layer. The kinetic friction rises linearly with load and is independent of system size, as predicted by Amontons’s laws. Variations in friction with commensurability are smaller for rough surfaces than for flat surfaces, because most of the contact area is in small patches. Asperity flattening increases patch sizes and thus the effect of commensurability on friction. Rough-on-rough contact leads to additional friction associated with the local slope of the contacting regions.