Experimental Verification of the Impact of the Contact Area between the Defect Site and the Scaffold on Bone Regeneration Efficacy

In the field of bone tissue engineering, which is being developed for the ideal restoration of bone defects, researchers are exploring the improvement of the bone regeneration efficacy of scaffolds through various approaches involving osteoconductive, osteoinductive, and angiogenic factors. In the current trend of research, there is also a suggestion that the topological factors of recent scaffolds may influence the attachment, migration, proliferation, and differentiation of bone cells. Building upon experimental confirmation of the effect of scaffold conformity with the defect site on enhanced bone regeneration in previous studies, we conducted this research to experimentally investigate the relationship between contact area with the defect site and bone regeneration efficacy. The results demonstrated that as the contact area of the scaffold increased, not only did the resistance to bone tissue growth increase, more significant bone regeneration also occurred, as evidenced through histological analysis and micro-CT analysis. This research confirms that the contact area between the scaffold and the defect site is a critical variable affecting bone regeneration efficacy, emphasizing its importance when designing customized scaffolds. This finding holds promising implications for future studies and applications in the field.

Effect of Indentation Depth on Friction Coefficient in Adhesive Contacts: Experiment and Simulation

The quasi-static regime of friction between a rigid steel indenter and a soft elastomer with high adhesion is studied experimentally. An analysis of the formally calculated dependencies of a friction coefficient on an external load (normal force) shows that the friction coefficient monotonically decreases with an increase in the load, following a power law relationship. Over the entire range of contact loads, a friction mode is realized in which constant shear stresses are maintained in the tangential contact, which corresponds to the "adhesive" friction mode. In this mode, Amonton's law is inapplicable, and the friction coefficient loses its original meaning. Some classical works, which show the existence of a transition between "adhesive" and "normal" friction, were analyzed. It is shown that, in fact, there is no such transition. A computer simulation of the indentation process was carried out within the framework of the boundary element method, which confirmed the experimental results.

Proximal Row Carpectomy Does Not Alter Contact Pressures of the Lunate Fossa: A Cadaveric Study

BACKGROUND

Previous studies have suggested that proximal row carpectomy (PRC) results in increased contact pressures and decreased contact areas in the radiocarpal joint. Such experiments, however, used older technologies that may be associated with considerable measurement errors. The purpose of this study was to determine whether there was a significant difference in contact pressure and contact area before and after PRC using Tekscan, a newer pressure sensing technology.

METHODS

Ten nonpaired cadaveric specimens were dissected proximal to the carpal row and potted. An ultra-thin Tekscan sensor was secured in the lunate fossa of the radius. The wrists were loaded with 200 N of force for 60 seconds to simulate clenched-fist grip; contact pressure and area was assessed before and after PRC.

RESULTS

Performing a PRC did not significantly increase mean contact pressure at the lunate fossa compared to the native state (mean increase of 17.4 ± 43.2 N/cm2, P = .184). Similarly, the PRC did not significantly alter peak contact pressures at the lunate fossa (intact: 617.2 ± 233.46 N/cm2, median = 637.5 N/cm2; PRC: 707.8 ± 156.6 N/cm2, median = 728.5 N/cm2; P = .169). In addition, the PRC (0.46 ± 0.15 cm2, median = 0.48 cm2) and intact states (0.49 ± 0.25 cm2, median = 0.44 cm2) demonstrated similar contact areas (P = .681).

CONCLUSIONS

In contrast to prior studies that demonstrated significant increases in contact pressure and decreases in contact area after PRC, our findings propose that performing a PRC does not significantly alter the contact pressures or area of the lunate fossa of the radiocarpal joint.

Distinct or Overlapping Areas of Mitochondrial Thioredoxin 2 May Be Used for Its Covalent and Strong Non-Covalent Interactions with Protein Ligands

In silico approaches were employed to examine the characteristics of interactions between human mitochondrial thioredoxin 2 (HsTrx2) and its 38 previously identified mitochondrial protein ligands. All interactions appeared driven mainly by electrostatic forces. The statistically significant residues of HsTrx2 for interactions were characterized as "contact hot spots". Since these were identical/adjacent to putative thermodynamic hot spots, an energy network approach identified their neighbors to highlight possible contact interfaces. Three distinct areas for binding emerged: (i) one around the active site for covalent interactions, (ii) another antipodal to the active site for strong non-covalent interactions, and (iii) a third area involved in both kinds of interactions. The contact interfaces of HsTrx2 were projected as respective interfaces for Escherichia coli Trx1 (EcoTrx1), 2, and HsTrx1. Comparison of the interfaces and contact hot spots of HsTrx2 to the contact residues of EcoTx1 and HsTrx1 from existing crystal complexes with protein ligands supported the hypothesis, except for a part of the cleft/groove adjacent to Trp30 preceding the active site. The outcomes of this study raise the possibility for the rational design of selective inhibitors for the interactions of HsTrx2 with specific protein ligands without affecting the entirety of the functions of the Trx system.

A New Digital Analysis Technique for the Mechanical Aperture and Contact Area of Rock Fractures

In this study, a new digital technique for the analysis of the mechanical aperture and contact area of rock fractures under various normal stresses is proposed. The technique requires point cloud data of the upper and lower fracture surfaces, pressure film image data of the fracture, and normal deformation data of the fracture as input data. Three steps of algorithms were constructed using these input data: (1) a primary matching algorithm that considers the shape of the fracture surfaces; (2) a secondary matching algorithm that uses pressure film images; and (3) a translation algorithm that considers the normal deformation of a fracture. The applicability of the proposed technique was investigated using natural fracture specimens sampled at an underground research facility in Korea. In this process, the technique was validated through a comparison with the empirical equation suggested in a previous study. The proposed technique has the advantage of being able to analyze changes in the mechanical aperture and contact area under various normal stresses without multiple experiments. In addition, the change in the contact area on the fracture surface according to the normal stress can be analyzed in detail.

Friction Behavior between Carbon Fiber Plain Weave and Metal Semi-Cylinder Tool

The deformations that occur during composite forming processes are governed by the friction between the fabrics and tooling material on the mesoscopic level. The effect of normal load and multi-plies on the frictional behavior of the carbon plain weave is investigated by simulating the friction between the fabric and metal semi-cylinder tool by using the experimental method. The periodic wavy friction-displacement curve between the metal tool and fabric is caused by the interwoven structure of the fabric. Both the increase in the normal load and the number of layers cause an increase in the real contact area during friction, leading to an increase in the friction force. The real contact area is calculated based on the Hertzian contact model and the self-designed testing method. The friction force values obtained from multiplying the real contact area with shear strength are closely aligned with the measured results.

In Situ Active Switching of Bipolar Current Rectification in 2D Semiconductor Vertical Diodes

Two-dimensional semiconducting transition-metal dichalcogenides (TMDCs) have attracted extensive attention as building blocks of miniaturized electronic and optical devices. However, as the characteristics of TMDC devices are predominately determined by their device structures, the function of TMDC devices is fixed once fabricated, leaving the reconfigurable active device and circuit a challenge. Here, we have demonstrated the current rectification switching in TMDC vertical diodes using a liquid metal (EGaIn) top electrode with a reconfigurable contact area. The rectification switching is closely related to the ultrathin gallium oxide layer on the surface of EGaIn. Under the small contact, with the existence of gallium oxide, photocurrent dominates the electrical transport showing a negative rectification, while as the contact increases, the broken gallium oxide leads to rectification switching to the positive bias direction. Such rectification switching applies to thin TMDC flakes down to 3 nm, benefitting from the soft electrical contact between the TMDC and the EGaIn electrode. Our work shows the new possibility of actively reconfigurable TMDC vertical diodes enabled by the liquid metal electrode and will promote promising applications of flexible and tunable TMDC-based nanoelectronic devices.

High-Precision Tribometer for Studies of Adhesive Contacts

Herein, we describe the design of a laboratory setup operating as a high-precision tribometer. The whole design procedure is presented, starting with a concept, followed by the creation of an exact 3D model and final assembly of all functional parts. The functional idea of the setup is based on a previously designed device that was used to perform more simple tasks. A series of experiments revealed certain disadvantages of the initial setup, for which pertinent solutions were found and implemented. Processing and correction of the data obtained from the device are demonstrated with an example involving backlash and signal drift errors. Correction of both linear and non-linear signal drift errors is considered. We also show that, depending on the research interests, the developed equipment can be further modified by alternating its peripheral parts without changing the main frame of the device.

Assessment of PCL between dental implant prosthesis and natural teeth using a digital force analyzer

BACKGROUND

The prime concern of an implant-supported prosthesis (ISP) is to maintain an optimal proximal contact tightness, which further maintains arch integrity, improves masticatory effectiveness, and minimizes peri-implantitis.

OBJECTIVE

To investigate the loss of proximal contact tightness between single tooth implant-supported prosthesis and the adjacent natural teeth.

METHODS

Forty patients treated by a single mandibular first molar ISP, aged between 18-50 years were selected. All were randomly allocated in Group I and Group II. Group I, 20 subjects who have received ISP without an insertion of Essix retainer, and Group II patients received an insertion with Essix retainer. The groups were subdivided into Subgroup A, B, and Subgroup C, D, in which A and C are control groups. To measure the tightness at proximal contact points, a digital force analyzer was used. Proximal contact tightness (PCT) was measured immediately after the placement of the prosthesis, 3 months, 6 months, and 1-year follow-up respectively, and the PCT values at end of 1 year were statistically evaluated. Statistical analysis was done, mean and standard deviation was calculated by independent sample t-test wit p< 0.05 as a statistically significant value.

RESULTS

In Group I, towards the end of 1 year, 2.09 N (65.5%) and 1.50 N (53.1%) loss of PCT were found on mesial and distal contact areas respectively. In Group II, loss of PCT at mesial contact area was 0.87 N (28.9%) and at distal contact area was 1.77 N (53.3%), which is significantly less compared with the non-usage of Essix retainer (p< 0.05).

CONCLUSION

The usage of Essix retainer, PCT increases especially on the mesial contact area. The frequency of contact loss was decreased. Thus, to minimize the loss of proximal contact the usage of Essix retainer is recommended.

Open-Source CFD Elucidating Mechanism of 3D Pillar Electrode in Improving All-Solid-State Battery Performance

All-solid-state batteries (ASSBs) have become an important technology because of their high performance and low-risk operation. However, the high interface resistance and low ionic conductivity of ASSBs hinder their application. In this study, a self-developed electrochemical model based on an open-source computational fluid dynamics platform is presented. The effect of contact area reduction at the electrode/solid-state electrolyte interface is investigated. Then, a new conceptual 3D structure is introduced to circumvent the existing barriers. The results demonstrate that the discharge time is shortened by over 20% when the area contact ratio reduces from 1.0 to 0.8 at 1 C-rate, owing to the increased overpotential. By adopting the new 3D pillar design, the energy density of ASSBs can be improved. However, it is only when a 3D current collector is contained in the cathode that the battery energy/power density, capacity, and material utilization can be greatly enhanced without being limited by pillar height issues. Therefore, this work provides important insight into the enhanced performance of 3D structures.

Investigation of Technological and Load Intensity Parameters of the Finishing Process of Materials on Equipment with Tools Translational Kinematics

The regularities of the formation of the resulting raster tool trajectories based on Lissajous figures for the lapping process of planes are established. This makes it possible to maximize the cutting ability of the tool, which contributes to its more uniform wear and increased productivity and processing quality. Optimal parameters of productivity and roughness of the treated surface during lapping of zirconium ceramics are achieved through the use of ASM paste 28/20 µm. Based on Preston’s hypothesis, an exponential dependence of the change in the contact area during the lapping of planes of different initial shape of the macrorelief is obtained. The obtained theoretical and practical results of the study of the process of flat lapping with constant and variable clamping force of the treated surface to the surface of the tool. The influence of the force factor on the formation of the surface in the process of abrasive lapping has been established. Studies have been carried out and the main technological recommendations of precision surface treatment of workpieces based on hard, brittle ceramic material and bronze samples on equipment with a raster trajectory of the tool movement are presented. The optimal pressure value when processing ceramics should be considered 203–270 kPa (2.1–2.8 kg/cm²).

The effect of hemiarthroplasty implant modulus on contact mechanics: an experimental investigation

BACKGROUND

Hemiarthroplasties cause damage to the cartilage that they articulate against, which is a major limitation to their use. This study investigated the use of lower-stiffness materials to determine whether they improve hemiarthroplasty contact mechanics and thus reduce the risk of cartilage damage.

METHODS

Eleven fresh-frozen cadaveric upper extremities were disarticulated and fixed in a custom-built jig that applied a static load of 50 N to the radiocapitellar joint. Flexion angles of 0°, 45°, 90°, and 135° were tested with radial head implants made of cobalt-chrome (CoCr) and ultrahigh-molecular-weight polyethylene (UHMWPE) compared with the native radial head. A Tekscan thin-film sensor was used to measure the contact area and contact pressure between the radius and capitellum.

RESULTS

UHMWPE and CoCr were too stiff in the application of hemiarthroplasty, resulting in lower contact areas and higher contact pressures relative to the native joint. The native contact area was, on average, 42 ± 20 mm² larger than that of UHMWPE (P < .001) and 55 ± 24 mm² larger than that of CoCr (P < .001). UHMWPE had a contact area 13 ± 10 mm² greater than that of CoCr (P = .014).

DISCUSSION AND CONCLUSION

This study shows that even though UHMWPE has a stiffness several times lower than CoCr, the use of this material in hemiarthroplasty led to only a minor improvement in contact mechanics. Neither implant restored contact similar to the native articulation. Investigations into new materials to improve the contact mechanics of hemiarthroplasty should focus on materials with a lower stiffness than UHMWPE.

Plantar Pressure and Contact Area Measurement of Foot Abnormalities in Stroke Rehabilitation

BACKGROUND

Evaluation of plantar pressure in stroke patients is a parameter that could be used for monitoring and comparing how the timing of starting a rehabilitation program effects patient improvement.

METHODS

We performed the following clinical and functional evaluations: initial moment (T1), intermediate (T2), and final evaluation at one year (T3). At T1 we studied 100 stroke patients in two groups, A and B (each 50 patients). The first group, A, started rehabilitation in the first three months after having a stroke, and group B started after three months from the time of stroke. Due to the impediments observed during rehabilitation, we made biomechanic evaluation for two lots, I and II (each 25 patients). Assessment of the patient was carried out by clinical (neurologic examination), functional (using the Tinetti Functional Gait Assessment Test for classifying the gait), and biomechanical evaluation (maximal plantar pressure (Pmax), contact area (CA), and pressure distribution (COP)).

RESULTS

The Tinetti scale for gait had the following scores: for group A, from 1.34 at the initial moment (T1) to 10.64 at final evaluation (T3), and for group B, 3.08 at initial moment (T1) to 9 at final evaluation (T3). Distribution of COP in the left hemiparesis was uneven at T1 but evolved after rehabilitation. The right hemiparesis had uniform COP distribution even at T1, explained by motor dominance on the right side. CA and Pmax for lot I increased more than 100%, meaning that there is a possibility for favorable improvement if the patients start the rehabilitation program in the first three months after stroke. For lot II, increases of the parameters were less than lot I.

DISCUSSIONS

The recovery potential is higher for patients with right hemiparesis. Biomechanic evaluation showed diversity regarding compensatory mechanisms for the paretic and nonparetic lower limb.

CONCLUSIONS

CA and Pmax are relevant assessments for evaluating the effects on timing of starting a rehabilitation program after a stroke.

OXIS Contacts as a Risk Factor for Approximal Caries: A Retrospective Cohort Study

Purpose: The purpose of the present study was to evaluate the individual susceptibility of four different types of OXIS contact areas (open [O], point [X], straight [I], and curved [S]) to approximal caries in children. Methods: A retrospective cohort study was performed using clinical photographs and cone-beam computed tomography images of children, available from January 1, 2014, to August 31, 2015, showing the presence of at least one caries-free contact area between the primary molars. A single calibrated examiner scored 1,102 selected contacts using OXIS criteria from the occlusal view and subsequently evaluated the same contacts with a minimum follow-up period of one year for the presence of approximal caries. Results: Of the 1,102 contacts, 259 (23.5 percent) were found to be carious or restored due to approximal caries. Multivariate logistic regression analysis showed that only the type of contact played a significant role in caries prevalence (P<0.05). The odds ratios of OXIS contacts for the development of approximal caries were: S contact-147.4 (95 percent confidence interval [95% CI] equals 19.7 to 1101.7); I contact-24.5 (95% CI equals 3.4 to 177.9); X contact-1.1 (95% CI equals 1.0 to 12.5); and O contact-1.00 (reference). Conclusions: Among the OXIS contacts, the S type was most susceptible to approximal caries due to its complex morphology. The broad contact areas, namely, I and S types, are at greater risk for approximal caries in primary molars than O and X contacts.

Fracture asperity evolution during the transition from stick slip to stable sliding

Fracture asperities interlock or break during stick slip and ride over each other during stable sliding. The evolution of fracture asperities during the transition between stick slip and stable sliding has attracted less attention, but is important to predict fracture behaviour. Here, we conduct a series of direct shear experiments on simulated fractures in homogeneous polycarbonate to examine the evolution of fracture asperities in the transition stage. Our results show that the transition stage occurs between the stick slip and stable sliding stages during the progressive reduction in normal stress on the smooth and rough fractures. Both the fractures exhibit the alternative occurrence of small and large shear stress drops followed by the deterministic chaos in the transition stage. Our data indicate that the asperity radius of curvature correlates linearly with the dimensionless contact area under a given normal stress. For the rough fracture, a bifurcation of acoustic energy release appears when the dimensionless contact area decreases in the transition stage. The evolution of fracture asperities is stress-dependent and velocity-dependent. This article is part of the theme issue 'Fracture dynamics of solid materials: from particles to the globe'.

Vision-Based Tactile Sensor Mechanism for the Estimation of Contact Position and Force Distribution Using Deep Learning

This work describes the development of a vision-based tactile sensor system that utilizes the image-based information of the tactile sensor in conjunction with input loads at various motions to train the neural network for the estimation of tactile contact position, area, and force distribution. The current study also addresses pragmatic aspects, such as choice of the thickness and materials for the tactile fingertips and surface tendency, etc. The overall vision-based tactile sensor equipment interacts with an actuating motion controller, force gauge, and control PC (personal computer) with a LabVIEW software on it. The image acquisition was carried out using a compact stereo camera setup mounted inside the elastic body to observe and measure the amount of deformation by the motion and input load. The vision-based tactile sensor test bench was employed to collect the output contact position, angle, and force distribution caused by various randomly considered input loads for motion in X, Y, Z directions and RxRy rotational motion. The retrieved image information, contact position, area, and force distribution from different input loads with specified 3D position and angle are utilized for deep learning. A convolutional neural network VGG-16 classification modelhas been modified to a regression network model and transfer learning was applied to suit the regression task of estimating contact position and force distribution. Several experiments were carried out using thick and thin sized tactile sensors with various shapes, such as circle, square, hexagon, for better validation of the predicted contact position, contact area, and force distribution.

Nondestructive Quantitative Evaluation of Yarns and Fabrics and Determination of Contact Area of Fabrics Using the X-ray Microcomputed Tomography System for Skin-Textile Friction Analysis

In different mechanical conditions, repetitive friction in combination with pressure, shear, temperature, and moisture leads to skin discomfort and imposes the risks of developing skin injuries such as blisters and pressure ulcers, frequently reported in athletes, military personnel, and in people with compromised skin conditions and/or immobility. Textiles next to skin govern the skin microclimate, have the potential to influence the mechanical contact with skin, and contribute to skin comfort and health. The adhesion-friction theory suggests that contact area is a critical factor to influence adhesion, and therefore, friction force. Friction being a surface phenomenon, most of the studies concentrated on the surface profile or topographic analysis of textiles. This study investigated both the surface profiles and the inner construction of the fabrics through X-ray microcomputed tomographic three-dimensional image analysis. A novel nondestructive method to evaluate yarn and fabric structural details quantitatively and calculate contact area (in fiber area %) experimentally has been reported in this paper. Plain and satin-woven fabrics with different thread densities and made from 100% cotton ring-spun yarns with two different linear densities (40 and 60 Ne) were investigated in this study. The measurements from the tomographic images (pixel size: 1.13 μm) and the fiber area % analysis were in good agreement to comprehend and compare the yarn and fabric properties reported. The fiber area % as reported in this paper can be used to evaluate the skin-textile interfaces and quantitatively determine the contact area under different physical, mechanical, and microclimatic conditions to understand the actual skin-textile interaction during any physical activity or sports. The proposed method can be helpful in engineering textiles to enhance skin comfort and prevent injuries, such as blisters and pressure ulcers, in diversified application areas, including but not limited to, sports and healthcare apparel, military apparel, and firefighter's protective clothing. In addition, the images were capable of precisely evaluating yarn diameters, crimp %, and packing factor as well as fabric thickness, volumetric densities, and cover factors as compared with those obtained from theoretical evaluation and existing classical test methods. All these findings suggest that the proposed new method can reliably be used to quantify the yarn and fabric characteristics, compare their functionality, and understand the structural impacts in an objective and nondestructive way.

Highly Sensitive Textile-Based Capacitive Pressure Sensors Using PVDF-HFP/Ionic Liquid Composite Films

Textile-based pressure sensors have garnered considerable interest in electronic textiles due to their diverse applications, including human–machine interface and healthcare monitoring systems. We studied a textile-based capacitive pressure sensor array using a poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP)/ionic liquid (IL) composite film. By constructing a capacitor structure with Ag-plated conductive fiber electrodes that are embedded in fabrics, a capacitive pressure sensor showing high sensitivity, good operation stability, and a wide sensing range could be created. By optimizing the PVDF-HFP:IL ratio (6.5:3.5), the fabricated textile pressure sensors showed sensitivity of 9.51 kPa⁻¹ and 0.69 kPa⁻¹ in the pressure ranges of 0–20 kPa and 20–100 kPa, respectively. The pressure-dependent capacitance variation in our device was explained based on the change in the contact-area formed between the multi-filament fiber electrodes and the PVDF-HFP/IL film. To demonstrate the applicability and scalability of the sensor device, a 3 × 3 pressure sensor array was fabricated. Due to its matrix-type array structure and capacitive sensing mechanism, multi-point detection was possible, and the different positions and the weights of the objects could be identified.

Current Concepts of Contemporary Expandable Lumbar Interbody Fusion Cage Designs, Part 1: An Editorial on Their Biomechanical Characteristics

BACKGROUND

Bidirectional expandable designs for lumbar interbody fusion cages are the latest iteration of expandable spacers employed to address some of the common problems inherent to static interbody fusion cages.

OBJECTIVE

To describe the rationales for contemporary bidirectional, multimaterial expandable lumbar interbody fusion cage designs to achieve in situ expansion for maximum anterior column support while decreasing insertion size during minimal-access surgeries.

METHODS

The authors summarize the current concepts behind expandable spinal fusion open architecture cage designs focusing on advanced minimally invasive spinal surgery techniques, such as endoscopy. A cage capable of bidirectional expansion in both height and width to address constrained surgical access problems was of particular interest to the authors while they analyzed the relationship between implant material stiffness and geometric design regarding the risk of subsidence and reduced graft loading.

CONCLUSIONS

Biomechanical advantages of new bidirectional, multimaterial expandable interbody fusion cages allow insertion through minimal surgical access and combine the advantages of proven device configurations and advanced material selection. The final construct stiffness is sufficient to provide immediate anterior column support while accommodating reduced sizes required for minimally invasive surgery applications.

LEVEL OF EVIDENCE

7.

Is the abnormal conduction zone of the left atrium a precursor to a low voltage area in patients with atrial fibrillation?

BACKGROUND

The abnormal conduction zone (ACZ) in the left atrium (LA) has attracted attention as an arrhythmia source in atrial fibrillation (AF). We investigated the hypothesis that the ACZ is related to the low voltage area (LVA) or the LA anatomical contact areas (CoAs) with other organs.

METHODS AND RESULTS

We studied 100 patients (49 non-paroxysmal AF, 66 males, and 67.9 ± 9.9 years) who received catheter ablation for AF. High-density LA mapping during high right atrial pacing was constructed. Isochronal activation maps were created at 5-ms interval setting, and the ACZ was identified on the activation map by locating a site with isochronal crowding of ≥3 isochrones, which are calculated as ≤27 cm/s. The LVA was defined as the following; mild ( < 1.3 mV), moderate (<1.0 mV), and severe LVA (<0.5 mV). The CoAs (ascending aorta-anterior LA, descending aorta-posterior LA, and vertebrae-posterior LA) were assessed using computed tomography. The ACZ was linearly distributed, and observed in 95 patients (95%). The ACZ was most frequently observed in the anterior wall region (77%). A longer ACZ was significantly associated with a larger LA size and a prevalence of non-PAF. The 51.2 ± 36.2% of ACZ overlapped with mild LVA, 32.9 ± 32.8% of ACZ with moderate LVA, and 14.6 ± 22.0% of ACZ with severe LVA. In contrast, only 25.6 ± 28.0% of ACZ matched with the CoAs.

CONCLUSION

The ACZ reflects LA electrical remodeling and may be a precursor finding of the low voltage zone and not the LA CoAs in patients with atrial fibrillation.

Introduction of a New In-Situ Measurement System for the Study of Touch-Feel Relevant Surface Properties

The touch-feel sensation of product surfaces arouses growing interest in various industry branches. To entangle the underlying physical and material parameters responsible for a specific touch-feel sensation, a new measurement system has been developed. This system aims to record the prime physical interaction parameters at a time, which is considered a necessary prerequisite for a successful physical description of the haptic sensation. The measurement setup enables one to measure the dynamic coefficient of friction, the macroscopic contact area of smooth and rough surfaces, the angle enclosed between the human finger and the soft-touch surfaces and the vibrations induced in the human finger during relative motion at a time. To validate the measurement stand, a test series has been conducted on two soft-touch surfaces of different roughness. While the individual results agree well with the literature, their combination revealed new insights. Finally, the investigation of the haptics of polymer coatings with the presented measuring system should facilitate the design of surfaces with tailor-made touch-feel properties.

How Flat Is the Tibial Osteotomy in Total Knee Arthroplasty?

BACKGROUND

Cementless total knee arthroplasty has been developed to decrease the incidence of failure in younger and more active patients. However, failures are still more common in cementless versus cemented components. It is hypothesized that this is triggered by incomplete bone-tray contact. The present study compares the final contact area of a cementless tray as a function of the initial osteotomy flatness.

METHODS

Eight surgeons prepared 14 cadaveric knees for cementless total knee replacement using standard instrumentation. The topography of each osteotomy was captured with a laser scanner; 3-dimensional computer models of the surfaces were generated. After scanning each tibia, the surgeons implanted cementless tibial trays using a manual impactor. Each tibia was then dissected, embedded in mounting resin, and sectioned. The sectioned blocks were observed under stereomicroscopy to identify points of bone-tray contact which were incorporated into the 3-dimensional models. Maps were then generated illustrating depicting contacting and noncontacting areas.

RESULTS

The mean initial flatness of all specimens was 1.1 ± 0.35 mm. After impaction, 79.4% ± 0.3% of the surface had established bony contact. Of the noncontacting areas, 17.6% were within 0.3 mm of the tray. Only 2.6% of the surface was at distances reported to impede ingrowth. Noncontacting areas were typically located centrally. A trend in decreasing percent contact area with increased flatness tolerance was observed (R² = 0.605).

CONCLUSION

(1) There is an inverse correlation between the flatness of the tibial osteotomy and the percentage of the bony surface in contact with underside of the tibial tray. (2) Almost all tray-tibia contact is generated during implantation through flattening of elevated features on the tibial surface. (3) Gaps between the tray and the tibia are consistently located in the central regions of the osteotomy proximal to the medullary canal.

Bone-Plug Versus Soft Tissue Fixation of Medial Meniscal Allograft Transplants: A Biomechanical Study

BACKGROUND

It is controversial whether soft tissue fixation only and bone-plug techniques for medial meniscal allograft transplantation provide equivalent fixation and restoration of load distribution. Prior studies on this topic did not re-create the clinical situation with use of size-, side-, and compartment-matched meniscal transplants.

HYPOTHESIS

Both techniques will provide equivalent fixation of the meniscal transplant and restore load distribution and contact pressures similar to those of the native knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine fresh-frozen human cadaveric knees underwent mean contact pressure, mean contact area, and peak contact pressure evaluation in 4 medial meniscal testing conditions (native, total meniscectomy, bone-plug fixation, and soft tissue fixation) at 3 flexion angles (0°, 30°, and 60°) using Tekscan sensors under a 700-N axial load.

RESULTS

Medial meniscectomy resulted in significantly decreased contact area and increased contact pressure compared with the native condition at all flexion angles (P < .0001). Compared with the native state, soft tissue fixation demonstrated significantly higher mean contact pressure and lower mean contact area at 0° and 30° of flexion (P < .05), while bone-plug fixation showed no significant difference. There was no significant difference in peak contact pressure between study conditions.

CONCLUSION

Total medial meniscectomy leads to significantly worsened load distribution within the knee. Medial meniscal allograft transplantation can restore load parameters close to those of the native condition. The bone-plug technique demonstrated improved tibiofemoral contact pressures compared with soft tissue fixation.

CLINICAL RELEVANCE

Medial meniscal allograft transplantation with bone-plug fixation is a viable option to restore biomechanics in patients with meniscal deficiency.

A Multiscale Model for Recruitment Aggregation of Platelets by Correlating with In Vitro Results

Introduction

We developed a multiscale model to simulate the dynamics of platelet aggregation by recruitment of unactivated platelets flowing in viscous shear flows by an activated platelet deposited onto a blood vessel wall. This model uses coarse grained molecular dynamics (CGMD) for platelets at the microscale and dissipative particle dynamics (DPD) for the shear flow at the macroscale. Under conditions of relatively low shear, aggregation is mediated by fibrinogen via αIIbβ3 receptors.

Methods

The binding of αIIbβ3 and fibrinogen is modeled by a molecular-level hybrid force field consisting of Morse potential and Hooke law for the nonbonded and bonded interactions, respectively. The force field, parametrized in two different interaction scales, is calculated by correlating with the platelet contact area measured in vitro and the detaching force between αIIbβ3 and fibrinogen.

Results

Using our model, we derived, the relationship between recruitment force and distance between the centers of mass of two platelets, by integrating the molecular-scale inter-platelet interactions during recruitment aggregation in shear flows. Our model indicates that assuming a rigid-platelet model, underestimates the contact area by 89% and the detaching force by 93% as compared to a model that takes into account the platelet deformability leading to a prediction of a significantly lower attachment during recruitment.

Conclusions

The molecular-level predictive capability of our model sheds a light on differences observed between transient and permanent platelet aggregation patterns. The model and simulation framework can be further adapted to simulate initial thrombus formation involving multiple flowing platelets as well as deposition and adhesion onto blood vessels.

Rectification Ratio and Tunneling Decay Coefficient Depend on the Contact Geometry Revealed by in Situ Imaging of the Formation of EGaIn Junctions

This paper describes how the intensive (tunneling decay coefficient β and rectification ratio R) and extensive (current density J) properties of Ag-S(CH₂) _n-1CH₃//GaO _x/EGaIn junctions ( n = 10, 14, 18) and molecular diodes of the form of Ag-S(CH₂)₁₁Fc//GaO _x/EGaIn depend on A_geo, the contact area between the self-assembled monolayer and the cone-shaped EGaIn tip. Large junctions with A_geo ≥ 1000 μm² are unreliable and defects, such as pinholes, dominate the charge transport characteristics. For S(CH₂)₁₁Fc SAMs, R decreases from 130 to unity with increasing A_geo due to an increase in the leakage current (the current flowing across the junction at reverse bias when the diodes block current flow). The value of β decreases from 1.00 ± 0.06 n^-1 to 0.70 ± 0.03 n^-1 with increasing A_geo which also indicates that large junctions suffer from defects. Small junctions with A_geo ≤ 300 μm² are not stable due to the high surface tension of the bulk EGaIn resulting in unstable EGaIn tips. In addition, the contact area for such small junctions is dominated by the rough tip apex reducing the effective contact area and reproducibility significantly. The contact area of very large junctions is dominated by the relatively smooth side walls of the tips. Our findings show that there is an optimum range for the value of A_geo between 300-500 μm² where the electrical properties of the junctions are dominated by molecular effects. In this range of A_geo, the value of J (defined by I/ A_geo where I is the measured current) increases with A_geo until it plateaus for junctions with A_geo > 1000 μm² in agreement with recently reported findings by the Whitesides group. In this regime reproducible measurements of J can be obtained provided A_geo is kept constant.