Spherical Tip Research Articles

Reference Intervals for Bone Impact Microindentation in Healthy Adults: A Multi-Centre International Study

Impact microindentation (IMI) is a novel technique for assessing bone material strength index (BMSi) in vivo, by measuring the depth of a micron-sized, spherical tip into cortical bone that is then indexed to the depth of the tip into a reference material. The aim of this study was to define the reference intervals for men and women by evaluating healthy adults from the United States of America, Europe and Australia. Participants included community-based volunteers and participants drawn from clinical and population-based studies. BMSi was measured on the tibial diaphysis using an OsteoProbe in 479 healthy adults (197 male and 282 female, ages 25 to 98 years) across seven research centres, between 2011 and 2018. Associations between BMSi, age, sex and areal bone mineral density (BMD) were examined following an a posteriori method. Unitless BMSi values ranged from 48 to 101. The mean (± standard deviation) BMSi for men was 84.4 ± 6.9 and for women, 79.0 ± 9.1. Healthy reference intervals for BMSi were identified as 71.0 to 97.9 for men and 59.8 to 95.2 for women. This study provides healthy reference data that can be used to calculate T- and Z-scores for BMSi and assist in determining the utility of BMSi in fracture prediction. These data will be useful for positioning individuals within the population and for identifying those with BMSi at the extremes of the population.

Experimental investigation of effects of indentation depth and probe tip radius on apparent young's modulus of Xenopus laevis oocytes

Throughout their lifespan cells are constantly subjected to mechanical forces. Numerous studies have been conducted to measure mechanical properties of animal cells and understand their effects of the cells’ biological processes. However, the range of the apparent Young's moduli reported in the literature spans three orders of magnitude from 0.1 kPa to 100 kPa, and no clear explanation is given for the source of variation. One of the commonly used experimental techniques to measure material properties at nano- and microscale is nanoindentation. Nanoindentation works by applying a force on a sample via a small probe and recording a force-displacement curve. Probes with different tip shapes and sizes are available. However, there is little guidance on the appropriate choice of probe geometry and size for measurement of properties of animal cells. Eukaryotic cells have a complex structure including a membrane, an actin cortex, a cytoplasm, a nucleus and a cytoskeleton which consists of microfilaments, intermediate filaments and microtubules. These components have different mechanical properties contributing to the overall properties of cells. This work focuses on the effect of tip size and indentation depth on the apparent Young's modulus of Xenopus laevis oocytes measuring approximately 1 mm in diameter. Live cell fluorescent labeling using Lifeact-EGFP and confocal microscopy was used to measure the thickness of the oocyte actin cortex which is expected to have a significant contribution to the cell's stiffness. Apparent mechanical properties were measured using the JPK NanoWizard 4 BioAFM system. Indentations 5, 100 and 400 nm deep using probes with spherical tips of 0.1, 1, and 10 μm radii were performed. Contributions of the membrane and the actin cortex on the overall mechanical properties of the oocytes are analyzed.

Deep learning based nanoindentation method for evaluating mechanical properties of polymers

In this study, a deep learning based nanoindentation method is proposed to reduce the complexities in evaluating mechanical properties of polymers. To uniquely identify the material parameters, a set of nanoindentation simulations are performed by employing spherical and Berkovich tips. A database that represents the material behavior of polymers under nanoindentation is generated for a set of Drucker-Prager model parameters. A deep neural network (DNN) is trained based on optimized hyper-parameters identified through Bayesian hyperparameter tuning process. The performance of trained DNN model is experimentally validated by performing nanoindentation tests on PC and PMMA. From nanoindentation load-depth (P-h) data, the trained DNN model accurately predicts the material parameters, which are in good agreement with those in the literature.

Extremely long nanojet formation from a ballpoint photonic pen

Certain microelements can facilitate light manipulation in the form of an intense electromagnetic beam known as a “photonic nanojet” (PNJ), which is an emerging candidate in the field of spectroscopy, nanolithography, and bio/chemical sensing. However, inherent limitations of the PNJs such as short jet length, focal point, and working length minimize their application areas. Herein, by considering readily available materials and technologies, we report a simple and physically realizable “photonic pen” (PP)-like microstructure to yield extremely long PNJs under plane-wave illumination. Essentially, by semi-immersing a sphere of certain diameter (acting as pen tip) in a barrel material with the width equal to and height 5 times the sphere diameter, a “ballpoint pen”-like microstructure is formed where illuminated light acts as the ink. Finite-difference time-domain analysis shows the use of low refractive index (RI) spherical tips ( n = 1.48 ) with 10 µm diameter, and a high RI SU-8 barrel ( n = 1.62 ) creating a net index difference of Δ n = 0.14 to effectively form PNJs with extremely long jet length, working distance, and full width at half-maximum of over 330 λ (121.6 µm), 319.45 λ (116.6 µm), and 4.22 λ (1.54 µm) respectively, and a figure of merit of ∼ 155 in water environment. S i O 2 / SU- 8 PPs show over ∼ 3 times longer jet length than previous studies. We show that such SU- 8 / SiO 2 PPs with extremely long PNJs can act as epidermal photonic imagers to scan biological tissues such as trilayer human skin to detect melanoma (skin cancer), both in contact and in noncontact mode with efficiency enhancement reaching ∼ 45 % compared to plain microspheres without barrels.

Influence of Methodological Variables on Fracture Strength Test Results of Intact Premolars: an ex-vivo study

The present ex vivo study evaluated the influence of periodontal ligament simulation, load inclination, and tip morphology on fracture strength test results on intact premolars. Forty maxillary premolars were divided into four groups, Group 1, with a 90° load inclination, spherical tip with a diameter of 3mm and periodontal ligament simulation (PDL+); Group 2, with a 90° load inclination, flat tip with a diameter of 2mm, PDL+; Group 3, with a 45° load inclination, flat tip with 2mm of diameter, PDL+; Group 4, 90° load inclination, spherical tip with 3mm diameter, without periodontal ligament reproduction. Interactions among variables and intergroup significance were tested with Wilcoxon rank-sum and Kruskal Wallis’s tests (p≤0.05). Statistically significant differences were found between groups B and C, but they were not found for the others. A 90° load inclination significantly increases fracture strength, while periodontal ligament simulation and tip morphology did not significantly influence the results.

Uma nova abordagem para acesso endodôntico em dentes anteriores - estudo piloto

Abstract Introduction The coronal opening is essential, during endodontic treatment, for direct access to the root canals. Usually, in the anterior teeth, endodontic access is achieved on the palatal/lingual surface, more specifically in the cingulum region. However, the lack of observation for dental positioning can lead to some accidents and complications, such as buccal perforations, causing esthetic damage and compromising the treatment. Objective To evaluate the applicability of a new approach for performing coronal opening in anterior teeth, regarding the wear caused on the tooth crown, and to evaluate the ease of performing the new technique to minimize the risk of perforation. Material and method Ten students (n=10) from the Improvement in Endodontics program participated in the present study. Twenty artificial teeth were used, which were upper, central incisors. Each participant performed two coronal openings. First, with no guidance (Group A - Conventional Technique) and afterward, a new opening, but with guidance with the spherical diamond tip placed parallel to the long axis of the tooth (Group B - Modified Technique). Result The results showed that 90% of the participants considered the Modified Technique as having lower risk of accidents, as well as being easier for locating the pulp chamber. There was a statistical difference both in the measurement of the total area of wear and in the width, while there was no statistical difference in the height. Conclusion Preliminary data collected with the survey were satisfactory for the Modified Technique. Statistically, it showed a favorable difference in relation to the area of wear and the width. However, in height there was no statistical difference.

Pop-in phenomenon at nanoindentation and fracture toughness of two-phase ceramic composites

Material’s resistance to crack propagation corresponds to its fracture toughness. This characteristic can be calculated in laboratory tests, e.g. 3-point bending of notched bars or by indentation test. Spherical, conical, or pyramidal tips can be used during nanoindentation and micro indentation tests, e.g. Vickers, Berkovich, or Cube-Corner tip.The lower level of fracture toughness is a key parameter of ceramic materials and this attribute is not frequently investigated by nanoindentation. If the load force is quite small, an extra increase in penetration depth can occur, which can be described as the pop-in phenomenon.This paper shows the results of nanoindentation tests with the use of cube-corner tips and load levels of 2 mN and 5mN. Five types of ceramic composites Al2O3/ZrO2 with composition ratios of 20, 40, 60, and 80 wt% of Al2O3 content were tested. To estimate the fracture toughness by calculating the crack length force–displacement curves with visible pop-in phenomenon were selected for analysis.

Impact of electrode tip shape on catheter performance in cardiac radiofrequency ablation.

The role of catheter tip shape on the safety and efficacy of radiofrequency (RF) ablation has been overlooked, although differences have been observed in clinical and research fields. The purpose of this study was to analyze the role of electrode tip shape in RF ablation using a computational model. We simulated 108 RF ablations through a realistic 3-dimensional computational model considering 2 clinically used, open-irrigated catheters (spherical and cylindrical tip), varying contact force (CF), blood flow, and irrigation. Lesions are defined by the 50°C isotherm contour and evaluated by means of width, depth, depth at maximum width, and volume. Ablations are deemed as safe, critical (tissue temperature >90°C), and pop (tissue temperature >100°C). Tissue-electrode contact is less for the spherical tip at low CF but the relationship is inverted at high CF. At low CF, the cylindrical tip generates deeper and wider lesions and a 4-fold larger volume. With increasing CF, the lesions generated by the spherical tip become comparable to those generated by the cylindrical tip. The 2 tips feature different safety profiles: CF and power are the main determinants of pops for the spherical tip; power is the main factor for the cylindrical tip; and CF has a marginal effect. The cylindrical tip is more prone to pop generation at higher powers. Saline irrigation and blood flow effect do not depend on tip shape. Tip shape determines the performance of ablation catheters and has a major impact on their safety profile. The cylindrical tip shows more predictable behavior in a wide range of CF values.

AFM Force Measurements to Explore Grain Contacts with Relevance for Planetary Materials

Most small asteroids are defined as “rubble piles” or bodies with zero tensile strength and large bulk porosity. The cohesive forces that hold them together act at the grain scale, and their magnitude is often estimated from similar materials when used in simulations. Improving the accuracy of predictions of asteroid strengths requires suitable laboratory measurements of relevant materials, as well as increasing the availability of materials from sample return. Atomic force microscopy (AFM) is well suited for force measurements relative to particle–particle interactions. In this work, we use AFM force measurements to evaluate the cohesive forces that act between micron-sized grains. We investigate the effect of the sizes of the interacting grains of JSC-1 lunar simulant using three sample sizes (<45, 75–125, and 125–250 μm) and three spherical AFM tip diameters (2 μm, 15 μm, and 45 μm). In all cases, adhesion forces were larger at ambient relative humidity (RH), where the water layer on the surface of the grains is more prominent, creating a larger meniscus between the tip and the grain upon contact. We observed weaker adhesion with larger grain/tip size, which can be attributed to the changing contact area between the samples and the tips. We expect that our approach will pave the way to a better understanding of regolith surface properties such as adhesion and cohesion and provide suitable input for models that can be used to predict the evolution of asteroids and their particle behaviors.

ANALYSIS OF THE METHODS FOR BENDING SMALL-SIZED DISKS ON A RING SUPPORT

A number of methods for testing bending of thin discs on an annular support designed to determine the tensile strength of brittle materials, are considered. The methods differ in the type of a loading indenter (with flat, spherical, or toroidal tips), support devices, and calculation equations for determination of the breaking stress. The results of testing samples on an annular support made of two model materials which differ in the degree of brittleness, i.e., cast iron and graphite, are presented. It is shown that the calculated strength of the tested materials depends on the character of the sample destruction and on the type of bending diagram. Cast iron samples were destructed under a significant plastic deformation (characteristic bending diagram passed through the maximum), and the tensile strength of the samples corresponded to the compressive strength of the material being several times higher than the tensile strength of the material. Graphite samples underwent brittle fracture (within the linear section of the bending diagram), and the calculated strength value was comparable to the tensile strength of the material. A conclusion is made that the use of the test method of thin disk samples on an annular support for determination of the tensile strength of the material is substantiated only in the case of absolutely brittle fracture of samples with a bending diagram similar to the fracture diagram of graphite samples. Disk samples made of aluminum oxide obtained by electro-pulse sintering were tested using two methods (with flat and spherical tips). In both cases, the bending diagram of aluminum oxide samples was similar to that of graphite samples, i.e., their destruction occurred at the initial linear section of the diagram and was absolutely brittle. The results of comparative testing of the samples made of aluminum oxide, taking into account the results of testing samples made of model materials (cast iron and graphite), showed that tests on the annular support of disks using a flat-tipped indenter are the most grounded. The samples should be made of brittle materials having a linear bending diagram up to the sample destruction.

Highly Sensitive Zinc Oxide Fiber-Optic Biosensor for the Detection of CD44 Protein

Currently, significant progress is being made in the prevention, treatment and prognosis of many types of cancer, using biological markers to assess current physiological processes in the body, including risk assessment, differential diagnosis, screening, treatment determination and monitoring of disease progression. The interaction of protein coding gene CD44 with the corresponding ligands promotes the processes of invasion and migration in metastases. The study of new and rapid methods for the quantitative determination of the CD44 protein is essential for timely diagnosis and therapy. Current methods for detecting this protein use labeled assay reagents and are time consuming. In this paper, a fiber-optic biosensor with a spherical tip coated with a thin layer of zinc oxide (ZnO) with a thickness of 100 nm, deposited using a low-cost sol-gel method, is developed to measure the CD44 protein in the range from 100 aM to 100 nM. This sensor is easy to manufacture, has a good response to the protein change with detection limit of 0.8 fM, and has high sensitivity to the changes in the refractive index (RI) of the environment. In addition, this work demonstrates the possibility of achieving sensor regeneration without damage to the functionalized surface. The sensitivity of the obtained sensor was tested in relation to the concentration of the control protein, as well as without antibodies-CD44.

Nanomechanical Mapping of Hard Tissues by Atomic Force Microscopy: An Application to Cortical Bone.

Force mapping of biological tissues via atomic force microscopy (AFM) probes the mechanical properties of samples within a given topography, revealing the interplay between tissue organization and nanometer-level composition. Despite considerable attention to soft biological samples, constructing elasticity maps on hard tissues is not routine for standard AFM equipment due to the difficulty of interpreting nanoindentation data in light of the available models of surface deformation. To tackle this issue, we proposed a protocol to construct elasticity maps of surfaces up to several GPa in moduli by AFM nanoindentation using standard experimental conditions (air operation, nanometrically sharp spherical tips, and cantilever stiffness below 30 N/m). We showed how to process both elastic and inelastic sample deformations simultaneously and independently and quantify the degree of elasticity of the sample to decide which regime is more suitable for moduli calculation. Afterwards, we used the frequency distributions of Young's moduli to quantitatively assess differences between sample regions different for structure and composition, and to evaluate the presence of mechanical inhomogeneities. We tested our method on histological sections of sheep cortical bone, measuring the mechanical response of different osseous districts, and mapped the surface down to the single collagen fibril level.

Multi-scale constitutive model of human trabecular bone

The present study aims to formulate a new multiscale constitutive model of human trabecular bone. The trabecular bone was modelled as a nonlinear viscoelastic material. The viscoelastic effects of single trabeculae were considered by means of a hereditary integral in which stress depends on time and strain, while the elastic response was described by the hyperelastic Mooney–Rivlin model. The cuboid bone sample was extracted from the femoral head during the hip replacement surgery. The material constants in the constitutive equation were identified based on the stress relaxation test performed on the cuboid sample and the microindentation tests performed on trabeculae using the curve-fitting procedure. The microindentation tests were performed using a spherical tip instead of Vickers or Berkovich tip to minimize plastic effects during trabecular deformation. In order to validate formulated constitutive model, results from a FE simulation of stress relaxation test and uniaxial compression test were compared to the results of the corresponding experiments conducted on a macroscopic bone sample. Good agreement was observed between numerical and experimental results. The viscoelastic behaviour predicted by the proposed constitutive equation corresponds well to the response of human trabecular bone under various types of load conditions. This demonstrates the high ability of our constitutive model to simulate the behaviour of trabecular bone on a micro- and macroscopic scale. Thus, we conclude that the model, which was formulated for a single trabecula, can be successfully applied to simulate mechanical behaviour of the tissue in a macroscale.

Thrust characteristics of a truncated Laval nozzle with a bell-shaped tip

This paper presents the results of a thrust performance study of an unconventionally shaped supersonic nozzle in the form of a truncated Laval nozzle with a bell-shaped tip. This nozzle shape may be used in the development of compact layouts of multistage rockets. The study was carried out using the ANSYS software package in a 3D formulation. The methodological approaches to the numerical calculation of a complex separated gas flow used in this study were verified in a previous study of the flow pattern in similar nozzle. Some results of exact calculations were compared with the results of experimental studies carried out at the Institute of Technical mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine for a model of a similar truncated nozzle with a bell-shaped tip blown with a cold air. This study detailed the features of the separated gas flow in a spherical tip connected (at the corner point) to a truncated supersonic Laval nozzle of conical shape. It was found that the pattern of the separated flow in the tip depends on the nozzle flow expansion degree (nozzle inlet pressure). At a relatively low nozzle inlet pressure, a developed separation zone is observed in the nozzle tip (between the jet boundary and the nozzle wall) with a subsonic flow from the external environment, which forms an almost constant static pressure from the tip inlet cross-section to the tip exit. At a nozzle inlet pressure at which the free boundary of the jet flowing from the truncated nozzle adjoins the nozzle wall, the static pressure in the tip varies almost linearly along the tip length from the corner point with the minimum pressure to the tip exit. The dependence of the thrust of a tipped nozzle on the nozzle inlet pressure is nonlinear. As the pressure upstream of the nozzle increases (or the ambient pressure decreases), the effect of the external environment on the tipped-nozzle thrust diminishes. It is shown that under "terrestrial conditions" the thrust of a truncated nozzle with a tip exceeds the thrust of a profiled nozzle with the same geometric expansion degree (due to the atmosphere “entering” the tip). Under "vacuum” conditions, the former is 8% less than the latter.

Determination of peak ordering in the CrCoNi medium-entropy alloy via nanoindentation

Local chemical ordering (LCO) in the CrCoNi medium-entropy alloy was investigated by transmission electron microscopy (TEM) after different annealing treatments and their corresponding mechanical properties by bulk tensile tests and nanoindentation. A cold-rolled alloy was annealed at 1000°C for 0.5 h followed by ice water quenching and then aged at a number of different temperatures (600°C, 700°C, 800°C, 900°C, and 1000°C) under vacuum for 240 h to generate different degrees of chemical ordering. A splat-quenched sample rapidly cooled from the liquid phase was also examined. While bulk mechanical properties did not vary among samples with equivalent grain sizes, nanoindentation tests revealed notable differences. As indicated by the load at first pop-in using a Berkovich tip or the indentation yield strength via continuous stiffness measurements using a 10 μm spherical tip, the nanoindentation tests revealed that the stress for onset of plasticity during indentation varied with heat treatment and peaked in the 900°C aged sample. Energy-filtered TEM characterization indicated the presence of ordering in all specimens, with a higher degree of LCO in the aged samples relative to the splat-quenched and 1000°C-quenched samples. The evolution of LCO during aging was determined to occur on the time scale similar to those of bulk diffusion. The difference in nanoindentation strength was attributed to the difference in dislocation nucleation barriers imposed by different degrees of LCO.

Indentation and puncture of double-network tough hydrogel membranes

Hydrogel membranes are commonly used in soft devices and soft robotics, which are prone to puncture failure when penetrated by external spiny objects. In this work, the indentation and puncture of double-network hydrogel (DNH) membranes are experimentally and theoretically investigated by using cylindrical indenters with both flat and spherical tips of various sizes. It is found that when a hydrogel membrane contacts with the side surface of a cylindrical indenter with a large area, the puncture force increases dramatically due to the friction force from the side contact, leading to the critical puncture force insensitive to the geometry of indenter tip. In the theory, the stretch field of the DNH membrane in the indentation is obtained and the contribution of friction force to the puncture force on the indenter is quantified. This work reveals the puncture mechanism of hydrogel membranes under the influence of friction, especially for that from the side surface of indenter.

Friction and wear of AISI 304 by the SiC ball and its monitoring via Barkhausen noise emission

This study deals with the friction and wear of AISI 304 austenitic steel by the SiC ball. The surface state in the affected region was investigated as a function of the time duration of the friction process due to a single ceramic spherical SiC ball tip in a reversible linear motion under a load of 10 N (ball-on-flat test method). Only minor alterations in the loaded region could be found in the initial phase of friction, which was followed by an abrupt increase in the size of the wear track produced. Wear tracks were investigated in terms of their size, residual stress state, phase composition, delamination, and chemistry. Due to the phase transformation from austenite to martensite, the magnetic Barkhausen noise technique was also employed, and its sensitivity to alterations arising during friction and wear was investigated. It was found that magnetic Barkhausen noise was sensitive to the volume fraction of strain-induced martensite. Moreover, pronounced surface oxidation could be detected in the region of surface delamination, in contrast to the initial phase of friction.

Gas flow in a truncated Laval nozzle with a bell-shaped tip

Flow in a truncated supersonic Laval nozzle with a bell-shaped tip (“bell”) is investigated. This nozzle configuration can be used in tight layouts of multistage rockets of short length with improved energy-mass characteristics. Similar types of nozzles were developed at the Institute of Technical Mechanics of the National Academy of Sciences and the State Space Agency of Ukraine in the 1990s. Using approximate methods, the parameters of variously configured truncated nozzles were calculated, and their models were made. Some of the models were blown with cold air, and their characteristics were measured. Shadow patterns of gas flow downstream of the nozzle and soot-oil patterns of streamlines on the nozzle wall were obtained. These results were used in the formulation of this work. In this work, a numerical study with the ANSYS package was carried out for gas flow in a truncated Laval nozzle with a spherical tip. For this nozzle configuration, its model was blown with cold air. The calculated results were verified by comparing the velocity distribution in the gas flow downstream of the nozzle exit with the experimental shadow patterns. An additional confirmation of the correctness of the calculated results was a comparison of the flow downstream of a streamline-profiled Laval nozzle with the underexpanded flow pattern downstream of the nozzle exit in the first “cask” (up to the Mach disk) studied in detail. The same initial data and initial conditions that give the best results in terms of verifiability were chosen in both cases. The study of flow in a truncated supersonic nozzle showed the following results. Downstream of the corner exit point of the truncated section of a Laval nozzle, flow separation is observed where the gas flow enters the “bell”. The separation is retained as the pressure upstream of the nozzle increases up to a certain critical (for a given tip type) value of the underexpansion ratio, after which (with a further increase in the underexpansion ratio) the flow attaches to the nozzle wall and remains attached with a further increase in the pressure upstream of the nozzle. The impulse response of a truncated nozzle with a bell-shaped tip is lower than that of a streamline-profiled Laval nozzle of the same geometric expansion ratio.

Deformation behaviour of ion-irradiated FeCr: A nanoindentation study

Understanding the mechanisms of plasticity in structural steels is essential for the operation of next-generation fusion reactors. This work on the deformation behaviour of FeCr, focusses on distinguishing the nucleation of dislocations to initiate plasticity, from their propagation through the material. Fe3Cr, Fe5Cr, and Fe10Cr were irradiated with 20 MeV Fe3+ ions at room temperature to doses of 0.008 dpa and 0.08 dpa. Nanoindentation was then carried out with Berkovich and spherical indenter tips. Our results show that the nucleation of dislocations is mainly from pre-existing sources, which are not significantly affected by the presence of irradiation defects or Cr%. Yield strength, an indicator of dislocation mobility, increases with irradiation damage and Cr content, while work hardening capacity decreases mainly due to irradiation defects. The synergistic effects of Cr and irradiation damage in FeCr appear to be more important for the propagation of dislocations than for their nucleation.Graphical abstract

Investigation of the adhesive and abrasive wear mechanisms at the atomic scale using molecular dynamic simulations

In this study, the effect of adhesion on material removal is numerically investigated at the nanoscale level. In this regard, Molecular Dynamics (MD) simulations are conducted to distinguish the contribution of adhesive and abrasive wear mechanisms during a scratching process in terms of the degree of interfacial adhesion and scratching depth. The numerical model simulates the scratching of a flat workpiece made of a single crystalline aluminum using a rigid conical indenter with a blunted spherical tip at four different indentation depths (i.e. 0, 3, 7, and 10 Å). The classical Leonard-Jones interatomic potential is used to mimic the degree of adhesion by varying the adhesion parameter between 5–70% of the aluminum bonding energy. It is shown that, at shallow scratching depths, the contribution of adhesive work to the frictional work is much larger than the ploughing work. On the contrary, the ratio of adhesive to ploughing work reduces by increasing the scratching depth.