Establishing finite element model credibility of a pedicle screw system under compression-bending: An end-to-end example of the ASME V&V 40 standard.

Computational modeling and simulation (CM&S) is a key tool in medical device design, development, and regulatory approval. For example, finite element analysis (FEA) is widely used to understand the mechanical integrity and durability of orthopaedic implants. The ASME V&V 40 standard and supporting FDA guidance provide a framework for establishing model credibility, enabling deeper reliance on CM&S throughout the total product lifecycle. Examples of how to apply the principles outlined in the ASME V&V 40 standard are important to facilitating greater adoption by the medical device community, but few published examples are available that demonstrate best practices. Therefore, this paper outlines an end-to-end (E2E) example of the ASME V&V 40 standard applied to an orthopaedic implant. The objective of this study was to illustrate how to establish the credibility of a computational model intended for use as part of regulatory evaluation. In particular, this study focused on whether a design change to a spinal pedicle screw construct (specifically, the addition of a cannulation to an existing non-cannulated pedicle screw) would compromise the rod-screw construct mechanical performance. This question of interest (?OI) was addressed by establishing model credibility requirements according to the ASME V&V 40 standard. Experimental testing to support model validation was performed using spinal rods and non-cannulated pedicle screw constructs made with medical grade titanium (Ti-6Al-4V ELI). FEA replicating the experimental tests was performed by three independent modelers and validated through comparisons of common mechanical properties such as stiffness and yield force. The validated model was then used to simulate F1717 compression-bending testing on the new cannulated pedicle screw design to answer the ?OI, without performing any additional experimental testing. This E2E example provides a realistic scenario for the application of the ASME V&V 40 standard to orthopedic medical device applications.

Taring the scales: Weight-of-evidence framework for biocompatibility evaluations.

ISO 10993-1:2018 describes evaluating the biocompatibility profile of a medical device from a risk-based approach. This standard details the battery of information that should be considered within the assessment of a device, including raw material composition data, manufacturing processes, and endpoint testing. The ISO 10993/18562 series requires worst-case assumptions and exposure scenarios to be used in the evaluation, which may result in an over-estimation of patient safety risk. Currently, biocompatibility assessments evaluate each data set independently, and the consequence of this individualized assessment of exaggerated inputs is potential false alarms regarding patient safety. To evaluate these safety concerns, the ISO standards indicate that professional judgement should be used to estimate patient risk but does not provide guidance on incorporating a holistic review of the data into the risk assessment. Recalibrating these worst-case data to evaluate them in a weight-of-evidence (WoE) approach may provide a more realistic data set to determine actual patient risk. This proposed WoE framework combines understanding data applicability with a method for gauging the strength of data that can provide additional support for the final safety conclusion. Using a WoE framework will allow risk assessors to contextualize the data and utilize it to comprehensively estimate patient safety.

Characterization of performance and disinfection resilience of nonwoven filter materials for use in 3D-printed N95 respirators.

The COVID-19 pandemic has caused a high demand for respiratory protection among health care workers in hospitals, especially surgical N95 filtering facepiece respirators (FFRs). To aid in alleviating that demand, a survey of commercially available filter media was conducted to determine whether any could serve as a substitute for an N95 FFR while held in a 3D-printed mask (Stopgap Surgical Face Mask from the NIH 3D Print Exchange). Fourteen filter media types and eight combinations were evaluated for filtration efficiency, breathing resistance (pressure drop), and liquid penetration. Additional testing was conducted to evaluate two filter media disinfection methods in the event that the filters were reused in a hospital setting. Efficiency testing was conducted in accordance with the procedures established for approving an N95 FFR. One apparatus used a filter-holding device and another apparatus employed a manikin head to which the 3D-printed mask could be sealed. The filter media and combinations exhibited collection efficiencies varied between 3.9% and 98.8% when tested with a face velocity comparable to that of a standard N95 FFR at the 85 L min-1 used in the approval procedure. Breathing resistance varied between 10.8 to >637 Pa (1.1 to > 65 mm H2O). When applied to the 3D-printed mask efficiency decreased by an average of 13% and breathing resistance increased 4-fold as a result of the smaller surface area of the filter media when held in that mask compared to that of an N95 FFR. Disinfection by dry heat, even after 25 cycles, did not significantly affect filter efficiency and reduced viral infectivity by > 99.9%. However, 10 cycles of 59% vaporized H2O2 significantly (p < 0.001) reduced filter efficiency of the media tested. Several commercially available filter media were found to be potential replacements for the media used to construct the typical cup-like N95 FFR. However, their use in the 3D-printed mask demonstrated reduced efficiency and increased breathing resistance at 85 L min-1.

Histology Strategies for Medical Implants and Interventional Device Studies.

Histology of medical devices poses a variety of unique challenges. Comprehensive histologic assessment of medical devices often requires spatial context and high-quality retention of the device-tissue interface. However, the composition of many medical devices is often not amenable to traditional paraffin embedding and thus alternative specialized methodologies such as hard resin embedding must be used. Hard resin embedding requires specialized laboratory technical expertise and equipment, and the fixation techniques and resin composition used markedly impact the feasibility of immunohistochemistry. For the continuity of spatial context during histologic evaluation, additional imaging methods such as macrophotography, radiography, micro-Computerized Tomography (microCT), or magnetic resonance imaging (MRI) can be used to guide sectioning and to complement histologic findings. Although standardized approaches are scarce for medical devices, important considerations specific to medical device histology are discussed, including general specimen preparation, special considerations for devices by organ system, and the challenges of immunohistochemistry. Histologic preparation of medical devices must be thoughtful, thorough, and tailored to achieve optimal histologic outcomes for complex, valuable, and often limited implant specimens.

Medical Device Histology and Pathology: A Horse of a Different Color.

Medical devices comprise a wide variety of therapeutic tools aimed at modulating or restoring organ function. Devices may be implanted or activated temporally or permanently, and are used to deliver a wide range of therapies such as drugs, electrical stimulation, laser, thermal energy, offer mechanical support, and restore sensory functions. Technological advancements allow improvement and development of devices at a rapid pace. This special issue of Toxicologic Pathology addresses a need for more publications focused on pathology evaluation of medical devices in preclinical studies and highlights fundamental approaches through practical examples bringing into perspective the essential role of pathologists in this field.

Compilation of International Standards and Regulatory Guidance Documents for Evaluation of Biomaterials, Medical Devices, and 3-D Printed and Regenerative Medicine Products.

The development of biomaterials, medical device components, finished medical products, and 3-D printed and regenerative medicine products is governed by a variety of international and country-specific standards and guidelines. Of greatest importance to planning, executing, and reporting biocompatibility, safety and efficacy studies for most biomaterials and medical components or products are the International Organization for Standardization guidelines, U.S. Pharmacopeial Convention, ASTM International, and Conformité Européenne (European Conformity) marking. The International Medical Device Regulators Forum publishes harmonized standards similar to the International Council for Harmonization. Good Laboratory Practices are applicable and guidance documents for the development of drugs and biologics can also be relevant to biomaterials, medical device components, and medical products and more recently to products produced by 3-D printing or additive manufacturing. Regenerative products may have medical device-based scaffolding and may be treated as biologics, reflecting the cell and tissue components. This compilation of international standards and guidelines provides toxicologic pathologists, toxicologists, bioengineers, and allied professionals with an overview of and source for important regulatory documents that may apply to the nonclinical development of their products.

Material failure in dynamic spine implants: are the standardized implant tests before market launch sufficient?

PURPOSE: International Standards Organization (ISO) 12189 and American Society for Testing and Materials F2624 are two standard material specification and test methods for spinal implant devices. The aim of this study was to assess whether the existing and required tests before market launch are sufficient. METHODS: In three prospective studies, patients were treated due to degenerative disease of the lumbar spine or spondylolisthesis with lumbar interbody fusion and dynamic stabilization of the cranial adjacent level. The CD HORIZON BalanC rod and S4 Dynamic rod were implanted in 45 and 11 patients, respectively. RESULTS: A fatigue fracture of the material of the topping off system has been found in five cases (11%) for the group fitted with the CD HORIZON BalanC rod. In the group using the S4 Dynamic rod group, a material failure of the dynamic part was demonstrated in seven patients (64%). All three studies were interrupted due to these results, and a report to the Federal Institute for Drugs and Medical Devices was generated. CONCLUSION: Spinal implants have to be checked by a notified body before market launch. The notified body verifies whether the implants fulfil the requirements of the current standards. These declared studies suggest that the current standards for the testing of load bearing capacity and stand ability of dynamic spine implants might be insufficient. Revised standards depicting sufficient deformation and load pattern have to be developed and counted as a requirement for the market launch of an implant. These slides can be retrieved under Electronic Supplementary Material.

Glove permeation of chemicals: The state of the art of current practice, Part 1: Basics and the permeation standards.

Skin exposure to chemicals in the workplace environment is a major concern, the hands being the major exposure sites. Employers purchase gloves that have permeation data generated from permeation "standards" of the American Society for Testing and Materials International (ASTM International), European Committee for Standardization (EN), and the International Organization for Standardization (ISO) that test pieces of glove material and allow a user-defined temperature. The relevant standards based on continuous contact are ASTM F739, ASTM D6978, EN 374, EN 16523, and ISO 6529. The aim was to analyze the current state of the scientific literature on glove permeation in the 21st century up to December 2018. The introduction sets out the background, objectives and rationale of the review and its methodology followed by presentation of basic glove chemical resistance terms and Fick's first law of diffusion, the details of the major permeation standards, their comparison, their critique, their research gaps; the scientific literature on whole glove permeation, and final conclusions. The major recommendation was to harmonize all the permeation standards and perform them at realistic work conditions, especially temperature. The whole glove system would be most useful for testing the thinnest gloves.

Toxicologic Pathology Forum Opinion Paper: Considerations for Toxicologic Pathologists Evaluating the Safety of Biomaterials and Finished Medical Devices.

Safety ("biocompatibility") assessment of medical devices has evolved along a different path than that of drugs, being historically governed more by the considerations and needs of engineers rather than chemists and biologists. As a result, the involvement of veterinary pathologists has been much more limited-almost entirely to evaluating tissue responses in tissues in direct contact with implanted devices. As devices have become more complex in composition, structure, placement, and use, concerns as to adverse systemic responses in patients have called for more comprehensive and thoughtful evaluations of effects throughout the body. Further complexities arise from the increasing marriage of devices and drug/biologic therapeutics to achieve either better dose control and, specifically, in delivery to target organs/tissues or better tolerance of the body to medical devices (i.e., minimization of the foreign body response). The challenge to pathologists is to integrate in new technologies (such as in vivo imaging and immunology) and ways of viewing interactions with patient bodies. To fail to do so will allow the methods and standards for medical device safety evaluation to be based on chemical analysis and then the limited details inherent in literature-based risk assessments.

Effect of ageing on the calibration of ballistic gelatin.

PURPOSE: Ballistic gelatin is commonly used as a validated surrogate for soft tissue during terminal ballistic testing. However, the effect of a delay between production and testing of a gelatin mould remains unknown. The aim of this study was to determine any potential effects of ageing on ballistic gelatin. METHODS: Depth of penetration (DoP) of 4.5 mm spherical fragment simulating projectiles was ascertained using mixtures of 10%, 11.25% and 20% Type A 250 Bloom ballistic gelatin. Testing was performed daily for 5 days using velocities between 75 and 210 m/s. DoP at day 5 was statistically compared with day 1, and net mass change was recorded daily. RESULTS: No significant difference was found for DoP observed with time in any of the samples (P>0.05). Spearman correlation was excellent in all moulds. The moulds with known standard calibrations remained in calibration throughout the study period. Mass loss of less than 1% was noted in all samples. CONCLUSION: Mass loss was the only quantifiable measure of changes in the blocks with time, but did not correlate with any changes in DoP. This may provide reassurance when undertaking such testing that an inadvertent delay will not significantly alter the penetration properties of the mould. Future research is recommended to determine any potential effect on the mechanical properties of gelatin at higher velocity impacts and whether the calibration corresponds to an adequate simulation under such conditions.

Development of Standardized Material Testing Protocols for Prosthetic Liners.

A set of protocols was created to characterize prosthetic liners across six clinically relevant material properties. Properties included compressive elasticity, shear elasticity, tensile elasticity, volumetric elasticity, coefficient of friction (CoF), and thermal conductivity. Eighteen prosthetic liners representing the diverse range of commercial products were evaluated to create test procedures that maximized repeatability, minimized error, and provided clinically meaningful results. Shear and tensile elasticity test designs were augmented with finite element analysis (FEA) to optimize specimen geometries. Results showed that because of the wide range of available liner products, the compressive elasticity and tensile elasticity tests required two test maxima; samples were tested until they met either a strain-based or a stress-based maximum, whichever was reached first. The shear and tensile elasticity tests required that no cyclic conditioning be conducted because of limited endurance of the mounting adhesive with some liner materials. The coefficient of friction test was based on dynamic coefficient of friction, as it proved to be a more reliable measurement than static coefficient of friction. The volumetric elasticity test required that air be released beneath samples in the test chamber before testing. The thermal conductivity test best reflected the clinical environment when thermal grease was omitted and when liner samples were placed under pressure consistent with load bearing conditions. The developed procedures provide a standardized approach for evaluating liner products in the prosthetics industry. Test results can be used to improve clinical selection of liners for individual patients and guide development of new liner products.

Contact stresses, pressure and area in a fixed-bearing total ankle replacement: a finite element analysis.

BACKGROUND: Mobile-bearing ankle implants with good clinical results continued to increase the popularity of total ankle arthroplasty to address endstage ankle osteoarthritis preserving joint movement. Alternative solutions used fixed-bearing designs, which increase stability and reduce the risk of bearing dislocation, but with a theoretical increase of contact stresses leading to a higher polyethylene wear. The purpose of this study was to investigate the contact stresses, pressure and area in the polyethylene component of a new total ankle replacement with a fixed-bearing design, using 3D finite element analysis. METHODS: A three-dimensional finite element model of the Zimmer Trabecular Metal Total Ankle was developed and assembled based on computed tomography images. Three different sizes of the polyethylene insert were modeled, and a finite element analysis was conducted to investigate the contact pressure, the von Mises stresses and the contact area of the polyethylene component during the stance phase of the gait cycle. RESULTS: The peak value of pressure was found in the anterior region of the articulating surface, where it reached 19.8 MPa at 40% of the gait cycle. The average contact pressure during the stance phase was 6.9 MPa. The maximum von Mises stress of 14.1 MPa was reached at 40% of the gait cycle in the anterior section. In the central section, the maximum von Mises stress of 10.8 MPa was reached at 37% of the gait cycle, whereas in the posterior section the maximum stress of 5.4 MPa was reached at the end of the stance phase. DISCUSSION: The new fixed-bearing total ankle replacement showed a safe mechanical behavior and many clinical advantages. However, advanced models to quantitatively estimate the wear are need. CONCLUSION: To the light of the clinical advantages, we conclude that the presented prosthesis is a good alternative to the other products present in the market.

A newly developed tracheal tube offering 'pressurised sealing' outperforms currently available tubes in preventing cuff leakage: A benchtop study.

BACKGROUND: No currently used tracheal tube offers full protection against aspiration of oropharyngeal secretions into the lower airways. OBJECTIVE: We developed a tracheal tube equipped with two polyvinylchloride (PVC) cuffs with a supplementary port opening between the cuffs through which a continuous positive pressure of 5 cmH2O is provided [double-cuffed PVC (PVCdc)]. We compared this PVCdc with four different cuff types (cylindrical PVC, conical PVC, cylindrical polyurethane and conical polyurethane). DESIGN: A comparison study using an in-vitro benchtop model of an artificial rigid trachea. INTERVENTIONS: Tracheal tubes were placed in the artificial trachea. Both cuffs were kept inflated at 25 cmH2O. Total 3 ml dyed water was placed above the cuff and leakage recorded under static and dynamic [5 cmH2O positive end-expiratory pressure (PEEP) alone or positive pressure ventilation plus 5 cmH2O PEEP] conditions. At the end of the dynamic experiments, PEEP was zeroed (PEEP alone) or the tracheal tubes were disconnected from the ventilator (positive pressure ventilation plus PEEP). RESULTS: In the static model, leakage flows [medians (range)] were 9.8 (6.2 to 20) for the cylindrical PVC, 1.3 (0.2 to 3.8) for the conical PVC, 0.03 (0.007 to 0.1) for the cylindrical polyurethane, 0.04 (0.003 to 0.2) for the conical polyurethane and 0.0 (0.0 to 0.0) ml min for the PVCdc cuff (P < 0.001, PVCdc vs. all other cuffs). In the dynamic setting, no leakage was detected for up to 60 min with any of the cuffs studied. Loss of PEEP or tracheal tube disconnection resulted in dye inflow alongside all cuffs except for the PVCdc (P < 0.001, PVCdc vs. all other cuffs). CONCLUSION: A 'pressure seal' incorporated in a double-cuffed tracheal tube prevented fluid passage into the lower airways. Clinically, this may translate into absence of inflow of bacteriologically contaminated secretions into the lungs and thus a lower incidence of ventilator-associated infection.

Stability determinants of bone-borne force-transmitting components in three RME hybrid expanders-an in vitro study.

BACKGROUND: The aim was to test which component [wire arm, connecting abutment attachment, and orthodontic mini-implant (OMI)] of the force-transmitting system (FTS) in the anterior palate of three commonly used hybrid expanders (HEs; WILMES-HE, LUDWIG-HE, and WINSAUER-HE) deforms under increasing load. MATERIALS AND METHODS: Crude single and double wire arms were tested individually. Non-opening of the maxillae halves was simulated in artificial bone blocks with single wire and double wire FTS specimens. OMIs were inserted 8mm and underwent 6mm of continuous static lateral loading. Deformation angles were measured (X-ray, n = 6) at 0, 3 and 6mm feed. OMIs and abutments were scan electron microscope (SEM) evaluated. RESULTS: After 1.0mm of loading, the single wire arm of all FTS deformed between 63.4 (16.5) N and 76.2 (18.4) N, and the double wire arm of reinforced FTS (wires positioned 'side by side') deformed after 1.0mm between 110.0 (18.4) N and 134.8 (22.3) N. The crude single wire resisted 89 (5.1) N until plastic deformation, whereas the crude double wire positioned 'on top of each other' resisted 438 (21.3) N. At 6mm loading, the reinforced WINSAUER-HE FTS withstood a maximum load of 320.9 (31.1) N and the reinforced LUDWIG-HE FTS 19% less, both under great deformation of double wires and OMIs. The screw-fixated WILMES-HE FTS abutment attachment (overlapping OMI head 34%) detached around 250N. The bonded WINSAUER-HE and LUDWIG-HE abutment attachments did not detach. Nor did the modified bonded plus the modified screw-fixated WILMES-HE abutment attachment when overlapping 100%. CONCLUSION: Early OMI and single wire arm deformation in HEs are crucial for unsuccessful RME in more mature maxillae. Double wire arms should be obligatory. OMIs with inner diameter greater 1.36mm are recommended. One hundred per cent overlapping abutment attachments do not detach.

[Cytotoxicity in vitro as the principal parameter for evaluation of biocompatibility of medical devices].

According to the Polish Ministry of Health decree, the medical devices and all raw materials used for their manufacturing are in force to be compatible with biological tissues, cells and body fluids regarding its clinical use. It is defined as biocompatibility. The scope of the methods proposed in the norm PN-EN ISO 10993-1 makes possible to get full preclinical characteristics of the medical device and allows to form the opinion about safety of it to the patients after its marketing. The test directed as the principal to make, independently on characteristics, kind, contact duration and clinical use of the device is cytotoxicity in vitro. This test defines the impact of the device on the cells through microscopic evaluation or through activities of the enzymes specific for living cells. Toxicity of the material to the cells may be reflected in: change of single cells or whole cell culture morphology, change of cellular metabolic activity, DNA damage or disadvantage of cell proliferation. Biocompatibility of the medical devices is one of the main elements considered in a risk management process at the stage of designing and manufacturing as well of the raw materials as the final product and the critical point in this matter is sterilization.

A New Miniature Respirable Sampler for In-mask Sampling: Part 2-Tests Performed Inside the Mask.

This paper is the second in a series of two describing the performance of a miniature and low-weight respirable sampler designed to fit inside filtering facepiece (FFP) and half-mask type respirators. The first paper described the design of the miniature sampler and evaluated the particle and collection performance of the miniature sampler. This paper assesses its comparability with the traditional inward leakage measurement technique, and its safe use. Simultaneous mass measurements of a respirable sodium chloride aerosol were taken inside a total inward leakage chamber by a miniature sampler and by sodium flame photometry. Direct side-by-side comparison of the two methods yielded excellent correlation (R 2 = 0.99), as did comparison when sampling from inside four different masks when worn by a breathing Sheffield dummy head. In addition, comparison tests were carried out using three models of FFP worn by human volunteers both with and without the miniature sampler, in order to test whether or not the presence of the miniature sampler negatively affected the protection offered. The difference between the tests carried out with the miniature sampler and without the miniature sampler was not statistically significant (P = 0.3). In all cases, the masks performed within their protection class, whether the miniature sampler was fitted or not. We therefore conclude that the miniature sampler does not significantly affect the protection offered by the masks. The miniature sampler may prove a viable option for in-mask measurements of respirable dust where low air concentrations of hazardous material are expected.

Efficiency of five chemical protective clothing materials against nano and submicron aerosols when submitted to mechanical deformations.

Due to their potential toxicity, the use of nanoparticles in the workplace is a growing concern. Some studies indicate that nanoparticles can penetrate the skin and lead to adverse health effects. Since chemical protective clothing is the last barrier to protect the skin, this study aims to better understand nanoparticle penetration behaviour in dermal protective clothing under mechanical deformation. For this purpose, five of the most common types of fabrics used in protective clothing, one woven and four nonwoven, were chosen and submitted to different simulated exposure conditions. They were tested against polydispersed NaCl aerosols having an electrical-mobility diameter between 14 and 400 nm. A bench-scale exposure setup and a sampling protocol was developed to measure the level of penetration of the aerosols through the material samples of disposable coveralls and lab coat, while subjecting them to mechanical deformations to simulate the conditions of usage in the workplace. Particle size distribution of the aerosol was determined upstream and downstream using a scanning mobility particle sizer (SMPS). The measured efficiencies demonstrated that the performances of nonwoven materials were similar. Three nonwovens had efficiencies above 99%, while the woven fabric was by far, the least effective. Moreover, the results established that mechanical deformations, as simulated for this study, did not have a significant effect on the fabrics' efficiencies.

Interferometric Detection of Single Gold Nanoparticles Calibrated against TEM Size Distributions.

Single nanoparticle analysis: An interferometric optical approach calibrates sizes of gold nanoparticles (AuNPs) from the interference intensities by calibrating their interferometric signals against the corresponding transmission electron microscopy measurements. This method is used to investigate whether size affects the diffusion behavior of AuNPs conjugated to supported lipid bilayer membranes and to multiplex the simultaneous detection of three different AuNP labels.

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants.

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Effect of punch and orifice base sizes in different push-out test setups: stress distribution analysis.

PURPOSE: This study evaluated the influence of punch and base orifice diameters on push-out test results by means of finite element analysis (FEA). MATERIALS AND METHODS: FEA was performed using 3D models of the push-out test with 3 base orifice diameters (2.5, 3.0, and 3.5 mm) and 3 punch diameters (0.5, 1.0, and 1.5 mm) using MARC/MENTAT (MSC.Software). The image of a cervical slice from a root restored with a fiberglass post was used to construct the models. The mechanical properties of dentin, post, and resin cement were obtained from the literature. Bases and punches were constructed as rigid bodies. A 10-N force was applied by the punch in the center of the post in a nonlinear contact analysis. Modified von Mises stress, maximum principal stress, as well as shear and normal stress components were calculated. RESULTS: Both punch and base orifice sizes influenced the stress distribution of the push-out test. Bases with larger diameters and punches with smaller diameters caused higher stress in dentin and at the dentin/cement interface. CONCLUSION: FEA showed that the diameter of the orifice base had a more significant influence on the stress distribution than did the punch diameter. For this reason, both factors should be taken into account during push-out experimental tests.