Test Material Research Articles

Molecular Biomarkers for In Vitro Thrombogenicity Assessment of Medical Device Materials.

To develop standardized in vitro thrombogenicity test methods for evaluating medical device materials, three platelet activation biomarkers, beta-thromboglobulin (β-TG), platelet factor 4 (PF4), soluble p-selectin (CD62P), and a plasma coagulation marker, thrombin-antithrombin complex (TAT), were investigated. Whole blood, drawn from six healthy human volunteers into Anticoagulant Citrate Dextrose Solution A was recalcified and heparinized over a concentration range of 0.5-1.5 U/mL. The blood was incubated with test materials with different thrombogenic potentials for 60 min at 37°C, using a 6 cm2/mL material surface area to blood volume ratio. After incubation, the blood platelet count was measured before centrifuging the blood to prepare platelet-poor plasma (PPP) and platelet-free plasma (PFP) for enzyme-linked immunosorbent assay analysis of the biomarkers. The results show that all four markers effectively differentiated the materials with different thrombogenic potentials at heparin concentrations from 1.0 to 1.5 U/mL. When a donor-specific heparin concentration (determined by activated clotting time) was used, the markers were able to differentiate materials consistently for blood from all the donors. Additionally, using PFP instead of PPP further improved the test method's ability to differentiate the thrombogenic materials from the negative control for β-TG and TAT. Moreover, the platelet activation markers were able to detect reversible platelet activation induced by adenosine diphosphate (ADP). In summary, all three platelet activation markers (β-TG, PF4, and CD62P) can distinguish thrombogenic potentials of different materials and detect ADP-induced reversible platelet activation. Test consistency and sensitivity can be enhanced by using a donor-specific heparin concentration and PFP. The same test conditions are applicable to the measurement of coagulation marker TAT.

Feasibility study of YSO/SiPM based detectors for virtual monochromatic image synthesis.

The development of photon-counting CT systems has focused on semiconductor detectors like cadmium zinc telluride (CZT) and cadmium telluride (CdTe). However, these detectors face high costs and charge-sharing issues, distorting the energy spectrum. Indirect detection using Yttrium Orthosilicate (YSO) scintillators with silicon photomultiplier (SiPM) offers a cost-effective alternative with high detection efficiency, low dark count rate, and high sensor gain. This work aims to demonstrate the feasibility of the YSO/SiPM detector (DexScanner L103) based on the Multi-Voltage Threshold (MVT) sampling method as a photon-counting CT detector by evaluating the synthesis error of virtual monochromatic images. In this study, we developed a proof-of-concept benchtop photon-counting CT system, and employed a direct method for empirical virtual monochromatic image synthesis (EVMIS) by polynomial fitting under the principle of least square deviation without X-ray spectral information. The accuracy of the empirical energy calibration techniques was evaluated by comparing the reconstructed and actual attenuation coefficients of calibration and test materials using mean relative error (MRE) and mean square error (MSE). In dual-material imaging experiments, the overall average synthesis error for three monoenergetic images of distinct materials is 2.53% ±2.43%. Similarly, in K-edge imaging experiments encompassing four materials, the overall average synthesis error for three monoenergetic images is 4.04% ±2.63%. In rat biological soft-tissue imaging experiments, we further predicted the densities of various rat tissues as follows: bone density is 1.41±0.07 g/cm3, adipose tissue density is 0.91±0.06 g/cm3, heart tissue density is 1.09±0.04 g/cm3, and lung tissue density is 0.32±0.07 g/cm3. Those results showed that the reconstructed virtual monochromatic images had good conformance for each material. This study indicates the SiPM-based photon-counting detector could be used for monochromatic image synthesis and is a promising method for developing spectral computed tomography systems.

An Update on the Waste Management of the Amazonian Açaí Berry for the Civil Engineering Sector

The rising demand for açaí berries in Amazonian Brazil and French Guiana generates a significant amount of waste, namely the fruit’s stone, which accounts for 80% of the dry fruit’s mass. Recently, various studies have explored the potential valorization of açaí waste in the civil engineering sector, including the functionalization of the fibers surrounding the stone and the multiphysics testing of composite materials based on açaí fibers and/or stones, treated or untreated. This literature review aims to provide an overview of the technology readiness levels (TRLs) of the existing techniques capable of reducing the environmental impact of both the cultivation and management of naturally occurring açaí. While the research to date is promising, it remains at the prototype stage, and the mass ratio of waste in composites, regardless of their type, limits addressing the underlying ecological problem of açaí waste processing. Further experimental investigations are required to improve the functionalization processes, enabling the use of higher proportions of fibers and/or stones in cementitious composites and their large-scale production.

DEVELOPMENT OF INNOVATIVE TECHNOLOGY AND HARDENING EQUIPMENT FOR THE IMPLEMENTATION OF HARDENING HEAT TREATMENT OF METAL PRODUCTS USING FLUIDIZED BULK MATERIALS (PART 1)

Statement of the problem. One of the main problems faced by a modern enterprise is the search for ways to improve the efficiency of its activities. For the effective functioning of the thermal units of toolmaking industries, the simultaneous availability of heating and quenching devices with different heating and cooling media is required. This explains the desire of manufacturers and scientists to find technological, cheap, environmentally friendly heating and cooling media that can provide the required heat treatment parameters and high quality of the processed parts. The purpose of the article is to analyze the state-of-the-art of hardening thermal (combined) treatment methods using bulk materials as media for volumetric heating and forced cooling of metal products and the design and technological features of hardening devices that can ensure a rational structural state of metal parts of complex geometric shapes with a minimum level of their warping and deformation on the example of using vibro-fluidized bulk materials (in the technical literature, the term vibro-gravity particles of heat is used). Research results. To analyze the results of tests of bulk materials as quenching media for high-alloy steel grades and their effect on the structure and properties of the metal in comparison with the traditional oil quenching regime. To consider the features of quenching devices that use mechanical vibration to produce vibro-s bulk material and the possibility of their use in the implementation of quenching modes (including isothermal) of steel products of complex geometric shapes. Conclusion. The use of fluidized bulk materials in industry as media for volumetric heating and hardening of metal products and the design of devices for their use has been investigated. The advantages of the fluidized bed cooling method for the effective implementation of hardening heat treatment regimes are determined. It is shown that this method of forced volumetric cooling of toolmaking products is rational in terms of various indicators. The structural and technological parameters of devices for its implementation are analyzed, which can consistently provide the required level of properties of alloyed and high-alloy tool steels with a minimum level of warping and deformation.

Experimental and numerical studies on the collapse of Titanium alloy ring-stiffened cylinder

This paper investigates the collapse of ring-stiffened Titanium alloy cylinders used for subsea resource exploration under hydrostatic pressure through experimental and numerical methods. Extensive material tests were first conducted on Titanium alloy specimens to obtain the fundamental mechanical properties and variation characteristics. Then, a 4236 mm-long test cylinder was fabricated with an inner radius of 650 mm and a thickness (ts) of 18.85 mm. The initial geometric imperfection was measured at evenly-spaced positions in the axial direction and 48 locations around the circumference by dial gauges. Afterward, the test cylinder was transferred into a custom hyperbaric pressure vessel and pressurized to collapse. As to the numerical analysis, a user-defined material subroutine implementing the incremental J2 deformation theory was developed to predict plastic bifurcation pressure. Moreover, a nonlinear finite element (FE) model, which incorporated the measured geometric imperfection and material nonlinearity, was used to reproduce the experiment. The numerical results were found to exhibit reasonably good agreement with the test data. In addition, parametric studies were conducted regarding material properties, geometric parameters, and imperfection sizes on the load-carrying capacity of Titanium alloy ring-stiffened cylinders.

Dermal Acute Toxicity Test

The aim of the dermal acute toxicity test is to identify the intrinsic toxicity of a product by assessing its hazard potential following acute skin exposure. This test also provides preliminary data that can be used to determine the appropriate dosage level and guide the design of subsequent toxicity studies, including determining the LD50 value and information about skin absorption. In this study, female rats (Rattus Nervegicus) are used as test subjects. The test material is prepared by diluting 15 ml of the sample to a final concentration of 994.9 mg/mL. The rats are exposed to the material for 24 hours. Post-exposure, microanatomical observations, and surgery in the abdominal and thoracic areas revealed no abnormalities.

Development of a Method for the Determination of Rifaximin and Rifampicin Residues in Foods of Animal Origin.

Rifaximin and rifampicin are good broad-spectrum antimicrobials. The irrational use of antimicrobial drugs in veterinary clinics could threaten public health and food safety. It is necessary to develop a reliable detection method of the residue for enhancing the rational supervision of the use of such drugs, reducing and slowing down the generation of bacterial resistance, and promoting animal food safety and human health. So, this study developed an LC-MS/MS method for the detection of rifaximin and rifampicin residues in animal-origin foods. The residual rifaximin and rifampicin of homogenized test materials were extracted with acetonitrile-dichloromethane solution or acetonitrile in the presence of anhydrous sodium sulfate and vitamin C, purified by dispersible solid phase extraction, determined by LC-MS/MS, and quantified by the internal standard method. The specificity, sensitivity, matrix effect, accuracy, and precision of the method were investigated in the edible tissues of cattle, swine, or chicken. In addition, the stability of the standard stock solution and the standard working solution was also investigated. The method was suitable for the muscle, liver, kidney, fat, milk, and eggs of cattle, swine, or chicken, as well as fish and shrimp. The specificity of the method was good, and the detection of the analytes was not affected by different matrices. Both the LOD and LOQ of the two analytes were 5 μg/kg and 10 μg/kg, respectively. The results of matrix effects in each tissue were in the range of 80-120%; there were no significant matrix effects. The average accuracy of rifaximin and rifampicin in different foodstuffs of animal origin was between 80% and 120%, and the method precision was below 20% (RSD). The proposed method showed good performance for determination, which could be employed for the extraction, purification, and detection of residual rifaximin and rifampicin in edible animal tissues. The pretreatment procedure of tissue samples was simple and feasible. The method was highly specific, stable, reliable, and with high sensitivity, accuracy, and precision, which met the requirements of quantitative detection of veterinary drug residues.

Penetrative fracture behavior of monolayer graphene oxide: nanoscale experiment and molecular dynamics simulation

Abstract Graphene, a two-dimensional material, is expected to be employed as a next-generation component for structural and functional applications because of its light weight and excellent mechanical properties. For applications requiring lightness and impact resistance, preventing penetrative damage upon particle impact is critical for applications in mechanical protection. However, graphene is known to have high defect sensitivity. Graphene oxide (GO) may be a better candidate, as functional groups (e.g., hydroxy and epoxy groups) bonded to the C–C network in GO result in better deformability, ductility, and durability compared to graphene. For mechanical applications, it is crucial to understand the fracture behavior, especially the penetrative fracture behavior, of GO membranes. This study characterizes the penetration behavior and fracture morphology of GO membranes subjected to particle impact. Nanoscale experiments were conducted using an atomic force microscope and laser-induced particle impact test for GO. These material testing methods employ nanoscale spheres to induce particle penetration, with the former experiment conducted under quasi-static loading and the latter under dynamic loading. Additionally, molecular dynamics simulations were performed to elucidate the fracture mechanisms of GO. Finally, cyclic fatigue experiments and simulations revealed that GO’s ductility provides resistance to catastrophic failure, indicating its durability. These comprehensive investigations provide valuable insights into the fracture properties of GO membranes under impact penetration.

Fatigue research of metro car body based on operational loads

PurposeThe principle of infinite life design currently directs fatigue resistance strategies for metro car bodies. However, this principle might not fully account for the dynamic influence of operational loads and the inevitable presence of defects. This study aims to integrate methods of service life estimation and residual life assessment, which are based on operational loads, into the existing infinite life verification framework to further ensure the operational safety of subway trains.Design/methodology/approachOperational loads and fatigue loading spectra were determined through the field test. The material test was conducted to investigate characteristics of the fracture toughness and the crack growth rate. The fatigue strength of the metro car body was first verified using the finite element method and Moore–Kommers–Japer diagrams. The service life was then estimated by applying the Miner rule and high-cycle fatigue curves in a modified form of the Basquin equation. Finally, the residual life was assessed utilizing a fracture assessment diagram and a fitted curve of crack growth rate adhered to the Paris formula.FindingsNeither the maximum utilization factor nor the cumulative damage exceeds the threshold value of 1.0, the metro car body could meet the design life requirement of 30 years or 6.6 million km. However, three out of five fatigue key points were significantly influenced by the operational loads, which indicates that a single fatigue strength verification cannot achieve the infinite life design objective of the metro car body. For a projected design life of 30 years, the tolerance depth is 12.2 mm, which can underscore a relatively robust damage tolerance capability.Originality/valueThe influence of operational loads on fatigue life was presented by the discrepancy analysis between fatigue strength verification results and service life estimation results. The fracture properties of butt-welded joints were tested and used for the damage tolerance assessment. The damage tolerance life can be effectively related by a newly developed equation in this study. It can be a valuable tool to provide the theoretical guidance and technical support for the structural improvements and maintenance decisions of the metro car body.

Experimental investigation of the impact of additives in low clinker cementitious materials on multi-ion transference numbers and diffusion coefficients

In this paper, multi-ion transference numbers were determined throughout the chloride migration testing of low clinker cement-based materials. For this purpose, five cement pastes were studied: pure Portland paste (as a reference) and four other pastes, based on limestone filler, fly ash, slag or silica fume. The transference numbers were calculated from the concentration evolution in the three zones of the migration cell (catholyte, anolyte and sample), considering that: (i) ions moved in the catholyte and anolyte; (ii) ions leached from the sample; (iii) ions were generated from the electrode processes, and (iv) the pore solution of the sample evolved during the test. The chloride transference numbers of pastes with pure Portland cement, limestone filler, fly ash, slag or silica fume are almost zero at the beginning of the migration test but 0.23; 0.18; 0.06; 0.05 and 0.20 at the end of the test, respectively. The ion transference numbers obtained were used for the calculation of diffusion coefficients of chlorides, sodium and potassium using the Nernst-Einstein equation.

Cementation characteristics and hydration mechanism of magnesium slag-phosphogypsum composite cementitious materials

The selection and mixing proportion of cementitious materials in cemented backfills are of great engineering importance to ensure the quality of the backfill. Therefore, based on the mixing proportion test of magnesium slag-phosphogypsum composite cementitious materials, the strength change characteristics and volume change rate of the cemented backfill under different cementitious material proportions were investigated. Combined with indoor tests such as hydration heat test, X-ray diffraction, thermogravimetric-differential thermogravimetric, scanning electron microscopy, and mercury intrusion porosimetry, the hydration mechanism of the cemented backfill under different cementitious material proportions was investigated. The results showed that the highest strength of the cemented backfill was observed with only magnesium slag as the activator. The strength of magnesium slag-phosphogypsum and magnesium slag-desulfurized gypsum cemented backfill was greater than that of cement cemented backfill, yet lower than that of magnesium slag alone cemented backfill. The shrinkage trend and magnitude of magnesium slag alone excites blast furnace slag cemented backfill and cement cemented backfill were similar. With the increasing content of phosphogypsum and desulfurized gypsum, the shrinkage of the backfill tended to increase, especially when the content was 18%. The gel-like products of backfill with magnesium slag-based cementitious materials increased rapidly at 7 days, which strongly bonded the aggregates and filled the backfill pores, resulting in high backfill strength. Although the porosity of backfill with magnesium slag-based cementitious material showed an increasing trend with the increase of age, its most available pore size decreased and harmful pores became less. The results can provide a reference for the application of magnesium slag-phosphogypsum composite cementitious materials.

Novel High-Strength and High-Temperature Resistant Composite Material for In-Space Optical Mining Applications: Modeling, Design, and Simulation at the Polymer and Atomic/Molecular Levels.

This study explores the modeling, design, simulation, and testing of a new composite material designed for high-strength and high-temperature resistance in in-space optical mining, examining its properties at both the polymer and atomic/molecular levels. At the polymer level, the investigation includes mechanical and thermal performance analyses using COMSOL Multiphysics 6.1, employing layerwise theory, equivalent single layer (ESL) theory, and a multiple-model approach for mechanical modeling, alongside virtual thermal experiments simulating laser heating. Experimentally, porous Polyaniline (PANI) films are fabricated via electrochemical polymerization, with variations in voltage and deposition time, to study their morphology, optical performance, and electrochemical behavior. At the atomic and molecular levels, this study involves modeling the composite material, composed of Nomex, Kevlar, and Spirooxazine-Doped PANI, and simulating its behavior. The significance of this work lies in developing a novel composite material for in-space optical mining, integrating it into optical mining systems, and introducing innovative thermal management solutions, which contribute to future space exploration by improving resource efficiency and sustainability, while also enhancing the understanding of PANI film properties for in-space applications.

Billet Size Optimization for Hot Forging of AISI 1045 Medium Carbon Steel Using Zener-Hollomon and Cingara-McQueen Model

This study investigates the effects of initial billet size variations on material flow behavior in hot forging processes, aiming to optimize the forging process using validated predictive models. Material and high-temperature compressive tests inform mathematical models, while simulations are conducted via the finite element method (FEM). Results align with the Zener-Hollomon and Cingara-McQueen approaches. The Arrhenius model predicts AISI 1045 steel flow stress with an R2 of 0.968 and an average absolute relative error (AARE) of 7.079%. The Cingara-McQueen equation achieves an R2 of 0.997 and an AARE of 2.960%. Reducing billets size from 260 mm to 230 mm decreases the material usage by up to 11.5%, while maintaining workpiece integrity. Experimental and simulated loads exhibit an AARE of about 2.69%, thereby indicating potential cost and efficiency improvements in hot forging processes.

Digital Representation of Materials Testing Data for Semantic Web Analytics: Tensile Stress Relaxation Testing Use Case

This study aims to represent an approach for transferring the materials testing datasets to the digital schema that meets the prerequisites of the semantic web. As a use case, the tensile stress relaxation testing method was evaluated and the testing datasets for several copper alloys were prepared. The tensile stress relaxation testing ontology (TSRTO) was modeled following the test standard requirements and by utilizing the appropriate upper-level ontologies. Eventually, mapping the testing datasets into the knowledge graph and converting the data-mapped graphs to the machine-readable Resource Description Framework (RDF) schema led to the preparation of the digital version of testing data which can be efficiently queried on the web.

Study of hydrogen embrittlement in steels using modified pressurized disks

The integration of hydrogen into natural gas pipelines presents challenges due to Hydrogen Embrittlement (HE), requiring critical material selection and testing methods. One such test is the Disk Pressure Test (DPT), which consists in pressurizing a clamped disk to failure. However, failure happens often at the clamping zone, making analysis difficult. This study aims to develop new disk geometries to control failure location while maintaining the test setup. Using two steel grades (a vintage X52 pipeline steel and a modern E355 modified steel with potential for pipeline use), new disk geometries were tested under helium and hydrogen at various pressure rise rates. Results show successful displacement of failure away from the clamping zones, demonstrating the effectiveness of the new geometries. Hydrogen embrittlement is demonstrated by comparing failure pressures under helium and hydrogen at various pressure rise rates. Using both material testing and simulation, this study provides insights into hydrogen embrittlement.

Selection of signature peptide biomarkers for the sesame allergens in commercial food based on LC-MS/MS

Sesame is a commonly used food ingredient, yet it is one of the eight major allergens. As sesame is often consumed in various processed forms, it is important to establish methods for detecting sesame allergens in processed foods. Liquid chromatography-tandem mass spectrometry (LC-MS/MS), using characteristic peptides as biomarkers, detects multiple allergenic proteins simultaneously with high sensitivity and accuracy. Choosing robust biomarkers is beneficial for developing a specific, universal, and sensitive method. To obtain excellent peptides of sesame allergens, sixteen commercial products were used as test materials. Proteins from these materials were extracted, digested, and analyzed. Peptides were screened based on several criteria, including specificity and amino acid composition. Only peptides showing process robustness were retained. Ultimately, nine peptides were selected as the best biomarkers. Based on the above peptides, it is possible to achieve precise and high-sensitivity detection of sesame allergens in processed products.

Uji Efektivitas Daya Hambat Ekstrak dan Perasan Lidah Buaya (Aloe barbadensis Miller) pada Bakteri Staphylococcus Aureus dengan Metode Difusi

Aloe vera is a plant that is rich in minerals, vitamins, and antibacterial properties. A study to analyze the antibacterial effectiveness of aloe vera in inhibiting the growth of Staphylococcus aureus bacteria isolated from acne pus. This study was an experimental laboratory study using the disc diffusion method, located at the Bacteriology Laboratory, Department of Medical Laboratory Technology, Poltekkes Kemenkes Surabaya, from February to May 2024. There were 6 sample treatments with 4 replications, 4 treatments of extract and juice concentration variations, namely concentrations of 70%, 80%, 90%, 100%, positive control using penicillin antibiotics, and negative control using clean distilled water. The results of this study show that at aloe vera extract concentrations of 70%, 80%, 90%, and 100%, the average diameter of the inhibition zone was 9 mm, 10 mm, 11 mm, and 12 mm, respectively, while in aloe vera juice, these concentrations did not form an inhibition zone. So it was concluded that aloe vera extract is more effective than aloe vera juice, the most successful test material to slow the growth of Staphylococcus aureus bacteria in this study was aloe vera extract with a concentration of 100%. This study also conducted qualitative phytochemical testing on aloe vera extract which has antibacterial compounds, namely saponins, tannins, flavonoids, and terpenoids. The results of the study on the effectiveness of the inhibitory power of aloe vera extract and juice against Staphylococcus aureus bacteria using the disc diffusion method were analyzed using quantitative descriptive and presented in tabulation form in the form of the diameter of the inhibition zone formed.

The influence of lumbar vertebra and cage related factors on cage-endplate contact after lumbar interbody fusion: An in-vitro experimental study

Lumbar interbody fusion (LIF) using interbody cages is an established treatment for lumbar degenerative disc disease, but fusion results are known to be affected by risk factors such as bone mineral density (BMD), endplate geometry and cage position. At present, direct measurement of endplate-cage contact variables that affect LIF have not been fully identified. The aim of this study was to use cadaveric experiments to investigate the dependency between BMD, endplate geometry, cage parameters like type, orientation, position, and contact variables like stress and area. One vertebral body specimen from each of the five lumbar positions was harvested from five male donors. The lower half of each vertebra was potted and placed in a material testing machine (Instron 8874). A spinal cage was clamped to the machine then lowered to bring it into contact against the superior endplate. A lockable ball-joint was used to rotate the cage such that its inferior surface was congruent with the local endplate surface. A pressure sensor (Tekscan) was placed between the cage and endplate to record contact area and the peak and average contact pressures. Axial compression of 400 N was performed for five positions using a straight cage, and in one anterior position using a curved cage. The linear mixed model was utilised to perform data analyses for experimental results with statistical significance set at p < 0.05. The results indicated two trends toward significance for contact area, one for volumetric BMD (vBMD) of the vertebra (p = 0.081), and another for predicted contact area (p = 0.057). Peak contact pressure correlated significantly with vBMD (p = 0.041), and there was a trend between average contact pressure and lateral position of cage (p = 0.051). In addition, predicted contact area correlated significantly with cage orientation (p < 0.001). These results indicated that high vBMD of vertebra and a medially positioned cage led to higher contact pressures. Logically, low vBMD of vertebra and transverse cage orientation increased the contact area between the cage and endplate. In conclusion, the study identified significant influence of vBMD of vertebra, cage position and orientation on cage-endplate contact which may help to inform cage selection and design for LIF.

In Vivo Leaf Inoculation: An Alternative Method to Assess the Disease Resistance of Hybrid Clones in Poplar Breeding of Stem Canker Disease.

Stem canker diseases caused by the pathogen Cytospora chrysosperma (Pers.) Fr.) and Botryosphaeria dothidea (Moug. ex Fr.) Ces. & de Not. are the two major forest diseases in the poplar plantations in China, sometimes which can destroy all the poplar seedlings or severely damage mature poplar forests. Hybrid breeding is the most direct and efficient method of controlling and managing tree diseases. However, assessing disease resistance or selecting disease-resistance clones based on In vitro stem inoculation is inefficient, time-consuming, and expensive, limiting the development of hybrid breeding of poplar stem canker disease. In this study, we proposed an alternative method to assess disease resistance to stem canker pathogens through in vivo leaf inoculation. The test materials used in this method can be on 1-year-old poplar saplings or the annual branches of perennial poplars in the greenhouse or the field. The critical step of this alternative method is the selection of inoculating leaves: the 5-7th newly matured leaves might be the most suitable. The second critical step of the leaf inoculation method is to make wounds on plant leaves through needle pierces, providing sufficient lesions to measure disease severity. For the adequate number of leaves produced in the early stage of poplar breeding, this in vivo leaf inoculation contributes to the rapid, accurate, and large-scale screening of the disease-resistance poplar clones to stem canker pathogens. Moreover, this leaf inoculation method will also serve as an efficient method for screening pathotypes of stem canker disease pathogen C. chrysosperma, B.dothidea, or other poplar stem canker pathogens.

On the experimental identification of equilibrium relations and the separation of inelastic effects in soft biological tissues

The mechanical characterization of vascular tissues has been mainly focused on the measurement of elastic properties, while the investigation of inelastic effects has received comparatively little attention. Even the relatively simple, purely elastic description of the material behavior requires an appropriate set of experimental data that cannot be easily isolated using standard testing procedures. The presence of viscous and damage-related phenomena poses some challenges in the definition of appropriate testing protocols capable of identifying an equilibrium response, which in general does not solely represent the elastic material behavior. The primary goal of the present study is therefore to devise an experimental procedure that can distinguish and evaluate the different constitutive phenomena separately. To this end, we apply methodologies widely used in the mechanical testing of rubber-like materials and transfer them to the field of biomechanics. We performed two types of experiments in equibiaxial extension on porcine thoracic aorta: a continuous cyclic test followed by a single-step relaxation test and a cyclic multi-step relaxation test, each at varying stretch rates. We demonstrate that the approximation of quasi-stationarity through continuous testing at slow rates is inadequate for the identification of an equilibrium relation. Alternatively, a step-wise protocol allows for the separation of equilibrium and viscous effects. This motivates a thermodynamic discussion of the experimental results in terms of energy dissipation and a closer look at the interplay of inelastic phenomena.