Literatura académica sobre el tema "Exposition bovine"

The effect of high-intensity ultrasound (HIU) system (bath, 37 kHz and 90 W/cm2; or probe, 24 kHz and 400 W) and application time (25 or 50 min, one-side exposition) on the properties of bovine Longissimus lumborum after 7 d of storage at 4 °C was studied. The bath system significantly increased the lightness of the muscle, while other color parameters (a*, b*, hue, and chroma) were not different from the control. The water holding capacity and shear force decreased significantly (3.1–5% and 0.59–0.72 kgf, respectively) in sonicated meat independently of the system, favoring the tenderization of the muscle after storage. Microstructural changes observed in the HIU-exposed surface provided evidence of a higher area of interfibrillar spaces (1813 vs. 705 µm2 in the control), producing tenderization of the muscle, compared with the control. HIU significantly increased counts of total aerobic and coliform bacteria, especially after 50 min of ultrasonication. HIU also increased lactic acid bacterial counts in the bath system. Single-sided muscle exposition to ultrasound may produce sufficient significant changes in muscle properties, which could decrease long treatment times that would be needed for the exposition of both sides. HIU in bath systems increases tenderness by modifying meat ultrastructure, with no significant changes in physicochemical parameters. Nevertheless, microbiological quality may need to be considered during the process due to a slight increase in bacterial counts.

AbstractBackgroundDevelopment of Pressurized IntraPeritoneal Aerosol Chemotherapy (PIPAC) requires adequate preclinical models.MethodsThe model should be easy to use, reproducible and cost-effective. It should have a volume similar to the human abdominal cavity, and an oval shape. The inner surface should be lined with serosa. The model should allow pharmacological and biological analysis, including histology. No living animals should be used.ResultsThe fresh urinary bladder is explanted from an adult bovine in the slaughterhouse. A 4-cm incision is performed into the bladder neck. The bladder can be inverted through the incision, which allows exposition of the serosa on its inner side. A balloon trocar is inserted through the incision and a ligature placed, ensuring full tightness. The therapeutic capnoperitoneum is installed. The bovine bladder has a volume somewhat smaller (2–3 L) than the human abdominal cavity (3–5 L). Costs are minimal. There is no significant bacteriological contamination. Manipulation is simple.ConclusionsThe (inverted) bovine urinary bladder is an innovative and versatile ex vivo model for optimizing drug delivery with therapeutic aerosols both onto the mucosa or the serosa. This model can be used for pharmaceutical Quality-by-Design approaches and will replace a large number of experiments in the animal.

The study of the effect of millimeter range electromagnetic waves (MM EMW) on bovine serum albumin (BSA) structure at the frequencies both resonant (51.8 GHz) and non-resonant (41.8 GHz) for water has been conducted. The absorption and fluorescence spectra of non-irradiated and irradiated samples of physiological solution and BSA with exposition 60 min were obtained. It was revealed that the spectral characteristics of physiological solution did not change under the effect of MM EMW, while the analogous characteristics of BSA change relevantly. It was also shown that the absorption spectra of the irradiated samples significantly differ from those of non-irradiated protein.

In this study the effect of increasing ethylene glycol (EG) concentrations in the vitrification media (VM) and its relation with oocyte activation and in vitro embryo production were evaluated. Cumulus-oocytes complexes (COC) were matured in vitro for 22 h and then partially denuded by gently pipetting with hyaluronidase, and randomly assigned to 4 treatments: T1 = control group; T2 = COC exposed to 10% EG + 10% DMSO (VM1), 20% EG + 20% DMSO (VM2); T3 = 15% EG + 5% DMSO (VM1), 30% EG + 10% DMSO (VM2); T4 = 20% EG + 0% DMSO (VM1), 40% EG + 0% DMSO (VM2). Exposition to VM1 and VM2 lasted 3 min and 30 s, respectively. After treatment COC were incubated in maturation medium up to 24 h. In Experiment 1 COC were cultured for 24 h in fertilization TALP supplemented with 50 μg mL-1 of heparin, then completely denuded and cultured 24 h in CR1-aa. After this, oocytes were stained with bisbenzimide (Hoechst 33342) and the number of nuclei and cells were recorded. Structures presenting 2 cells or 2 nuclei were considered as activated oocytes. In Experiment 2 matured COC exposed to cryoprotectants as in Experiment 1 were fertilized and cultured for 6 days as previously described (Mucci et al. 2006). Variables analyzed included oocyte activation, cleavage rate at 48 h, and percentage of viable embryos at Day 7. Data were analyzed by PROC GENMOD (SAS Institute Inc., Cary, NC, USA). Activated oocytes percentage did not differ between EG concentrations in VM and were higher (T2, 24.7%, n = 101; T3, 25.0%, n = 96; T4, 30.2%, n = 119) compared with controls (T1, 9.8%, n = 61). In Experiment 2 no differences were found in cleavage rates (T1, 81.9%, n = 68; T2, 87%, n = 67; T3, 85.9%, n = 61; T4, 84.2%, n = 64) and Day 7 percentage of viable embryos (T1, 34.9%, n = 29; T2, 28.6%, n = 22; T3, 26.8%, n = 19; T4, 27.6%, n = 21) in treated COC. The exposition of COC to cryoprotectants per se could trigger oocyte activation in the range of 10 to 40%. Thanks toAdriana Cano (Instituto Nacional de Tecnología Agropecuaria) for contributions in statistical analysis.

We studied the simultaneous binding of galactose and mannose-exposing ligands in sinusoidal rat liver cells during development and aging. The galactose-specific receptors were visualized using 17 nm diameter colloidal gold particles coupled with Lactosylated bovine serum albumine (LacBSA), while mannose-specific receptors were localized by means of 5 nm diameter particles adsorbed with mannan. We observed the presence of four different classes of Kupffer cells in relation to the ligands bound. The percentage of each group of Kupffer cells varied in relation to the age of the subject from which the sample was taken. There were few double-labelled cells in the livers from newborn rats, with numbers increasing with age to adulthood, and decreasing again in the older animals. Cells without labelling were in the majority after birth, but they decreased in number up to adulthood and increased again during subsequent aging. The numbers of single-labelled cells did not change significantly during liver maturation. We hypothesize that the exposition of galactose and mannose-specific receptorial systems is regulated by developmental conditions.

Interactions between proteins and drugs, which can lead to formation of stable drug-protein complexes, have important implications on several processes related to human health. These interactions can affect, for instance, free concentration, biological activity, and metabolism of the drugs in the blood stream. Here, we report on the UV-Visible spectroscopic investigation on the interaction of bovine serum albumin (BSA) with chlorophyll (Chl) in aqueous solution under physiological conditions. Binding constants at different temperatures—obtained by using the Benesi-Hildebrand equation—were found to be of the same order of magnitude (~104 M−1) indicating low affinity of Chl with BSA. We have found a hyperchromism, which suggested an interaction between BSA and Chl occurring through conformational changes of BSA caused by exposition of tryptophan to solvent. Films from BSA and Chl obtained at different Chl concentrations showed fractal structures, which were characterized by fractal dimension calculated from microscopic image analysis.

This study aimed to determine the effect of high-intensity ultrasound (HIU. F = 37 kHz, I = 28W/cm2, bath for 30 min, 5 °C) on physicochemical characteristics and sensorial preference of seven aged (23 d ageing) bovine muscles (L. dorsi lumborum, L. dorsi thoracis, Psoas major, Semimembranosus, Biceps femoris, Rectus femoris, and Gluteus medius). Muscles were randomly distributed in two treatments: with and without ultrasonication. Colour (L*, a*, b* and C*), water-holding capacity (WHC), and shear force (N) were determined before and after simulated retail display (SRD) in modified atmosphere packing (MAP; 75% O2: 25% CO2, 3 °C, 13 h led light exposition) for 5 d. Sensorial toughness was also evaluated at the end of the SRD. Ultrasonication slightly reduces 6–9% WHC of beef. HIU did not affect (p ˃ 0.05) water loss, meat colour, shear force and sensorial toughness of the meat. The Semimembranosus was the toughest muscle. Ultrasonication of 23-day-aged beef did not show improvements on quality characteristics, and despite minor changes in water loss and slight increase in shear force, consumers did not detect differences.

Various forms of zinc oxide (ZnO) are frequently used in the design of optical and electrochemical sensors. However, the optical and electrochemical properties of ZnO should be properly adjusted depending on the application area. Therefore, in this work, we have investigated changing/tuning the properties of ZnO by depositing a layer of polydopamine (PDA) on its surface. In order to perform this investigation, the surface of fluorine-doped tin oxide (FTO) was modified with the layer of ZnO nanorods and PDA. ZnO nanorods were synthesized by hydrothermal synthesis technique, and after the synthesis, they were coated with polydopamine exploiting the self-polymerization of dopamine. The nanostructures were investigated by using electrochemical and optical methods. Electrochemical impedance spectroscopy measurements showed that electrochemical properties of FTO-ZnO and FTO-ZnO-PDA nanostructures could be changed by the variation of both—applied electrical potential and/or exposition towards lighting. Interaction between ZnO-PDA and bovine serum albumin (BSA) molecules has been investigated by (photo)electrochemical and photoluminescence methods. A mechanism of possible interaction between BSA and the ZnO-PDA surface has been proposed.

The detection of early stages of caries is still one of the major challenges in preservative dentistry. Since it is known from polarized light microscopy (PLM) that intrinsic enamel birefringence is affected by demineralization, polarization-sensitive optical coherence tomography (PSOCT) could facilitate the noninvasive detection and assessment of early carious lesions. The present study aims to correlate enamel lesion progression and depolarization measurements based on PSOCT in an artificial demineralization model. A total of 18 enamel slabs were prepared from bovine incisor teeth and demineralized in an acetic buffer solution for up to 49 days. The degree of polarization (DOP)—indicating depolarization and thus, demineralization—was calculated from PSOCT measurements and compared to lesion depth which was measured from PLM images. Artificial lesions showed characteristic zones of natural enamel demineralization in PLM images. DOP representations showed no depolarization for sound, nondemineralized enamel, whereas significant changes were found after 15 days of acid-exposition. The linear regression analysis of the DOP and the measured lesion depth showed a substantial correlation ( R 2 = 0.71 ). The results indicate that PSOCT-based depolarization imaging provides an unambiguous contrast for initial enamel demineralization which is correlated to the lesion progression.

Nanotechnology provides the opportunity for the development of new materials in the nanometer size range with many potential applications in biological sciences and clinical medicine. RD (muscle cancer cell line) was seeded out in 25 cm2plastic tissue culture flasks (NuncWiesbaden Germany) individually, in Minimum Essential Medium (MEM) with Hanks salts, containing 10% fetal bovine serum (FBS) and 2 mM L-Glutamine along with some nonessential amino acids and were incubated for 24 h for proper attachment to the substratum and kept at a 96 wells plate, incubated at 37°C and 5% CO2. SEM was employed to the nanoparticles and size of α-Fe2O3and SiO2nanoparticles were about 66 nm and 250 nm. Moreover 10-80μg/mL of Hematite (α-Fe2O3) and SiO2nanoparticles dispersed solution were labeled for each row of 96 wells plate. The present study evaluates the different parameters, e.g. time of incubation, cytotoxicity and cellular viability of the Human Rhabdomyosarcoma cell line (RD) as an experimental model. The viability of cells was determined by means of neutral red assay (NRA) after the cell-exposition to different concentrations of Hematite (α-Fe2O3) and SiO2nanoparticles into mentioned tumoricidal cells

Le virus de l'encéphalite à tiques (TBEV) - genre Orthoflavivirus - est l'arbovirus le plus fréquent en Europe. Le sous-type européen affecte le système nerveux central chez l'homme et peut être fatal dans 0,5 à 2% des cas. L'homme s'infecte soit par la piqûre d'une tique infectée soit par l'ingestion de produits laitiers contaminés non pasteurisés, principalement de chèvre. Le virus circule naturellement entre la tique Ixodes ricinus et les rongeurs forestiers. La distribution du TBEV en France, plus restreinte que celle de son vecteur, est à ce jour méconnue et peut être plus importante que ne le laisse supposer la surveillance évènementielle des cas humains. Depuis 2016, le nombre de cas tend à augmenter en France avec de nouveaux foyers en dehors de l'Alsace, la Savoie et la Haute-Savoie, zones endémiques historiques. L'année 2020 a été marquée par le premier cluster de contaminations alimentaires dans l'Ain avec 43 cas dus à la consommation de fromage de chèvre non pasteurisé. Ce foyer pose la question du risque de transmission du virus TBEV par voie alimentaire en France. Ce risque dépend notamment de l'excrétion du virus dans le lait par les ruminants (exposition au virus et excrétion virale), de sa persistance dans le lait et les produits laitiers et des pratiques de consommation alimentaire de produits au lait cru. L'objectif général de ce projet est de mieux comprendre ce risque en France en s'intéressant (i) à la distribution du virus, à l'exposition des ruminants au TBEV et aux facteurs associés, (ii) aux spécificités de la filière lait cru petits ruminants en France, en se focalisant sur l'Ain et le Puy-de-Dôme, deux départements avec des cas alimentaires de TBE avérés ou suspectés et (iii) à la persistance de TBEV infectieux dans le lait cru. Pour répondre à ces questions, (i) une enquête de séroprévalence a été conduite sur 4483 bovins dans cinq départements du nord-est de la France pour étudier l'exposition des ruminants domestiques à TBEV. Afin d'adapter la stratégie d'analyses sérologiques, les performances de deux tests ELISA commerciaux pour détecter les anticorps anti-TBEV ont été étudiées au préalable. L'enquête montre que le virus est présent dans la zone d'étude avec des bovins très exposés dans le Massif Vosgien. D'après les résultats d'un modèle multivarié Random Forest spatial, les principaux facteurs associés à une augmentation de l'exposition des bovins vis-à-vis du TBEV dans cette région étaient une température moyenne annuelle basse, une proportion de forêt et une surface de l'interface pâture-bois élevées, zones favorables à l'abondance de tiques. (ii) Par ailleurs, l'étude de filière départementale documente le risque alimentaire lié au TBEV. Elle montre une petite filière peu organisée, d'élevages principalement fermiers qui pratiquent le pâturage souvent à proximité de bois et une production de produits frais au lait cru. (iii) Enfin, nous montrons que le virus reste infectieux jusqu'à 48 h à 4°C et 21°C dans du lait cru de vache et de chèvre artificiellement contaminé par la souche de TBEV isolée dans l'Ain en 2020. De plus, le TBEV est plus stable dans le lait de vache que de chèvre à 4°C. Des études complémentaires sont nécessaires pour mieux comprendre les facteurs qui influencent la distribution du TBEV en France et prédire les zones favorables à sa présence. Du fait des pratiques de la filière caprine, la région Auvergne Rhône-Alpes et le sud de la Bourgogne apparaissent cependant comme des régions à risque pour la transmission alimentaire du TBEV. Limiter le contact des animaux avec les surfaces boisées pourrait être une mesure de gestion en cas de foyer pour diminuer leur exposition. Enfin, l'utilisation de lait artificiellement contaminé introduit un biais. Etudier l'excrétion virale à l'échelle du tissu épithélial mammaire selon les espèces serait nécessaire avant de conclure sur l'influence des conditions de conservation du lait naturellement contaminé sur la persistance de TBEV
TBEV, belonging to the Orthoflavivirus genus, is the most prevalent arbovirus in Europe and. Affecting the central nervous system in humans, it can result in mortality in 0.5 to 2% of cases. Humans become infected either through the bite of an infected tick or by ingesting contaminated unpasteurised dairy products. The virus circulates naturally between Ixodes ricinus ticks and forest rodents. TBEV distribution is more limited than that of its vector. To date, the distribution of TBEV in France is hardly known, and it is expected to be more widespread than suggested by event-based surveillance of human cases. Since 2016, the number of human cases has tended to increase in France ( Alsace, Savoie, Haute-Savoie, . In 2020, the first cluster of foodborne cases was identified in the Ain department, with 43 cases due to the consumption of raw goat's cheese. This outbreak raises the question of the risk of food-borne transmission of TBEV in France. This risk is contingent upon the excretion of the virus into the milk by ruminants (exposure to the virus and viral excretion), its persistence in the milk and dairy products, and dietary consumption practices for raw dairy products. The overarching objective of this thesis project is to gain a deeper comprehension of the risk in France. We studied : (i) the distribution of the virus, exposure of ruminants to TBEV and associated factors; (ii) the distinctive characteristics of the small ruminant raw milk sector in France, with a particular focus on Ain and Puy-de-Dôme, two departments with confirmed or suspected cases of TBE in food; and (iii) the persistence of infectious TBEV in raw milk. To address these questions, (i) a seroprevalence survey was conducted on 4483 cattle in five departments of north-eastern France to study the exposure of domestic ruminants to TBEV. To adapt the serological analysis strategy, the performance of two commercial ELISA tests for detecting TBEV antibodies was first studied. The results of this survey demonstrated that the virus is present throughout the study area, with cattle exhibiting a high level of exposure to TBEV in Vosgian Mountains. The results of a multivariate spatial Random Forest model indicated that the main factors associated with an elevated risk of TBEV exposure in this region were a low mean annual temperature, a high proportion of forest, and the surface area of the pasture-woodland interface, which are suitable habitats for ticks. Furthermore, (ii) the study of the departmental dairy industry documented the food safety risk associated with TBEV. The industry is characterised by a small, poorly organised sector of mainly free-range livestock farms, which often graze on the edge of woodland and produce fresh products from raw milk. (iii) Finally, we demonstrate that the virus remains infectious for up to 48 hours at 4°C and 21°C in raw cow's and goat's milk artificially contaminated with the TBEV strain isolated in the Ain in 2020. Additionally, our results indicate that TBEV was more stable in cow's milk than in goat's milk at 4°C. Further studies are required to gain a more comprehensive understanding of the factors influencing the distribution of TBEV in France and to predict the areas where it is most likely to occur. However, given the practices of the goat industry, the Auvergne Rhône-Alpes region and southern Burgundy appear to be at risk for foodborne TBEV transmission. Limiting animal contact with wooded areas could be a management measure in the event of an outbreak to reduce cattle exposure. Finally, the use of artificially contaminated milk introduces a bias, and further studies are required to investigate viral excretion at the level of mammary epithelial tissue, depending on the species

OBJETIVO: Identificar las innovaciones en la formación del personal en buenas prácticas de higiene en un rastro bovino privado categoría “A” de Villa Nueva basados en las normas HACCP, con la finalidad de garantizar la inocuidad de los alimentos en el “Rastro La Vaca”. MÉTODO: Método científico, a través de la indagación se utilizó con la aplicación de cuestionarios y entrevistas para lograr determinar la propuesta del programa de higiene y seguridad a través de la fase expositiva conceptualizando y la fase demostrativa comprobando las variables expuestas en la hipótesis. RESULTADOS: Se analizaron medidas de control en los Puntos Críticos de Control para garantizar el cumplimiento de los límites críticos establecidos, incluyeron la implementación de procedimientos operativos estandarizados de saneamiento, la formación del personal en buenas prácticas de higiene, el control de la temperatura y la aplicación de métodos de desinfección efectivos. CONCLUSIÓN: La falta de innovación de un Programa de Higiene y Seguridad basado en las normas del sistema HACCP en el “Rastro La Vaca” provoca que existan deficiencias en el proceso de faenado y sacrificio para la obtención de carne de res totalmente inocua.

Abstract Characterizing the rheological properties of liver tissue, especially within the linear viscoelastic region, is useful for investigating the behaviour of the tissue under mechanical loads. This paper reports three types of experiments of rheological properties of liver tissue that were carried out recently, including strain sweep oscillation, shear stress relaxation and strain controlled oscillation. These experiments were designed to investigate the following: a) the domain of linear viscoelasticity of liver tissue, b) the time dependent behavior of liver tissue, and c) the dynamic storage modulus and loss modulus. Fresh bovine liver tissues were used for the experiments. All the liver tissues were bathed in a 0.9% sodium chloride solution immediately after harvesting. The test samples were cut to a disk of diameter 20–30mm with 1.5–2.5mm thick. Several strain sweep oscillation tests were performed to measure the sample behavior at stepwise changing strain amplitude at 1 Hz frequency. The results showed that the linear viscoelastic limit of bovine liver tissue is of the order of 0.2% strain. The shear stress relaxation test indicated that there is no apparent long-term elastic modulus reached before 3000 seconds within the linear viscoelastic region. The dynamic storage modulus and loss modulus were obtained in the frequency range of 0.001–20 Hz.

Pores (namely lacunae, clusters of canaliculi, Haversian canals, and resorption cavities) are present throughout cortical bone. This paper characterizes the area fraction (AF, %)) of each type of these pores as function of distance from the bone’s geometric center while noting the region in which such pores are located: midcortical or periosteal. Optical slides (at 20X) are taken from 2 cortical bone biopsies named bone 1 and bone 2 and cut at mid-diaphysis femur from 2 different (about 2 year-old) bovine cows. The slides are collected from posterior (pericortical) and anterior (intracortical) locations. The area of each of these biopsies is about 2.5mm × 3mm located near the outer cortex of the bone. In polar coordinates from the bone’s center, the areas cover radial distance of about 3.3 mm (of radius, R) and encompass an arc of 10°. Automated segmentation is used to locate and identify all pores in the optical slides the shapes of which are best fitted into ellipses. Values of area fraction, AF (%) of said fitted ellipses are then automatically calculated in secondary osteons for both regions. Variations in values of area fraction AF (%) are related to actual areas of pores (based on their defining equations). Observations suggest that area fractions (%) of all pores (but to lesser degree for Haversian canals), to significantly decrease linearly and in a steep fashion with R (statistically significant, p < 0.01) in the anterior region where osteonal growth is expected to have continued to develop. However, in the posterior region where osteonal growth appears to have matured, area fraction (%) values seem to have reached a steady state resulting in fairly flat behavior versus R. All observations are equally applicable for biopsies collected from bone 1 and bone 2.

The frequency dependent viscoelastic properties of bovine liver are investigated in support of the development of an ultrasonic vibration imaging system for the detection of hard lesions in soft tissue. This system, which we call sonoelastography, is being applied to imaging coagulation necrosis lesions induced in liver tissue using radio frequency ablation. Detectability of lesions in sonoelastography depends on the relative contrast between the elastic modulus of the lesion and background tissue. Unconfined uniaxial cyclic compression is used to determine the complex Young’s modulus of bovine liver and is fit to a Kelvin-Voigt fractional derivative model (KVFD). Extracted model parameters and goodness of fit are presented.

Abstract Liver tissue plays a role in many physiological systems and is characterized as a soft tissue. Changes in the perceived stiffness of the liver by palpation may indicate Cirrhosis or other liver ailments. New ultrasound techniques that use an applied force such as sonoelastography may aid physicians in diagnosis by providing a quantitative comparison of the mechanical properties for the tissue [1]. At this time, these mechanical characteristics remain to be fully defined. In this study, a four-parameter model composed of springs and dashpots has been used to describe the response of liver under unconfined creep compression tests.

Abstract Seventy-one microtensile samples of bone-cartilage-bone from the lateral, central and medial portions of the proximal tibial growth plate were tested to failure at three speeds. Tensile strength, toe modulus, tangent modulus, and strain energy density varied by both location and strain rate, being stronger and stiffer on the lateral side and at higher strain rates. No differences could be detected in the ultimate strains by either region or strain rate.

Abstract Genetic engineering of milk proteins allows control of their physicochemical properties in foods and dairy products during processing, storage, and consumption. Robust methods for the estimation of the quality and function of the proteins during downstream processing are sought. The focus of this study is a systematic microscopic investigation of the freezing of sub-microliter pendent droplets of buffer solution of glycosylated bovine beta-casein. The freezing and crystallization is observed with a scanning confocal microscope fitted with a stage cooled with vapor boiled off a liquid nitrogen dewar. Four liquid samples (with glycosylated bovine beta-casein concentrations of 35, 125, 500, and 1000 μg/ml) are compared against the control (10 mg/ml of wild type non-glycosylated bovine beta-casein). The freezing of similar size samples consisting of de-ionized water, ice-nucleating mixture (Pseudomonas syringae), and pure buffer solution is also examined for comparison. Higher concentrations of the engineered-beta casein result in increasing antifreeze action, corresponding to depression of the freezing point, and thermal stabilization of the supercooled liquid. This conclusion is supported by a non-parametric statistical analysis based on the Jonckheere test. A freezing point assay can thus be made to assess the quality of glyco-bovine beta-casein.

Abstract Microcracks are present in normal human bone, and microcracks are thought to be a stimulus for bone remodeling. When there is an imbalance between microcrack creation and repair, microdamage can accumulate and result in bone fracture. Seventeen specimens were tested in monotonic compression to one of six total strain levels. Chelating fluorochromes were used to label cracks and distinguish between microdamage created before and during testing. Histology specimens were observed under epifluorescence for microdamage in the form of microcracks. The number of cracks, sum of the crack lengths, and frequency distribution were recorded for each specimen. Microdamage accumulated non-linearly with increasing total strain on the specimen, but the mean crack length remained the same with increasing damage.

Abstract Chemically treated bovine pericardium (BP) has been used extensively in the fabrication of bioprosthetic heart valves (BHV), which have compared to mechanical valves, superior fluid dynamical properties. However, BHVs continue to suffer limited long-term durability and will fail in 8–10 years, as result of calcification and mechanical damage. Our long-term goal is to improve BHV functional performance through the development of improved constitutive models. These models lead to a better understanding of the role tissue microstructure in determining overall mechanical behavior and limited long-term durability.

This study investigates the hypothesis that the equilibrium friction coefficient of cartilage decreases with increasing compressive strain. Furthermore, when accounting for this strain-dependence, it is hypothesized that the temporal response of the friction coefficient correlates linearly with interstitial fluid load support, in the configuration of unconfined compression stress-relaxation. Both hypotheses were confirmed from theory and experiment.

Recent experimental studies on human and bovine cortical bone shows that fracture strength of a cortical bone cannot be characterized by a single value of fracture toughness, but rather by variable crack growth resistance values. The mechanism of resistance of a crack extension in a bone is generally defined by R-curve behavior, which can be expressed as the relation between crack growth resistance values and crack extension. Crack bridging stress in front of a crack has been shown to be the main source of this resistance of the bone crack extension. The calculation of this bridging stress is important for predicting fracture stress in cortical bone material. In this study, a theoretical model based on weight function was developed to evaluate the bridging stress in front of a cortical bone crack tip. The main goal of this research was to investigate the role of specimen orientation on bridging stress. The hypothesis used was that specimen orientation has significant influence on the bridging stress. Two specific aims are developed to support this hypothesis: determination of the bridging stress along a crack length and investigation of the orientation effect on bridging stress. A weight function formulation was used to calculate crack opening displacements. The bridging stress along a crack can be found by minimizing the experimental and calculated crack opening displacements using a least square formulation. Finally, the bridging stress variation along a crack extension was examined in the specimen along two different orientations. The developed analytical model produces a gradually increasing trend of bridging stress with crack extension which depends on the orientation of the specimen extraction.