Soft tissues are pseudoelastic anisotropic materials; various formulas for their strain energy density have been proposed for modelling of their constitutive behaviour. However, the individual variance of elastic parameters is often more pronounced than their anisotropy, so that their constitutive relations can be modelled as either isotropic or orthotropic. Any hyperelastic model requires more mechanical tests to be input for an identification of its parameters than mere uniaxial tension tests; especially biaxial tension tests are very important also for isotropic hyperelastic materials. A design of a testing rig produced in cooperation of our institute with some local companies is presented. It enables us to carry out not only equibiaxial tension tests, but also some other biaxial tensile tests, because displacements in both mutually perpendicular directions can be controlled independently. The proposal of various types of biaxial tests is presented in the paper, with examples of their realization with porcine aortic wall tissue. The contribution focuses on ways of evaluation of the results and on identification of parameters of various constitutive models. The use of more mechanical tests in identification of constitutive parameters can improve the predictive capability of the models substantially.

• MeSH
• arterie fyziologie   MeSH
• biomechanika MeSH
• elastická tkáň fyziologie   MeSH
• mechanický stres MeSH
• pevnost v tahu MeSH
• počítačová simulace MeSH
• pojivová tkáň fyziologie   MeSH
• prasata MeSH
• pružnost MeSH
• statistické modely MeSH
• teoretické modely MeSH
• testování materiálů MeSH
• zobrazování trojrozměrné MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• hodnotící studie MeSH

This study concerns procedural aspects of planar biaxial experiments on aortic tissues that have not been exhaustively addressed in the literature. The following questions are explored. First, is there a difference in the apparent mechanical properties if the experiments are conducted in a force-controlled regime or a displacement-controlled regime. Second, does it matter whether the deformations of the surface are tracked from one side of the tissue or the other (luminal vs. abluminal surface). The study provides answers to these questions with the help of a series of experiments on porcine aortic tissue, constitutive modelling and statistical analysis. It was found that the loading protocol does not substantially affect the constitutive response, while the surface orientation does.

• MeSH
• biomechanika MeSH
• mechanické jevy * MeSH
• mechanický stres MeSH
• prasata MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

V našem sdělení představujeme dosavadní výsledky společného výzkumu pracovišť Krajské nemocnice Liberec, a.s., a Technické univerzity v Liberci. Cílem projektu bylo sestrojit prototyp přístroje pro dvouosé měření mechanických vlastností lidské kůže in vivo. Dvouosé zatěžování umožní vyhodnocovat specifické parametry lidské kůže, které pro její anizotropii nelze zjistit při jednoosé tahové zkoušce. Prototyp byl nazván „BiEx“ (biaxial extensometer).

In our article we would like to present the results of joint research carried out at the Regional Hospital in Liberec and the Technical University of Liberec. The aim of this research was to design a prototype for biaxial measuring of mechanical properties of the human skin in vivo. Biaxial application of the load will allow for the evaluation of specific human skin parameters which cannot be determined during a uniaxial tensile test because of the skin anisotropy. This prototype was called “BiEx” (biaxial extensometer).

• Klíčová slova
• biomechanické vlastnosti kůže, dvouosý průtahoměr,
• MeSH
• biomechanika fyziologie   MeSH
• financování organizované MeSH
• fyziologie kůže MeSH
• lidé MeSH
• pružnost MeSH
• Check Tag
• lidé MeSH

Structure-based constitutive models might help in exploring mechanisms by which arterial wall histology is linked to wall mechanics. This study aims to validate a recently proposed structure-based constitutive model. Specifically, the model's ability to predict mechanical biaxial response of porcine aortic tissue with predefined collagen structure was tested. Histological slices from porcine thoracic aorta wall (n=9) were automatically processed to quantify the collagen fiber organization, and mechanical testing identified the non-linear properties of the wall samples (n=18) over a wide range of biaxial stretches. Histological and mechanical experimental data were used to identify the model parameters of a recently proposed multi-scale constitutive description for arterial layers. The model predictive capability was tested with respect to interpolation and extrapolation. Collagen in the media was predominantly aligned in circumferential direction (planar von Mises distribution with concentration parameter bM=1.03 ± 0.23), and its coherence decreased gradually from the luminal to the abluminal tissue layers (inner media, b=1.54 ± 0.40; outer media, b=0.72 ± 0.20). In contrast, the collagen in the adventitia was aligned almost isotropically (bA=0.27 ± 0.11), and no features, such as families of coherent fibers, were identified. The applied constitutive model captured the aorta biaxial properties accurately (coefficient of determination R(2)=0.95 ± 0.03) over the entire range of biaxial deformations and with physically meaningful model parameters. Good predictive properties, well outside the parameter identification space, were observed (R(2)=0.92 ± 0.04). Multi-scale constitutive models equipped with realistic micro-histological data can predict macroscopic non-linear aorta wall properties. Collagen largely defines already low strain properties of media, which explains the origin of wall anisotropy seen at this strain level. The structure and mechanical properties of adventitia are well designed to protect the media from axial and circumferential overloads.

• MeSH
• aorta thoracica anatomie a histologie   fyziologie   MeSH
• biologické modely * MeSH
• biomechanika MeSH
• kolagen metabolismus   MeSH
• mechanický stres MeSH
• reprodukovatelnost výsledků MeSH
• Sus scrofa MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

BACKGROUND: Intracapsular fractures of the femoral neck are mostly treated using individual cancellous screws or a dynamic hip screw in combination with anti-rotational cancellous screws. The goal of this study was to evaluate the possibility of using proximal femoral nails for the surgical stabilisation of intracapsular fractures of the femoral neck. METHODS: A total of 58 patients (30 male, 28 female) were evaluated in a retrospective study after a minimum postoperative follow-up of 24 months. The average length of time after surgery was 33.1 months. According to the AO classification, the following numbers of type 31B intracapsular fractures of the femoral neck were included in the study: by number, 20 cases of type 31B1, 12 cases of type 31B2 and 26 cases of 31B3. The biaxial proximal femoral nail (Targon PF, B. Braun, Aesculap(R), Germany) was the tested implant and was inserted using standard surgical techniques. RESULTS: No complications in healing were noted in 48 patients (82.8% of the study group) 2 years following injury. The most frequent complication found was avascular necrosis of the head in seven patients (12.1%). Pseudoarthrosis formation was seen in two patients (3.4%), and other severe peroperative complications were observed in two other patients (3.4%). Reoperations were indicated in five patients, all of whom received a total hip endoprosthesis. We did not observe any refracture in the area of the implant. After 12 months 83% of the patients stated that they felt no or little pain. CONCLUSION: The results of our study have proven that the Targon PF biaxial proximal femoral nail may be used in treating intracapsular fractures of the femoral neck.

• MeSH
• dospělí MeSH
• fraktury krčku femuru chirurgie   radiografie   MeSH
• hojení fraktur fyziologie   MeSH
• intramedulární fixace fraktury přístrojové vybavení   MeSH
• kloubní pouzdro chirurgie   radiografie   zranění   MeSH
• kostní hřeby MeSH
• lidé středního věku MeSH
• lidé MeSH
• následné studie MeSH
• pooperační komplikace radiografie   MeSH
• retrospektivní studie MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• hodnotící studie MeSH

INTRODUCTION: Aim of this study is to validate some constitutive models by assessing their capabilities in describing and predicting uniaxial and biaxial behavior of porcine aortic tissue. METHODS: 14 samples from porcine aortas were used to perform 2 uniaxial and 5 biaxial tensile tests. Transversal strains were furthermore stored for uniaxial data. The experimental data were fitted by four constitutive models: Holzapfel-Gasser-Ogden model (HGO), model based on generalized structure tensor (GST), Four-Fiber-Family model (FFF) and Microfiber model. Fitting was performed to uniaxial and biaxial data sets separately and descriptive capabilities of the models were compared. Their predictive capabilities were assessed in two ways. Firstly each model was fitted to biaxial data and its accuracy (in term of R2 and NRMSE) in prediction of both uniaxial responses was evaluated. Then this procedure was performed conversely: each model was fitted to both uniaxial tests and its accuracy in prediction of 5 biaxial responses was observed. RESULTS: Descriptive capabilities of all models were excellent. In predicting uniaxial response from biaxial data, microfiber model was the most accurate while the other models showed also reasonable accuracy. Microfiber and FFF models were capable to reasonably predict biaxial responses from uniaxial data while HGO and GST models failed completely in this task. CONCLUSIONS: HGO and GST models are not capable to predict biaxial arterial wall behavior while FFF model is the most robust of the investigated constitutive models. Knowledge of transversal strains in uniaxial tests improves robustness of constitutive models.

• MeSH
• aorta thoracica * MeSH
• biologické modely * MeSH
• biomechanika MeSH
• mechanické jevy * MeSH
• pevnost v tahu MeSH
• prasata MeSH
• testování materiálů MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Příspěvek informuje o přístroji SenseWear Armband™ , který na principu zaznamenávání několika fyziologických ukazatelů vypočítává energetický výdej. Primárně se jedná o dvouosé (v novější verzi již tříosé) akcelerometrické zařízení, které současně měří teplotu kůže, odpor kůže pro galvanický proud a teplotu v blízkém okolí těla. Prezentace přístroje je zasazena do kontextu dnešních možností výpočtu energetického výdeje při pohybové aktivitě. V rámci sdělení je představena vlastní studie, která testovala přístroj během chůze na elektronickém běhátku, přičemž vykázaný energetický výdej byl porovnán s výsledky nepřímé kalorimetrie.

The paper informs about the SenseWear Armband device, which on the principle of recording several physiological parameters calculates the energy expenditure. Primarily, it is a biaxial (in a newer version already triaxial) accelerometrical device that simultaneously measures the skin temperature, the galvanic skin response and the near-body temperature. The presentation of the device is set in the context of today's possibilities of calculating energy expenditure during physical activity. We present our own study that tested the device during walking on an electronic treadmill, and reported energy expenditure by the SenseWear Armband (version Pro3) was compared with the results of indirect calorimetry. Úvod

• Klíčová slova
• senseWear Armband, energetický výdej,
• MeSH
• ambulantní monitorování přístrojové vybavení   MeSH
• chůze MeSH
• dítě MeSH
• dospělí MeSH
• energetický metabolismus fyziologie   MeSH
• financování organizované MeSH
• interpretace statistických dat MeSH
• lidé MeSH
• mladý dospělý MeSH
• nepřímá kalorimetrie MeSH
• pohybová aktivita fyziologie   MeSH
• reprodukovatelnost výsledků MeSH
• statistika jako téma MeSH
• výzkum statistika a číselné údaje   MeSH
• zátěžový test přístrojové vybavení   MeSH
• Check Tag
• dítě MeSH
• dospělí MeSH
• lidé MeSH
• mladý dospělý MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH

BACKGROUND: Results of biomechanical simulation of the abdominal aortic aneurysm (AAA) depend on the constitutive description of the wall. Based on in vitro and in vivo experimental data several constitutive models for the AAA wall have been proposed in the literature. Those models differ strongly from each other and their impact on the computed stress in biomechanical simulation is not clearly understood. METHODS: Finite element (FE) models of AAAs from 7 patients who underwent elective surgical repair were used to compute wall stresses. AAA geometry was reconstructed from CT angiography (CT-A) data and patient-specific (PS) constitutive descriptions of the wall were derived from planar biaxial testing of anterior wall tissue samples. In total 28 FE models were used, where the wall was described by either patient-specific or previously reported study-average properties. This data was derived from either uniaxial or biaxial in vitro testing. Computed wall stress fields were compared on node-by-node basis. RESULTS: Different constitutive models for the AAA wall cause significantly different predictions of wall stress. While study-average data from biaxial testing gives globally the same stress field as the patient-specific wall properties, the material model based on uniaxial test data overestimates the wall stress on average by 30 kPa or about 67% of the mean stress. A quasi-linear description based on the in vivo measured distensibility of the AAA wall leads to a completely altered stress field and overestimates the wall stress by about 75 kPa or about 167% of the mean stress. CONCLUSION: The present study demonstrated that the constitutive description of the wall is crucial for AAA wall stress prediction. Consequently, results obtained using different models should not be mutually compared unless different stress gradients across the wall are not taken into account. Highly nonlinear material models should be preferred when the response of AAA to increased blood pressure is investigated, while the quasi-linear model with high initial stiffness produces negligible stress gradients across the wall and thus, it is more appropriate when response to mean blood pressure is calculated.

• MeSH
• analýza metodou konečných prvků * MeSH
• aneurysma břišní aorty * MeSH
• aorta abdominalis * MeSH
• biomechanika MeSH
• lidé MeSH
• mechanický stres * MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

INTRODUCTION: There is a striking difference in the reported mean response of abdominal aortic aneurysm tissue in academic literature depending on the type of tests (uniaxial vs biaxial) performed. In this paper, the hypothesis variability caused by differences in experimental protocols is explored using porcine aortic tissue as a substitute for aneurysmal tissue. METHODS: Nine samples of porcine aorta were created and both uniaxial and biaxial tests were performed. Three effects were investigated. (i) Effect of sample (non) preconditioning, (ii) effect of objective function used (normalised vs non-normalised), and (iii) effect of chosen procedure used for mean response calculation: constant averaging (CA) vs fit to averaged response (FAR) vs fit to all data (FAD). Both the overall shape of mean curve and mean initial stiffness were compared. RESULTS: (i) Non-preconditioning led to a much stiffer response, and initial stiffness was about three times higher for a non-preconditioned response based on uniaxial data compared to a preconditioned biaxial response. (ii) CA led to a much stiffer response compared to FAR and FAD procedures which gave similar results. (iii) Normalised objective function produced a mean response with six times lower initial stiffness and more pronounced nonlinearity compared to non-normalised objective function. DISCUSSION: It is possible to reproduce a mechanically inconsistent response purely by using the chosen experimental protocol. Non-preconditioned data from failure tests should be used for FE simulation of the elastic response of aneurysms. CA should not be used to obtain a mean response.

• MeSH
• aneurysma břišní aorty * MeSH
• aorta abdominalis MeSH
• aorta MeSH
• biomechanika MeSH
• mechanický stres MeSH
• počítačová simulace MeSH
• prasata MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

This study investigates the biomechanical properties of ascending aortic aneurysms focusing on the inter-patient differences vs. the heterogeneity within a patient's aneurysm. Each specimen was tested on a biaxial testing device and the resulting stress-strain response was fitted to a four-parameter Fung constitutive model. We postulate that the inter-patient variability (differences between patients) blurs possible intra-patient variability (regional heterogeneity) and, thus, that both effects must be considered to shed light on the role of heterogeneity in aneurysm progression. We propose, demonstrate, and discuss two techniques to assess differences by, first, comparing conventional biomechanical properties and, second, the overall constitutive response. Results show that both inter- and intra-patient variability contribute to errors when using population averaged models to fit individual tissue behaviour. When inter-patient variability was accounted for and its effects excluded, intra-patient heterogeneity could be assessed, showing a wide degree of heterogeneity at the individual patient level. Furthermore, the right lateral region (from the patient's perspective) appeared different (stiffer) than the other regions. We posit that this heterogeneity could be a consequence of maladaptive remodelling due to altered loading conditions that hastens microstructural changes naturally occurring with age. Further validation of these results should be sought from a larger cohort study.

• MeSH
• aneurysma hrudní aorty * MeSH
• aortální aneurysma * MeSH
• kohortové studie MeSH
• lidé MeSH
• mechanický stres MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH