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

Material properties of soft-tissue samples are often derived through uniaxial tensile testing. For engineering materials, testing parameters (e.g., sample geometries and clamping conditions) are described by international standards; for biological tissues, such standards do not exist. To investigate what testing parameters have been reported for tensile testing of human soft-tissue samples, a systematic review of the literature was performed using PRISMA guidelines. Soft tissues are described as anisotropic and/or hyperelastic. Thus, we explored how the retrieved parameters compared against standards for engineering materials of similar characteristics. All research articles published in English, with an Abstract, and before 1 January 2023 were retrieved from databases of PubMed, Web of Science, and BASE. After screening of articles based on search terms and exclusion criteria, a total 1,096 articles were assessed for eligibility, from which 361 studies were retrieved and included in this review. We found that a non-tapered shape is most common (209 of 361), followed by a tapered sample shape (92 of 361). However, clamping conditions varied and were underreported (156 of 361). As a preliminary attempt to explore how the retrieved parameters might influence the stress distribution under tensile loading, a pilot study was performed using finite element analysis (FEA) and constitutive modeling for a clamped sample of little or no fiber dispersion. The preliminary FE simulation results might suggest the hypothesis that different sample geometries could have a profound influence on the stress-distribution under tensile loading. However, no conclusions can be drawn from these simulations, and future studies should involve exploring different sample geometries under different computational models and sample parameters (such as fiber dispersion and clamping effects). Taken together, reporting and choice of testing parameters remain as challenges, and as such, recommendations towards standard reporting of uniaxial tensile testing parameters for human soft tissues are proposed.

• Publikační typ
• systematický přehled 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

AIMS: Stress urinary incontinence and pelvic organ prolapse are very common conditions with a proportion of patients requiring implantation of synthetic materials for a durable repair. However increasing numbers of post-surgical complications have been reported related to the use of polypropylene meshes. One hypothesis for the adverse response is poor mechanical matching of the relatively stiff polypropylene mesh particularly as materials in the pelvic floor will need to cope with decades of distension as occurs with increase of intraabdominal pressure on coughing, laughing, or sneezing. METHODS: In this study we have undertaken a very simple fatigue testing regime to compare the mechanical abilities of six materials. Four commercial meshes in clinical use and two novel electrospun materials not yet evaluated in the clinic were assessed using a uniaxial tensile test. This was performed on six samples of each dry material and on another six samples of each material after just 3 days of fatigue conditions using a dynamic bioreactor. RESULTS: The four commercial materials showed permanent mechanical deformation after just 3 days of stretching these materials by 25% elongation on a regular dynamic cycle, whereas the two new materials presented more elastic properties without deformation. CONCLUSIONS: We suggest that a test as simple as this 3-day fatigue testing is sufficient to distinguish between materials which have already been found to cause complications clinically and newer materials yet to be tested clinically which will hopefully prove more mechanically appropriate for implantation in the pelvic floor.

• MeSH
• chirurgické síťky * MeSH
• lidé MeSH
• mechanické jevy MeSH
• pánevní dno chirurgie   MeSH
• pevnost v tahu MeSH
• polypropyleny MeSH
• prolaps pánevních orgánů chirurgie   MeSH
• stresová inkontinence moči chirurgie   MeSH
• testování materiálů * MeSH
• Check Tag
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Decellularized human pericardium is under study as an allogenic material for cardiovascular applications. The effects of crosslinking on the mechanical properties of decellularized pericardium were determined with a uniaxial tensile test, and the effects of crosslinking on the collagen structure of decellularized pericardium were determined by multiphoton microscopy. The viability of human umbilical vein endothelial cells seeded on decellularized human pericardium and on pericardium strongly and weakly crosslinked with glutaraldehyde and with genipin was evaluated by means of an MTS assay. The viability of the cells, measured by their metabolic activity, decreased considerably when the pericardium was crosslinked with glutaraldehyde. Conversely, the cell viability increased when the pericardium was crosslinked with genipin. Coating both non-modified pericardium and crosslinked pericardium with a fibrin mesh or with a mesh containing attached heparin and/or fibronectin led to a significant increase in cell viability. The highest degree of viability was attained for samples that were weakly crosslinked with genipin and modified by means of a fibrin and fibronectin coating. The results indicate a method by which in vivo endothelialization of human cardiac allografts or xenografts could potentially be encouraged.

• MeSH
• alografty MeSH
• biokompatibilní materiály * chemie   MeSH
• biomechanika MeSH
• endoteliální buňky pupečníkové žíly (lidské) cytologie   metabolismus   MeSH
• fibrin MeSH
• fibronektiny MeSH
• glutaraldehyd MeSH
• heterografty MeSH
• iridoidy MeSH
• kolagen chemie   ultrastruktura   MeSH
• lidé MeSH
• mikroskopie fluorescenční multifotonová MeSH
• perikard chemie   transplantace   ultrastruktura   MeSH
• pevnost v tahu MeSH
• povrchová plasmonová rezonance MeSH
• reagencia zkříženě vázaná MeSH
• testování materiálů MeSH
• viabilita buněk MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

OBJECTIVE: Hair quality and scalp characteristics are considered to be a significant marker of health. This marker is reflected in mechanical properties of hair. To investigate these properties, hair samples have been collected among women of different age and then analyzed. The thickness, Young's modulus of elasticity and ultimate strength limit were the main observed parameters. METHODS: The diameter of each hair has been measured using an optical microscope equipped with a digital camera. The hair was then clipped into the uniaxial tensile testing device. Each sample has been stretched to failure at a speed of 2 mm/min and force vs. elongation was recorded. The mechanical results were converted with respect to the diameter and Stress-Strain curve was obtained for each sample. In addition, all the analyzed samples were divided into two groups in dependence on the age, namely samples from women younger than 35 and over 35 years of age. All the measured parameters were statistically evaluated. RESULTS: Young's modulus, yield and elongation parameters showed no significant difference among samples. On the other hand there was a significant difference among the samples in ultimate strength values. Findings from group analysis showed that women under 35 years show about 5 times greater variability in hair strength than that of women above that age. CONCLUSION: The results of our study indicate that hair tendency to grow persists up to 30 years of age, then slowly decreases and then achieves a steady state around 60 years of age.

• MeSH
• biologické modely * MeSH
• dospělí MeSH
• elastografie MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanický stres MeSH
• pevnost v tahu fyziologie   MeSH
• pružnost * MeSH
• stárnutí fyziologie   MeSH
• vlasy, chlupy anatomie a histologie   růst a vývoj   fyziologie   MeSH
• zdravotní stav * MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Textile-based implant (mesh) treatment is considered as a standard of care for abdominal wall hernia repair. Computational models and simulations have appeared as one of the most promising approach to investigate biomechanics related to hernia repair and to improve clinical outcomes. This paper presents a novel anisotropic hypo-elastoplastic constitutive model specifically established for surgical knitted textile implants. The major mechanical characteristics of these materials such as anisotropy and permanent set have been reproduced. For the first time ever, we report an extensive mechanical characterization of one of these meshes, including cyclic uniaxial tension, planar equibiaxial tension and plunger type testing. These tests highlight the complex mechanical behavior with strong nonlinearity, anisotropy and permanent set. The novel anisotropic hypo-elasto-plastic constitutive model has been identified based on the tensile experiments and validated successfully against the data of the plunger experiment. In the future, implementation of this characterization and modeling approach to additional surgical knitted textiles should be the direction to follow in order to develop clinical decision support software for abdominal wall repair.

• MeSH
• chirurgické síťky * MeSH
• lidé MeSH
• operace kýly MeSH
• protézy a implantáty MeSH
• testování materiálů MeSH
• textilie MeSH
• ventrální hernie * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

OBJECTIVES: The technique of meshed skin grafting is known since 1960s. It was shown that there is a difference between the declared and real expansion ratio of the skin meshed graft. We hypothesize that the orientation of the Langer's lines in a split thickness skin graft is a key parameter in the resulting expansion ratio. METHODS: The skin graft meshing process was analyzed in two steps. In the first step, ex vivo uniaxial tests of human skin were performed. This served as an input for the constitutive model used for numerical simulations. In the second step, finite element analyses were performed so that stress distributions and expansion ratios could be determined. RESULTS: It was shown that peaks of true stress tended to be concentrated around the vertex of the mesh pattern region for all cases. The declared expansion was impossible to obtain for all expansion ratios having the meshing incision perpendicular to the Langer's lines. The highest difference between declared and real expansion ratio reaches 37%. CONCLUSIONS: With regard to literature dealing with expansion of skin grafts by meshing, a high scatter amongst data results is observed. This finding was also explained by our research, demonstrating the significance of Langer's lines and their relative orientation to the direction of meshing.

• MeSH
• analýza metodou konečných prvků MeSH
• biomechanika MeSH
• dermatochirurgické výkony * MeSH
• expanze tkáně MeSH
• fyziologie kůže * MeSH
• kůže * MeSH
• lidé MeSH
• mechanický stres MeSH
• pevnost v tahu MeSH
• transplantace kůže metody   MeSH
• transplantáty fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články 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

Our study aims to show that perivascular adipose tissue may significantly change the mechanical state of the abdominal aorta. To this end, uniaxial tensile tests with perivascular fat tissue were carried out. In the subsequent regression analysis, stress-strain data were fitted by the polynomial strain energy density. A constitutive model of adipose tissue was used in the analytical simulation of the inflation-extension behavior of the human abdominal aorta. The computational model was based on the theory of the bi-layered thick-walled tube. In addition to the effect of perivascular tissue, the effect of axial prestretch was also studied. It was found that the presence of perivascular tissue reduces the distensibility of the aorta. Axial prestretch applied to the aorta embedded in adipose tissue had an effect opposite to that of adipose tissue. Axially prestrained aorta exhibited higher distensiblity than non-prestrained aorta. It was also shown that the perivascular envelope bears some portion of the pressure loading and thus reduces the mechanical stresses inside the wall of aorta. A similar effect was found for axial prestretch.

• MeSH
• algoritmy MeSH
• aorta abdominalis fyziologie   MeSH
• biomechanika MeSH
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanický stres * MeSH
• senioři MeSH
• tuková tkáň krevní zásobení   MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH