Biomechanical and biochemical properties of the thoracic aorta in warmblood horses, Friesian horses, and Friesians with aortic rupture

Background: Thoracic aortic rupture and aortopulmonary fistulation are rare conditions in horses. It mainly affects Friesian horses. Intrinsic differences in biomechanical properties of the aortic wall might predispose this breed. The biomechanical and biochemical properties of the thoracic aorta were characterized in warmblood horses, unaffected Friesian horses and Friesians with aortic rupture in an attempt to unravel the underlying pathogenesis of aortic rupture in Friesian horses. Samples of the thoracic aorta at the ligamentum arteriosum (LA), mid thoracic aorta (T1) and distal thoracic aorta (T2) were obtained from Friesian horses with aortic rupture (A), nonaffected Friesian (NA) and warmblood horses (WB). The biomechanical properties of these samples were determined using uniaxial tensile and rupture assays. The percentages of collagen and elastin (mg/mg dry weight) were quantified. Results: Data revealed no significant biomechanical nor biochemical differences among the different groups of horses. The distal thoracic aorta displayed an increased stiffness associated with a higher collagen percentage in this area and a higher load-bearing capacity compared to the more proximal segments. Conclusions: Our findings match reported findings in other animal species. Study results did not provide evidence that the predisposition of the Friesian horse breed for aortic rupture can be attributed to altered biomechanical properties of the aortic wall

A new approach for noninvasive assessment of patient-specific material properties of arterial tissue

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Noninvasive Constitutive Model Parameter Identification Method for Arterial Tissue

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Determination of patient-specific material properties of cardiovascular tissue through noninvasive measurements

The mechanical properties of human biological tissue vary greatly. Hence, patient-specific material properties are a must for realistic intra-operative simulations. The determination of arterial material properties should be based on experimental data (i.e. diameter, length, intramural pressure, axial force and stress-free geometry). Currently, clinical data provide only non-invasively measured pressure-diameter data for superficial arteries (e.g. common carotid and femoral artery). To overcome this lack of information, an approach has been proposed taking into account certain assumptions regarding the in situ configuration and stress states of arterial walls [2]. This paper presents a method towards validation of this and other approaches. A finite element model of a simplified artery was used as a mock experimental situation. This method enables exact knowledge of the actual material properties, thereby allowing a qualitative evaluation of the different approaches. The results of the validation show that the material parameters estimated with the noninvasive approaches can deviate quite a lot from the real material properties. Future work is directed towards improving the existing noninvasive parameter estimation approaches.status: publishe

Non-invasive, energy-based assessment of patient-specific material properties of arterial tissue

The mechanical properties of human biological tissue vary greatly. The determination of arterial material properties should be based on experimental data, i.e. diameter, length, intramural pressure, axial force and stress-free geometry. Currently, clinical data provide only non-invasively measured pressure-diameter data for superficial arteries (e.g. common carotid and femoral artery). The lack of information forces us to take into account certain assumptions regarding the in situ configuration to estimate material properties in vivo. This paper proposes a new, non-invasive, energy-based approach for arterial material property estimation. This approach is compared with an approach proposed in the literature. For this purpose, a simplified finite element model of an artery was used as a mock experimental situation. This method enables exact knowledge of the actual material properties, thereby allowing a quantitative evaluation of material property estimation approaches. The results show that imposing conditions on strain energy can provide a good estimation of the material properties from the non-invasively measured pressure and diameter data.status: publishe

Planar biaxial testing of soft biological tissue using rakes: a critical analysis of protocol and fitting process

Mechanical characterization of soft biological tissue is becoming more and more prevalent. Despite the growing use of planar biaxial testing for soft tissue characterization, testing conditions and subsequent data analysis have not been standardized and vary widely. This also influences the quality of the result of the parameter fitting. Moreover, the testing conditions and data analysis are often not or incompletely reported, which impedes the proper comparison of parameters obtained from different studies. With a focus on planar biaxial tests using rakes, this paper investigates varying testing conditions and varying data analysis methods and their effect on the quality of the parameter fitting results. By means of a series of finite element simulations, aspects such as number of rakes, rakes׳ width, loading protocol, constitutive model, material stiffness and anisotropy are evaluated based on the degree of homogeneity of the stress field, and on the correlation between the experimentally obtained stress and the stress derived from the constitutive model. When calculating the aforementioned stresses, different definitions of the section width and deformation gradient are used in literature, each of which are looked into. Apart from this degree of homogeneity and correlation, also the effect on the quality of the parameter fitting result is evaluated. The results show that inhomogeneities can be reduced to a minimum for wise choices of testing conditions and analysis methods, but never completely eliminated. Therefore, a new parameter optimization procedure is proposed that corrects for the inhomogeneities in the stress field and induces significant improvements to the fitting results. Recommendations are made for best practice in rake-based planar biaxial testing of soft biological tissues and subsequent parameter fitting, and guidelines are formulated for reporting thereof in publications.publisher: Elsevier articletitle: Planar biaxial testing of soft biological tissue using rakes: A critical analysis of protocol and fitting process journaltitle: Journal of the Mechanical Behavior of Biomedical Materials articlelink: http://dx.doi.org/10.1016/j.jmbbm.2016.01.011 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Biaxial testing of soft tissue: a finite element analysis of protocol and fitting process

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Determination of layer-specific properties from planar biaxial tests on intact aortic wall

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Determination of layer-specific material properties from planar biaxial tension tests and uniaxial tests on intact arterial wall

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Mechanical characterization of arterial tissue: Simultaneous confocal imaging and tensile testing

To avoid damage as a consequence of a surgical procedure, it is important to define loading thresholds that can safely be applied to soft tissues. The goal of this research is to determine the mechanical properties of cardiovascular tissue, more specifically the sensitivity of the tissue to damage. To be able to quantify this sensitivity to damage, an experimental setup was designed. This setup can stretch a piece of cardiovascular tissue stepwise. After each elongation of the tissue a microscopic image can be taken with a confocal microscope. These images can then be analyzed in order to determine the strain of the tissue, the orientation of the fibers and the damage to the tissue. To study the elasticity of the tissue, the stress-strain curve was calculated for one of the tissue samples. The orientation of the fibers was compared at different depths in the sample. To determine the damage of the tissue, the number of microruptures in the tissue were analyzed. These first results are promising and serve as a proof of concept of the experimental setup.status: publishe