In this article, we present the design and validation of a non-contact scanning system for the development of a three-dimensional (3D) model of moist biological samples. Due to the irregular shapes and low stiffness of soft tissue samples, the use of a non-contact, reliable geometry scanning system with good accuracy and repeatability is required. We propose a reliable 3D scanning system consisting of a blue light profile sensor, stationary and rotating frames with stepper motors, gears and a five-phase stepping motor unit, single-axis robot, control system, and replaceable sample grips, which once mounted onto the sample, are used for both scanning and mechanical tests. The proposed system was validated by comparison of the cross-sectional areas calculated based on 3D models, digital caliper, and vision-based methods. Validation was done on regularly-shaped samples, a wooden twig, as well as tendon fascicle bundles. The 3D profiles were used for the development of the 3D computational model of the sample, including surface concavities. Our system allowed for 3D model development of samples with a relative error of less than 1.2% and high repeatability in approximately three minutes. This was crucial for the extraction of the mechanical properties and subsequent inverse analysis, enabling the calibration of complex material models.
The challenge for researchers is to develop measurement techniques that can deal with biological specimens (e.g. the human Achilles tendon) characterized by high deformation during examination. The relevant quantity which has to be investigated in laboratory experiments is the deformation or strain field of the specimen subjected to a given load. In experimental mechanics, the most remarkable technique used for strain field computation is the Digital Image Correlation (DIC) method. In the paper, the DIC method is employed to study biomaterial parameters of human Achilles tendons (AT) subjected to tensile uniaxial loadings. The application of DIC allows the heterogeneity of tendon deformation to be taken into consideration. Young's modulus of AT based on the strain field obtained from a vision-based measurement is estimated and the results are discussed. A map of Young's modulus (YM) is demonstrated as well.
In this study, we develop a modeling and experimental framework for multiscale identification of the biomechanical properties of the human Achilles tendon (AT). For this purpose, we extend our coarse-grained model of collagen fibrous materials with a chemomechanical model of collagen type I decomposition. High-temperature degradation of molecular chains of collagen in a water environment was simulated using a reactive molecular dynamics (MD) method. The results from MDs simulations allowed us to define the Arrhenius equation for collagen degradation kinetics and calculate the energy of activation together with the frequency factor. Kinetic coefficients obtained from a MD simulations were further used to provide better calibration of the a coarse grained (CG) model of collagen denaturation. For the experimental part of our framework, we performed a uniaxial tensile test of the human AT with additional use of digital image correlation (DIC) for ex vivo strain tracking. Using a different path of strain tracking, we were able to include the inhomogeneity of deformation and, therefore, regional variations in tissue stiffness. Our results, both in modeling and the experimental part of the study, are in line with already existing reports and thus provide an improved approach for multiscale biomechanical and chemomechanical studies of the human AT.
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