The anisotropic and region-dependent mechanical response of wrap-around tendons under tensile, compressive and combined multiaxial loads.

The present work reports on the multiaxial region and orientation-dependent mechanical properties of two porcine wrap-around tendons under tensile, compressive and combined loads based on an extensive study with n=175 samples. The results provide a detailed dataset of the anisotropic tensile and compressive longitudinal properties and document a pronounced tension-compression asymmetry. Motivated by the physiological loading conditions of these tendons, which include transversal compression at bony abutments in addition to longitudinal tension, we systematically investigated the change in axial tension when the tendon is compressed transversally along one or both perpendicular directions.

On multiscale tension-compression asymmetry in skeletal muscle.

Skeletal muscle tissue shows a clear asymmetry with regard to the passive stresses under tensile and compressive deformation, referred to as tension-compression asymmetry (TCA). The present study is the first one reporting on TCA at different length scales, associated with muscle tissue and muscle fibres, respectively. This allows for the first time the comparison of TCA between the tissue and one of its individual components, and thus to identify the length scale at which this phenomenon originates.

Age-dependent mechanical and microstructural properties of the rabbit soleus muscle.

During growth there are serious changes in the skeletal muscles to compensate for the changed requirements in terms of body weight and size. In this study, the age-dependent (between 21 and 100 days) mechanical and microstructural properties of rabbit soleus muscle tissue were investigated. For this purpose, morphological properties (animal mass, soleus muscle mass, tibial length) were measured at 5 different times during aging.

On a phase-field approach to model fracture of small intestine walls.

We address anisotropic elasticity and fracture in small intestine walls (SIWs) with both experimental and computational methods. Uniaxial tension experiments are performed on porcine SIW samples with varying alignments and quantify their nonlinear elastic anisotropic behavior. Fracture experiments on notched SIW strips reveal a high sensitivity of the crack propagation direction and the failure stress on the tissue orientation.

Predicting muscle tissue response from calibrated component models and histology-based finite element models.

Skeletal muscle is an anisotropic soft biological tissue composed of muscle fibres embedded in a structurally complex, hierarchically organised extracellular matrix. In a recent work (Kuravi et al., 2021) we have developed 3D finite element models from series of histological sections.

Direct measurement of the direction-dependent mechanical behaviour of skeletal muscle extracellular matrix.

This paper reports the first comprehensive data set on the anisotropic mechanical properties of isolated endo- and perimysial extracellular matrix of skeletal muscle, and presents the corresponding protocols for preparing and testing the samples. In particular, decellularisation of porcine skeletal muscle is achieved with caustic soda solution, and mechanical parameters are defined based on compressive and tensile testing in order to identify the optimal treatment time such that muscle fibres are dissolved whereas the extracellular matrix remains largely intact and mechanically functional. At around 18 h, a time window was found and confirmed by histology, in which axial tensile experiments were performed to characterise the direction-dependent mechanical response of the extracellular matrix samples, and the effect of lateral pre-compression was studied.

Exhaustion of Skeletal Muscle Fibers Within Seconds: Incorporating Phosphate Kinetics Into a Hill-Type Model.

Initiated by neural impulses and subsequent calcium release, skeletal muscle fibers contract (actively generate force) as a result of repetitive power strokes of acto-myosin cross-bridges. The energy required for performing these cross-bridge cycles is provided by the hydrolysis of adenosine triphosphate (ATP). The reaction products, adenosine diphosphate (ADP) and inorganic phosphate (P ), are then used-among other reactants, such as creatine phosphate-to refuel the ATP energy storage.

Changes in three-dimensional muscle structure of rabbit gastrocnemius, flexor digitorum longus, and tibialis anterior during growth.

Muscular contraction dynamics depends on active and passive muscle properties (e.g., the force-velocity relation) as well as on the three-dimensional (3D) muscle structure (e.

Effects of Growth on Muscle, Tendon, and Aponeurosis Tissues in Rabbit Shank Musculature.

There exist several studies using morphological analyses of skeletal muscles to obtain a better understanding of muscle structure. The structural information obtained are primarily determined from single muscle components using individual animals of discrete ages. Further, little is known about changing dimensions of the aponeurosis, which is an important load-transferring interface in muscle mechanics.

Intermuscular pressure between synergistic muscles correlates with muscle force.

The purpose of the study was to examine the relationship between muscle force generated during isometric contractions (i.e. at a constant muscle-tendon unit length) and the intermuscular (between adjacent muscles) pressure in synergistic muscles.

Long-term mechanical behaviour of skeletal muscle tissue in semi-confined compression experiments.

In this study, porcine skeletal muscle tissue was tested until 112 hours post mortem using a semi-confined compression device that induces fascicles to enter one of the states of compression (mode I), tension (mode II), or constant length (mode III). Based on the authors׳ previous studies (Böl et al., 2014, 2015a), the anisotropic mechanical behaviour of the tissue was analysed, with a special focus on the testing time post mortem.

Novel microstructural findings in M. plantaris and their impact during active and passive loading at the macro level.

There are several studies dealing with experimental and structural analyses of skeletal muscles that are aimed at gaining a better understanding of three-dimensional muscle deformation and force generation. A variety of these contributions have performed structural or mechanical analyses, but very few have combined these approaches at different levels. To fill this gap, the present study aims to bring together three-dimensional micro-structural and mechanical findings in rabbit M.

Three-Dimensional Muscle Architecture and Comprehensive Dynamic Properties of Rabbit Gastrocnemius, Plantaris and Soleus: Input for Simulation Studies.

The vastly increasing number of neuro-muscular simulation studies (with increasing numbers of muscles used per simulation) is in sharp contrast to a narrow database of necessary muscle parameters. Simulation results depend heavily on rough parameter estimates often obtained by scaling of one muscle parameter set. However, in vivo muscles differ in their individual properties and architecture.

Tissue-scale anisotropy and compressibility of tendon in semi-confined compression tests.

In this study, porcine tendon tissue was tested with a dedicated semi-confined compression set-up that enables us to induce states of either fibrils in compression (mode I), tension (mode II) or at constant length (mode III), respectively. The results suggest that tendon tissue is compressible and demonstrates a significantly stiffer response in mode I than in mode III. This implies that the fibril direction remains the axis of transverse isotropy in compression and that it provides an anisotropic contribution to the tissue stress.

On the anisotropy of skeletal muscle tissue under compression.

This paper deals with the role of the muscle fibres and extracellular matrix (ECM) components when muscle tissue is subjected to compressive loads. To this end, dissected tissue samples were tested in compression modes which induced states of fibres in compression (I), in tension (II) or at constant length (III), respectively. A comparison of the stress responses indicated that the tissue behaviour is significantly different for these modes, including differences between the modes (I) and (III).

Three-dimensional surface geometries of the rabbit soleus muscle during contraction: input for biomechanical modelling and its validation.

There exists several numerical approaches to describe the active contractile behaviour of skeletal muscles. These models range from simple one-dimensional to more advanced three-dimensional ones; especially, three-dimensional models take up the cause of describing complex contraction modes in a realistic way. However, the validation of such concepts is challenging, as the combination of geometry, material and force characteristics is so far not available from the same muscle.

Compressive properties of passive skeletal muscle-the impact of precise sample geometry on parameter identification in inverse finite element analysis.

Due to the increasing developments in modelling of biological material, adequate parameter identification techniques are urgently needed. The majority of recent contributions on passive muscle tissue identify material parameters solely by comparing characteristic, compressive stress-stretch curves from experiments and simulation. In doing so, different assumptions concerning e.