Anisotropic Compressive Properties of Passive Porcine Muscle Tissue

Abstract

The body has approximately 434 muscles, which makes up 40-50% of the body by weight. Muscle is hierarchical in nature and organized in progressively larger units encased in connective tissue. Like many soft tissues, muscle has nonlinear visco-elastic behavior, but muscle also has unique characteristics of excitability and contractibility. Mechanical testing of muscle has been done for crash models, pressure sore models, back pain, and other disease models. The majority of previous biomechanical studies on muscle have been associated with tensile properties in the longitudinal direction as this is muscle's primary mode of operation under normal physiological conditions. Injury conditions, particularly high rate injuries, can expose muscle to multiple stress states. Compressive stresses can lead to tissue damage, which may not be reversible. In this study, we evaluate the structure-property relationships of porcine muscle tissue under compression, in both the transverse and longitudinal orientations at 0.1 s-1, 0.01 s-1, or 0.001 s-1. Our results show an initial toe region followed by an increase in stress for muscle in both the longitudinal and transverse directions tested to 50% strain. Strain rate dependency was also observed with the higher strain rates showing significantly more stress at 50% strain. Muscle in the transverse orientation was significantly stiffer than in the longitudinal orientation indicating anisotropy. The mean area of fibers in the longitudinal orientation shows an increasing mean fiber area and a decreasing mean fiber area in the transverse orientation. Data obtained in this study can help provide insight on how muscle injuries are caused, ranging from low energy strains to high rate blast events, and can also be used in developing computational injury models.

A case for poroelasticity in skeletal muscle finite element analysis: experiment and modeling

“…Model calculated stresses had good agreement with previously published experimental work under compression (Pietsch et al, 2014; Van Loocke et al, 2006) which gives greater confidence in these results. Statistical results showed no dependence of permeability on strain level or orientation, while modeling results indicated strain and orientation dependence played less of a role than even a simple poroelastic model versus a solid model.…”

“…Cylindrical samples (4 mm height and 8 mm diameter) were removed from the muscle mid-belly using a drop cutter and a biopsy punch. As skeletal muscle exhibits transversely isotropic passive behavior (Pietsch et al, 2014; Takaza et al, 2012), samples were obtained in the longitudinal and the transverse directions.…”

Skeletal muscle tensile strain dependence: Hyperviscoelastic nonlinearity

“…A. Morrow et al, 2010; Pietsch et al, 2014; Takaza et al, 2012). However, the number of studies examining the time dependency are limited to compressive conditions (Bosboom et al, 2001; Pietsch et al, 2014; Van Loocke et al, 2009, 2008, 2006), single fiber (Bensamoun et al, 2006; Meyer et al, 2011) or whole muscle investigations (Anderson et al, 2002; Best et al, 1994; Grover et al, 2007), or utilize a linear or quasi-linear viscoelastic response (Gras et al, 2013, 2014; Myers et al, 1998). Thus, to the author's knowledge, there have been no previous modeling efforts which have included nonlinear tissue level strain dependent viscoelastic behavior for skeletal muscle in tension.…”

“…This is derived from a need for a more complete understanding of the material behavior of these tissues, enabling simulations to accurately predict both local and global tissue function. While computational models of skeletal muscle have been developing since the introduction of the Hill model in 1938 (Hill, 1938), there have been relatively few studies of muscle tensile material properties at the tissue level (Abraham et al, 2012; Takaza et al, 2012), with the majority of studies evaluating compressive properties (Böl et al, 2014; Pietsch et al, 2014; Van Loocke et al, 2009, 2008, 2006). Studies of the structural response of individual muscle fibers (Meyer et al, 2011) and intact muscles (Calvo et al, 2010; Gras et al, 2012; Myers et al, 1998) are more prevalent.…”

How does tissue preparation affect skeletal muscle transverse isotropy?

“…In the case of skeletal muscle these passive properties have a multifaceted purpose: allowing for the transmission of internal force generated at muscle fibers to tendons (Gindre et al, 2013; Huijing, 1999), storing energy during locomotion (Cavanagh and Komi, 1979; Ettema, 1996), and maintaining proper resting length for maximum force generation (Fridén and Lieber, 1998). Muscle fiber alignment results in tissue transverse isotropy (Morrow et al, 2010; Pietsch et al, 2014; Takaza et al, 2012; Van Loocke et al, 2006) as the material properties of the aligned fibers differ from those of the organized extracellular matrix (Meyer and Lieber, 2011). …”