Influence of layer separation on the determination of stomach smooth muscle properties

Abstract

Uniaxial tensile experiments are a standard method to determine the contractile properties of smooth muscles. Smooth muscle strips from organs of the urogenital and gastrointestinal tract contain multiple muscle layers with different muscle fiber orientations, which are frequently not separated for the experiments. During strip activation, these muscle fibers contract in deviant orientations from the force-measuring axis, affecting the biomechanical characteristics of the tissue strips. This study aimed to investigate the influence of muscle layer separation on the determination of smooth muscle properties. Smooth muscle strips, consisting of longitudinal and circumferential muscle layers (whole-muscle strips [WMS]), and smooth muscle strips, consisting of only the circumferential muscle layer (separated layer strips [SLS]), have been prepared from the fundus of the porcine stomach. Strips were mounted with muscle fibers of the circumferential layer inline with the force-measuring axis of the uniaxial testing setup. The force–length (FLR) and force–velocity relationships (FVR) were determined through a series of isometric and isotonic contractions, respectively. Muscle layer separation revealed no changes in the FLR. However, the SLS exhibited a higher maximal shortening velocity and a lower curvature factor than WMS. During WMS activation, the transversally oriented muscle fibers of the longitudinal layer shortened, resulting in a narrowing of this layer. Expecting volume constancy of muscle tissue, this narrowing leads to a lengthening of the longitudinal layer, which counteracted the shortening of the circumferential layer during isotonic contractions. Consequently, the shortening velocities of the WMS were decreased significantly. This effect was stronger at high shortening velocities.

Dynamic viscoelastic properties of porcine gastric tissue: Effects of loading frequency, region and direction

“…Error bars represent standard deviations (n = 6). For significant differences, see table 2. which the maximum force is generated, has been found to be 2.7 times slack length (Borsdorf et al, 2021). This is significantly greater elongations than applied in this study, which may have the consequence that the muscle layers do not generate any active force.…”

“…Contractility of smooth muscle fibers, which are oriented in several directions in muscularis is characterized as the active component, whereas the passive component is mainly determined by the elastic fibers in submucosa and muscularis (Bauer et al, 2020;Brandstaeter et al, 2019). The smooth muscle contractions have high impacts on understanding of function and development of biomaterials thus examined in several studies (Borsdorf et al, 2021;Gilja et al, 2005;Klemm et al, 2020;Tomalka et al, 2017).…”

Mechanical experimentation of the gastrointestinal tract: a systematic review

“…( 2020 ) studied both the intact wall of the stomach from pigs (mucosal and muscular layers) and just its muscle layer to determine the contribution of each layer in the tissue’s active behaviour, while Borsdorf et al. ( 2021 ) investigated the active response of the combined muscle layer (oblique, longitudinal and circular muscle) and just the circular gastric smooth muscle layer to compare their influence on the mechanical behaviour of the stomach from domestic pigs.…”

“…( 2020 ); Borsdorf et al. ( 2021 ) Indentation Kunkel et al. ( 2008 ) Compressive elastography Dargar et al.…”

“… 2015 ; Borsdorf et al. 2021 ). Therefore, nonlinear elastic laws, rather than linear elastic (which are used for traditional engineering materials such as metals and concrete, or for hard tissue like bone), are often used to describe the behaviour of such tissues (and more modern engineering materials such as polymers) (Holzapfel and Ogden 2006 ; Chagnon et al.…”