Anisotropic Mechanics of Vascular Smooth Muscle Cells Exposed to Dynamic Loads

Abstract

Vascular smooth muscle cells (VSMCs) are the most prevalent cells in the arterial wall. In vivo, arteries are exposed to dynamic biaxial loads, thus when characterizing VSMC mechanics it is important to determine their anisotropic and time-dependent mechanical properties. Here, we use cellular microbiaxial stretching (CµBS) to apply complex deformations to single micropatterned VSMCs and measure the resulting changes in cell stress. Previously, CµBS has been used to measure VSMC mechanical properties in response to extensional strain. Here, we measure changes in cell stress in response to both extension and compression. Additionally, we measure immediate temporal changes in stress in response to cyclically applied deformations. We find that the VSMCs display clear hysteresis when incrementally stretched and compressed and demonstrate cycle-dependent stress-relaxation when exposed to cyclic step change extension and compression. Finally, we demonstrate that a Hill-type active fiber model is capable of replicating all observed hysteresis and cycle-dependent stress-relaxation, suggesting that the temporal stress-strain behavior of the cell is regulated by acto-myosin contraction and relaxation, rather than passive viscoelasticity. This study improves upon previous studies of cellular mechanical properties by considering cellular architecture and more complex deformations when measuring the time-dependent mechanical properties of VSMCs. These findings have important implications for modeling in mechanobiology as VSMCs are mechanosensitive and actively respond to changes in their mechanical environment to maintain vascular function.

Cellular Microbiaxial Stretching Assay for Measurement and Characterization of the Anisotropic Mechanical Properties of Micropatterned Cells

“…These studies showed that cells have anisotropic mechanical properties related to their internal actin cytoskeleton and demonstrate hysteresis in which stress is greater during loading than unloading. CμBS has also been used to study VSMCs under both tensile and compressive deformations ( strain = ±15%) and demonstrated that VSMCs demonstrate hysteresis in response to both types of loading (Rothermel, Franczek, & Alford, 2021). These studies are quasi-static, but CμBS can also be used to measure time-dependent cellular mechanical properties.…”

“…These studies are quasi‐static, but CμBS can also be used to measure time‐dependent cellular mechanical properties. VSMC stress was measured over time in response to cyclically applied tensile and compressive deformations and showed that VSMCs demonstrate cycle‐dependent stress relaxation (Rothermel et al., 2021). CμBS can also be used on longer time scales to measure mechanoadaptation in response to a sustained step change in strain.…”

“…The orientation of actomyosin fibers also influences hysteresis (Win et al., 2018) and is a primary mediator of cell anisotropic stress (Rothermel et al., 2020; Win et al., 2017). Using the measurements of cell stress and cytoskeletal architecture we are able to characterize the mechanical properties of VSMCs using architecture dependent models, such as Holzapfel‐Gasser‐Ogden type strain energy density functions (Rothermel et al., 2020; Win et al., 2017), Hill‐type descriptions (Rothermel et al., 2021; Win et al., 2018), or fiber‐based mechanoadaptation laws (Cook et al., 2021). These models are able to recapitulate the experimentally observed mechanical behaviors.…”