Vol 2 - Issue 1

State of the Art in Bioengineering

List of Articles

Human skeletal muscle is a complex tissue with a strict and ordered hierarchy (muscle, fiber, myofibril) similar to rodent animal used to study the mechanical properties of healthy and pathological muscles (e.g. mdx mouse to mimic Duchenne disease). Collagen envelopes, actin and titin are the structures implicated in the passive mechanical properties. The active mechanical properties are related to the formation of actin-myosin cross bridges. This article presents the most commonly used mechanical tests to measure in vitro, at different scales, the passive (incremental stepwise extension test, stretch-release test, compressive test, fatigue-recovery test, eccentric contraction test) and active (force-frequency test, tetanus and twitch contraction tests) behaviors of rodent muscles. The next section of this literature review covers the need for in vivo protocols to be as close as possible to physiological conditions, allowing to keep the animal alive and to perform longitudinal mechanical studies, with the presentation of imaging methods (MRI and ultrasound-based elastography) in living rodents. Then the main factors (protocol heterogeneity, aging, etc.) influencing the mechanical properties are presented.

Magnetic resonance elastography (MRE) is a non-invasive imaging technique which is becoming more commonly used in radiology departments to assess different stages of liver fibrosis. In the last decade, numerous MRE protocols have been developed to measure the shear stiffness of different tissues such as skeletal muscle, breast, kidney, and brain to characterize the mechanical behavior of living tissues. Thus, in addition to the anatomical and textural images obtained with the classical magnetic resonance imaging (MRI) exam, it is now possible to correlate the morphological features with the mechanical properties, allowing for more accurate follow-up and treatment of lung pathology. During the COVID-19 pandemic, MRE has found another relevant application in the assessment of damage to the lung parenchyma resulting from viral infection. This review provides a better understanding of how to assess pulmonary biomechanics using the MRE technique.