We tested the hypothesis that matrix glycosaminoglycans contribute to lung tissue viscoelasticity. We exposed lung parenchymal strips to specific degradative enzymes (chondroitinase ABC, heparitina...

Effect of glycosaminoglycan degradation on lung tissue viscoelasticity.

In fibrous connective tissue networks, mechanical loads may be transferred from one fiber to the next by friction between slipping fibers (J. Appl. Physiol. 74: 665–681, 1993). Here we tested that ...

Dynamic moduli of rabbit lung tissue and pigeon ligamentum propatagiale undergoing uniaxial cyclic loading.

We describe a novel constitutive model of lung parenchyma, which can be used for continuum mechanics based predictive simulations. To develop this model, we experimentally determined the nonlinear material behavior of rat lung parenchyma. This was achieved via uni-axial tension tests on living precision-cut rat lung slices. The resulting force-displacement curves were then used as inputs for an inverse analysis. The Levenberg-Marquardt algorithm was utilized to optimize the material parameters of combinations and recombinations of established strain-energy density functions (SEFs). Comparing the best-fits of the tested SEFs we found Wpar = 4.1 kPa(I1-3)2 + 20.7 kPa(I1 - 3)3 + 4.1 kPa(-2 ln J + J2 - 1) to be the optimal constitutive model. This SEF consists of three summands: the first can be interpreted as the contribution of the elastin fibers and the ground substance, the second as the contribution of the collagen fibers while the third controls the volumetric change. The presented approach will help to model the behavior of the pulmonary parenchyma and to quantify the strains and stresses during ventilation.

https://www.tpbin.com/Uploads/Subjects/2eca6d1a-14c5-4fe9-9063-08c8ca9287fe.pdf

Material model of lung parenchyma based on living precision-cut lung slice testing.

A computer-controlled optical electromechanical biaxial test system was employed to study the mechanical response of excised sheets of canine visceral pleura. Three classes of tests were performed: uniform biaxial stretching tests and tests in which the specimen was cyclically stretched along one axis while either the load or dimension was maintained at a prescribed level in the orthogonal direction. The tests were defined completely within the software. Strain was inferred from tracking four particles affixed to the central region of the specimen surface. The visceral pleura was found to behave similarly to other biological soft tissues and required preconditioning to yield repeatable responses. In addition, the visceral pleura appeared to possess in-plane transverse isotropic material symmetry and to exhibit strong in-plane mechanical coupling at lower loads. The data presented herein is sufficient for determination of certain three-dimensional constitutive laws which are essential for further biomechanical analyses of the visceral pleura's role in lung response.

Mechanical behavior of excised canine visceral pleura

The rheological properties of lung tissue are complex and nonlinear and contribute significantly to both the elastic and dissipative mechanical properties of the lung. Nevertheless, there remain large gaps in our understanding of precisely how the bulk rheological behavior of lung tissue is linked to the properties of its constituents and their interactions. In this paper a model is developed that attempts to provide such a link. The model consists of a sheet of randomly aligned fibers whose orientations are constantly changing due to thermal motion. When the sheet is suddenly stretched uniaxially, the fibers align themselves preferentially in the direction of strain. However, as a result of the continual thermal motion of the fibers, there is a net transfer of momentum between the fibers and the rest of the tissue. This produces a restoring force in the tissue sheet. The thermal motion also makes the fibers gradually revert back to a random orientation, so that the strain-generated stress within the tissue decays asymptotically to zero. It is shown that the behavior of this model closely approximates quasilinear viscoelasticity, in which the static stress–strain behavior is separable from the dynamic stress relaxation behavior. © 1998 Biomedical Engineering Society.

A micromechanical model of lung tissue rheology.

We examined the temperature dependence of small degassed hamster lung strip mechanics to develop insights into the molecular basis of lung elasticity Quasi-static length-tension curves of adapted 

J. T. Bowers

Papers

Thermoelastic properties of uniaxially deformed lung strips.