The Functionally Grading Elastic and Viscoelastic Properties of the Body Region of the Knee Meniscus

Abstract

The knee meniscus is a highly porous structure which exhibits a grading architecture through the depth of the tissue. The superficial layers on both femoral and tibial sides are constituted by a fine mesh of randomly distributed collagen fibers while the internal layer is constituted by a network of collagen channels of a mean size of 22.14 $$\mu $$ μ m aligned at a $$30^{\circ }$$ 30 ∘ inclination with respect to the vertical. Horizontal dog-bone samples extracted from different depths of the tissue were mechanically tested in uniaxial tension to examine the variation of elastic and viscoelastic properties across the meniscus. The tests show that a random alignment of the collagen fibers in the superficial layers leads to stiffer mechanical responses (E = 105 and 189 MPa) in comparison to the internal regions (E = 34 MPa). All regions exhibit two modes of relaxation at a constant strain ($$\tau _1 = 6.4$$ τ 1 = 6.4 to 7.7 s, $$\tau _2$$ τ 2 = 49.9 to 59.7 s).

On the Fractional Transversely Isotropic - Functionally Graded - Nature of Soft Biological Tissues Under Confined Consolidation

“…Biological soft tissues, such as the meniscal tissue (Figure 1), exhibit a hierarchical porous solid matrix and an interstitial fluid flowing into the pores [1][2][3][4][5]. The overall mechanical behaviour depends not only on the solid matrix deformation but also on the movement of the fluid in and out of the pores during the deformation.…”

“…They perform several functions like load bearing, lubrication, energy absorption and stability [7,8]. In light of our recent experimental, theoretical and numerical studies [1,2,[9][10][11], we understand that each region has different functions. In [1,2], the unique structure of the body region that fulfils load-bearing and energy absorption capabilities is discussed.…”

The Human Meniscus Behaves as a Functionally Graded Fractional Porous Medium under Confined Compression Conditions

“…Currently, the clinical outcomes of these implants are not ideal [5] due to the fact that they do not mimic the structure-property relationships of the tissue as these are still not well understood [6]. Among many biologic tissues, the meniscal tissue is composed of porous solid matrices-mainly collagen-with fluid filling the pores [7][8][9][10]. The overall mechanical behaviour of this type of tissues depends not only on the solid matrix deformation, but also on the movement of the fluid in and out of the collagen channels [7,8] during the deformation.…”

“…Among many biologic tissues, the meniscal tissue is composed of porous solid matrices-mainly collagen-with fluid filling the pores [7][8][9][10]. The overall mechanical behaviour of this type of tissues depends not only on the solid matrix deformation, but also on the movement of the fluid in and out of the collagen channels [7,8] during the deformation.…”

“…Meniscal tissue exhibit a non-uniform and anisotropic porosity, which is related to the graded material properties. Such graded material properties are fundamental for the correct functioning of this tissue [8]. The investigation of the material properties, coupled with the quantification of architectural parameters, such as the porosity and channel interconnectivity, will enable the design of artificial cellular structure, which can resemble the native behaviour of the tissue (see, for instance, [11]).…”