Bio‐Inspired 3D Environments for Cartilage Engineering

Abstract

José Luis Gómez Ribelles to Concha Articular Cartilage HistologyHyaline cartilage is a very specialized tissue in which a small number of cells, chondrocytes, are distributed in a quite particular organization. The extracellular matrix (ECM) is composed mainly of collagen type II fibers and proteoglycan aggregates, which are mainly formed by the association of aggrecan with a large number of glycosaminoglycan chains. The combination of the collagen fiber stiffness and the high water sorption capacity of glycosaminoglycans (GAGs) produces a hard tissue that is able to sustain the high compression loading to which articular cartilage is subjected [1-3] and is very permeable to water-soluble substances allowing the diffusion of nutrients and waste products of cell metabolism, which is crucial in the avascular tissue. Healthy articular cartilage contains between 70% and 75% of water, the GAGs content can be up to 20% depending on the joints and cartilage sites [4,5], and collagen type II can represent between 11% and 20% of the wet weight [6].Furthermore, ECM composition, and consequently its mechanical properties, cell shape, and cell distribution are not homogeneous. Different tissue layers, going from articular surface to subchondral bone, with quite different characteristics can be distinguished [7][8][9][10][11]. The articular surface layer contains flat chondrocytes dispersed in a network of collagen type II fibers preferentially aligned parallel to the surface, which gives the tissue a special ability to sustain the shear stress to which the articular surface is subjected. The transition zone contains dispersed rounded chondrocytes in a disordered network of collagen fibers. The deep zone contains large rounded chondrocytes ordered in columns perpendicular to articular surface and collagen fibers aligned in the same direction. Finally, the calcified cartilage is the interface with subchondral bone. It is characterized by hypertrophic chondrocytes, a high content of collagen type X in the ECM and by tissue mineralization. The level of GAGs is lower in the surface layer, increases in the transition zone, and is the highest in the deep zone. The elastic modulus of hyaline cartilage continuously increases with depth from the articular surface. Schinagl et al. [10] measured values Biomimetic Approaches for Biomaterials Development, First Edition. Edited by João F. Mano.

An “in vitro” experimental model to predict the mechanical behavior of macroporous scaffolds implanted in articular cartilage

“…In previous work authors have conducted indentation studies of the articular cartilage of rabbits [30,32].…”

Tissue engineering techniques to regenerate articular cartilage using polymeric scaffolds.

“…It has been proven that chondrocytes expanded in monolayer culture can redifferentiate when seeded in a 3D construct. Different types of 3D environments can be used, from gels to macroporous scaffolds [81,82].…”