Tensile mechanical properties of bovine articular cartilage: Variations with growth and relationships to collagen network components

Abstract

One approach to repairing articular defects is to regenerate cartilage by recapitulating the changes that occur during fetal and postnatal growth into adulthood, and to thereby restore functional biomechanical properties, especially those of the normally strong superficial region. The objectives of this study were ( I ) to characterize and compare tensile biomechanical properties of the superficial region of articular cartilage of the patellofemoral groove (PFG) and femoral condyle (FC) from bovine animals over a range of growth stages (third-trimester fetal, 1-3 week-old calf, and adult), and (2) to determine if these properties were correlated with collagen network components. With growth from the fetus to the adult, the equilibrium and dynamic tensile moduli and strength of cartilage samples increased by an average of 391-1060%, while the strain at the failure decreased by 43%. The collagen concentration (per wet weight) increased by 98'%), and the pyridinoline cross-link concentration increased by 730%, while the glycosaminoglycan concentration remained unchanged or decreased slightly. Some growth-associated changes were location-specific, with tensile moduli and strength attaining higher values in the PFG than the FC. The growth-associated variation in tensile moduli and strength were associated strongly with variation in the contents of collagen and pyridinoline cross-link, but not sulfated glycosaminoglycan. The marked changes in the tensile properties and collagen network components of articular cartilage with growth suggest that such parameters may be used to evaluate the degrees to which regenerated cartilage recapitulates normal development and growth.

Mechanisms of cartilage growth: Modulation of balance between proteoglycan and collagen in vitro using chondroitinase ABC

“…While aggrecan contains most of the chondroitinase ABC-susceptible material of the tissue, depletion of GAG with chondroitinase ABC may alter or displace some of these other chondroitin sulfate-or dermatan sulfate-containing molecules and allow new interactions between collagen fibrils that enhance the tensile integrity of the collagen network. Thus, although the tensile behavior of cartilage in the high-strain region is generally attributed to the tensile response of the collagen network (15,26), these results demonstrate an indirect, but dramatic, contribution of the GAG component.…”

“…Because the various zones of normal cartilage exhibit differences in biochemical composition and mechanical properties, the middle layer was also analyzed, and it displayed an initial state different from that of the superficial layer. The patellofemoral groove was used as the source of tissue, similar to tissue used in previous studies (15,19,21). Consequently, the biochemical and biomechanical properties of tissue samples at the time of explant were similar to those reported previously (15,21).…”

“…In articular cartilage, the incidence of cell division is low and matrix deposition is the major contributor to the increase in size (i.e., growth) and changes in biochemical composition (i.e., remodeling) of this tissue in vivo (13)(14)(15). Since articular cartilage tissue may undergo both appositional and interstitial growth, and the major contributor to cartilage growth is matrix deposition, the term "growth" is used subsequently in this article to refer collectively to both growth and remodeling, which can occur in the presence or absence of cellular proliferation.…”

“…During maturation of articular cartilage from fetus to skeletal maturity, there is an increase in collagen and pyridinoline (Pyr) crosslink densities, but little or no change in the content of glycosaminoglycans (GAGs) (14,(16)(17)(18). These biochemical changes are accompanied by an increase in tensile modulus and strength (15). In contrast to this type of in vivo growth and maturation, growth of cartilage explants in vitro in serum-supplemented medium results in a net deposition of proteoglycan that is greater than that of collagen, along with a decrease in mechanical integrity.…”

Boundary lubrication of articular cartilage: Role of synovial fluid constituents

“…Fresh osteochondral samples (n ϭ 40) were prepared for friction testing from the patellofemoral groove of 10 skeletally mature bovine stifle joints (ϳ1 year old, ϳ0.86 moles pyridinoline/mole collagen [40]), as described previously (7). Briefly, each sample consisted of an osteochondral core (radius 6 mm) and an apposed osteochondral annulus (outer radius [R o ] 3.2 mm, inner radius [R i ] 1.5 mm), both with central holes (radius 0.5 mm) drilled down into and exiting the bone to facilitate fluid depressurization.…”