Scaffold-free cartilage subjected to frictional shear stress demonstrates damage by cracking and surface peeling

摘要

Scaffold-free engineered cartilage is being explored as a treatment for osteoarthritis. In this study, frictional shear stress was applied to determine the friction and damage behavior of scaffold-free engineered cartilage, and tissue composition was investigated as it relates to damage. Scaffold-free engineered cartilage frictional shear stress was found to exhibit a time-varying response similar to that of native cartilage. However, damage occurred which was not seen in native cartilage, manifesting primarily as tearing through the central plane of the constructs. In engineered cartilage, cells occupied a significantly larger portion of the tissue in the central region where damage was most prominent (18 ± 3% of tissue was comprised of cells in the central region vs. 5 ± 1% in the peripheral region, p < 0.0001). In native cartilage, cells comprised between 1% and 4% of tissue for all regions. Average bulk cellularity of engineered cartilage was also greater (68 × 10³ ± 4 × 10³ vs. 52 × 10³ ± 22 × 10³ cells/mg), though this difference was not significant. Bulk tissue comparisons showed significant differences between engineered and native cartilage in hydroxyproline content (8 ± 2 vs. 45 ± 3 μg HYP/mg dry weight), solid content (12.5 ± 0.4% vs. 17.9 ± 1.2%), shear modulus (0.06 ± 0.02 vs. 0.15 ± 0.07 MPa), and aggregate modulus (0.12 ± 0.03 vs. 0.32 ± 0.14 MPa respectively). These data indicate that enhanced collagen content and more uniform extracellular matrix distribution are necessary to reduce damage susceptibility.