A framework to assess mechano-tribological, structural and biochemical properties of articular cartilage

Articular cartilage (AC) is a specialized tissue with a unique biphasic structure that enables the high load-bearing ability and near-frictionless joint motion. The macroscale mechanical and tribological behavior of AC is dominated by interstitial fluid pressurization. Hence, microscale studies provide an opportunity to characterise local mechanical, tribological, structural and biochemical properties that may otherwise be limited during macroscale evaluation.

This study investigates an integrated assessment of the microscale surface properties of bovine AC by combining microscale indentation and reciprocating sliding experiments alongside Raman spectroscopy, scanning electron microscopy, and histomorphometry.

Microscale mechanical testing revealed a uniform effective instantaneous modulus at the surface with varying load (ranging 0.43-0.51 MPa, p = 0.452) and varying indentation rate (ranging 0.38-0.46 MPa, p = 0.621), along with compressive strain dependent viscoelastic behavior. Tribological testing revealed low microscale coefficients of friction with varying load (ranging 0.001-0.036, p = 0.005) and varying speed (ranging 0.002-0.047, p = 0.012). Further, zonal characterization showed uniquely arranged ECM orientation patterns across superficial, middle, and deep zones alongside depth-dependent variations in cellular attributes (cellular density, orientation, and proteoglycan intensity) and biochemical constituents (collagen organisation and proteoglycan distribution).

Collectively, these findings highlight the feasibility of combining microscale mechano-tribological testing with structural and biochemical characterisation to assess local properties of AC. The framework demonstrates load and rate-dependent functional behaviour at the surface and cross-sectional variations in cartilage structure and composition that are often dominated by interstitial fluid pressurisation during macroscale evaluation.