Viscoelastic properties of bovine knee joint articular cartilage: dependency on thickness and loading frequency

Abstract

BackgroundThe knee is an incongruent joint predisposed to developing osteoarthritis, with certain regions being more at risk of cartilage degeneration even in non-osteoarthrosed joints.At present it is unknown if knee regions prone to cartilage degeneration have similar storage and/or loss stiffness, and frequency-dependent trends, to other knee joint cartilage. The aim of this study was to determine the range of frequency-dependent, viscoelastic stiffness of articular cartilage across the bovine knee joint. Such changes were determined at frequencies associated with normal and rapid heel-strike rise times.MethodsCartilage on bone, obtained from bovine knee joints, was tested using dynamic mechanical analysis (DMA). DMA was performed at a range of frequencies between 1 and 88 Hz (i.e. relevant to normal and rapid heel-strike rise times). Viscoelastic stiffness of cartilage from the tibial plateau, femoral condyles and patellar groove were compared.ResultsFor all samples the storage stiffness increased, but the loss stiffness remained constant, with frequency. They were also dependent on cartilage thickness. Both the loss stiffness and the storage stiffness decreased with cartilage thickness. Femoral condyles had the thinnest cartilage but had the highest storage and loss stiffness. Tibial plateau cartilage not covered by the meniscus had the thickest cartilage and lowest storage and loss stiffness.ConclusionDifferences in regional thickness of knee joint cartilage correspond to altered frequency-dependent, viscoelastic stiffness.

Nanoscopic dynamic mechanical analysis of resin–infiltrated dentine, under in vitro chewing and bruxism events

“…Thereby, if the energy stored is too great, then excess energy would potentially be dissipated through cracking the tissue; i.e., resin-dentine interface failure. This mechanism would be consistent with resin-dentine inter-diffusion zone breakdown, preferentially the hybrid layer, occurring through increased energy during impact loading (Espino et al, 2014). This failure coincides with the gap that was formed within the resin-dentine interface which clearly detached the hybrid layer from the bottom of the hybrid layer, though both structures became deeply remineralised (Fig 2D).…”

“…The work performed by the probe of the nanoindentator in the adhesive interface is divided into two parts that follow two different routes: i) elastic energy, which is stored in the material and returned to the probe within each oscillating cycle; ii) viscous energy, which is dissipated as heat (Gong and Guan, 2003;Espino et al, 2014). Storage and viscous moduli account respectively for the energy stored and dissipated.…”

Ions-modified nanoparticles affect functional remineralization and energy dissipation through the resin-dentin interface

“…A general idea of the behavior of a viscoelastic material can be obtained by the value of the ratio between the loss and the storage modulus (E"/E'). This quotient is represented by tan δ (Espino et al, 2014), being a measure of the ratio of the energy dissipated by the system to the energy stored in the system that enables its elastic recoil.…”

“…The lower tan δ, the greater the proportion of energy available in the system for recoil and/or failure (Espino et al, 2014). As a consequence, a general trend to lower levels of accumulated energies at the interface can be appreciated after 21 days of SBFS storage, when dentin samples are infiltrated with Ca-NPs.…”

“…As stated above, storage modulus represents the elastic energy stored which is released after deformation, characterizing the elastic behavior (Espino et al, 2014;Ryou et al, 2015). Mapping of the bonded interfaces enabled identification of both peritubular and intertubular dentin in the property maps as one of the most crucial junctions in preventing crack generation and propagation across the boundary between the two different phases (Angker and Swain, 2006).…”