Failure in articular cartilage: Finite element predictions of stress, strain, and pressure under micro-indentation induced fracture.

Articular cartilage is found at the distal end of long bones and is responsible for assisting in joint articulation. While articular cartilage has remarkable resistance to failure, once initially damaged, degeneration is nearly irreversible. Thus, understanding damage initiation is important.

Effect of mineral diets on the development of cartilage material properties.

Vitamin D and minerals, including zinc (Zn) and manganese (Mn), are vital in the development of bones, but their roles in the development of articular cartilage material behavior are not well understood. In this study, articular cartilage material properties from a hypovitaminosis D porcine model were evaluated. Pigs were produced by sows fed vitamin D deficient diets during gestation and lactation, and the offspring were subsequently fed vitamin D deficient diets for 3 weeks during the nursery period.

Correlation of mineral density and elastic modulus of dog dentin using μ-CT and nanoindentation.

This study sought to 1) investigate the spatial distribution of mineral density of dog dentin using µ-CT and 2) characterize the relationship between the elastic modulus and mineral density of dog dentin using nanoindentation and µ-CT. Maxillary canine teeth of 10 mature dogs were scanned with a µ-CT then sectioned in the transverse and vertical planes and tested using nanoindentation. Spatial distribution of mineral density and elastic modulus was quantified.

Morphological quantification of the maxillary canine tooth in the domestic dog (Canis lupus familiaris).

Canine tooth shape is known to vary with diet and killing behavior in wild animals and the relationship between form and function is driven in part by selective pressure. However, comparative investigation of the domestic dog (Canis lupus familiaris) is of interest. How do they compare to their wild counterparts? This study sought to quantify and characterize the morphology of the canine tooth in the domestic dog, and to provide a preliminary investigation into the variance in canine tooth morphology across individual dogs of varying breeds.

Effect of osmolarity and displacement rate on cartilage microfracture clusters failure into two regimes.

Articular cartilage is a poroviscoelastic (PVE) material with remarkable resistance to fracture and fatigue failure. Cartilage failure mechanisms and material properties that govern failure are incompletely understood. Because cartilage is partially comprised of negatively charged glycosaminoglycans, altering solvent osmolarity can influence PVE relaxations.

Vitamin D deficiency and anatomical region alters porcine growth plate properties.

Ossification of growth plate cartilage mediates longitudinal extension of long bones. Biomechanical and biochemical disruptions of growth plate function may lead to abnormal bone growth. In humans and animals, severe dietary vitamin D deficiency can lead to rickets which features growth plate widening, resulting in abnormalities in growth.

Structure-function relationships in dog dentin.

Investigations into teeth mechanical properties provide insight into physiological functions and pathological changes. This study sought to 1) quantify the spatial distribution of elastic modulus, hardness and the microstructural features of dog dentin and to 2) investigate quantitative relationships between the mechanical properties and the complex microstructure of dog dentin. Maxillary canine teeth of 10 mature dogs were sectioned in the transverse and vertical planes, then tested using nanoindentation and scanning electron microscopy (SEM).

Effects of solvent osmolarity and viscosity on cartilage energy dissipation under high-frequency loading.

Articular cartilage is a spatially heterogeneous, dissipative biological hydrogel with a high fluid volume fraction. Although energy dissipation is important in the context of delaying cartilage damage, the dynamic behavior of articular cartilage equilibrated in media of varied osmolarity and viscosity is not widely understood. This study investigated the mechanical behaviors of cartilage when equilibrated to media of varying osmolarity and viscosity.

Maturation- and degeneration-dependent articular cartilage metabolism via optical redox ratio imaging.

From the two metabolic processes in healthy cartilage, glycolysis has been associated with proliferation and oxidative phosphorylation (oxphos) with matrix synthesis. Recently, metabolic dysregulation was significantly correlated with cartilage degradation and osteoarthritis progression. While these findings suggest maturation predisposes cartilage to metabolic instability with consequences for tissue maintenance, these links have not been shown.

Microindentation Technique to Create Localized Cartilage Microfractures.

Articular cartilage is a multiphasic, anisotropic, and heterogeneous material. Although cartilage possesses excellent mechanical and biological properties, it can undergo mechanical damage, resulting in osteoarthritis. Thus, it is important to understand the microscale failure behavior of cartilage in both basic science and clinical contexts.

Assessing collagen alterations in enzymatic degradation models of osteoarthritis via second harmonic generation microscopy.

Introduction: Structural changes in the collagen II architecture of osteoarthritis (OA) are poorly understood, which is a large shortcoming in the early diagnosis of this disease. Though degradation can be simulated by enzymes including trypsin and bacterial collagenase, the specific structural features of each digestion and their relationship to naturally occurring OA remain unclear.

Experimental Design: We used collagen sensitive/specific Second Harmonic Generation (SHG) microscopy in conjunction with optical scattering measurements to probe the resulting architecture changes in bovine knee cartilage upon trypsin and collagenase degradation.

Relaxation capacity of cartilage is a critical factor in rate- and integrity-dependent fracture.

Articular cartilage heals poorly but experiences mechanically induced damage across a broad range of loading rates and matrix integrity. Because loading rates and matrix integrity affect cartilage mechanical responses due to poroviscoelastic relaxation mechanisms, their effects on cartilage failure are important for assessing and preventing failure. This paper investigated rate- and integrity-dependent crack nucleation in cartilage from pre- to post-relaxation timescales.

Bi-component T2 mapping correlates with articular cartilage material properties.

Non-invasive estimation of cartilage material properties is useful for understanding cartilage health and creating subject-specific computational models. Bi-component T2 mapping measured using Multi-Component Driven Equilibrium Single Shot Observation of T and T (mcDESPOT) is sensitive for detecting cartilage degeneration within the human knee joint, but has not been correlated with cartilage composition and mechanical properties. Therefore, the purpose of this study was to investigate the relationship between bi-component T parameters measured using mcDESPOT at 3.

Evaluation of patient tissue selection methods for deriving equivalent density calibration for femoral bone quantitative CT analyses.

Osteoporosis affects an increasing number of people every year and patient specific finite element analysis of the femur has been proposed to identify patients that could benefit from preventative treatment. The aim of this study was to demonstrate, verify, and validate an objective process for selecting tissues for use as the basis of phantomless calibration to enable patient specific finite element analysis derived hip fracture risk prediction. Retrospective reanalysis of patient computed tomography (CT) scans has the potential to yield insights into more accurate prediction of osteoporotic fracture.

Glycosaminoglycan depletion increases energy dissipation in articular cartilage under high-frequency loading.

High-frequency material behavior of cartilage at macroscopic lengths is not widely understood, despite a wide range of frequencies and contact lengths experienced in vivo. For example, cartilage at different stages of matrix integrity can experience high-frequency loading during traumatic impact, making high-frequency behavior relevant in the context of structural failure. Therefore, this study examined macroscopic dissipative and mechanical responses of intact and glycosaminoglycan (GAG)-depleted cartilage under previously unexplored high-frequency loading.

Mechanobiology of Cartilage Impact Via Real-Time Metabolic Imaging.

Cartilage loading is important in both structural and biological contexts, with overloading known to cause osteoarthritis (OA). Cellular metabolism, which can be evaluated through the relative measures of glycolysis and oxidative phosphorylation, is important in disease processes across tissues. Details of structural damage coupled with cellular metabolism in cartilage have not been evaluated.

Maturity-dependent cartilage cell plasticity and sensitivity to external perturbation.

Objective: Articular cartilage undergoes biological and morphological changes throughout maturation. The prevalence of osteoarthritis in the aged population suggests that maturation predisposes cartilage to degradation and/or impaired regeneration, but this process is not fully understood. Therefore, the objective of this study was to characterize the cellular and genetic profile of cartilage, as well as biological plasticity in response to mechanical and culture time stimuli, as a function of animal maturity.

Interfibrillar shear behavior is altered in aging tendon fascicles.

Tendon elongation involves both stretching and sliding between adjacent fascicles and fibers. Hence, age-related changes in tendon matrix properties may alter sliding behavior and thereby affect injury thresholds. The objective of this study was to investigate the effects of age on interfibrillar shear behavior in partial cut tendon fascicles.

Rate-dependent adhesion of cartilage and its relation to relaxation mechanisms.

Cartilage adhesion has been found to play an important role in friction responses in the boundary lubrication regime, but its underlying mechanisms have only been partially understood. This study investigates the rate dependence of adhesion from pre-to post-relaxation timescales of cartilage and its possible relation to relaxation responses of the tissue. Adhesion tests on cartilage were performed to obtain rate-dependent cartilage adhesion from relaxed to unrelaxed states and corresponding relaxation responses.

Real-time optical redox imaging of cartilage metabolic response to mechanical loading.

Objective: Metabolic dysregulation has recently been identified as a key feature of osteoarthritis. Mechanical overloading has been postulated as a primary cause of this metabolic response. Current methods of real-time metabolic activity analysis in cartilage are limited and challenging.

Subject-specific geometry affects acetabular contact pressure during gait more than subject-specific loading patterns.

Finite element modeling (FEM) can predict hip cartilage contact mechanics. This study investigated how subject-specific boundary conditions and joint geometry affect acetabular cartilage contact mechanics using a multi-scale workflow. For two healthy subjects, musculoskeletal models calculated subject-specific hip kinematics and loading, which were used as boundary conditions for FEM.

Cartilage-on-cartilage cyclic loading induces mechanical and structural damage.

Cartilage breaks down during mechanically-mediated osteoarthritis (OA). While previous research has begun to elucidate mechanical, structural and cellular damage in response to cyclic loading, gaps remain in our understanding of the link between cyclic cartilage loading and OA-like mechanical damage. Thus, the aim of this study was to quantify irreversible cartilage damage in response to cyclic loading.