Cortical Bone Trabecular Bone Meniscus Articular Cartilage Hyaline Cartilage articular cartilage larynx rib and costal cartilage nasal septum Elastic Cartilage epiglottis Fibrocartilage Intervertebral disk meniscus Cortical Bone Trabecular Bone Meniscus Articular Cartilage Fdsafsdaf Tissues are classified by their biochemical composition, molecular microstructure, biomechanical properties and function.

Support large loads Lubrication AC/Meniscus Functions: gymnastics Walking Lubrication Interested in these structures because when they “breakdown” we get osteoarthritis

Articular Cartilage Important to understand Mechanical properties of normal cartilage Manner by which biochemical and structural factors contribute to the material properties of cartilage Manner by which changes in tissue composition affect the mechanical properties of cartilage

Diarthrodial joint Fibrous capsule Inside lined with synovium which secretes synovial fluid

Microstructure (Solid and Fluid Phase) Interstitial water Articular cartilage 68-85%, meniscus 60-70%

Interstitial Water Constant with age Increases with OA or degeneration Amount of water is dependent on

Interstitial water Ions- As tissue is compressed-Frictional drag force on walls of the pores of the solid matrix due to interstitial fluid flow through the pores of collagen-PG matrix

Microstructure (Solid and Fluid Phase) Collagen Proteoglycans Cells No blood or nerves in cartilage

Collagen: made up of molecules (tropocollagen--1 Collagen: made up of molecules (tropocollagen--1.4 nm) that polymerize to form fibrils Type II (AC), forms bundles, with diam.=2 to 10 microns Type I (meniscus), forms fibrils, with diam. = 20-200 nm

Collagen Orientation

Collagen Orientation

Proteoglycan: protein with bound side chains (glycosaminoglycans)

Proteoglycans Negative charge attracts +ions (K and Na) Swelling pressure PG want to be 5-10 times larger, but not enough room in cartilage

Cells: Chondrocytes

Material Properties Steel is linear elastic (E,) Soft tissues ARE NOT!! Water movement (forces depend on rate-damping) STEEL

Material Properties Viscoelastic behavior are dominated by frictional drag of interstitial fluid flow through the porous collagen-proteoglycan solid matrix, thus causing viscous dissipation

Material Properties-Anisotropy/Inhomogeneous Transversely Isotropic Inhomogeneous

Constitutive Equation: Linear Elastic Materials (Steel) Hookes’ Law:  = E Viscoelastic materials (AC/meniscus) Biphasic Theory (2 phase) Triphasic Theory (3 phase)

Tension Equilibrium Tensile Modulus (1-30 MPa) Type of tissue Age of animal Type of joint Sample location Depth of sample (surface = 10MPa, Middle =4.5MPa) Relative orientation Biochemical comp/ molecular structure State of degeneration (Normal =10MPa, OA=1.4MPa) Deform. time Force Tensile Stress Relaxation Test

Tension

Compression Compressive Aggregate Modulus (HA)(0.4-1.5 MPa) Force Deform time time Confined Compression Creep Test

Compression HA varies inversely with water content *OA patients have increased water HA varies directly with PG content Not dependent on collagen content

Shear

Shear

Methods of Failure-Cartilage Fracture – Fracture with Bone Wear Degeneration Blunt Trauma (intense compression and shear forces) Bone Bone

Methods of Failure - Meniscus Degeneration Tearing