Cortical Bone Hyaline Cartilage articular cartilage larynx rib
Cortical Bone • Hyaline Cartilage – – articular cartilage larynx rib and costal cartilage nasal septum • Elastic Cartilage – epiglottis • Fibrocartilage Trabecular Bone Meniscus Articular Cartilage – Intervertebral disk – meniscus Tissues are classified by their biochemical composition, molecular microstructure, biomechanical properties and function.
AC/Meniscus Functions: • Support large loads – 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. 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 • Steel is linear elastic (E, ) • Soft tissues ARE NOT!! • Water movement (forces depend on rate -damping)
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 -30 MPa) Deform. time – – – Force time Tensile Stress Relaxation Test (1 Type of tissue Age of animal Type of joint Sample location Depth of sample (surface = 10 MPa, Middle =4. 5 MPa) – Relative orientation – Biochemical comp/ molecular structure – State of degeneration (Normal =10 MPa, OA=1. 4 MPa)
Tension
Compression • Compressive Aggregate Modulus (HA)(0. 4 -1. 5 MPa) Force Deform 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
Methods of Failure - Meniscus Degeneration Tearing
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