Hyaline Cartilage

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Cortical Bone

• Hyaline Cartilage
• articular cartilage
• larynx
• rib and costal cartilage
• nasal septum
• Elastic Cartilage
• epiglottis
• Fibrocartilage
• Intervertebral disk
• meniscus

Trabecular Bone
Meniscus
Articular Cartilage
Tissues are classified by their biochemical
composition, molecular microstructure,
biomechanical properties and function.
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AC/Meniscus Functions

• Support large loads
• gymnastics
• Walking
• Lubrication

Interested in these structures because when they
breakdown we get osteoarthritis
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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

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Diarthrodial joint

• Fibrous capsule
• Inside lined with synovium which secretes
  synovial fluid

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Microstructure (Solid and Fluid Phase)

• Interstitial water
• Articular cartilage 68-85, meniscus 60-70

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Interstitial Water

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

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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

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Microstructure (Solid and Fluid Phase)

• Collagen
• Proteoglycans
• Cells

No blood or nerves in cartilage
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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

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Collagen Orientation
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Collagen Orientation
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Proteoglycan protein with bound side chains
(glycosaminoglycans)
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Proteoglycans

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

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Cells Chondrocytes
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Material Properties

• Steel is linear elastic (E,?)
• Soft tissues ARE NOT!!
• Water movement (forces depend on rate-damping)

STEEL
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Material Properties

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

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Material Properties-Anisotropy/Inhomogeneous

• Transversely Isotropic
• Inhomogeneous

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Constitutive Equation

• Linear Elastic Materials (Steel)
• Hookes Law ? E?
• Viscoelastic materials (AC/meniscus)
• Biphasic Theory (2 phase)
• Triphasic Theory (3 phase)

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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, OA1.4MPa)

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Tension
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Compression

• Compressive Aggregate Modulus (HA)(0.4-1.5 MPa)

Force
Deform
time
time
Confined Compression Creep Test
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Compression

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

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Shear
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Shear
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Methods of Failure-Cartilage

• Fracture
• Fracture with Bone
• Wear
• Degeneration
• Blunt Trauma (intense compression and shear
  forces)

Bone
Bone
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Methods of Failure - Meniscus

• Degeneration
• Tearing

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