• Hyaline Cartilage– articular cartilage– larynx– rib and costal cartilage– nasal septum

• Elastic Cartilage– epiglottis

• Fibrocartilage– Intervertebral disk– meniscus

Meniscus Articular Cartilage

Trabecular Bone

Cortical Bone

Tissues are classified by their biochemical composition, molecular microstructure, biomechanical properties and function.

• Support large loads– gymnastics – Walking

• Lubrication

AC/Meniscus Functions:

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 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

time

Tensile Stress Relaxation Test

Tension

Compression

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

Force

time

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-CartilageFracture –Fracture with Bone Wear Degeneration Blunt Trauma (intense compression and shear

forces)Bone

Bone

Methods of Failure - Meniscus

DegenerationTearing