國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
主要參考書：
1. Mow VC & Hung CT: Biomechanics of articular cartilage. In Nordin M & Frankel VH:
Biomechanics of the Musculoskeletal System, 3rd ed. Philadelphia: Lea & Febiger, 2001.
2. Nordin M, Lorenz T, Campello M: Biomechanics of tendons and ligaments. In Nordin M &
Frankel VH: Biomechanics of the Musculoskeletal System, 3rd ed. Philadelphia: Lea & Febiger,
2001.
3. Chaffin & Andersson, 1999.
Collagenous Tissues
A. Functions of collagenous tissues
1. dense connective tissues
a. tendon
-- to attach muscles to bone
-- to transit tensile loads from muscle to bone
b. ligament
-- to augment the mechanical stability of the joints
-- to guide joint motions
-- to prevent or check excessive motion
2. loose connective tissues
a. capsule
-- to augment the mechanical stability of the joints
-- to prevent or check excessive motion
b. skin
-- to protect internal structures
-- to prevent or check excessive motion
3. cartilage
a. articular cartilage
-- to absorb the compressive and/or shear loads
-- to allow motions between joint surfaces with minimal friction
b. fibrocartilage
-- to absorb the compressive and/or shear loads
B. Components of collagenous tissues
1. cells: chondrocytes or fibroblast
2. fibers
a. collagen fibers: to provide strength and stiffness
-- the most abundant protein in the body
-- tropocollagen: 3 procollagen polypeptide chains ( chains) coiled about each other into
a right-handed helixes
b. elastin fibers: to provide extensibility
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國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
c. reticulin fibers: to provide mass
3. ground substance
C. Viscoelastic properties of the collagen fiber
1. stress-strain curve
microtrauma
failure
stress
injury
clinical
test
physiological
loading
strain
2. creep phenomenon
-- progressive deformation of a viscoelastic structure as the amount of load remains constant
over an extended time.
As load remains constant
strain
time
3. load relaxation phenomenon
-- progressive decrease in load as the deformation of the structure remains constant over an
extended time.
stress
As deformation remains constant
time
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國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
4. Hysteresis
-- Energy stored in a viscoelastic material when a load is given and then relaxed.
energy
stored
loading
stres
s
unloading
strain
Connective Tissues
A. Components of connective tissues
1. cell: fibroblast 20%
2. matrix: 80%
-- water: 60-70% for ligaments
-- collagen: 70-80% of dry weight; molecular cross-link
B. Factors influencing mechanical properties of connective tissues
1. the structural orientation of the collagen fibers
a. tendon: almost completely parallel to withstand high tensile load
b. ligament: nearly parallel; depending on its function
c. skin: nonparallel to have good extensibility
tendon
ligament
capsule
2. properties of collagen and elastin fibers
-- collagen fiber
a. failure with 6-8% deformation
b. tolerate about 1/4 the stress tolerated by cortical bone in tension
-- elastin fiber
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國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
a. significant deformation with very low load
b. tolerate about 1/10 the stress tolerated by cortical bone in tension
3. proportion between collagen and elastic fibers
-- collagen fiber: to withstand tensile force e.g. anterior cruciate ligament
-- elastic fiber: to provide extensibility e.g. ligamentum flavum
C. Factors affecting mechanical behaviors of tendons and ligaments
1. maturation and aging process
a. before adolescent: ligament strength < bone strength
b. maturation: # and quality of cross-links and collagen fibril diameter increase
c. aging: # of collagen fibers decreases
2. pregnancy and the postpartum period
-- increase laxity and decrease tensile strength of tendons and ligaments during later stages of
pregnancy and the postpartum period
3. mobilization vs. immobilization
-- remodel in response to the mechanical demands placed upon it
a. stronger and stiffer when subjected to increased stresses
b. weaker and less stiff when the stress is reduced
control
100
immobilized 8 wk
80
recovery 5m
recovery 12 m
60
40
20
0
maximal load
energy stored
4. steroid vs. nonsteroidal anti-inflammatory drugs (NSAID)
5. pathological conditions
a. diabetes mellitus (DM)
b. hemodialysis
c. grafts
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國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
Articular Cartilage
A. Compositions
1. 1- 5 mm hyaline cartilage -- dense connective tissue
2. no blood vessels or nerves
3. components:
a. condrocyte: < 10%
b. extracellular matrix:
i. collagen fibers
ii. proteoglycans
iii. water 65-80%
4. mechanical properties of collagen fibers in articular cartilage
a. biological unit: tropocollagen
b. mechanical properties: tensile stiffness and strength
c. distribution of collagen in articular cartilage:
i. superficial tangential zone: parallel to the articular surface
ii. middle zone: randomly distributed
iii. deep zone: perpendicular to cartilage-calcified cartilage interface (tidemark)
superficial tengential zone
(10-20% of total thickness)
transitional area
(40-60% of total thickness)
deep layer
(30% of total thickness)
calcified cartilage
subchondral bone
5. mechanical properties of proteoglycans
a. basic unit: glycosaminoglycans (GAGs)
b. mutually repelled between neighboring GAG chains
B. Mechanical properties of articular cartilage
1. biphasic creep response
-- accompanied by exudation of fluid
-- up to 50% of the fluid can be squeezed out)
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國立台灣大學九十學年度生物力學
BIOMECHANICS OF COLLAGENOUS TISSUES
2. biphasic load relaxion phenomeon
-- stress increased as fluid exudation
-- stress decreased as fluid redistribution
3. non-linear permeability
4. rate dependency of the material behavior
a. rapid loading: like elastic material
b. slow loading: like viscoelastic
C. Lubrication mechanism
1. boundary lubrication: the chemical adsorption of a monolayer of lubricant molecules onto the
articular surfaces
2. fluid film lubrication: a much thicker film of lubricant causing a relatively large separation of
the two bearing surface
a. Elastohydrodynamic fluid films of both the sliding and the squeeze type probably play an
important role in lubricating the joint
b. With high load and low speeds of relative motion, the fluid film will decrease in thickness
as the fluid is squeezed our from between the surfaces.
c. Under very high loading conditions, the fluid film may be eliminated , allowing
surface-to-surface contact
D. Failure of articular cartilage
1. mechanical loading and unloading prevent cartilage degeneration
2. limited ability to remodel itself if articular cartilage is damaged
3. loads leading to wear
-- acute: active loading or impact loading
-- chronic: interfacial or fatigue loads
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