1. Properties of Biological Materials -- Collagenous Tissues
柴惠敏
台灣大學 物理治療學系

2. 主要參考書
Nordin, M. & Frankel V.H., Basic Biomechanics of the Musculoskeletal System, 3rd ed. Philadelphia, PA, Lea & Febiger. Chapter 3 & 4.
Chaffin & Addersson, 1999.
Biomechnics is a discipline of science, newly developed and in the process of becoming established.

3. Biomechanics of Collagenous Tissues
Basic Concepts

4. Collagenous Tissues Dense connective tissues Loose connective tissues
ligament: tensile load
tendon: tensile load
Loose connective tissues
capsule: tensile load
Skin: tensile load
Cartilage
articular cartilage: compressive/ shear
fibrocartilage: compressive/ shear

5. Components of Collagenous Tissues
Cells: chondrocytes or fibroblasts
Extracellular Matrix
Fibers: collagen fiber -- strength
elastin -- felxibility
reticulin -- mass
Ground substance
Biomechnics is a discipline of science, newly developed and in the process of becoming established.

6. Collagen Fiber the most abundant protein in the body
to resist tensile stress
tropocollagen: 3 procollagen polypeptide chains ( chains) coiled about each other into a right-handed triple helixes
 chain
1.4 nm

7. Types of Collagen Fiber
Type I
found in bone, tendon, ligament, and skin
Type II
found in articular cartilage, nasal septum, and sternal cartilage

8. Tensile Strength of Collagen Fiber
strain
stress
microtrauma
physiological
loading
clinical
test
injury
failure
toe region

9. Compression Strength of Collagen Fiber
only able to resist low compression loads
buckle under compression load
slenderness ratio
ratio of length to thickness

10. As load remains constant
Creep Phenomenon
Progressive deformation of a viscoelastic structure with time as the amount of load remains constant
time
strain
As load remains constant

11. As deformation remains constant
Load Relaxation
Progressive decrease in load with time as the deformation of the structure remains constant
time
stress
As deformation remains constant

12. Hysteresis
Energy stored in a viscoelastic material when a load is given and then relaxed.
strain
stress
loading
unloading
energy
stored

13. Aged Heel Pad
strain
stress
young
aged

14. Biomechanics of Collagenous Tissues
Basic Concepts
Biomechanics of Connective Tissues

15. Functions of Connective Tissues
Ligament
to connect two adjacent bones
to augment stability of joints
to check excessive motions
Tendon
to attach muscle to bone
to transmit forces from muscle to bone

16. Components of Connective Tissues
cell: fibroblast 20%
matrix: 80%
water: 60-70% for ligaments
collagen: 70-80% of dry weight molecular cross-link: for strength

17. Factors Influencing Mechanical Properties of Connective Tissues
structure of the orientation of the collagen fibers
properties of the collagen and elastin fibers
proportion between collagen and elastin fibers
ligamentum flava: 60% of elastin fibers
ACL: 94% of collagen
tendon
ligament
capsule

18. Strength-Stress Curve of Collagen Fiber
plastic
region
elastic
toe
strain
stress
failure
ultimate strain
= 6-8%

19. Modulus of Elasticity Young’s modulus or stiffness E =  / 
where  = stress = F / A (unit: Pa)
 = strain (unit: %)

20. Strength-Stress Curve of Elastin Fiber
strain
stress
failure
ultimate strain
~ 70%

21. Effect of Age before adolescent: maturation aging
ligament strength < bone strength
maturation
# and quality of cross-links increases
collagen fibril diameter increases
aging
# of collagen fibers decreases

22. Other Factors Influencing Mechanical Behaviors of Connective Tissues
pregnancy and postpartum period
increase laxity
decrease tensile strength
mobilization vs. immobilization
steroid vs. NSAID
diabetes mellitus
hemodialysis
grafts

23. Mobilization vs. Immobilization

24. Biomechanics of Collagenous Tissues
Basic Concepts
Biomechanics of Connective Tissues
Biomechanics of Articular Cartilage

25. Components of Articular Cartilage
cell: chondrocyte <10%
matrix:
water: 65-80%
collagen fibers: to resist tensile stresses
proteoglycans: ~10%; to resist compression

26. Heterogeneous Zones of Articular Cartilage
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
tidemark

27. Proteoglycans link protein hyaluronic acid protein core
compression recovery

28. Biphasic Viscoelastic Properties in Compression
Biphasic creep response
creep + fluid exuadation
up to 50% of fluid be squeezed out
Biphasic load relaxation
stress increased as fluid exudation
stress decreased as fluid redistribuation

29. Permeability under Compressive Strain
low load
high load
compressive strain

30. Lubrication of Articular Cartilage
Boundary lubrication
a single layer of lubricant molecules absorbed onto each bearing surface
depends on the chemical property of lubricants
Fluid film lubrication
a thicker fluid film provides greater surface separation

31. Fluid Film Lubrication on Deformable Materials
hydrodynamic squeeze film
lubrication lubrication

32. Failure of Articular Cartilage
mechanical loading and unloading prevent cartilage degeneration
limited ability to remodel itself if articular cartilage is damaged
loads leading to wear
acute: active loading or impact loading
chronic: interfacial or fatigue loads