Load and Deformation

Question 1

how does collagen act under tensile loads?

Answer 1

they straighten/lengthen

Question 2

how does collagen act with relaxation?

Answer 2

they return to original length

Question 3

do collagen fibers exhibit elastic or viscoelastic behavior? why?

Answer 3

viscoelastic because of the mostly water ground substance

Question 4

What types of loading does collagen exhibit?

Answer 4

high tensile strength, high stiffness, poor resistance to compression

Question 5

What is elastin made of?

Answer 5

fibrous elastin protein and microfibrils

Question 6

What qualities do elastin fibers carry?

Answer 6

high extensibility, low stiffness

Question 7

what kind of deformation do elastin fibers display?

Answer 7

elastic until rupture

Question 8

What are tendons composed of?

Answer 8

elastic elastin fibers and viscoelastic collagen fibers

Question 9

what do tendons do in the body?

Answer 9

help execute joint motion by transmitting tensile forces from muscles to bones

Question 10

What part of tendons act under low strains?

Answer 10

elastic fibers are predominantly used as they are easier to stretch

Question 11

What part of tendons act under high strains?

Answer 11

collagen fibers take over because elastic fiber crimp is straightened (become stiffer, more viscoelastic)

Question 12

How do tendons compare to bones?

Answer 12

stiffer, higher tensile strength, support large loads with small deformations

Question 13

What are ligaments composed of?

Answer 13

elastic elastin fibers and viscoelastic collagen fibers

Question 14

what do ligaments do in the body?

Answer 14

they help stabilize joints by transmitting forces from bone to bone

Question 15

What is a main difference between ligaments and tendons?

Answer 15

Ligaments have an increased proportion of elastin compared with the tendon

Question 16

what load qualities do ligaments display?

Answer 16

greater extensibility/elasticity
lower strength
lower stiffness

Question 17

true or false: ligaments only run in parallel to the load?

Answer 17

false:
while they do mostly run in parallel and provide tensile strength, some fibers are oblique and run in other directions

Question 18

What does bone do in the body?

Answer 18

provide mechanical support as the central structure of each body segment

Question 19

what factors affect bone mechanics?

Answer 19

-age
-geometry (influence of moment arms)
-mode of loading (compression, tension, shear, bending, torsion)
-frequency of loading
-pathology

Question 20

What mechanical properties affect cortical/compact bone?

Answer 20

-direction of load
(stronger in compression than tension. stronger, stiffer, and more ductile in longitudinal loading than transverse)
-rate of loading
(stronger and stiffer with fast vs slow loading)
- designed to resist torsion, bending, longitudinal compression

Question 21

what are the mechanical properties of trabecular/spongey bone?

Answer 21

• difference from cortical due to physical makeup
• compared to cortical bone it is
  1) 25-35% less dense
  2) 5-10% as stiff
  3) 5x as ductile
  4) brittle in tension

Question 22

What effects does age have on bone density?

Answer 22

• increased mineral content (change in quality of bone)
• decreased stress and strain required to reach yield point
• increased sitffness
  -less ductility

Question 23

how does decreased density change bone properties?

Answer 23

• quantity of bone changes
• decreased toughness
• decreased stiffness
• deforms easier
• fractures at lower loads -> compression fractures

Question 24

What is Wolff’s Law?

Answer 24

• mechanical loads increase bone remodeling
• increase load = increased density
  -decreased load = decreased density
• strength increases in the direction of loading

Question 25

What does cartilage do in the body?

Answer 25

facilitate relative movement of articulating bones
- increases contact area
- reduces wear due to decreased friction
- is viscoelastic

Question 26

what is cartilage composed of?

Answer 26

-75% water, 25% solid
- collagen (strong in tension)
-ground substance (strong in compression)
- tensile/compressive strengths depend on the relative amount of each