Tissue Mechanics Principles

Question 1

What are two hydrated proteins in extracellular matrix?

Answer 1

Proteoglycans (PG’s)
Glycoproteins

Question 2

What are proteoglycans (PG)?

Answer 2

• attached are one or more polysaccharide chains called glycosaminoglycans (GAG)
• resist compression
  -lose as people age

Question 3

What effects the hydration of extracellular matrix?

Answer 3

-Proportion of PG’s

Question 4

What causes swelling pressure in the extracellular matrix & what happens as a result?

Answer 4

GAG’s are negatively charged so concentration of negatively charged PG;s creates the swelling pressure. Causing water to flow into the extracellular matrix

Question 5

What contains the swelling and what does this create?

Answer 5

Collagen fibers resist & contain swelling via tensile stress w/ osmotic swelling pressure.
-Creates rigidity of matrix, resisting compressive forces

Question 6

If a tissue is subject to high compression forces what will be the PG/GAG content versus ones that resist tensile loads?

Answer 6

-Subject to high compression with have high levels of PG/ GAG
-Subject to low levels will have low levels of PG/GAG

Question 7

Fibrillar Component?

Answer 7

Collagen & Elastin

Question 8

Collagen?

Answer 8

-Most abundant protein in body
-Strength of steel

Question 9

Type I collagen?

Answer 9

-Predominantly in Type II, tendons, menisci, & joint capsules

Question 10

Type II collagen?

Answer 10

Predominantly in hyaline articular cartilage & nucleus pulpous of disc

Question 11

Elastin?

Answer 11

• Yellow fibrous tissue
• Properties allow fibers to deform under force & return to original state

Question 12

Composition & structure of fibrillar

Answer 12

-Sparsely vascularized, parallel
-Primiarly type I collagen
-Dense connective tissue in tendon & ligament

Question 13

What are cross links?

Answer 13

-Formed by GAG’s between collagen molecules that provide strength to fibrils
-Few & fairly easily broken in new collagen
-Become stronger with maturation

Question 14

Elastin Content

Answer 14

-More in ligament
-Proportion of ligament determines mechanical properties

Question 15

Overload

Answer 15

tissues increase their structural or functional capability in response to overloading (stimulus & response)

Question 16

Specificity

Answer 16

specific stimulus for adaption elicits specific structural & functional changes in specific element of tissue

Question 17

Reversibilty

Answer 17

discontinuing training stimulus will result in de-training and the adaptive changes regress

Question 18

Elasticity

Answer 18

property of a material or structure to return to its original form following removal of deforming load

Question 19

Plasticity

Answer 19

property of material to deform permanently when its loaded beyond plastic range

Question 20

Viscosity

Answer 20

property of a material to resist loads that produce shear, controls fluid rate of flow

Question 21

What does higher viscosity indicate?

Answer 21

slower deformation/rate of flow

Question 22

Elastic materials

Answer 22

-Return to normal form/shape following removal of a deforming load

Question 23

In elastic materials when is energy stored and released?

Answer 23

-Stored during loading
-Released completely during unloading
Thus no energy loss

Question 24

In Visco-Elastic materials what does rate influence?

Answer 24

fracture pattern and amount of soft tissue damage at fracture

Question 25

Visco-Elastic materials are sensitive to the rate of loading or deformation so what does a high rate mean?

Answer 25

greater energy stored cannot dissipate rapidly through a single crack, comminution of bone & extensive soft tissue damage occurs

Question 26

Visco-Elastic materials are sensitive to the rate of loading or deformation so what does a low rate mean?

Answer 26

Energy can dissipate through a crack, bone and soft tissue remain relatively intact, little displacement occurs

Question 27

What is creep?

Answer 27

-Load is suddenly applied and then held constant over time
-Continued deformation over time through load is held constant

Question 28

What is stress relaxation?

Answer 28

-Deformation held constant
-Force required to maintain deformation decrease over time
-Sensation of stress decreases over time b/c straightening fibers and fluid moving

Question 29

What is cyclical loading?

Answer 29

-Causes a shift of curve to right
-Shift decreased in magnitude with each rep

Question 30

What is hysteresis?

Answer 30

area under loading cycle is energy of deformation - energy loss in form of heat