31. Biomechanics

Question 1

Sigma = F/A

What is this equation for? Explain its parts

Answer 1

Sigma = stress (pa)
F = force (N)
A = area (m2)

Question 2

ε = ∆L / L

Answer 2

ε = strain, no dimension
∆L=extension (m)
L= original length (m)

Question 3

F = -K * x

Answer 3

Hooke’s law
F = restoring force
X = displacement
K = spring constant

Question 4

Young’s modulus equation

Answer 4

E = σ/ε (Pa)
E = (F*L0)/(A0* ∆L)

Question 5

Maximum stress of collagen

Answer 5

60 MPa

Question 6

Maximum strain of collagen

Answer 6

0.08

Question 7

Young modulus of collagen

Answer 7

750MPa (stiff)

Question 8

Maximum stress of elastin

Answer 8

0.6 MPa

Question 9

Maximum strain of elastin

Answer 9

3

Question 10

Young modulus of elastin

Answer 10

0.2 MPa (pretty flexible)

Question 11

Distensibility equation

Answer 11

κ= (-∆V)/(∆p*V0)

∆V/V0 : relative expansion
P : transmural pressure

Question 12

What equation is this?

σ=(r*p)/(R-r)

Answer 12

Laplace-Frank equation

σ: tangential stress (wall tension)
r : inner radius of blood vessel
R : outer radius of blood vessel
R-r : wall thickness
p : transmural pressure

Question 13

What is the % composition of bone?

Answer 13

30% organic matrix (collagen) and 70% inorganic salts (hydroxyapatite)

Question 14

Young’s modulus of bone

Answer 14

5-20GPa

Question 15

Which part of the bone has higher and lower Young modulus value?

Answer 15

Greater in dense cortical bone

Lower in trabecular part

Question 16

Young modulus of enamel

Answer 16

100GPa

Question 17

Which equation describes the decrease of stress in a viscoelastic material?

Answer 17

σ= σ0*e^(-t/τ)

τ : time constant

Question 18

What is transmural pressure?

Answer 18

Difference in pressure between 2 sides of a wall

Question 19

What is tangential stress?

Answer 19

Direction of deforming / external force is parallel to the cross sectional area. It results in deformation of the body

Question 20

What is Young’s modulus a measure of?

Answer 20

a measure of the ability of a material to withstand changes in length

Question 21

What is collagen made up of?

Answer 21

AA wound together in a triple-helix (glycine, proline, hydroxyproline)

Question 22

What is the protein that makes up elastin?

Answer 22

Tropo-elastin (contains primarily glycine, valine, and modified alanine and proline residues)

Question 23

What is distensibility?

Answer 23

Ability to be able to stretch and expand under pressure (or change in the vessel volume under pressure)

Question 24

What does the Frank-Laplace law state?

Answer 24

tangential stress on the blood vessel is proportional to the transmural pressure, the diameter of the lumen and the thickness of the blood vessel wall

Question 25

What does energy dissipation depend on? (3)

Answer 25

• mass
• atomic number (Z)
• Energy of the substance