6: Tissue Mechanics II - Vardaxis

Question 1

which is greater in bone: organic or inorganic matrix?

Answer 1

organic matrix 40% dw; inorganic matrix 60% dw

Question 2

what is the major component of inorganic matrix?

Answer 2

calcium hydroxyapatite

Question 3

total percentage water of bone

Answer 3

10%

Question 4

collagen is _____ organic matrix

Answer 4

90%

- provides tensile strength to the bone

Question 5

structure of collagen in bone

Answer 5

• type I
• triple helix -> fibril
• hole zone b/w fibrils
• pores b/w sides of parallel molecules

Question 6

x-linking in bone collagen _____ solubility and _____ tensile strength

Answer 6

• decreases

- increases

Question 7

what are proteoglycans?

Answer 7

glycosaminoglycan complexes

Question 8

proteoglycans __________ mineralization

Answer 8

inhibit

Question 9

proteoglycans are partially responsible for ________ strength of bone

Answer 9

compressive

Question 10

non-collagenous matrix prtns (osteocalcin/osteonectin/osteopontin) ________ mineralization and bone formation

Answer 10

promote

Question 11

produced by osteoblasts, related to regulation of bone density, most abundant non-collagen matrix prtn

Answer 11

• osteocalcin
• other non-collagenous matrix prtns are osteonectin (secreted by patelets and osteoblasts, organization of mineral within matrix) and osteopontin (cell binding prtn)

Question 12

inorganic matrix provides the _______ strenght of bones

Answer 12

compressive

- also responsible for mineralization of bone; primary mineralization occurs in holes and pores

Question 13

seven hierarchical levels of bone

Answer 13

1. isolated crystals and collagen fibrils
2. mineralized collagen fibril
3. mineralized fibril array
4. fibril array patterns
5. single osteon
6. spongy and compact bone
7. whole bone

Question 14

cortical v. cancellous bone

Answer 14

cortical = 5-30% porous
cancellous = 30-90% porous, no osteons

Question 15

woven v. lamellar cortical bone

Answer 15

lamellar: parallel layers of lamellae; mineralized collagen fibers are parallel within each lamella; direction of fibers may alternate between adjacent lamellae
woven = quickly formed; poorly organized; more mineralized than lamellar; weaker than lamellar

Question 16

which is weaker: lamellar or woven cortical bone?

Answer 16

woven

Question 17

compact cortical bone has a _______ resistance to torsion and bending than cancellous

Answer 17

higher

Question 18

describe compact/cortical boen

Answer 18

• 80% of skeleton
• osteons connected by haversian canals
• cement line define outer border of osteon
• slow turnover
• high young’s modulus

Question 19

immature or pathologic bone

Answer 19

woven bone

the collagen is arranged irregularly

Question 20

where might you find woven bone?

Answer 20

fetal skelton
fx callus
tooth sockets
bone forming tumors
stages of accelerated bone formation

Question 21

isotropic

Answer 21

mechanical properties independent of orientation of stresses applied

woven bone is isotropic

Question 22

trabecular bone aka

Answer 22

cancellous bone or spongy bone

Question 23

describe cancellous bone

Answer 23

• less dense
• more remodeling along lines of stress
• LARGE surface area
• high turnover
• low apparent modulus

Question 24

which type of bone is more elastic?

Answer 24

cancellous bone

also more resistant to compressive forces

Question 25

wolff's law and bone

Answer 25

- bone remodels in response to the stresses applied to it | - remodeling occurs to keep strain (NOT STRESS) between certain limits

Question 26

if strain is too high, how does bone respond?

Answer 26

new bone is laid down along the lines of stress, and the bone becomes both thicker and denser - if strain too low, bone is lost, making the bone less dense, this inactivity may lead to osteoporosis

Question 27

_________ modeling to reduce bone diameter during growth; ______ modeling to increase bone diameter

Answer 27

metaphyseal; | diaphyseal

Question 28

describe diaphyseal modeling

Answer 28

- addition of bone on the periosteum - resorption of bone at endosteum - diaphyseal modeling to increase bone diameter - diaphyseal modeling can alter curvature

Question 29

describe the stress-strain relationship of bone

Answer 29

- nonlinear elastic behavior | - moderate plastic region

Question 30

________ is stiffer than ______ bone

Answer 30

cortical; cancellous

Question 31

deformation is greater in ________ bone

Answer 31

cancellous

Question 32

load is greater in ______ bone

Answer 32

cortical

Question 33

energy stored is greater in _______ bone

Answer 33

- cancellous | - trabecular bone can absorb considerable energy while maintaining a minimum mass

Question 34

anisotropic behavior of bone

Answer 34

bone exhibits different mechanical properties when loaded along different axes ( longitudinal - stiffer more plasticity; transverese - less stiffness, no plasticity)

Question 35

magnitude of stress from torsional load is proportional to ...

Answer 35

distance from axis

Question 36

increased loading rate = ____ stiffness and _______ load

Answer 36

increased both

Question 37

bed rest reduces bone mass by _____ when immobilized

Answer 37

1%/wk

Question 38

what part of the strain-stress relationship changes with aging?

Answer 38

- decreased strain | - decreased energy storage

Question 39

aging variations in tibial trabecular bone

Answer 39

- peak E 40-50 yo - peak ultimate stress 40-50 yo - energy to fail decreases with age - strain decreased - tissue density did not change - apparent density (amount of bone) decreased