6: Tissue Mechanics II - Vardaxis Flashcards
which is greater in bone: organic or inorganic matrix?
organic matrix 40% dw; inorganic matrix 60% dw
what is the major component of inorganic matrix?
calcium hydroxyapatite
total percentage water of bone
10%
collagen is _____ organic matrix
90%
- provides tensile strength to the bone
structure of collagen in bone
- type I
- triple helix -> fibril
- hole zone b/w fibrils
- pores b/w sides of parallel molecules
x-linking in bone collagen _____ solubility and _____ tensile strength
- decreases
- increases
what are proteoglycans?
glycosaminoglycan complexes
proteoglycans __________ mineralization
inhibit
proteoglycans are partially responsible for ________ strength of bone
compressive
non-collagenous matrix prtns (osteocalcin/osteonectin/osteopontin) ________ mineralization and bone formation
promote
produced by osteoblasts, related to regulation of bone density, most abundant non-collagen matrix prtn
- osteocalcin
- other non-collagenous matrix prtns are osteonectin (secreted by patelets and osteoblasts, organization of mineral within matrix) and osteopontin (cell binding prtn)
inorganic matrix provides the _______ strenght of bones
compressive
- also responsible for mineralization of bone; primary mineralization occurs in holes and pores
seven hierarchical levels of bone
- isolated crystals and collagen fibrils
- mineralized collagen fibril
- mineralized fibril array
- fibril array patterns
- single osteon
- spongy and compact bone
- whole bone
cortical v. cancellous bone
cortical = 5-30% porous cancellous = 30-90% porous, no osteons
woven v. lamellar cortical bone
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
which is weaker: lamellar or woven cortical bone?
woven
compact cortical bone has a _______ resistance to torsion and bending than cancellous
higher
describe compact/cortical boen
- 80% of skeleton
- osteons connected by haversian canals
- cement line define outer border of osteon
- slow turnover
- high young’s modulus
immature or pathologic bone
woven bone
the collagen is arranged irregularly
where might you find woven bone?
fetal skelton fx callus tooth sockets bone forming tumors stages of accelerated bone formation
isotropic
mechanical properties independent of orientation of stresses applied
woven bone is isotropic
trabecular bone aka
cancellous bone or spongy bone
describe cancellous bone
- less dense
- more remodeling along lines of stress
- LARGE surface area
- high turnover
- low apparent modulus
which type of bone is more elastic?
cancellous bone
also more resistant to compressive forces
wolff’s law and bone
- bone remodels in response to the stresses applied to it
- remodeling occurs to keep strain (NOT STRESS) between certain limits
if strain is too high, how does bone respond?
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
_________ modeling to reduce bone diameter during growth; ______ modeling to increase bone diameter
metaphyseal;
diaphyseal
describe diaphyseal modeling
- addition of bone on the periosteum
- resorption of bone at endosteum
- diaphyseal modeling to increase bone diameter
- diaphyseal modeling can alter curvature
describe the stress-strain relationship of bone
- nonlinear elastic behavior
- moderate plastic region
________ is stiffer than ______ bone
cortical; cancellous
deformation is greater in ________ bone
cancellous
load is greater in ______ bone
cortical
energy stored is greater in _______ bone
- cancellous
- trabecular bone can absorb considerable energy while maintaining a minimum mass
anisotropic behavior of bone
bone exhibits different mechanical properties when loaded along different axes
( longitudinal - stiffer more plasticity; transverese - less stiffness, no plasticity)
magnitude of stress from torsional load is proportional to …
distance from axis
increased loading rate = ____ stiffness and _______ load
increased both
bed rest reduces bone mass by _____ when immobilized
1%/wk
what part of the strain-stress relationship changes with aging?
- decreased strain
- decreased energy storage
aging variations in tibial trabecular bone
- 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
