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BIOE 4710/5710 Bone Tissue
Function, physiology and composition ofbone tissue cortical
trabecular
Biomechanics of bone tissue mechanical properties
viscoelasticity
Textbook: Skeletal Tissue Mechanics, (Martin RB et al.)
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Bone: Structural Hierarchy
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Bone: Composition
collagen + water + mineral +proteoglycans + noncollagenousproteins
mineral: bioapatite
Ca10 (PO4)6-x (OH)2-y(CO3)x+y 6u x u0 and 2u y u0
substitutions include HPO4, CO3, Mg, Fl
rod or plate shaped (5x5x40 nm)
proteoglycans decorin
biglycan
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Bone: Composition
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Bone: Composition
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Bone: Composition
proteoglycans may control mineralization
decorin
collagen fibrillogenesis
protein core-GAG
biglycan
interaction with collagen ?
noncollagenous proteins osteocalcin, osteonectin, osteopontin
osteocalcin abundant
chemoattractant for bone cells
suppresses excess mineralization
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Bone: Trabecular vs. Cortical
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Bone: Trabecular Bone
Trabecular bone(a.k.a. cancellousor spongy bone)
found in cuboidalbones, flat bonesand the ends oflong bones
range of porosity75%-95%
interconnectedpores
filled with marrow
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Bone: Trabecular Bone
Trabecular bone (cont:)
formed by organization of plate- and rod-likestruts called trabeculae
trabeculae are about 200 Qm thick.
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Bone: Cortical Bone
Cortical bone (a.k.a. compact bone) shafts of long bones shell around cuboidal bones
porosity 5-10% Haversian canal
aligned with the long axis of bone contains capillaries and nerves 50 Qm in diameter
Volkmanns canal transverse canals connecting Haversian canals contains blood vessels
Resorption cavities temporary spaces created by osteoclasts 200 Qm in diameter
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Bone: Cortical Bone
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Bone: Cortical Bone
Cortical bone (cont) types of cortical bone
lamellar parallel layers of lamellae mineralized collagen fibers are parallel within each
lamella direction of fibers may alternate between adjacent
lamellae
woven bone quickly formed
poorly organized, fibers are more or less randomlyarranged more mineralized than lamellar weaker than mineralized
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Bone: Primary and secondary
primary bone: laiddown on existingbone surface
circumferentiallamellar
lamellae areparallel to bonesurface
primary osteonsaround bloodvessels
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Bone: Primary and secondary
primary bone:(cont)
plexiform
construction of atrabecularnetwork followedby filling in thegaps
mixture of wovenand lamellarbone
large and fastgrowing animals
(cows)
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Bone: Primary and secondary
secondary bone: resultsfrom resorption andreplacement of existingbone with lamellar bone
(remodeling) cortical bone: secondary
tissue consists ofcylindrical structurescalled secondaryosteons or Haversian
systems 200 Qm in diameter
16 concentriccylindrical lamellae
outer boundarycement line
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Bone: Primary and secondary
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Bone: Primary and secondary
secondary bone:
(cont) trabecular bone:
remodelingproducestrenches on theexisting surfaces
filling of these
trenches createtrabecularpackets
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Bone: Modeling and remodeling
modeling customized the
shape of bones inaccordance with
mechanical needs metaphyseal
modeling to reducebone diameterduring growth
diaphysealmodeling toincrease bonediameter addition of bone
on theperiosteum
resorption ofbone at
endosteum
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Bone: Modeling and remodeling
modeling (cont) customized the shape of bones in accordance
with mechanical needs diaphyseal modeling to alter curvature
cross section drifts sideways relative to the endsof the bone
modeling of flat bones resorption on the inner surface and formation on
the outer surface of cranial bone to accommodatethe growth in size of brain
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Bone: Modeling and remodeling
remodeling removes older bone and replaces with new
bone prevents accumulation of fatigue damage
draws calcium from bones to be usedmetabolically elsewhere fine tunes mechanical properties accomplished by teams of about 10 osteoclasts
and several hundred osteoblasts that worktogether in basic multicellular units (BMUs)
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Bone: Modeling and remodeling
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Bone: Modeling and remodeling
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Bone: Modeling and remodeling
remodeling (cont.) three stages in BMUs lifetime (ARF)
Activation Resorption Formation
resorption in the form of a tunnel orditch about 200 Qm in diameter at arate of 40 Qm/day
mesenchymal cells differentiate intoosteoblasts
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Bone: Modeling and remodeling
remodeling (cont.) osteoblasts fill the tunnel with osteoid
tissue at a rate of 0.5 Qm/day
resorption lasts for3
weeks remodeling sequence lasts for 4months
BMUs replace 5% of cortical bone and25% of trabecular bone each year
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Bone: Modeling and remodeling
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Bone: Modeling and remodeling
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Bone: Modeling and remodeling
modeling-remodeling: differences action of osteoclasts and osteblasts are
independent in modeling and coupledin remodeling
modeling results in change of bonessize, shape or both whereas remodelingdoes not effect size or shape usually
rate of modeling reduced aftermaturation, remodeling occurs
throughout life modeling is continuous and prolonged
whereas remodeling is episodic
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Bone: Strength of cortical bone
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Bone: Strength of cortical bone
determinants of osteonal bonemechanical properties porosity
holes weaken structures
voids in bone range from a few to severalhundred micrometers
Schaffler and Burr (1988) (up to 31%porosity) E = 33.9 (1-p)10.9, p:porosity, E:modulus
Currey (1988) (up to 7.8% porosity) E = 23.4 (1-p)5.74
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Bone: Strength of cortical bone
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Bone: Strength of cortical bone
determinants of osteonal bonemechanical properties (cont) mineralization
amount of mineral per volume of bonematrix (specific mineralization)
amount of mineral per unit volume ofwhole bone (volumetric mineralization,affected by porosity)
Schaffler and Burr (1988) E = 89.1 A3.91
A: percent ash by mass
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Bone: Strength of cortical bone
determinants of osteonal bone mechanicalproperties (cont) density
apparent density: mass per unit bulk volume
(function of porosity and mineralization) Carter and Hayes (1977)
: strain rate, E: modulus
d: density
apparent density of cortical bone 1.8-2.0 g/cm3
histologic architecture osteonal density
amount of primary lamellar bone
collagen fiber organization
I
306.03790 dE I!
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Bone: Strength of cortical bone
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Bone: Strength of cortical bone
determinants of osteonal bone mechanicalproperties (cont)
fatigue damage
rate of deformation
osteoid tissue
fluid flow within interconnected spaces
cement lines
energy absorption capacity optimized in therange of 0.01-0.1 s-1
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Bone: Strength of cortical bone
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Bone: Strength of Cancellous Bone
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Bone: Strength of Cancellous Bone
determinants of cancellous bonemechanical properties
apparent density apparent density of trabecular bone 1.0-
1.4 g/cm3
the relationship given by Carter andHayes (1977) applies to trabecular bone
trabecular density
mean trabecular thickness
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Bone: Strength of Cancellous Bone
determinants ofcancellous bonemechanicalproperties trabecular
orientation (meanintercept length)
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Bone: Viscoelastic models
Sedlin (1965)
three-parameter solid
a frictional element to account for plastic
deformation
Bargren et al. (1974)
Kelvin is good enough for physiological rates
Laird and Kingsbury (1973)
three-parameter solid cannot model thedependency on frequency
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Bone: Fatigue properties