biomechanics of solids - umbc: an honors …...17. hip joint 18. femur 19. patella 20. tibia 21....
TRANSCRIPT
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Biomechanics of Solids
Devendra BajajGraduate Student, LAMP
Department of Mechanical EngineeringUMBC
ENCH 484/693: Biomedical Engineering. (April 18, 2007)
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Historical Facts
Anatomical studies of the ShoulderDrawings of the torsoand the arms
Leonardo da
Vinci1452-1519
Studies of the human skull
www.davinciandthebrain.org
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Historical Facts
Illustration of skull from the 1918 editionAn illustration from 1918 edition
Henry Grey1827-1860
www.wikipedia.org
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List of bones of Human Skeleton1. Frontal bone 2. Parietal bone 3. Temporal bone 4. Occipital bone 5. Zygomatic
bone 6. Superior and inferior maxilla 7. Mandible 8. Cervical vertebrae incl. atlas & axis thoracic vertebrae9. Nasal bone 10. Sternum11. Humerus12. Ilna13. Radius14. Lumbar vertebrae 15. Pelvis
16. Sacrum 17. Hip joint18. Femur19. Patella20. Tibia21. Fibula22. Greater trochanter
of femur 23. Condyles
of femur25. Clavicle or collarbone 26. Condyles
of humerus27. Head of radius28. Ribs29. Scapula or shoulder blade
www.wikipedia.org
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Loads Transmitted
Bone: Femur
www.wikipedia.org
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Major Concerns
Bone health issues, such as osteoporosis, are expected to affect 50% of Americans by the year 2010*
*Bone Health and Osteoporosis: A Report of the Surgeon General, HHS 2004
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Fracture and Treatment of Hip Joints
Statistics show that about 80 % of all failures that lead to the revision operation of a total hip are caused by aseptic loosening of the total hip.
http://www.doereport.com/imagescooked/12945W.jpg
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Human Tooth
http://www.nlm.nih.gov
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Restorative Dentistry
Demineralization
ExcavationRestoration
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Failure of Restored Teeth
100 µm
500 µm
Arola et al., J. Mat Sci.:Materials in Medicine, 1998
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The story so far…..
Hard Tissues: Historical perspectiveTypes of bonesLoad distributionAge related problemsFailure and treatment of Hip jointRestorative dentistryFracture of restored toothMicrostructure of BONE AND HUMAN TOOTHInfluence of AGING?
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Microstructure of Bone
Nalla et al., Materials Science and Engineering, 2006
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Bone: Influence of Aging
Young 34 years
Aged 85 years
Nalla et al., Materials Science and Engineering, 2006
Bone becomes more porous with age
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Microstructure of Dentin
peritubular dentin
intertubular dentin
5 µm
Ten Cate, Oral Histology 1998Porter et al., Biomaterials 2005
67 nm
~10-12 nm
Collagen Debanding
Mineral Crystal
Dentinal Tubule
Molar
OcclusalSurface
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Dentin: Influence of Aging
Bajaj
et al., Biomaterials 2006
Young 17 years
Aged 50 years
Dentin becomes less porous with age
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Dentin v/s
Bone
Which one has reparative properties ?BONE or DENTIN
“Teeth are exquisitely sensitive to local stress and trauma and we are conscious of our teeth in a way quite unlike our sense of what our bones are up to.” -
John D. Curry
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Why study the MECHANICAL properties of hard tissues???
“It is unfortunate that we have so little idea of the mechanical properties of many of the interesting bio materials. This is because of the small size and conventional shape of many of the structures in which they are found. Their histological structure shows that they are often very well designed mechanically, but, unfortunately, we usually cannot quantify them well.” John D. Curry
Structure Tubule orientation
Aging
Applications to other engineering materials (MEMS/NEMS)
10 nm
Rouland, 2002
Ritchie et al., 2002
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Testing of Hard Tissues
Tensile
0
20
40
60
80
100
120
0.000 0.005 0.010 0.015 0.020 0.025
Stre
ss (M
Pa)
Strain
Sano et al., J Dent Mat. 1984
σut
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Testing of Hard Tissues
Flexure
P(t)/2P(t)/2
P(t)
0
50
100
150
200
0.000 0.005 0.010 0.015 0.020
Ben
d S
tress
(MP
a)
Strain (m/m)
Elastic Modulus
Strength
Energy to
Fracture
Arola and Reprogel, Biomaterials 2006
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Tubule Orientation
θ=0° θ=90°
0
20
40
60
80
100
120
140
160
0.000 0.005 0.010 0.015 0.020
θ=0o
θ=90o
Stre
ss (M
Pa)
StrainArola and Reprogel, Biomaterials 2006
θ=0°
θ=90°
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Tubule Orientation
θ=0° θ=90°
Arola and Reprogel, Biomaterials 2006
θ=0°
θ=90°
0
10
20
30
40
50
60
70
80
102 103 104 105 106 107
θ = 0ο
θ = 90ο
Stre
ss a
mpl
itude
, σa (M
Pa)
Cycles, N
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Dentin: Influence of Aging
Arola and Reprogel, Biomaterials 2005
Young 18 years
Old 66 years
0
20
40
60
80
100
120
140
0.000 0.005 0.010 0.015 0.020
OldYoung
Stre
ss (M
Pa)
Strain (m/m)
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Dentin: Influence of Aging
Arola and Reprogel, Biomaterials 2005
Young 18 years
Old 66 years
0
10
20
30
40
50
60
70
80
102 103 104 105 106 107
YoungOld
Stre
ss a
mpl
itude
, σa (M
Pa)
Cycles, N
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10-7
10-6
10-5
10-4
0.8 0.9 1.0
da/d
N (m
m/c
ycle
)
ΔK (MPa∗m0.5)ΔK
th
mC
Testing of Hard TissuesFatigue
4.0
2.01.0
a
6.0
1.0
2.0High Crack Growth
Resistance
Low Crack Growth ResistanceI II III
Bajaj
et al., Biomaterials 2006
Primary section
Possible specimen
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Fatigue Crack Growth
10-7
10-6
10-5
10-4
10-3
0.5 0.6 0.7 0.8 0.9 1.0 2.0
OldYoungda
/dN
(mm
/cyc
le)
ΔK (MPa∗m0.5)
Dentin
Bajaj
et al., Biomaterials 2006
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Mechanisms of Crack Growth
Bajaj
et al., J Biomed Mat Res, 2007b (submitted)
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Fatigue Crack Growth
Bone
Nalla
et al., Biomaterials, 2005
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The story so far…..
Microstructure of BONE and DENTINInfluence of AGE on structureTesting of hard tissuesTensile Flexure Fatigue
Fatigue in DENTINFatigue in BONE
Why do we see differences in properties with AGING ?STRUCTURECHEMISTRY
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Changes in Structure & Chemistry
Specimen Surface
Depth of the source of secondaryelectron information (~5nm)
Depth of the source of Backscatteredelectron information (~1/3 total depth)
Depth of the source of X-Rayinformation (~3µm)
SEX-Rays
Incidence Electron Beam
BSE
Binary
1.0 μmThreshold
Energy Dispersive x-ray Analysis
Bajaj, Masters Thesis, 2006
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Influence of Structure
0.00
0.05
0.10
0.15
0.20
0.25
10 20 30 40 50 60 70 80 90Are
a of
Lum
en /
Are
a of
Tub
ule
Age (years)
0
5
10
15
20
25
30
0.00 0.05 0.10 0.15 0.20
Cra
ck G
row
th E
xpon
ent (
m)
Area of Lumen/Area of Tubule
r = 0.799P = 0.0028
OcclusionofDegreeTubuleofAreaLumenofArea
=
Dentin
Bajaj, Masters Thesis, 2006
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Influence of Chemistry
2.0
2.1
2.2
2.3
2.4
2.5
2.6
10 20 30 40 50 60 70 80 90
Ca
/ P
Age (years)
10
15
20
25
30
2.0 2.1 2.2 2.3 2.4 2.5 2.6
Cra
ck G
row
th E
xpon
ent (
m)
Ca/P
r = 0.878P = 0.0056
Dentin
Bajaj, Masters Thesis, 2006
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Influence of Structure
Nalla
et al., Materials Science and Engineering, 2006
Bone
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Influence of Chemistry
Ager
et al., J Biomed Optics, 2005
Bone
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Conclusions
Aging results in changes in properties of hard tissues
Changes in structure and chemistry are responsible for changes in properties
Enamel (E)
Dentin (D)
PulpDEJ
2 mm
250 µm
D
E
What is the biological seed to aging?How does the mineral and non-mineral component contribute
to strength?How much damage accumulates in these tissues per day?Can we arrest these cracks mechanically or chemically?