elastic properties of bones skin and muscles

1. BONES

2.  It is a ceramic-polymer composite.
 There are two principal types of bone
1) cortical or compact
•It is found in long bones (femur,tibia,fibula,etc.).
2) cancellous or trabecular or porous
It is found it the core of bones and in flat bones.

3. STRUCTURE OF BONES
b
a. Longitudinal section of a femur( source: Mann[7, Fig. 2.9, p.11]
b. A cross section of elk antler.
(source: https://guerillaarchaeology.wordpress.com)

4. MECHANICAL BEHAVIOUR OF BONES
Source: Design of artificial human joints and organs by Subratha pal (ch 2)

5. The mineral content of bone affects its mechanical
property. Higher mineralization makes the bone stronger
and stiffer (higher modulus of elasticity), but it lowers the
toughness.
Effect of mineral volume fraction on (a) tensile strength and (b) toughness (as measured by area
under
stress–strain curve) of different bones (reproduced from Currey [2, Fig. 4.3, p.132 and Fig. 4.5, p.
135]).

6. FRACTURE AND FRACTURE TOUGHNESS OF
BONES
There are various mode of fracture in bones
Green fracture
Fissured fracture
Comminuted fracture
Transverse fracture
Oblique fracture
A spiral fracture
The fracture toughness varied in the range:
2 MPa m1/2< KIc < 5 MPa m1/2

7. SIX modes of fracture in bone
(adopted from Hall[181,Figs,4-6,p.102])

8. LIGAMENTS

9. • Function of a ligament is to connect bone to
another bone. Tendon connects bone to muscle
• The major constituents of ligaments are
collagen, elastin, glycoproteins, protein
polysaccharides, glycolipids, water, and cells
(mostly fibrocytes).
• Collagen constitutes 70–80% of the dry weight
of ligament, the majority being type I collagen,
which is also found in tendon, skin, and bone.
• Collagen has a relatively long turnover rate,
with its average half-life being 300 and 500
days, which is slightly longer than that of bone.

10. Fig. Hierarchical structure of ligaments. The basic structural element is
the tropocollagen molecule
Source: Design of artificial human joints and organs by Subratha pal (ch 2)
Closely packed, parallel collagen fi ber bundles are oriented to provide motion
and stability for the musculoskeletal system.
Properties can change according to strain rate, temperature, hydration,
maturation, aging, immobilization, exercise, and healing.

11. MECHANICAL BEHAVIOUR OF LIGAMENTS
Force-elongation diagram obtained during tensile test of ligaments
The force- elongation curve represents structural properties of the ligament.
That is, the shape of the curve depends on the geometry of the specimen tested
(e.g., tissue length and cross- sectional area).

12. • Ligaments exhibit significant time- and history-
dependent viscoelastic properties. Time-
dependent behaviuor means that during daily
activities, ligaments are subjected to a variety of
load conditions that affect their mechanical
properties
• For example, they become softer and less
resistant after some minutes of running,
returning to normal hardness when the exercise
is interrupted
Fig. Stress–strain relationship
for human ligament
(Source: Design of artificial human
joints and organs by Subratha pal (ch 2)

13. (Source: Design of artificial human joints and organs by Subratha pal (table 2.2)
Comparative properties of biological
materials

14. skin

15. -The protective layer from external
environment
- living complex material composed of
• epidermis
• dermis
• hypodermis
skin

16. mechanical properties of skin
• indentation method
Source:In vivo measurement of the elastic mechanical properties of human skin by indentatio tests

17. Analysis of skin indentation
• curve is reversible and
hysteresis due to low
dissipated energy
• No plastic depth observed
• Approximate youngs
modulus is 12.5kpa
fig:Indentation curve

18. skin young's modulus
• skin is analysed as thin
soft layer onto rigid
substrate muscle
• approximate young's
modulus of muscle is
12kpa to 24kpa
• thus muscles is more rigid
fig:variation of skin young's modulus vs penetration
depth for 10 subject taking subject 1 as mean

19. comparison of measured and apparent young's
modulus
for a/e<0.5
fig:apparent vs theoretical young's modulus

20. fig:Mechanical equivalent model for two thin layers on half space
Dermis:E1*=35kpa and e1=1.2mm
Hypodermis:E2*=2kpa and e2=0.8mm
• Two layer mechanical model describes the decrease in
youngs modulus at low penetration depth

21. Result
• skin behave elastically for considered load
range
• Epidermis doesn't influence the mechanical
behavior
• Two layer model describes the elastic
behaviour of the skin up to a penetration depth
equal to thickness

22. Muscles

23. Muscles
• composed of 70-80% water, 10-15% collagen,5-
7%fat
• composed of fascicles containing bundles of
fibres
• exhibits a fibre oriented structure to fulfill force
producing function
• Types: cardiac,smooth and skeletal

24. Experiment on skeletal muscles tissue
• for strain evaluation, nine black dots are marked on the
sample
• tighten the sample with clamps with minimum stress at
clamp
fig:
testing sample

25. Data analysis
• Nine black dots are used
for image analysis for
displacement calcualation
fig:typical cross-fibre directiion sample

26. fig:schematic illustration of ths sample before(a) and after(b) deformation.(c) stretch regions (d) poisson's
ratio regions

27. Result
fig: sample after testing
• undeformed initially at Λ=1 and deformed at Λ=1.35

28. • test were performed along and perpendicular as
well at 30°,45°and 60° to the muscle fibre
direction
• cross-fibre direction is linear and stiffest (77kpa
stress at a strech)
• failure occurs at low streches(Λ=1.15)
• the fibre direction is non-linear and less
stiff(10kpa stress at a strech)
• failure occurs at high streches(Λ=1.65)
• An approximately sinusoidal variation in stiffness
was observed at intermediate angles.