about the biomaterials used in orthopaedics and trauma and their biomechanics

1. Biomaterials in Orthopaedics
& Trauma
Zahid Askar
FCPS(Ortho), FRCS (Ortho)
Prof of Orthopaedics & Trauma
Khyber Medical College, Peshawer

2. Study of Biomaterials
The physical and biological study of
materials and their interactions with
the biological environment.
Increase use of biomaterials
-Their interactions
-Increasing Duration and stresses

3. Biomechanics
• The science of movement of a living
body, including how muscles, bones,
tendons and ligaments work together to
produce movement.

4. Response to Load

5. • Force applied will lead to deformation
and if continued beyond a certain point
will lead to ultimate failure
• The force ----- STRESS and
Deformation is known as
STRAIN

6. Stress & Strain
Stress:- Force per unit area
Units NM/Sq M or Pascal
Strain:- Change in length per unit original
length

7. Stress
Strain
Elastic
Plastic
Yield Stress
Ultimate Stress
Breaking Stress

8. The path to failure

9. TENSILE STRENGTH/ ULTIMATE TENSILE STRENGTH -
The maximum stress on the curve before breakage (N/M2)
YIELD STRESS-
Point at which elastic behaviour changes to plastic behaviour.
BREAKING STRESS
Point at which the substance fails/brakes

10. Young’s modulus E
• Stress /Strain
For elastic part of curve or the slope
of the elastic part of the curve
SI unit =
pascal (Pa or N/m2 or m−1·kg·s−2).
megapascals (MPa or N/mm2) or
gigapascals (GPa or kN/mm2)

11. • DUCTILITY/ BRITTLENESS- The amount by
which a material deforms (i.e. the strain
that occurs) before it breaks.
Represented by %age elongation or
reduction in cross section.
• HARDNESS- The ability of the surface of a
material to withstand forces.

12. • The Yield Point = marks the onset of
plastic deformation
• Plastic Region = Beyond the yield point,
irreversible (plastic) deformation takes
place

14. Elastic Modulus of Common Materials in
Orthopaedics
• Stainless Steel 200
• Titanium 100
• Cortical Bone 7-21
• Bone Cement 2.5-3.5
• Cancellous Bone 0.7-4.9
• UHMWPE 1.4-4.2

15. Relative values of
Young's modulus of
elasticity (numbers
correspond to
numbers on illustration
to right)
1.Ceramic (Al2O3)
2.Alloy (Co-Cr-Mo)
3.Stainless steel
4.Titanium
5.Cortical bone
6.Matrix polymers
7.PMMA
8.Polyethylene
9.Cancellous bone
10.Tendon / ligament
11.Cartilage

18. Bone Mechanics
• Bone Density
– Subtle density changes greatly changes
strength and elastic modulus
• Density changes
– Normal aging,Disease,Use,Disuse
Figure from: Browner et al: Skeletal Trauma
2nd Ed. Saunders, 1998.

20. Bone Biomechanics
• Bone is anisotropic - its modulus is dependent
upon the direction of loading.
Bone Type Load Type
Elastic
Modulus
(×10 E9 N/m2)
Ultimate
Stress
(× 10 E6 N/m2)
Cortical Tension 11.4-19.1 107-146
Compression 15.1-19.7 156-212
Shear 73-82
Cancellous Tension ~0.2-5.0 ~3-20
Compression 0.1-3 1.5-50
Shear 6.6 +/- 1.7

21. Material Ultimate
Strength
Tensile
(MPa)
Ultimate
Strength
Compressive
(MPa)
Yield
Strength
0.2% Offset
(MPa)
Elastic
Modulus
(MPa)
Cortical bone 100 175 80 15,000
Cancellous bone 2 3 1000
Polyethylene 40 20 20 1000
PTFE Teflon 25 500
Acrylic bone cement 40 80 2000
Stainless steel (316 L)
(annealed)
>500 >200 200,000
Titanium (Al-4V)
(alloy F 136)
900 800 100,000
Cobalt chrome
(wrought, cold work)
1500 1000 230,000
Super alloys
(CoNiMo)
1800 1600 230,000

22. ORTHOPAEDIC
BIOMATERIALS

23. BIOMATERIAL - A non-viable material used in a medical device,
intended to interact with biological systems.
State of Mutual Coexistance between a
Biomaterial and the Physiological Environment
Such as Neither has an Undesirable Effect on
the Other.
.
BIOCOMPATIBILITY
No host response to the materialBIOINERT

24. Ideal Biomaterial
• Suitable mechanical properties to fulfil
its intended function
• Must not corrode in biologic
environment
• Must not release potentially harmful
degradation by-products locally and
systemically.
• To permit fabrication in the optimum
design configuration,

25. Ideal Biomaterial
• Be like the natural and mimic its
biomechanical properties
• Not elicit a response- Bioinert
• Elicit a favourable response- Biocompatible
• Economical and Reproducible

26. Implants- Uses
• Help
• Substitution

27. 􀁺
Mechanical Properties of Bone
• Young’s Modulus(E) 17.0 GN/m2
• Ultimate Tensile Strength (UTS)
0.132GN/m2
• Compressive Strength(σc) 0.192
GN/m2
• Shear Modulus(K) 2.01 GN/m2
• Poisson’s Ratio(ν) 0.3

28. Materials used in Orthopaedics
• Metals -Stainless Steel 316L.
-Co-Cr-Mo.
-Ti-6AL-4V.
Ceramics- Alumina/Zirconium
Polymers- UHWPE, PMMA, Silicones.PEEK

29. Stainless steel-(316L)
• Iron- 60%,
• Chromium- 20%
• Nickel- 14%
• Molybdenum- 3%
• Carbon- 0.03%
• Manganese, Silicon,P,S,- 3%

30. Functions
• Iron
• Chromium/Nickel/
Molybdenum-
• Carbon-
• Manganese, Silicon -
• Strength
• Corrosion
• Strength
• Manufacturing
Problems
The chromium forms an oxide layer when dipped in
nitric acid to reduce corrosion and the molybdenum
increases this protection when compared to other
steels.

31. Stainless Steel
• Strong
• Cheap
• Relatively ductile
• Relatively biocompatible

32. • High Young’s modulus – 200 GPascals
(10 that of bone)
• Leads to stress shielding of surrounding
bone which can cause bone resorption.
• susceptible to corrosion

33. Titanium and its alloys
• Ti 6AL-4V ELI (Grade 23)
• Ti 6Al-4V (Grade 5)
• Excellent resistance to corrosion
• Young’s modulus
• Stronger than stainless steels
• MRI complaint

35. Disadvantages
opoor resistance to
wear
o Can be brittle i.e. less
ductile
generates more
metal debris than
cobalt chrome

36. Cobalt-Chromium-Molybdenum alloy
(Co-Cr-Mo)
• COBALT-BASED ALLOYS
Two main types of cobalt-based alloys
• A cast alloy
• A wrought alloy,
• Also known as Vitallium (or in Britain,
"Stellite") is often applied to both alloys.

38. Advantages
strength and corrosion resistance
high abrasion resistance
Superior to stainless steel
Disadvantages
More expensive to
manufacture
cannot be
contoured at the
time of surgery.

39. USES
• Usually for bearing surfaces
• THR
• Metal-on-metal devices.

41. Material Elastic Yield U.Tensile
Modulus Strength Strength
(GN/m2) (MN/m2) (MN/m2)
316L 200 795 965
Co-Cr-Mo 210 950 1450
Ti-6Al-4V 105 895 1173
Mechanical Properties of
Orthopaedic Alloys

42. POLYMETHYLMETHACRYLATE
(PMMA)
• Prepolymerized methylmethacrylate( powder)
• Liquid monomer
• Exothermic Reaction
• 10 min at 23 0 C .
• 60 0 C in the center of the material
and 40 0 C at the surface.
• A grouting agent
• Good in compression
• Hard but brittle

44. •2 component material
•Powder
•polymer
•benzoyl peroxide (initiator)
•barium sulfate (radio-opacifier)
•Liquid
•monomer
•DMPT (accelerator) N,N-
Dimethyl-p-toluidine
•hydroquinone (stabilizer)

45. The curing process is divided into 4 stages:
a) mixing,
The mixing can be done by hand or with
the aid of centrifugation or vacuum technologies.
b) sticky/waiting,
c) working, and
d) hardening.
It is recommended that the unopened cement
components are stored at 73 °F (23 °C) for a
minimum of 24 h before use.

46. First generation cementing technique
1)- Hand mixing
2)-Minimal preparation of the femoral canal
2)-Digital application of cement.
Second generation cementing techniques
1)-Preparation ,packing and drying of the femoral canal
2)-Distal cement restrictor
3)-Pulsatile irrigation,
4)-Retrograde insertion of cement with a cement gun.
Third generation cementing techniques
1)-Cement is prepared using a vacuum-centrifugation( reduces porosity).
2)-The femoral canal is irrigated with pulsatile lavage and then packed with
adrenaline soaked swabs.
3)-Insertion and pressurisation of the cement in a retrograde fashion
Fourth generation cementing techniques
Insertion using distal and proximal centralizers to ensure an even cement mantle
(4th generation).
Generations of Cementing Technique

47. First Second Third Fourth
Hand Mix with Spatula Hand mix with cement
gun
Vacuum /centrifuge
Mixing
Third with
Leave Cancellous
Bone
Remove bone from
the endoesteal
surface
Remove bone from the
endoesteal surface
PROXIMAL &
DISTAL
CENTRALISER
Vent Femoral canal Distal Cement
restrictor
Distal Cement restrictor
Minimal canal
Preparation
Brush Pulsatile
irrigation
Brush Pulsatile irrigation
Irrigate & Suck
femoral canal
Irrigation, Pack and
dry
Irrigation, Pack with
adrenaline gauze and dry
Manual Insertion of
the Dough
Cement Gun Insertion Cement Gun Insertion &
pressuriation
Manual Insertion of
the stem
Manual Position of
the Stem
Manual Position of the
Stem
FEmoral stem shapes Improved Femur
Design
Surface texturing and
contouring

49. USES
used for fixation and load
distribution in conjunction with
orthopeadic implants
Functions by interlocking with
bone
•May be used to fill tumor defects
and minimize local recurrence
Advantages
1)-Reaches ultimate
strength at 24 hours
2)-Strongest in
compression
3)-Young's modulus
between cortical and
cancellous bone
Disadvantages
•poor tensile and shear
strength
•insertion can lead to
dangerous drop in blood
pressure
•failure often caused by
microfracture and
fragmentation

50. Ceramic
• A ceramic material
may be defined as
any inorganic
crystalline material,
compounded of a
metal and a non-
metal
• Alumina
• Zirconia

52. Advantages
1)-best wear
characteristics with PE
2)-high compressive
strength
Disadvantages
1)-typically brittle,
low fracture
toughness
2)-high Young's
modulus
3)-Low tensile
strength
4)-Poor crack
resistance
characteri
stics

53. Ultra-high-molecular-weight polyethylene (
UHMWPE)
• Sterilised by Gamma irradiation
• Increases polymer chain cross-linking
which improves wear characteristics
• Decreases fatigue and fracture resistance

54. Advantages
1)-Tough
2)-Ductile
3)-Resilient
4)-Resistant to wear
Disadvantages
1)-Susceptible to abrasion
2)-Wear usually caused by third
body inclusions
3)-Thermoplastic (may be altered by
extreme temperatures)
weaker than bone in tension

55. Silicones
– Polymers that are often used for
replacement in non-weight bearing joints
– Disadvantages
• poor strength and wear capability responsible for
frequent synovitis

57. Polyether ether ketone (PEEK) is a
colourless organic thermoplastic polymer in
the polyaryletherketone (PAEK) family, used in
engineering applications.
Shape-memory polymers (SMPs) are
polymeric smart materials that have the ability
to return from a deformed state (temporary
shape) to their original (permanent) shape
induced by an external stimulus (trigger), such
as temperature change.

58. Polyetheretherketone, or PEEK, was
originally developed in the late 1970s by
the US aerospace industry, which was
taken by its properties of stability at high
temperatures and thus its potential for
high-load, high-temperature applications.
In the late 1990s, a highly pure and
implantable grade of PEEK known as
PEEK-OPTIMA was commercialised by
Invibio Biomaterial Solutions and
subsequently embraced by the medical
device industry

60. Angle stable interlocking screws,
which have a sleeve that expands to
fit tightly within the nail interlock to
improve construct stability of
intramedullary nailing of distal tibia
fractures
Angle stable interlocking screws
Horn J, Linke B, Höntzsch D, Gueorguiev B, Schwieger K: Angle stable interlocking
screws improve construct stability of intramedullary nailing of distal tibia
fractures: A biomechanical study.Injury 2009;40[7]:767-771.)

63. How do Materials fail????
• Corrosion
• Fatigue
• Wear

64. Corrosion
• A chemical reaction in which material is
removed from an object.

65. Galvanic corrosion-
due to two different metals being used e.g.
stainless steel screws and titanium plate.
Stress corrosion-
The presence of a crack due to stress
Crevice corrosion / fretting occurs
where components have a relative movement
against one another
Pit corrosion-
A local form of crevice corrosion due to
abrasion produces a pit
Types Of Corrosion

66. Fatigue-
• Progressive failure of a material due to
the application of cyclical stresses below
the ultimate stress of the material
causing failure.

67. • All implants will eventually break
if the fracture does not heal.

68. Basic Biomechanics
• Load to Failure
– Continuous application
of force until the
material breaks (failure
point at the ultimate
load).
– Common mode of failure
of bone and reported in
the implant literature.
• Fatigue Failure
– Cyclical sub-
threshold loading
may result in failure
due to fatigue.
– Common mode of
failure of
orthopaedic
implants and
fracture fixation
constructs.

69. Wear
• The removal of material from solid surfaces by
mechanical action

70. Interfacial wear - when bearing surfaces come
into direct contact , can occur in 2 ways:
1. Adhesive wear, when surface fragments
adhere to each other and are torn from the
surface during sliding
2. Abrasive wear, when a soft material is
scraped by a harder material.
Third Body Wear
Corrosion Wear
Fatigue Wear
due to accumulation of microscopic damage
within the bearing material due to repetitive/
cyclical stressing.
Types Of Wear