tribological properties of metal-on-metal hip implants
TRANSCRIPT
Tribological
Properties of
Metal-on-Metal
Hip Implants
Dr. Yılmaz Özmen
Outline
Identify different types of Biomaterials
Wear of Metal-on-Metal Hip Implants
Diamond-like Carbon Coating for Bio-
medical Implant Materials
4/29/20152
Biomaterials Classes
Metals
Ceramics
Polymers
4/29/20153
Metals
Metal is any element that
positively ionized in solution.
Metallic Bond: positively
charged ions in a cloud of
electrons.
Metals are crystalline
solids. (Regular Atomic
Arrangement)
4/29/20154
Metals
Metals composed of one or more than one element are alloys
The surface of metals are often oxides, if inert (Passive) leads to protection, if active leads to corrosion
Typical metal properties include:
• High melting points
• High density
• High thermal and electrical conductivities
• High stiffness, strength and hardness
• High ductility, fatigue resistance
Their properties depend on the composition and the processing method
4/29/20155
Metallic Biomaterials
Stainless steel alloys
Titanium and Titanium alloys
Cobalt Chromium alloys
4/29/20156
Stainless steel alloys
Alloys of iron (Fe), chromium (Cr), Nickel (Ni) and carbon (C)
•Chromium: increase corrosion resistance.
•Nickel : increase strength
•Carbon : increase corrosion in human body & strength
4/29/20157
Titanium and Titanium Alloys
Forms a very stable oxide layer of Titanium oxide (passive metal)
• Titanium Alloys: addition of Aluminium and Vanadium, enables it to have a wide range of properties.
4/29/20158
Co Cr Mo alloys
It is an alloy of cobalt (Co), Chromium (Cr),Nickel (Ni), Molybdenum (Mo) and Carbon (C)
•Chromium : Passivation element (Chromium oxide)
•Nickel : increase strength
•Molybdenum : increase strength and hardness
•Carbon : increase corrosion in the body and increase strength
4/29/20159
Mechanical Properties of Metals
4/29/201510
High strength, stiffness (E), fatigue resistance,
High wear resistance
But, it may wear when metal-on-metal hip replacement is used, wear particles may reduce its biocompatibility.
Wear of Metal-on-Metal
Hip Implants
4/29/201511
What is Tribology?4/29/201512
Tribology tries to describe everything that happens when things rub together
TRIBOLOGY TRIANGLE
Would Life Be Possible Without
Tribology ?????
4/29/201513
Contact of Two Surfaces
Surfaces may look smooth, but on a microscopic scale
they are rough.
If we want to slide one surface
over the other then we have to apply a force to
break those junctions.
4/29/201514
Keeping the Surfaces Apart
(Lubrication)
Definition: introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat.
• Boundary lub.
• Elasto-hydrodynamic lub.
• Hydrodynamic lub.
4/29/201515
Origins of friction:
adhesion between surfaces
4/29/201516
The degree of adhesion depends on:
- type of bond established between contacting surfaces
- deformation capability of the material (real area of contact,
orientation)
- surface oxidation, adsorption of molecules, contaminations
Origins of friction: deformation
4/29/201517
The deformation work (frictional work) depends on:
- geometry of indenter
- hardness of metal
Friction and Wear:
system-dependent phenomenon
4/29/201518
Wear
4/29/201519
Wear is the progressive material loss from solid surfaces in contact which occurs as a result of friction.
Wear is not a material property. It is a complex response of a material to the solicitations induced by the system in which it operates.
One can distinguish 4 fundamental mechanisms of wear :
•adhesive wear mechanism
•abrasive wear mechanism
•fatigue (delamination) wear mechanism
•tribochemical mechanism
Adhesive wear by strong interfacial bonding
4/29/201520
Critical factors
• size of contacting area
• bonding (ionic, covalent, metallic, Van der Waals)
• surface contamination
• surface oxydationSteel against steel contact
Abrasive wear by plastic deformation and microcutting
4/29/201521
Critical factors
• hardness ratio between indenting and abraded material > 1
• hardness of abraded material
• roughness of indenting material Aluminium abraded by SiC paper
Fatigue wear by repeated load and unload cycles
4/29/201522
Critical factors
•stress and number of cycles
• resistance to fatigue of the material
•surface defects and residual stresses
Fatigue failure of a steel ball bearing
Tribochemical wear by removal of reaction layers
4/29/201523
Critical factors
•mechanical properites of the reaction layer
• reaction kinetics
•kinematics and stresses
Agglomerated oxide
particles after wear of a
passive steel.
Tribological contacts in hip
joint implants
4/29/201524
Tribological tests for implants
4/29/201525
Tribological requirements for
contacting materials
4/29/201526
No seizure (blocking of joint by too strong interfacial adhesion).
High resistance against wear
High resistance against scratching
High resistance against fatigue and impacts
high hardness
high toughness
Materials for “low wear„ hip
joints
E = 200 E = 390 E = 200
K = 20 K = 2 – 4 K = 6 – 9
H = 350 H =2000 H = 1200E: Young's modulus [GPa]
K: Fracture toughness [MPa√m]
H: Vickers hardness [HV]
4/29/201527
In-vivo wear rates
4/29/201528
Annual linear wear rate of different material combinations as used
for cup and head in total hip replacement
Diamond-like Carbon
Coating for Bio-medical
Implant Materials
4/29/201529
Surface Engineering
Definition: Changing the properties of the surface of a material to give performance which cannot be achieved by the surface layer or bulk alone
Surface Engineering Processes
•Mechanical treatment (e.g. peening, shot blasting)
•Surface transformation (e.g. induction hardening, laser treatment)
•Surface composition changes (e.g. thermo chemical treatment, ion implantation)
•Chemical treatment (e.g. conversion coatings)
•Coating (e.g. painting, spraying, plating, vapor deposition)
•Surface activation (etching, plasma treatment of polymers)
4/29/201530
Diamond-like Carbon :
as a Strong Candidate Coating
Biological Compatibility
• Nontoxic, Noncarcinogenic, Noninflammatory
Chemical Compatibility
• Corrosion Resistance
Mechanical Compatibility
• Surface Hardness, Wear Resistance
4/29/201531
t-aC
sp2 H
sp3
DLC
No film
diamond
graphite
Polymer-like
Graphitic
t-aC:H
DLC: A Group of Carbon Mat’l4/29/201532
Use of DLC for
Bio-medical Implant Materials
Blood Contacting Applications
•Stents, Heart valves, Flow Accelerators
Load Bearing Applications
•Hip Joints, Knee Joints, Artificial Disk
4/29/201533
Load Bearing Implants
4/29/201534
Artificial Joints Application
•Needs an improved test method to obtain clinically relevant results.
•DLC/DLC or DLC/metal combinations show more promising results than other combinations.
