Medical devices are heavily regulated because of their intended uses in human beings. Generally medical devices are classified into different categories depending upon the degree of potential risks and regulated accordingly.Many medical devices are involved with relative moving parts, either in contact to the native tissues or within the biomaterials, and often under loading. Important issues, such as friction and wear of the moving parts, not only affect the functions of these devices but also the potential adverse effects on the natural tissues. Biotribology deals with the application of tribological principles, such as friction, wear and lubrication between relatively motions surfaces, to medical and biological systems. Biotribology plays an important role in a number of medical devices

1. Tribology for Medical devices
Karolinekersin.E
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2. Why Tribology ?
• Tribological properties associated with wear, friction and
lubrication are important to the implementation of many
biomedical applications.
• Medicine now allows for the replacement of biological
tissue with artificial devices.
• Over time, the implants can fail due to friction and wear
as seen commonly in artificial joints but also because of
the friction and corrosion produced from simple contact
with body fluids such as blood.
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3. Importance of Tribology
• Tribology is an important aspect in the
design of many biomedical devices,
including artificial joints, implants and
cardiovascular valves.
• Many medical devices are involved with
relative moving parts, either in contact to the
native tissues or within the biomaterials and
often under loading.
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4. Bio tribology
• Bio tribology deals with the application of
tribological principles such as friction, wear
and lubrication between relatively motions
surfaces, to medical and biological systems.
• Bio tribology plays an important role in a
number of medical devices
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5. Tribology involved Medical devices
Artificial Joints
• Articular surfaces
• Modular Junctions
• Fixation
Fracture Fixation
Cardiovascular devices
Contact lenses
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Artificial Joints Fracture Fixation
Cardiovascular devices Contact lenses

6. Artificial joints
• Artificial joints are one of the most successful
device in the human beings .
• There are 206 bones and 300 joints over the
body .
• It is estimated that more than one million joints
are implanted in a world wide .
• Artificial knee and hip replacements must
currently be replaced every 10-15 years
because friction and wear cause implant failure
through the aseptic loosening of the bond
between device and bone as well as the
formation of osteolysis
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7. Contd ..
• Friction, wear and lubrication play
important roles in the successful function
of artificial joints and the potential clinical
problems.
• Tribological issues at the articulating
surfaces as well as at the connection
between modular components and the
fixation to bone are important
considerations.
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8. Articular surfaces
• The major issue currently associated with
the bearing surfaces of artificial joints is
wear and subsequent wear debris which can
cause adverse tissue reactions and the
loosening of the prosthetic components.
• Therefore improving the wear resistance of
the bearing surfaces has been one of the
main drivers in the development of artificial
joints
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9. Articular surfaces
• Surface coatings of the metallic counter-face or
the use of harder materials such as ceramics
are introduced to maintain a low wear level.
However, the strength and the potential long
term durability associated with these coatings
remain problematic.
• Highly cross-linked Ultra High Molecular weight
Polyethyelene (UHMWPEs) are now mainly
used in the majority of artificial hip joints, while
their use in artificial knee joints is also receiving
attention.
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10. Modular junctions
• Modular connections are introduced in
artificial joints in order to facilitate their use in
patients and by surgeons.
• For example in the hip joint, modular head-
neck combinations and modular neck stems
allow for restoration of anatomy and
optimization of joint biomechanical functions.
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11. Modular junctions
• Different bio-materials are often involved in
the modular connection as well as in direct
contact with bone including cobalt chromium
alloy/titanium, ceramics/titanium etc resulted
in corrosion which is a major challenge.
• In many uses Poly Ether Ether Ketone
(PEEK )is used to reduce the corrosion .
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12. Fixation
• Artificial joints are fixed to bone, either using
bone cement(cemented fixation) or press-
fitting through bone in-growth(cementless
fixation). The micro-motion at the implant-
cement and cement-bone interfaces is
inevitable and can result in fretting and wear.
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13. Fixation
• The micro-motion at the implant-bone
interface affects the primary stability (mainly
achieved through press-fit and friction) and
consequently the long term secondary
stability (bone in-growth).
• Stem designs and particularly coatings affect
friction and the primary stability.
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14. Fracture fixation
• Bone fractures are common, with over 1.7 million
fractures in the hip alone worldwide
• In some hip fracture fixation devices such as an
intramedullary nail, modular constructs are some-
times preferred and for example, sliding of the lag
screw is important to the fracture consolidation
and transmission of forces through the fracture
site.
• In addition, fracture plates or nails are fixed to the
bone through screws, cables etc. and often with
different materials.
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15. Contd..
• Galvanic corrosion and fretting corrosion
are often involved between the components
of the construct as well as between the
constructs and bone.
• Fretting corrosion is often present in the
modular junction of an intramedullary nail .
• Friction and lubrication are important
considerations in the relative sliding of the lag
screw and hence the load transmission to the
fracture site.
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16. Cardiovascular Devices
• Friction and wear can lead to the failure of
cardiovascular devices such as artificial heart
valves and synthetic vascular grafts to repair
weak blood vessels.
• Pathological conditions have also been proven to
occur due to cardiovascular device wear including
the formation of blood clots and the rupture of red
blood cells.
• Friction can occur between moving components
of the medical device or from blood cells.
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17. Cardiovascular Devices
• Mechanical wear through friction has been
reported in the hinge regions and pivots of
mechanical heart valves.
• The friction force that occurs on a blood
vessel wall cell is calculated as shear stress
and is proportional to blood flow viscosity.
• The shear stress from blood flow has been
identified in numerous cardiovascular devices
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18. Cardiovascular Devices
• The tribological properties of medical
implants used to treat heart conditions are
being improved through the choice of
material pairs that reduce friction.
• Pyrolitic carbon shows particular promise as
a material for mechanical heart valve
fabrication because of its good wear
performance and biocompatibility
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19. Contact lenses
• Contact lenses are medical devices that
correct vision without the reduced peripheral
vision and problems with condensation that
spectacle wearing causes.
• The increased understanding of various
tribological properties has allowed for the
development of new contact lenses that
provide increased comfort for the wearer.
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20. Contact lenses
• One property that has to be balanced when
designing contact lenses is the modulus,
which is a measure of how a material strains
and deforms under tension.
• If the modulus of the lens is too low it will
increase the difficulty of handling and reduce
movement on blinking, if the modulus is too
high it may cause pathological lesions of the
cornea.
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21. Contact lenses
• The coefficient of friction measures the lubricity of
the lens and designs with low coefficients of
friction have been shown to provide more comfort
for the wearer.
• A further tribological property of contact lenses is
wettability or the degree to which a liquid
maintains contact with a solid surface.
• By improving the wettability property of a contact
lens, a thick coverage of the tear film can be
developed, allowing for good visual acuity after
eye closure.
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22. Reference
• J.J. Howard, Balancing innovation and medical device regulation: the case of
modern metal-on-metal hip replacements, Med. Devices.
• ] T.W. Bauer, P.A. Campbell, G. Hallerberg, Biological Working Group, How have
new bearing surfaces altered the local biological reactions to byproducts of wear and
modularity? Clin. Orthop. Relat. Res. 472 (12) (2014) 3687–3698,
http://dx.doi.org/10.1007/s11999-014-3817-1
• P. Massin, S. Achour, Wear products of total hip arthroplasty: the case of
polyethylene, Morphologie (2016) http://dx.doi.org/10.1016/j.morpho. 2016.06.001.
• Łapaj, J. Wendland, J. Markuszewski, A. Mróz, T. Wiśniewski, Retrieval analysis of
titanium nitride (TiN) coated prosthetic femoral heads articulating with polyethylene,
J. Mech. Behav. Biomed. Mater. 55 (2015) 127–139,
http://dx.doi.org/10.1016/j.jmbbm.2015.10.012.
• N.T. Dion, C. Bragdon, O. Muratoglu, A.A. Freiberg, Durability of highly cross-linked
polyethylene in total hip and total knee arthroplasty, Orthop. Clin. N. Am. 46 (3)
(2015) 321–327, http://dx.doi.org/10. 1016/j.ocl.2015.02.001.
• S. Williams, I. Leslie, G. Isaac, Z. Jin, E. Ingham, J. Fisher, Tribology and wear of
metal-on-metal hip prostheses: influence of cup angle and head position, J. Bone
Joint Surg. Am. 90 (Suppl 3) (2008)
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23. Thank you
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