This document discusses newer materials and advances for orthopedic implants. It describes ideal characteristics for biomaterials including biocompatibility, corrosion resistance, and osseointegration. Common biomaterials used in orthopedics like metals, ceramics, polymers, and composites are outlined. Specific materials discussed include titanium, cobalt alloys, UHMWPE, HA, PEEK, and tantalum. The document also covers mechanical properties, coating technologies, and 3D printing applications for orthopedic implants.

1. NEWER ADVANCES IN IMPLANT
MATERIALS

3. IDEAL CHARTERISTIC OF ANY
BIOMATERIAL
• BIOMECHANICAL COMPATIBILITY
• BIOCOMPATABILITY
• HIGH CORROSION RESISTENCE
• HIGH WEAR RESISTENCE
• OSSEOINTEGRATION
• PROCESSING FABRICATION AND HANDLING

4. Mechanical properties of biomaterials
can be divided into two groups
• Static
o Stiffness
o Strength
o Ductility
o Toughness
o Hardness
• Viscoelastic
o Fatigue
o Creep
o Stress Relaxation
o Hysteresis

5. Some basic definations:
• Stiffness is the material’s resistance to change
in shape and depends on elastic deformation.
• Strength is the load required to break a
material and depends on plastic deformation.
• Ductility describes the amount of deformation
a material undergoes before fracture.

6. • Toughness is the material’s ability to absorb
energy up to the fracture.
• Hardness describes the material’s resistance
to localized surface plastic deformation, e.g.
scratch or dent. Hardness determines the
wear resistance of a material.

7. • Creep is a time-dependent deformation of a material
under constant load that is below its yield strength.
• Stress relaxation is the decrease in stress required to
maintain constant strain over time, i.e. prevent creep.
• Hysteresis occurs when a Viscoelastic material is
cyclically loaded and unloaded. It is the ability of the
material to dissipate energy between the loading and
unloading cycles.
• Fatigue is a stress–time combination. Time increases
deformation produced by a given load. A given load
produces less deformation over a shorter time period
than over a longer time period.

8. GREEK ….ISN’T IT!!!!!!!

9. BIOMATERIALS IN ORTHOPAEDICS
• METAL AND ITS ALLOYS
• Stainless Steel
• Cobalt Chromium
• Titanium
• CERAMICS
• Bioinert ceramics used as bearing components in
THR eg. Aluminna & zirconia
• Bioactive ceramics used as surface scaffold coating in
uncemented implants and as bone graft substitutes.

10. • POLYMERS
• Long-term implantable polymers eg. Ultra-high
molecular weight polyethylene (UHMWPE)&
Polymethylmethacrylate (PMMA) bone cement.
• Biodegradable polymers include polyglycolide (PGA),
polylactide (PLA) and polydioxanone (PDS) developed
into sutures, staples
• COMPOSITES
• Plaster of paris and fibreglass
• Carbon fibre composites
• Synthetic sutures

11. Properties desirable as Joint
Replacement biomaterials
• High compression, bending and torsional
strength, fracture toughness, wear resistance
at sliding surfaces, and fatigue resistance
under cyclic loading
• Biocompatible
• Corrosion Resistence
• Osseointegration
• Easily processable

12. • CURRENT TKR DESIGN PROBLEMS
• POLY WEAR WEAK LINK
• ARTICULAR SURFACES WEAK LINK
• METAL BONE INTERFACE STRESS SHEILDING
• SOLUTION

13. Metal and its alloys
• Stainless steel
• Commonly used as temporary fixation devices as in
nails and plates.
• Restricted use in joint replacement due to very high
modulus than bone leading to stress shielding ,easily
degradable because of various surface corrosion
mechanisms and poor wear resistance.
• Better implant options available as bearing surfaces.

14. • Cobalt chromium and its alloys
• They have very good wear resistance, fatigue
strength and corrosion resistance and
comparatively less brittle.
• Spontaneous formation of passive oxide layer
within the human body environment
• However they have high modulus of elasticity
than bone leading to high stress shielding which
makes it unsuitable for uncemented use.

15. • Titanium and its alloys
• They are extremely strong, have half the stiffness of
cobalt–chrome alloys and also have the ability to
osteointegrate with bone therefore good for cementless
fixation.
• Spontaneous formation of passive oxide layer within the
human body environment which provides excellent
resistance to corrosion.
• Relatively poor wear resistance and high surface
coefficient of friction. Therefore not suitable for
developing articulating components like femoral heads.
• Also prone to notch sensitivity, and any surface defects
significantly increase the risk of fatigue failure.
• Titanium is also quite difficult to process during certain
stages of manufacturing, e.g. forging and machining

16. • Ceramics and its alloys
• Ceramics are typically stiffer, stronger and harder
than metals. They also have a greater resistance
to wear, low surface friction and excellent
resistance to corrosion. All this makes them
suitable for use as bearing surfaces in joint
prosthesis.
• Ceramics are extremely brittle and do not
deform significantly before breaking. Therefore,
ceramics have low fracture toughness and are
highly susceptible to fracture.

17. • Alumina is harder than zirconia. zirconia has a
superior wear resistance in a ‘hard-on-soft’
bearing combination. Therefore, zirconia-on-
polyethylene combination produces far less wear
debris than alumina-on-polyethylene
combination.
• However, as zirconia has a lower hardness than
alumina, it also has a lower wear resistance in a
‘hard-on-hard’ bearing combination.
• Zirconia-on-zirconia combination has a much
higher wear rate than alumina-on-alumina
combination, and therefore zirconia is not used
to make the acetabular cup.

18. • Bioactive ceramics
• This category of ceramics include calcium
phosphate, glass, glass–ceramic, and
composites, as these materials have the
capability to interact with the biological
environment to improve host response as well as
bind the injured tissue.
• These materials also undergo progressive
degradation while the new tissue regenerates.
• Though CaP itself is not an osteoinductive
material, it can be combined with materials like
growth factors, bioactive proteins, or osteogenic
drugs, and osteoinductivity can be induced

19. • Of the different types of calcium phosphate, HA
and β-tricalcium phosphate (β-TCP) are the most
commonly used biomaterials.
• Porous ceramic scaffolds have shown to better
support bone formation in comparison with
dense sintered scaffolds.
• Glass-based scaffolds can be classified into two
main groups: (1) glass/glass–ceramic porous
scaffolds (2) glass–polymer porous composites.

20. • Silicon substituted HA granules have higher
bone ingrowth when compared to pure HA.
• One of the main drawbacks of bioactive glass
is its low fracture toughness and mechanical
strength, especially in porous forms .
• Thus, similar to HA, these materials also have
limitations in usage as substitutes in load
bearing positions.

21. • Non-oxide ceramics—This category of materials
includes silicon nitride (Si3N4) and silicon carbide (SiC).
They can be considered as glass–ceramic composites.
• They possess a combination of properties such as good
wear and corrosion resistance, increased ductility, good
fracture and creep resistance, and relatively high
hardness in comparison to Alumina.
• Also they have excellent cytocompatibility and better
resistance to bacterial film formation in comparison
with Ti and polyether-ether ketone (PEEK).

22. Si3N4 ceramic formulation commercialized by Amedica (Salt Lake City,
UT,USA)

23. • POLYMERS
• UHMWPE and PMMA Bone cement are the two main
polymers used in joint replacement.
• Polymers tend to be less dense than metals and
ceramics. They are also not as stiff and strong as the
other materials.
• However, they are extremely ductile and pliable and
can be easily formed into complex structures.
• They have a low coefficient of friction and good
resistance to corrosion.
• Unlike metals and ceramics, polymers show
Viscoelastic behavior, i.e. their stiffness varies with
time.

24. • Mechanical properties of good wear resistance and low
friction.
• The main drawback of UHMWPE is the production of wear
particles, which initiate an inflammatory response that, over
time, leads to osteolysis and aseptic loosening of the
prosthesis.
• They are comparatively more brittle.
• The main applications of UHMWPE are in the form of articular
surfaces in joint replacements, e.g. acetabular component in
total hip replacements, tibial insert and patellar components
in total knee replacements and as a spacer in intervertebral
disc replacements.

25. • PMMA bone cement is used to fix implants
into bone in cemented total joint
replacements. Although referred to as
‘cement’, it acts as a grout (space filler), rather
than as an adhesive.
• It provides excellent primary fixation of the
prostheses, but does not simulate secondary
biological fixation. Therefore, the quality of
fixation degrades over time.

27. • Polyurethane (PU) biomaterials have lower modulus
values than UHMWPE and have been hypothesized to
operate under a microelastohydrodynamic lubrication
regime, which leads to reduced wear.
• PCU particles cause less of an inflammatory response
by macrophages than particles of UHMWPE.
• PCUs have been investigated as bearing materials for
total acetabular replacement due to high toughness,
ductility, oxidation resistance, and biostability.
• PCU hip implants have been limited clinically to a
European study related to the TriboFit® Hip System
(Active Implants, Memphis, TN, USA).

29. • VIT E POLY
• Polyethylene inserts can react with oxygen, creating
an effect similar to a browning apple. This reaction is
known as "oxidation." Over time, oxidation can
weaken the polyethylene inserts.
• Vitamin E, a natural antioxidant which has shown to
protect the material from the effects of oxidation.
• This Has Lead To Reduced Wear Rates And Increased
Strength.

31. • Polyether ether ketone (PEEK)
• Characteristics of strength, inertness, as
well as biocompatibility. They have stability
at high temperatures ,resistance to chemical
and radiation damage, compatibility with
reinforcing agents, and greater strength per
mass than many metals.
• PEEK-OPTIMA® and CFR PEEK-OPTIMA®
compounds and composites have
undergone biocompatibility testing to meet
criteria for US Food and Drug Administration
approval.

32. • However has limited fixation with bone. So
research efforts have emphasized improving
the bone–implant interface in order to
increase fixation.
• This has been performed by producing
composites with HA, by coating PEEK implants
with Ti and HA, and by creating porous PEEK
networks for bone ingrowth.

35. Mechanical Properties of Metallic
Materials used for Orthopedic Implants
Material Elastic Modulus (GPa) Fracture Toughness (MPa) Hardness (MPa) Compressive Strength
(MPa)
Density (cm−3)
Human cortical
bone
3–20 3–6 300–480 90–120 1.8–2.1
Stainless steel 190 50–200 130–180 170–310 7.6
Co–Cr alloys 200–300 N/A 300–400 450–1000 8.9
Ti and Ti alloys 110–116 55–115 310 758–1117 4.5
Tantalum and
alloys
3 96–124 240–393 42–78 –
Zirconium 96–100 – 210–235 276–345 6.51–6.64
Magnesium 41–45 15–40 – 65–345 1.74–1.84

37. The highest and lowest linear wear rates of various bearing surfaces

38. Mechanical Properties of Ceramics
Ceramics Compressive Strength (MPa) Tensile Strength (MPa) Elastic Modulus (GPa) Fracture Toughness (MPa)
Hydroxylapatite >400 ~40 ~ 100 ~ 1
45S5 ~500 42 35 0.5–1
Glass–ceramic 1080 215 118 2.0
Porous bioactive glass 2.25 – – –
Porous bioglass derived
glass ceramic 0.2–0.4 – – –
Porous HA (886%) 0.21–0.41 – 0.002–0.83 –
Non-oxide ceramic 4000–4500 450–1200 175–250 2.8–12

39. Mechanical Properties of some Polymers
Polymer Young’s Modulus (GPa) Compressive or Tensile Strength (MPa)
ultrahigh molecular weighted polyethylene (UHMWPE) 0.495 231.1
Poly(glycolic acid) – PGA 7–14 (FIBRE) 340–920 (FIBRE)
poly(L-lactic acid) – PLLA 10–16 (FIBRE) 870–2300 (FIBRE)
poly(L-lactic-co-glycolic acid) – PLGA 1.4–2.8 41.4–55.2
Poly(anhydrides) 0.14–1.4 25–27

40. POROUS TANTALUM
• Porous tantalum has been identified as a potential
alternative given its ability to integrate with the tissue
allowing bone–tissue ingrowth, biomechanical properties,
inert nature in vivo, and excellent chemical stability.
• The ductility of this material is less in comparison with the
metal implants but is high in comparison with other
naturally occurring substances, ceramics, composites, and
bone itself.Modulus of elasticity similar to trabecular bone.
• Tantalum implant possesses porosity of 400–600 μm with a
volume porosity of 75–85% in comparison with Co–Cr (30–
35%) and fiber metal (40–50%)
• Useful in revision scenarios with bone loss.

42. COATINGS
• The following should be considered for these
coatings:
• Biocompatibility
• Osteoconductive abilities
• Osteoinductive abilities, and
• Adequate mechanical strength of the
coating–implant interface.

43. • BMP coatings
• Biological coatings with growth factors, such as TGF-
β2 and BMP-2, have been incorporated on metallic
implants to help improve their osteoinductivity
• Combine BMP-2 and CaP coatings take advantage of
the osteoinductivity of BMP-2 and the
osteoconductivity of CaP.
• Bisphosphonates
• The use of bisphosphonates as an implant coating
has also been explored via an interposing layer of CaP
or fibrinogen.
• viable method to increase periprosthetic bone
density and improve overall implant stability

44. • CA-P like HA coatings
• for osteointegration.
• Inorganic ions may also be incorporated into HA to
better mimic the mineral component of bone like Si
and Sr. whhich stimulates cell growth.
• Silver-doped HA powder has also been used for
plasma spray coatings on commercially pure Ti
substrates with promising antimicrobial properties,
while not altering its adhesion strength to the
substrate.

45. • ANTI-MICROBIAL COATINGS
• Antifouling coatings, such as Si3N4 and silk
sericin-functionalized Ti surfaces, which aim
to reduce bacterial adhesion are
undergoing development.
• biodegradable polymers have been
developed that can prevent bacterial
adhesion by sloughing off the adhered
bacteria.
• controlled, time- delayed release of
antimicrobial agents from an implant
coating through hydrogels or chitosan.

46. TiNbN (Titanium Niobium
Nitride)coated implant
• Outstanding biocompatibility
• Allergy preventive
• Twice as hard as OXINIUM™ and over eight times harder
than conventional Cobalt Chrome. Surface hardness is
correlated with abrasion resistance and stiffness.
• Higher wettability with synovial fluids
• Low Friction articulation
• Long-term chemical stability
• Avoids inflammation and endoprosthetic loosening
• Extreme adhesive strength
• Release of cobalt ions with TiNbN coated implant is 1/10th
that of uncoated CoCrMo alloy.

48. NiTi shape memory alloys
• Properties of these materials are: one-way and
two-way shape memory effects, superelastic
effect, high damping property and rubber-like
effect.
• high wear resistance and low coefficient of
friction due to superelastic deformation,
pseudoelasticity effect and strength .Further, the
low Young’s modulus of this alloy also decreases
the maximum contact pressure and accordingly
the wear rate.

49. 3D PRINTING
• The reconstruction of complex bone defects
can benefit from the use of freely moldable
materials that enable the synthesis of patient-
specific implants. 3D-printed samples are
characterized by a high microporosity (above
30 vol%)which is an important characteristic
for bone generation.