CrN‐coated
metal‐on‐metal
hip
bearings
have
the
poten6al
to
reduce
wear
and
cobalt
ion
release


*1Royle,
M;
1Lu,
F;
2Fox,
A;
2Housden,
J;
3Leyland,
A;
4Ellison,
P;
4Collins,
S;
5Lali,
F
V;
5Hart,
A
J;
1Shelton,
J
C
1Queen
Mary
University
of
London,
UK;
2Tecvac,
UK;
3University
of
Sheffield,
UK;
4Corin,
UK;
5Imperial
College,
UK
*Corresponding
author:
MaQ
Royle,
m.royle@qmul.ac.uk.
School
of
Engineering
and
Materials
Science


INTRODUCTION
With
increased
use
of
large
diameter
metal‐on‐metal
(MoM)
hip
 bearings
 there
 are
 concerns
 with
 metal
 par\cles,
corrosion
 products
 and
 increased
 metal
 ion
 levels
 on
 the
incidence
 of
 adverse
 biological
 reac\ons
 [1].
More
 recently
there
have
been
reports
of
pseudotumours
[2,
3],
metallosis
[4]
 and
 asep\c
 lymphocy\c
 vasculi\c‐associated
 lesions
(ALVAL)
[5].
MoM
bearings
contain
27
‐
30%
Cr
and
57
‐
68%
Co.
In
vitro
wear
 par\cle
 cytotoxicity
 inves\ga\ons
 have
 studied
 the
effects
 
 of
 bulk
 CoCr
 par\cles
 [6].
 However,
 it
 has
 been
suggested
 that
 Co
 induces
 a
 greater
 cytotoxic
 reac\on
compared
to
Cr,
both
in
par\culate
and
ionic
form
[7].
Chromium
nitride
(CrN)
coa\ngs
have
been
used
in
a
variety
of
 engineering
 applica\ons
 including
 extrusion
 dies
 [8],
forming
and
machine
tools
[9],
and
aerospace
[10],
and
have
demonstrated
 excellent
 sliding
 wear
 resistance
 [11].
Furthermore,
 nanometer‐sized
 CrN
 par\cles
 have
 shown
improved
biocompa\bility
compared
to
CoCr
par\cles
[12].



AIMS
To
 compare
 the
wear
of
 conven\onal
MoM
bearings
with
a
hard
CrN‐coated
 surface,
 and
 to
 inves\gate
 the
poten\al
 of
the
coa\ng
to
reduce
Co
release.


MATERIALS
AND
METHODS
Test
components
Ten
 Ø48
mm
 heads
 and
 cups
were
manufactured
 from
 hot
isosta\cally
 pressed
 and
 solu\on
 annealed
 CoCrMo
 alloy
 to
ASTM
F75
(Corin,
UK).

Five
 bearings
 were
 tested
 uncoated
 as
MoM.
 Five
 bearings
were
 coated
with
 CrN
 using
 electron
 beam
 physical
 vapour
deposi\on
(EBPVD)
(Tecvac,
UK),
to
a
mean
thickness
of
8µm.
The
mean
diametrical
clearance
was
157
and
165
µm
for
the
MoM
and
CrN‐coated,
respec\vely.
Wear
tes\ng
was
performed
on
an
8‐sta\on
orbital
hip
joint
simulator
(MTS
Systems,
USA).
•  Load
profile:
2.45
kN
peak
load
at
1
Hz
frequency
•  Lubricant:
 Newborn
 calf
 serum
 diluted
 to
 25%
 (protein:

17g/L)
with
0.1%
w/v
sodium
azide
added


•  Fixtures:
PTFE‐coated
to
prevent
ion
contamina\on
•  Cup
inclina\on
angle: 
35°
(MoM
n=3;
CrN‐coated
n=2)



60°
(MoM
n=2;
CrN‐coated
n=3)
Wear
and
ion
release
Wear
was
determined
gravimetrically
at
0.17,
0.33,
0.67,
1.00
and
 2.00
million
 cycles
 (mc)
 using
 the
 densi\es
 0.0083
 and
0.0059
g/mm3
for
MoM
and
the
CrN
coa\ng,
respec\vely.

Total
Co
and
Cr
content
of
 the
 lubricant
 (ions
plus
par\cles)
was
 measured
 using
 graphite
 furnace
 atomic
 absorp\on
spectrometry
(GFAAS)
over
the
first
24
hrs
(86,400
cycles),
at
0.17
and
0.33
mc,
and
then
every
0.33
mc
up
to
2.00
mc.


DISCUSSION
Ion
 measurement
 is
 a
 complimentary
 technique
 to
 the
standard
 gravimetric
 method,
 which
 may
 avoid
 the
 piqalls
associated
with
taper‐fixture
wear
and
protein
deposi\on
etc.
During
phases
of
mass
gain,

established
from
the
gravimetric
measurements,
Cr
 release
measured
using
GFAAS
con\nued
from
 the
 CrN‐coated
 bearings
 indica\ng
 ultra‐low
 wear
behaviour.
 The
 reduced
 variance
 of
 gravimetric
 and
 ion
results
 indicated
that
 the
 
CrN
coa\ng
may
produce
a
more
homogeneous
bearing
surface,
with
more
reproducible
wear
proper\es
compared
to
MoM.


REFERENCES
[1]
Visuri
et
al.
(2005).
Proc
IMechE
Part
H:
Eng
Med,
220.
[2]
Pandit
et
al.
(2008).
JBJS
Br,
90.
[3]
Campbell
et
al.
(2010).
CORR,
468.
[4]
Campbell
et
al.
(2006).
52nd
Mee\ng
of
ORS,
Chicago,
USA.
[5]
Willert
et
al.
(2005).
JBJS
Am,
87.
[6]
Brown
et
al.
(2006).
Proc
IMechE
Part
H:
Eng
Med,
220.
[7]
Kwon
et
al.
(2009).
J
Biomed
Mater
Res
B,
4.
[8]
Björk
et
al.
(2001)
Surf
Coat
Tech,
146‐147.
[9]
Fuentes
et
al.
(2005).
J
Mater
Process
Tech,
167.
[10]
Swadzda
et
al.
(1996).
Surf
Coat
Tech,
78.
[11]
Bienk

et
al.
(1995).
Surf
Coat
Tech,
76‐77.
[12]
Williams
et
al.
(2003).
Proc
IMechE
Part
H:
Eng
Med,
217.
[13]
Leslie
et
al.
(2009).
J
Biomed
Mater
Res
B,
90.
[14]
Vassiliou
et
al.
(2006).
Proc
IMechE
Part
H:
Eng
Med,
220.



Figure
1.
Mean
gravimetric
wear
volume
•  Rela\ve
standard
devia\on
(%RSD)
shown
at
end
of
each
wear
 phase;
 it
 generally
 decreased
 as
 cycle
 number
increased,
tending
to
be
smaller
for
CrN‐coated



•  Mass
gain
for
low
angle
CrN‐coated
(35°)
indicated
ultra‐low
volumetric
wear
as
reported
previously
[13]


Figure
2.
Three
different
wear
phases
iden6fied
•  35°
MoM
wear
rates
consistent
with
literature
[13,
14]
•  60°
cup
inclina\on
had
minimal
effect
on
wear
•  CrN‐coated
 bedded‐in
 sooner
 than
MoM;
 the
 ultra‐low
wear
 became
 difficult
 to
 measure
 precisely
 using
 the
standard
gravimetric
technique


RESULTS


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