Choosing a Coating - Boyd Coatings Research Co.

Erik
Swain
Contributing
Writer
FEATURE
Choosing a Coating
Competence Center is in
Rockaway, N.J. “A parallel
objective is to provide a
protective barrier for alloysensitive patients. While
today no implant device
lasts forever, a longer-lasting implant benefits the patient and
helps to reduce healthcare costs.
IonBond works closely with the
device OEM to improve implant performance while satisfying each
OEM’s specific test and evaluation
protocols,” Elwood added.
As such, it is not surprising that
“there’s a lot of talk about reducing
wear, which increases the life of an
implant,” said Marie Vennstrom, deputy
R&D manager for Sandvik Medtech, a
coatings testing company based in
Sandviken, Sweden. “If you improve
surface conditions, there will be less
wear debris in the body. People are
sensitive to metals, so the less iron
released into the body, the better. And
reduced wear allows for implants that
stay in the body longer, which is
always better for patients.”
The right surface modification
technique brings benefits
to patients with implants.
he importance of selecting the
right coating or surface modification technique for an orthopedic implant cannot be understated.
Metals and ceramics that orthopedic
implants are made from are
not inherently compatible
with the body’s tissues and
organs and are prone to wear.
The more wear an implant
has, the shorter its lifespan in
a human body will be.
Selecting the right coating or surface modification
technique can help prevent
these problems. If processed
properly, these methods can reduce the
chances of the body having an adverse reaction to the
implant and help the body accept the
implant, even spurring bone to grow
around it.
“The primary objective is to improve
the long-term wear performance of the
implant,” said Gene Elwood, North
America senior medical accounts manager for Ionbond LLC. IonBond deposits BioCeramic coatings through
WW Medical Coating Competence
Centers. IonBond’s global headquarters is in Olten, Switzerland, and its
North American Medical Coating
T
Choosing the right coating or surface
modification technique is key for orthopedic implant firms. IonBond’s PVD
coating machine is used to deposit
titanium nitride on implants for
patients with alloy sensitivity issues.
Photo courtesy of IonBond.
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May/June 2009
Titanium, HA Coatings
There are a number of ways these
goals can be accomplished. To aid bone
growth onto implants, manufacturers
typically choose titanium or hydroxylapatite (HA) coatings, said Colin
McCracken, Ph.D., development manager of powder products for Reading
Alloys, a Robesonia, Pa.-based division
of Ametek Corp., which supplies titanium-based powders used by manu-
Orthopedic Design & Technology • www.odtmag.com
SURFACE MODIFICATION
facturers to coat hip, knee and dental
implants. “One of the main differences
between titanium-based coatings and
HA coatings is that titanium-based
coatings do not require any fixing
agent, while HA requires a fixing agent
or cement,” he said. “In the short term,
the recovery time is likely longer than
it would be with a cemented implant.
However, the non-cemented fixation
normally lasts longer because it relies
on bone ingrowth. HA relies on the
strength of the cement to keep the
implant in place.”
If an implant manufacturer opts for
a titanium-based coating, it can choose
between one that is pure titanium and
an alloy that contains 6 percent aluminum and 4 percent vanadium, called
Ti-6AI-4V, McCracken said.
“Both are engineered to spur bone
ingrowth,” he said. “The Ti-6AI-4V has
higher strength than pure titanium but
does cost more. The market is about 5050. Both go back a long way. Which gets
used often depends on which material
the orthopedics company started with,
which was grandfathered in. Companies generally don’t change those
kinds of preferences.”
New technologies are being developed that will do an even better job at
promoting bone ingrowth, McCracken
added. This in turn is prompting firms
such as Reading Alloys to develop new
powders that are more compatible with
these processes.
“Several medical companies are
developing new porous coatings for
implants that promote and increase
bone ingrowth and reduce bone shielding effects by the use of titanium-based
foams or scaffolds,” he explained. “Today’s technology works by plasmaspraying the powder onto the implant.
New technologies will not require plasma spraying. They will result in a higher level of porosity. And that will make
the implants much closer to the
strength of the bone and reduce the
amount of bone shielding that occurs. If
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May/June 2009
Several medical
companies are
developing new
porous coatings
for implants that
promote and
increase bone
ingrowth and
reduce bone
shielding effects
by the use of
titanium-based
foams or scaffolds.
you can reduce bone shielding, the life
of the implant increases. The scaffolding technology requires a finer particle
size distinction. So we are developing
new powders to aid those developments.” Also, he noted, “metal injection
molding is being used for very small
dental implants. Putting Sintering
titanium hydride powder in another
form through the sintering process
also allows the implant to achieve
higher density, which leads to improved strength.”
Similarly, the device industry is
looking into biologics to help promote
bone ingrowth, said Elwood. “The
device industry is evaluating biologic
growth surfaces to enhance cell attachment and promote bone ingrowth.
IonBond’s patented TST [titanium surface technology] is at the forefront
of enhanced bone cell attachment,”
he said.
Elwood also sees two other developments for metal- and ceramic-based
coatings coming to the forefront in the
near future.
“Primary deposition technologies
are PVD, PaCVD and CVD with PVD
being currently used to deposit TiN
(titanium nitride) on implants for
patients with alloy sensitivity issues,
currently used widely in Europe. A
more recent introduction is a device
coated with a multilayer coating, top
layer being ZrN (zirconium nitride);
addresses both wear and alloy sensitivity,” he said.
Advances in BioCeramic coatings for
spine implant applications also will
have a major impact to improve wear
and eliminate current issues for MRI
imaging that are produced by alloys
such as CoCr, he said. “Ti (titanium is
an excellent alternative biomaterial,
but its wear properties are poor; hence,
the need for a BioCeramic coating. The
unique properties of IonBond’s exclusive Medthin-Diamond (ADLC) has
demonstrated positive performance
results with cervical discs, for example.”
Polymer Coatings
Another option is polymer coatings.
These are sought by implant manufacturers who want to attain certain properties that metals don’t have, said Donald
Garcia, director of R&D, Boyd Coatings
Research Co. Inc., a Hudson, Mass.based supplier of polymer coatings.
“They are inert, biocompatible, nonstick, fission-reducing, lubricious, and
wear-resistant. Lubricity aids in range
of motion,” he said. “They are fairly
common and have been used for a long
time. They are plastics, as opposed to
metals or ceramics. Their inertness is
a key element. They are also nonthrombogenic, biocompatible and have
a low coefficient of friction. With metal
finishes, you have to add something to
get those properties.”
Available polymer coatings include:
• PTFE (polytetrafluoroethylene)
• PFA (perfluoroalkoxy)
• FEP (fluorinated ethylene propylene)
• PVDF (polyvinylidene fluoride)
Orthopedic Design & Technology • www.odtmag.com
SURFACE MODIFICATION
• ETFE (ethylenetetrafluoroethylene)
• PPS (polyphenylenesulfide)
• PAI (polyamideimide)
• PEEK (polyaryletheretherketone)
• MOS (molybdenumdisulfide)
• Nylon (polyamide)
“The key is developing coatings that
don’t react and don’t cause any reaction
in the patient,” he said. “Inert and biocompatible coatings can act as a barrier
coating to fend off offending materials.”
Just as others foresee nanotechnology playing a role in the development
of metal coatings, Garcia sees it playing a role in the development of polymer coatings as well.
“In the future, we might see more
use of nanotechnology that can allow
the molecules in coatings to perform
in a different way,” he said. “For example, you might see something that is
elastic at one point but stiff at another. As R&D continues, nanotech will
probably be the next big step. There is
not much in the way of new innovations for polymers.”
require all areas of the component to
have identical roughness. That is literally impossible to ensure when the components are processed by manual techniques. There is too much variation in
hand-blasting. Thus, you need automated blasting. It is often a robotic process.
The robot holds the blast nozzle, or
manipulates the gun, or is used as a
machine loader and unloader. Automated blasting comes in to the picture
as a means of eliminating the variability in quality that arises when you have
manual blasting procedures. Those are
difficult to control and duplicate.”
The technique also comes in handy
for surgical instruments, he added.
“We find that a tremendous number of implants and instruments are
bead-blasted, as opposed to grit-blast-
ed. For surface prep work, you would
grit blast, but for cosmetic finishing,
you would blast with a bead of something like stainless steel or glass. The
material is sometimes dictated by the
surgical community, especially for
instruments. Highly polished instruments can reflect light too harshly.
They need to be made less reflective.”
For the next wave of robotic blasting to catch on, manufacturers will
need to appreciate what advanced
programming techniques can accomplish, Carson said.
“With advanced programming
tools, preparing a new program for
processing a particular type of component can be done repeatedly,” he said.
“With a solid 3D-computer model and
advanced programming software, you
Surface Modifications
Another way to help an implant become
accepted by the body is to finish it in a
way that gives it a surface texture that
is similar to that of the bone it will have
to become compatible with.
There are many techniques that
can accomplish this goal. One is automated blasting, such as that provided
by Guyson Corp., based in Skipton, N.
Yorkshire, England, and Saratoga
Springs, N.Y.
“You normally use blasting when you
have a specific surface texture or roughness requirement,” sayid John Carson,
Guyson’s marketing manager and
group leader of its application team.
“Preparation for a coating and mechanical bonding are both improved by
attaining a specific degree of roughness.
We call it technical surface preparation.
With orthopedic implants, you often
Orthopedic Design & Technology • www.odtmag.com
May/June 2009
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