Cranial implants by OMP with EOS SLS Additive Manufacturing / 3D Printing

1. Additive Manufacturing
Produces Polymeric Cranial Implants
ADVANCED MATERIALS & PROCESSES • MAY 201436
W
ith regard to modern medical applica-
tions, additive manufacturing is making
headway—literally—when it comes to
building cranial implants. One company finding suc-
cess in this area is Oxford Performance Materials
(OPM), South Windsor, Conn., who received the first
FDA 510(k) clearance for its polymer laser-sintered
OsteoFab Patient-Specific Cranial Device (OPSCD).
The customizable implant restores voids in the skull
caused by trauma or disease. Manufactured in a mat-
ter of hours with additive manufacturing (AM) tech-
nology from EOS, Munich, Germany, the device was
successfully implanted in a patient missing a signifi-
cant portion of cranial bone a few days later. “It was
very large, measuring nearly six inches across,” says
OPM president Scott DeFelice. “It fit perfectly.”
OsteoFab technology, OPM’s brand for additively
manufactured medical and implant parts produced
from PEKK material contributed to the success.
PEKK (Poly-Ether-Ketone-Ketone) is a high-per-
formance thermoplastic with many exceptional prop-
erties (see sidebar). It has mechanical and thermal
qualities that make it highly suitable for cranial re-
construction. For example, PEKK has a density and
stiffness similar to bone, is lighter than traditional
implant materials such as titanium and stainless steel,
and is chemically inert and radiolucent so it will not
interfere with diagnostic imaging equipment. Most
importantly, PEKK is also osteoconductive, meaning
bone cells will grow onto it.
In some implants, the surrounding bone pulls
away over time. And with most implants, fasteners
are very important because if bone does not grow
into the implant, they hold everything in place. Be-
cause PEKK has osteoconductive properties, long-
term implant stability may be easier to achieve.
Laser sintering
Because low-volume parts with complex shapes
were needed, AM was the logical choice. PEKK was
already being sold as a raw material in pellet, film,
and extruded bar stock for orthopedic and spine ap-
plications, but occasionally OPM had requests for
a one-off product with a complex organic shape. It
was already being molded and machined, but be-
cause these processes have substantial limitations
in terms of tolerance and geometry, other options
were explored.
Laser sintering lifts manufacturability restrictions
that traditional processes impose—for instance, draft
angles in molding and corner design for CNC tool-
ing. It also does not require upfront costs such as
tooling and molding, so it is well suited for creating
one-off, patient-specific parts (Figs. 1 and 2). Laser
sintering does not generate the level of waste that
subtractive cutting and milling do.
PEKK, unlike its cousin PEEK, has a high melt-
ing point relative to other polymers, so all current
commercial AM processes were immediately re-
moved from consideration until OPM discovered
EOS, makers of the high-temperature EOSINT P 800
laser-sintering system (Fig. 3). “EOS is a clear leader
for high-temperature industrial 3D printers,” says De-
Felice. “We found their technology to be the only
laser-sintering system in the world that can run high-
temperature materials such as PEKK.”
Path to FDA approval
The path to commercialization of patient-spe-
cific implants was arduous. Aside from the not-
so-trivial prerequisite of the right molecule and
the right process, DeFelice says climbing the
mountain of regulatory requirements was a daunt-
ing task. “For starters, you need an ISO 13485
compliant facility that has design controls and an
appropriate clean manufacturing environment.
You also need to be compliant with CFR 21 cGMP
(current Good Manufacturing Practices). Add to
that a completely validated process and ISO 10993
TECHNICAL SPOTLIGHT
A Peek at PEKK:
Thermoplastic Shape Shifting
While PEKK shares some of the qualities of its better-known cousin
PEEK—high mechanical strength, heat resistance, and biocompatibil-
ity, to name a few—it is no ordinary thermoplastic. The difference is
structural: PEEK is a homopolymer, made up of identical monomer
units. By contrast, PEKK is polymorphous, which means it has lots of
molecular “knobs.” By adjusting the polymer’s manufacturing process,
or incorporating different additives, melting points, crystallization lev-
els, and mechanical properties, PEKK is capable of supporting many
different applications and a variety of customized materials from the
same base molecule.
OPM is a participating member of America Makes, the National
Additive Manufacturing Innovation Institute (NAMII), a White House
initiative to advance additive manufacturing as a critical process in the
U.S. “In the context of NAMII, we’re establishing what are called B-
Basis allowables, which are structural design parameters for aerospace
use, for PEKK,” says DeFelice. “We are very active in that market.”
In the broader market, in addition to its recently FDA-cleared Os-
teoFab cranial implant, OPM is providing OXFAB materials and criti-
cal parts for other demanding sectors such as the nuclear, aerospace,
chemical processing, and semiconductor industries. As DeFelice says,
“After fourteen years of mixing, blending, and modifying this molecule,
we’re just getting started.”
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2. ADVANCED MATERIALS & PROCESSES • MAY 2014 37
biocompatibility data on your finished parts.”
Once all that “stuff” is out of the way, the lifecy-
cle of a patient-specific cranial implant starts with
the patient. If someone comes to the hospital with a
skull injury, a CT or MRI scan is performed and pro-
duces a slice file similar to data used to build parts
via laser sintering.
That slice file is then sent to OPM where 3D de-
sign software is used to create an implant that pre-
cisely fits the patient’s anatomy. The implant is then
printed or “grown.” This “growing” phase is entirely
automatic—the laser-sintering system lays down a
thin layer of powder on its build platform. Guided by
the lowest slice of the implant design file, a high-tem-
perature laser melts a cross section of the implant.
When that layer is done, the build platform lowers,
and a new powder layer is distributed on top of the
old one, and the laser melts the next cross section.
The process repeats until the entire implant is built.
Laser sintering is capable of producing practically
any shape geometry to match the precise needs of in-
dividual patients.
When the implant is removed from the leftover
powder (Fig. 4), it must be inspected for quality. In
addition to mechanical and analytical testing, a struc-
tured light scanner is used to do 100% line-of-sight
metrology inspection to certify its dimensional accu-
racy. Finally, the implant is shipped to the hospital.
“The total process from receiving the data to ship-
ping the implant takes less than two weeks,” accord-
ing to DeFelice. (Figs. 5 and 6).
More implant types possible
Having successfully created and obtained clear-
ance for their cranial product, OPM is making plans
to move throughout the body to use the technology.
OPM will only operate in highly regulated, high-risk
markets such as medical. “We are after critical parts,
and biomedical is the pinnacle of that,” DeFelice says.
“That means you need the right material, the right
process, the right quality system, and the right
metrology. When the patient is on the operating table
and the part shows up and doesn’t fit, you are putting
someone’s life at risk. With the first implant case,
where the implant was very large, extensive areas of
critical tissues were exposed during surgery. Every
second is critical in that situation.”
For more information: Scott DeFelice is president and
CEO of Oxford Performance Materials (OPM), 30 South
Satellite Rd., South Windsor, CT 06074, 860/698-9300,
www.oxfordpm.com.
Fig. 1 — A batch of implants are set up for
production. The EOSINT P 800 system can
run multiple, different designs in a single
build. All images are courtesy of Fred Smith
Associates.
Fig. 2 — 3D digital model of a cranial
implant.
Fig. 3 — Using patient-specific 3D digital
data, the cranial implant is additively
manufactured with an EOSINT P 800
high-temperature plastic laser-sintering
system.
Fig. 4 —
The completed part
is cleaned of any
residue powder.
Fig. 5 —
Cleaned implants.
Fig. 6 —
Skull model
demonstrates how
an implant is
customized to fit the
cranial hole.
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