Rouse and the surgical teams at Walter Reed brainstormed the implant problem.
Requirements from surgeons included:
- Standard available non-gas sterilization methods;
- Porosity in the implant to reduce trapped fluid pooling underneath;
- Material compatibility with tissue ingrowth to reduce the free space for infection;
- Ability to conform to complex contours and thickness changes, regardless of location; and
implant needed to be visible on radiographs without causing
radiographic artifacts and be safe to use MRI (magnetic resonance
"The only material available to us for this
purpose is titanium alloy, with its proven biocompatibility, strength
and most importantly, its ability to promote fibrovascular ingrowth,"
says Rouse. "The only manufacturing method capable of producing such a
complex geometric structure is additive-based."
officials selected a new technology developed in Sweden by a company
called Arcam using the electron beam melting technique (EBM).
the EBM process, fully dense metal parts are built up layer-by-layer as
metal powder is melted by a powerful electron beam. Each layer is
melted to the exact geometry defined by a 3D CAD model.
build takes place in a vacuum at elevated temperatures, resulting in
stress-relieved parts with material properties better than cast and
comparable to wrought material, according to Magnus René, CEO of Arcam.
The vacuum system is designed to provide a base pressure of 1x10-4
or better throughout the entire build cycle. The EBM machine produces
precise titanium mesh shapes that allow bone ingrowth and prevent fluid
pooling under the implant that can lead to infection.
EBM technology is also used to make off-the-shelf orthopedic implants.
René says that pores can be engineered to improve bone fixation. The
goal is to improve bone ingrowth compared to current technologies of
coating cobalt-chrome implants with titanium beads or other materials.
The new implant technology is working well at WRAMC.
rates in the past three years have dropped to 4 percent. "None have had
to be removed following the healing process," says Rouse.
technologies such as Selective Laser Melting (SLM by MTT Technologies,
Staffordshire, UK), and Direct Metal Laser Sintering (DMLS by EOS,
Munich, Germany), were not available in the U.S. when Walter Reed began
The implants are designed after segmenting CT scan
data using Mimics software from Materialise that allows engineers to
bridge 2D data to 3D. 3Matic, also from Materialise, and/or FreeForm
Modeling Plus, from Sensable, are used for the actual implant design.
can be built in both mesh and solid, and the implant design includes
the fixation plates. A skull model is created using a stereolithography
machine and is sent with the completed implant to the surgeon for
Seven Day Limit
Speed is a critical factor.
goal is to keep the entire process, from CT scan to delivery of the
finished implant, to seven days," says Rouse. "In most cases, we are
successful. Some of the issues, or problems that we have experienced
include intermittent build failures, machine availability and shipping
One problem Rouse has faced is lack of space for a program that is rapidly growing due to its huge success.
five additive manufacturing machines are scattered across the Walter
Reed campus where space permits. That changes soon under the Base
Realignment Program (BRAC), which is designed to make more efficient use
of military assets.
Rouse's group will soon move to a medical
campus in Bethesda, MD, about six miles from WRAMC, which is located
near the outer border of Washington, D.C. The new campus will be called
the Walter Reed National Military Medical Center at Bethesda.
equipment and three-person staff will be in one location at the new
medical center. That equipment includes an SLA 7000, SLA 500, Z Corp.
650, Z Corp. 450, and an Arcam A-1. On order is a Connex 500 from Objet
The equipment serves a myriad of roles, ranging from pre-
and post-surgical medical models to custom cranial implants,
subperiosteal dental implants, facial bone implants and custom fixation
Use of the additive manufacturing machinery is not necessarily simple, unlike milling machines, which can be left unattended.
require monitoring to make sure there has been no warpage of the part.
It's also important to ensure that the part is being produced to
Rouse says the Ti6Al4V powder must be monitored
for oxygen content. The final part must be tested to ensure that
metallurgy is within specifications. Vigilant preventive maintenance is
required to make sure machines are available when needed. Units like the
EBM machine are too expensive to have backups on hand.
bottom line for this entire process is the ability to build an implant
that is designed for a specific patient's needs, that reduces the
operating room time requirement significantly, and provides better
outcomes with more resistance to infection," says Rouse.