medical
Laser-sintering speeds development and manufacture of parts for spinal surgery.
What the surgeon ordered
ONE of the world’s largest producers of implants and instruments
for spinal surgery, DePuy Spine of Raynham, Massachusetts, is dramatically
reducing lead times for making new and customised equipment for
minimally invasive surgery (MIS). DePuy Spine has worked and partnered
with leading clinicians and researchers for over 20 years to advance the
knowledge of both professionals and patients in spinal pathologies and to
develop products to treat spine disorders. The company makes over 70
products with tens of thousands of product codes that are distributed
globally from the US, the UK and Switzerland.
MIS is one of the fastest-growing techniques in treatment of the spine,
leading orthopaedic surgeons to demand increasingly sophisticated surgical
instruments. These instruments must deliver improved access and control
through smaller incisions, have sufficient strength to cut through cartilage
and bone, and be made from materials that are biocompatible. The
traditional process of prototyping, design revisions, materials selection,
cadaver testing and manufacturing can mean a lead time of many months;
the reduction follows the adoption of additive layer manufacturing by lasersintering
powdered metal, a technique developed by EOS.
Specifically, the company is using an Eosint M 270 Direct Metal Laser
Sintering (DMLS) machine. This machine fuses successive layers of stainless
steel to produce the instrument directly from a CAD model; in the first year
of use, DePuy processed 2,000 prototype parts including benders, extractors,
surgical screws, clamps and reduction devices. According to staff team leader
Peter Ostiguy, delivery times for surgical tool prototypes have shrunk from
several months to less than a week in some cases: ‘Laser-sintering is very well
suited to our environment because we need to produce our products quickly.
We’ve really impressed surgeons with our ability to turn around what they’re
looking for in a short amount of time.’
Those surgeons’ opinions are important, as some of them are active
consultants to DePuy throughout the product development process. ‘We
work with the thought-leaders in the industry, many of whom tour our
rapid prototyping lab every year, as do other surgeons not on the project
teams,’ continues Ostiguy. ‘What has cut development time so dramatically
lately is the capability of the M 270 to build multiple iterations of an
instrument prototype in a matter of days.’
The DePuy development team starts with a basic design idea, often
making a plastic prototype first on a different machine in their shop, and
shows it to the surgeons for feedback. After modifying the design according
to input from the medical profession, the M 270 is used to create a metal
prototype, if the application is appropriate. The DMLS process begins with a
CAD model of the product, which is cross-sectioned horizontally into thin
layers. A first layer of 17-4 stainless steel powder is deposited at a thickness of
20μm onto a platform in the machine’s work chamber. The layer is then
sintered by a focused laser beam. The work platform is lowered and the
process is repeated additively, layer by layer, until a three-dimensional metal
part is produced. In this way, extremely complex geometries are created
automatically, directly from CAD data, in just a few hours. Maximum
dimensions are 250 by 250 by 215mm high.
‘What’s nice about this technique is that we can easily make multiple
iterations of a tool to give our doctors more choice,’ says Ostiguy. ‘In many
instances, we used to have to go with just one iteration, but now we have
greater flexibility to present more options. When assessing an instrument,
there’s no substitute for actually holding it. The consulting doctors can be
very exacting about their requirements for tools such as blades, racks,
tweezers, and calipers. When they review the parts, they may ask for
different handle angles or different spring strengths; it’s very easy to adjust
the CAD design and make another iteration. Laser-sintering lets us make
virtually anything they ask for.’
The result of introducing laser-sintering into DePuy’s development centre
has been a paradigm shift in the thought process for designing tools,
according to Ostiguy. He says that the company is not designing for
manufacturability any more, but for functionality. Previously, during the
design process the preoccupation was how to make the part within process
limits. With laser-sintering, that no longer matters. Once the consulting
doctors are satisfied with an instrument design, DePuy quickly makes a final
metal prototype in the M 270 and sets up a cadaver section so the surgeons
can put the item through its paces. Cadaver testing of metal prototypes is the
last stage in product development before DePuy sends the 3D model file for
the approved piece to an outside company for manufacturing. The finished
items undergo a last round of mechanical testing and verification before
being used in actual surgery.
Unlike prototypes tested in cadavers, instruments for in vivo surgical use
must be made from materials that are biocompatible with the human body.
Success with DMLS for prototyping has prompted DePuy to purchase
another M 270 for manufacture. ‘If we can make products on our own
machine, we can save time and money and be even more responsive to our
doctors’ requirements,’ says Ostiguy.
The second M 270 will be dedicated to a single, heat-treatable material,
EOS Stainless Steel PH1, which is characterised by high hardness, strength
and corrosion resistance. PH1 can be machined, spark-eroded, welded, micro
shot-peened, polished and coated if required. The new machine is
programmable to run layers of either 20 or 40μm (a thicker layer cuts down
on run time, a thinner one provides finer detail) and can process multiple
materials as well. Although his group is concentrating on laser-sintering
PH1 material for now, Ostiguy says that the possibilities are endless for
future product development. www.eos.info www.depuyspine.com
36 MWP march 2009
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