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A producer of implants and instruments for spinal surgery has adopted additive layer manufacturing by laser-sintering powdered metal, a technique developed by German company, EOS.

Depuy Spine of Raynham, Massachusetts, is reducing lead times for producing equipment for minimally invasive surgery (MIS) following the adoption of the technique.

MIS is one of the fastest-growing areas in treatment of the spine, leading orthopaedic surgeons to demand increasingly sophisticated surgical instruments.

They must exhibit improved access and control through smaller incisions, have sufficient strength to cut through cartilage and bone, and be made from materials that are biocompatible.

An EOSINT M 270 direct metal laser sintering (DMLS) machine fuses successive layers of stainless steel to produce these instruments directly from a CAD model.

In the first year of using its M 270 DMLS machine, 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.

‘What has cut development time so dramatically is the capability of the M 270 to build multiple iterations of an instrument prototype in a matter of days,’ he said.

The Depuy development team starts with a basic design idea, often making a plastic prototype first on a different machine in its shop and showing it to the surgeons for feedback.

After modifying the design according to input from the medical profession, Depuy turns to the M 270 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 20um onto a platform in the machine’s work chamber.

The layer is then sintered by a focussed 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 250mm x 250mm x 215mm.

‘With this technique, we can make multiple iterations of a tool to give our doctors more choice,’ said Ostiguy.

‘In many instances, we had to go with just one iteration, but now we have greater flexibility to present more options.

‘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 said that they are not designing for manufacturability any more, but for functionality.

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.

Due to the success of DMLS for prototyping, Depuy recently purchased another M 270 for manufacture.

The second M 270 machine will be dedicated to a single, heat-treatable material, EOS stainless steel PH1 (precipitation hardening stainless steel).

PH1 can be machined, spark-eroded, welded, micro shot-peened, polished and coated if required.

The new M 270 is programmable to run layers of either 20 or 40 microns (a thicker layer cuts down on run time, a thinner one provides finer detail) and can process multiple materials.

EOS Electro Optical Systems

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