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Additive Manufacturing in Orthopedics

By Stephen Zeidler GE Additive

The case for additive manufacturing in orthopedics

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Scaling additive manufacturing is simply a question of adding more machines.

Within the healthcare and medical sector, it is the orthopedic sector that continues to adopt additive manufacturing, or 3D printing, at an astonishing rate.

Industry analyst SmarTech estimates that the orthopedic segment of the additive manufacturing (AM) market generated almost $200 million in 2016 and it is forecast to grow by around 30 percent CAGR until at least the middle of this decade.

Additive technology is expected to play a growing role in the ongoing evolution of more personalized medical treatment. Today, it is used for a wide range of orthopedic implants, helping designers and specialists to reimagine medical instruments and increasingly being incorporated into other types of medical equipment.

Choosing the Best Technology for Specific Applications

Using additive technology, an implant is built layer-by-layer using a high-powered laser or electron beam to selectively melt titanium alloy powder according to computer aided design data. Complex geometries, such as porous structures, or windows can be produced in one manufacturing step.

This offers the opportunity to increase the value of implants without adding cost or manufacturing time, due to the ability to design, and manufacture, unique and smart geometries with multiple design features.

By using powder bed fusion additive technologies, such as Direct Metal Laser Melting (DMLM) and Electron Beam Melting (EBM), implants of all kinds have been significantly improved.

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Implant created via additive manufacturing

As the only machine supplier with expertise in both DMLM and EBM, GE Additive works with customers in the sector to assess and choose which technology will best fulfill their design needs and production preferences.

DMLM’s strengths are in fine details, such as thin wall (strut) thickness, small pore sizes and low surface roughness, whilst EBM is well-suited for the production of large volumes and rougher surfaces, which can benefit fixation strength. EBM can also produce open cage architectures, without support structures or with only minimal supports needed.

Both DMLM and EBM reduce print time, post-processing time and powder waste significantly. Product designers can implement large central and lateral windows or porous, lattice structures, leading to less implant weight, material savings and reduced waste.

Today, design drives production, not vice versa. Before 3D printing, product designers typically had to choose one technique with one advantage, or another with a different advantage. AM allows designers to customize an implant that incorporates or combines all the design advantages using one technology.

Advanced Spinal Cage Structures

With additive technology proving to be game changer across orthopedics, it is in spinal cages where some of the most inventive applications are to be found.

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Additive manufactured spinal implants

In the first decade of the 2000s spinal implants, widely used to treat patients with back pain caused by degenerative disc disease, were milled from titanium or machined from polyether ether ketone (PEEK.) They were occasionally further developed with a secondary process, such as plasma-spray coating, to create a rough and porous surface that increases the osseointegration (bone ingrowth).

However, the solid cage design of this first generation of machine and milled titanium caused issues with subsidence and their bulky design restricted the post-operative evaluation due to limited radiolucency.

Whereas PEEK was introduced for its mechanical properties closer to the human bone (cancellous and cortical bone forms the vertebral discs), it is now also possible to adjust the mechanical properties of metal implants to more closely mimic the human bone. An optimized elastic modulus and the reduced stiffness of the titanium device potentially reduces the risk of stress shielding due to the stiffness mismatch between implant and bone tissue.

Additive technologies offer unique capabilities for creating, and manufacturing, open structures, often referred to as porous structures, that mimic trabecular bone. These structures are incorporated into an implant and produced in one production step—with no additional coating required. The major benefit of porous structures is that they can lead to enhanced bone in-growth that results in various other clinical benefits.

A titanium hip cup created with additive manufacturing

In combination with open structures, such as lateral or central windows, the overall stiffness of the spinal cage can be reduced. Less stiffness reduces the risk of stress shielding or the degeneration of the bone around an implant due to higher stiffness of the implant. Smooth edges and round shapes can promote the insertion of the cage and reduce the risk of damaging the soft tissue.

At the same time, it is possible to create porous structures or roughening features at selected areas of the cage to increase the coefficient of friction and the initial stability of the implant. In addition, angled teeth can be used to decrease the insertion force and increase the expulsion force.

While the patient is always the focus, AM design features are not only limited to providing benefits for patients and surgeons. Several such features, such as inspection notches contribute to automated post-processing, quality assurance, and cleaning, finishing and labeling requirements that must be considered to ensure safe and efficient production.

Scaling Additive Manufacturing

In comparison to conventional manufacturing techniques, such as milling or casting, AM offers a great opportunity to remove many technical and economic limitations to orthopedic implant production.

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Details of spinal cages can now be created with additive manufacturing rather than milled.

Naturally, equipment and powder costs heavily influence the business case to shift from conventional to AM, but the technology is now at a point where these costs are competitive and can compete with conventional manufacturing techniques.

When companies better understand the advantages of additive design and processes, it is easier to drive manufacturing to scale in everything from spinal implants, joints and hip cups to craniofacial surgery—where for example there are increasingly more specific and customized skull implants and trauma plates being developed.

Additive technology specifically allows new approaches to design where new solutions are needed and enables companies to implement a flexible and modular production strategy. This suits both volume production, as well as highly individualized small batch production, where designs and sizes can easily be produced at the same time without any change in hardware configuration.

Unlocking the Potential of Additive

AM is a relatively new process for many companies and, as with any new technology, there are different design, production and regulatory issues to be taken into consideration.

Once companies create the necessary knowledge, and experience, to take full advantage of the benefits of additive technologies, there are only opportunities.

These include freedom of design, the ability to embrace product complexity without increasing production steps or costs, high productivity and minimal waste for both volume and customized medical production.

Most importantly, AM allows for the development of medical devices with added value and increased clinical performance, because in the end it is all about making better products that lead to better care.

Stephan Zeidler is medical sector business development leader for GE Additive.

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