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A better way to develop 3D printed orthopaedic implants?

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Christopher Cho, staff application engineer at nTopology, explains how using a type of alloy, the engineers of Irish Manufacturing Research (IMR) and Renishaw developed an additively manufactured Anterior Cervical Interbody Device (ACID), and its effects on the process.

Additively manufactured orthopaedic implants have rapidly become one of the most exciting developments within the medical device industry.

With advancements in manufacturing outpacing regulatory guidance, the U.S. has been a hotbed for the sweeping innovation that additive has enabled within orthopaedic devices. Despite a reputation for leading in robust and expensive validation processes, the FDA has scrambled quite a bit to determine how best to regulate this emerging technology.

However, as the process for clearing additive orthopaedic devices became more widely understood, the largest obstacle to advancing 3D printed technology became apparent in the limitations of design software.

For as long as many of us can remember, CAD tools have served as the unchallenged monoliths of digital design, with parametric solid modelling and surfacing proving to be the modern successor to drafting by hand.

But as demand for additive-enabled complexity increased, traditional CAD tools have proven to be ineffective at designing 3D printable devices. With orthopaedic implants, next-generation devices have demanded wildly elaborate geometries not fit for the CAD paradigm of old. Whether the need be contoured organic shapes or dense trabecular structures, traditional parametric CAD falls short in both performance and practicality.

Enter nTopology, a design software solution that allows engineers to create high-performing parts and reusable design workflows that can be deployed across entire part families and product lines. Its core implicit modelling technology reduces the design cycle and engineering efforts necessary to develop an orthopaedic device by alleviating the process of lattice structure generation.

Case study: IMR develops spinal implants using nTopology

To develop spinal implants that feature osseointegrative lattice structures, Irish Manufacturing Research (IMR) leveraged nTopology's lattice generation capabilities. 

The goal was to create an additively manufactured Anterior Cervical Interbody Device (ACID) that could help restore intervertebral height in patients suffering from conditions ranging from degenerative intervertebral disc disease, spondylolisthesis, to spinal stenosis.

Using nTopology, IMR’s design engineers created controlled design processes and optimisation workflows that generated cage designs ready for additive manufacturing. The resulting implant design used a porous lattice that promoted osseointegration and vascularisation.

The challenge

The engineering teams approached this project with three main design requirements:

IMR’s engineers needed to control many design parameters and perform thousands of iterations to identify the most suitable design for the structural elements of the implant and its lattice. During later stages of development, file compatibility against downstream build preparation software also became a critical consideration.

The solution

To overcome these challenges, the engineering team used nTopology to optimise the design of the device via a segmented approach. The final implant design was composed of two distinct regions: a solid structural region and a porous lattice design region.

From there, IMR was able to validate the performance of these two regions both independently and in combination. During their development process, adjusting pore size and beam thickness was an exercise of relative ease, allowing a structure that best promoted osseointegration to be discovered rather quickly.

The Result

Using nTopology, IMR achieved rapid and performance-driven development of a spinal implant that improves patient outcomes in conditions where intervertebral height saw compromise. The engineering team reduced the expected project completion time from years to months and leveraged automation to consolidate the design cycle from hours to minutes.

Traceable design processes

Having a traceable design process means a proper “paper trail” lives alongside every product you develop. This trail is integral to tracking all product-defining parameters, critical design decisions, and generated design outputs.

Traceability ensures that your business is fully prepared to undertake all corrective and preventive actions to resolve arising concerns if anything were to go wrong.

Bluntly, whether you are working on sized products or even patient-specific devices, a traceable process indicates that you know what you are doing.

When designing a medical device in nTopology’s functional design environment, the final output is defined by the steps you took to get there. If even a single input parameter changes, the resultant output must differ. This may appear obvious, but it is not an implication often considered when wielding traditional CAD tools.

By implementing a "reporting workflow”, a design engineer can capture all relevant information in an automated fashion. Therefore, any adjustments made to the workflow generate a new design and automatically generate an accompanying report that updates alongside the 3D model.

These capabilities can help minimise risk in the design phase and facilitate a seamless design experience.

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