IMR and Renishaw streamline the additive manufacturing of spinal implants

The engineers of Irish Manufacturing Research (IMR) and Renishaw developed an additively manufactured Anterior Cervical Interbody Device (ACID) using nTop. The new additive implant utilized a porous lattice design that promotes osseointegration and mechanical properties that matched those of bone.

This project posed various design challenges, such as controlling a large number of design parameters, performing thousands of iterations, and ensuring the compatibility of design files with build preparation software.

Using nTop’s design software, the engineers of IMR and Renishaw created time-efficient optimization workflows and controllable design processes that output designs ready for additive manufacturing.

The result was the rapid, performance-driven development of a spinal implant that improves patient outcomes in conditions where intervertebral height is compromised.

Technical takeaways

• Complete control over geometry: Exercise precise spatial control over design parameters and control complex features.
• Time-efficient design iterations: Perform failure-proof iterations in minimum time and receive real-time feedback.
• Direct-to-manufacture outputs: Use nTop’s slicing capabilities to export complex designs in the native file format of your AM build preparation software.

Business value

• De-risking product development: Reduce the risk of human errors by creating reusable and automated design processes.
• Develop advanced products: Enhance the viability of your high-value products by achieving future-proof design optimization.
• Reduced time-to-market: Develop revolutionary products quicker by reducing the time your engineering team spends on manual design tasks.

Key Statistics

• Design time: A few minutes instead of hours
• Project completion time: Months instead of years
• Output files: 15 MB direct-to-slice file instead of 300 MB mesh
• Characterized per: ISO 13314, ASTM 1104, ASTM 1147
• Manufacturing process: Renishaw RenAM 500M
• Material: Ti 6Al-4V ELI alloy

Introduction

Irish Manufacturing Research (IMR) is a leading manufacturing research and technology organization founded in Dublin, Ireland, in 2014. IMR has already provided cutting-edge manufacturing research services to a wide variety of industries ranging from chilled water systems to implantable medical devices, in its relatively short lifespan.

Renishaw is a UK-based, globally recognized additive manufacturing company specializing in 3D printing critical components using metal powder bed fusion technologies. This industry leader has close to fifty years of experience in fields like agriculture, transport, electronics, and healthcare.

In this case study, we discuss how IMR and Renishaw leveraged the time-efficient design optimization capabilities of nTop to develop unique and lightweight spinal implants. The goal was to create a device that could help restore intervertebral height in patients suffering from conditions such as degenerative intervertebral disc disease, vertebral fusion, spondylolisthesis, herniated disc, osteoporosis, and spinal stenosis.

“In order to create a product using a new technology, you require software experts, hardware experts, and people who can control the design intent from the beginning to end. Using nTop and Renishaw [...] we were able to piece together the required parts to create this product.”

— Sean McConnel, Senior Additive Research Engineer, IMR

The design brief

The vision for these spinal implants was to have lattice structures that mimic the material properties of bone. At the same time, the surgeons had to be able to fix these implants in the vertebral column.

The engineering team had to address three main design requirements. They had to develop (1) a spinal implant that is additively manufacturable, (2) with a lattice that has a specific pore size allowing for osseointegration and vascularization (3) while maintaining mechanical properties that match those of a bone.

The key to overcoming this three-pronged challenge was optimizing the design of the implant in a function-driven manner so that it would meet all three functional requirements. nTop’s field-driven design and reusable workflows provided an opportunity to perform this optimization in reduced time and increased efficiency.

Overview of the solution

The final design of the implant was composed of two distinct regions: a solid region, which had a fixed structure, and a lattice region, which had a variable design that the manufacturing engineers optimized using nTop software.

It was essential first to test the functionality of these two regions separately, followed by an integrated test. Deciding upon a pore size for the lattice region was also critical to the functionality of the implant. The porosity of the lattice had to be large enough to promote osseointegration and vascularization but also small enough to give the structure a bone-like mechanical strength.

As such, designing these implants in a reasonable time was not going to be without its challenges using legacy software. Controlling the many aspects of implant design under one workflow was going to be difficult. Optimizing various parts of the implant with multiple iterations would exponentially increase the design time. Working with in-house additive manufacturing software could hinder the compatibility and shareability of the design files.

Controlling key design variables

The team realized that the complex, multi-part spinal implant design required a degree of control over the design parameters that is not possible with legacy design software. nTop enabled the engineering team to control all the design aspects of the ACID throughout the development process.

For example, to arrive at an optimum pore size for the implant’s lattice structure to promote osseointegration, the engineers of IMR varied parameters to get real-time feedback on their effect on their designs. They were able to not only vary design parameters in a spatially precise manner but also visualize and control physical fields such as pressure and strain across the implant volume. Field-driven design is a unique methodology enabled by the implicit modeling capabilities of nTop.

nTop further provided control over which parts of the design were modifiable and which had to remain fixed. The engineering team could also trace the entire design process, which allowed them to track the various parameters used in previous iterations of the implant design. These features of the software helped reduce risk in the design phase.

Expediting design cycles

Upon finalizing the implant’s design parameters, IMR generated and optimized the implant design using nTop.

IMR developed seven concepts that went through the complete design cycle, with multiple iterations in each design cycle. The number of individual parts in these spinal implant devices could be anywhere between 20 and 100. Designing these parts separately extends optimization time and reduces the efficiency of the workflow. This is particularly true when design development is an iterative process.

Indeed, iterative development is an inescapable aspect of creating a new implant. This requires a software platform that reduces iteration time, ensures that the iterations are failure-proof, and allows engineers to reuse previous workflows to alter their designs with minimal loss of time. nTop excels in all these areas.

nTop allows engineers to go through design parameters quickly and effectively. The software also provides real-time feedback for swift decision-making. nTop saves you time by letting users develop a single robust workflow for all the parts and by facilitating easy reuse of existing workflows.

In the words of Duann Scott, the VP of Business Development and Partnerships at nTop, “Projects like this usually take years, but the excellent collaboration between nTop, Renishaw, and IMR meant that we could complete the study in a matter of months.”

Streamlining slicing and manufacturing

Manufacturing is the last (but probably most important) step of any product development process. A critical capability that enables any design software to be effectively integrated into the product development process is its ability to export design files in formats compatible with the manufacturing software.

The engineers of IMR exported designs directly to the native file format used by Renishaw’s build preparation software (QuantAM). Renishaw’s software directly translated the slices and contours generated in nTopinto a laser toolpath and (ultimately) the 3D printed implants in an error-free manner.

“Easy translation from design software to an AM machine is especially important when producing spinal implants because intermediary stages and information transfer provide opportunities for errors and inconsistencies to occur.”

— Sean McConnel, Senior Additive Research Engineer, IMR

nTop gives users the capability to export designs in two different file formats that are relevant for manufacturing. The first option is a mesh file. STL or 3MF files are conventionally used in Additive Manufacturing. Yet, for complex designs, the file size becomes cumbersome to work with.

The second option is to slice the designs in nTopand export the slice data in formats used by industrial Additive Manufacturing build preparation software. This option is much lighter. Sharing the direct-to-slice files reduced the communication time between nTop’s design platform and Renishaw’s manufacturing platform.

The future of additive spinal implants

This collaborative project has shown that metal additive manufacturing can be tailored to develop complex spinal implants. The next step is to translate these 3D printed, lattice-based, and osseointegration-promoting spinal implants into clinically useful devices that help improve patient outcomes. This promising proof-of-concept study will make it easier to take these spinal implants forward into different stages of clinical translation.

Learn more about nTop

Would you like to learn more about how you can use nTop to develop complex device designs for your organization and why leading companies in the aerospace, automotive, medical, and consumer goods industries rely on it? Request a demo, and our nTop experts will get back to you promptly.