3D PRINTING FOR CUSTOM IMPLANTS - GETTING CLOSER EACH DAY

Miguel Á. Utrera Molina, Carlos M. Atienza Vicente, Arturo Gómez Pellín, Juan Alfonso Gómez Herrero, Fernando Mollà Doménech, Mª Jesús Solera Navarro, María José Vivas Broseta, Rosa María Porcar Seder

Instituto de Biomecánica de Valencia

A new generation of custom implants made by additive manufacturing technologies has been developed to compete with traditional manufacturing techniques in terms of time and cost. A consortium of companies, including Surgival Co. S.A.U., AMES S.A., Biotechnology Institute S.L., Grupo Hospitalario Quirón S.A. and Kanteron Systems S.L.U., in association with two technology centers, the Instituto de Biomecánica de Valencia (IBV) and the Instituto Tecnológico Metalmecánico (AIMME), have developed the ADDBIO project. This project has validated a new supply chain for the manufacture of custom medical devices, thereby fully defining all its phases. It has thus taken the definitive step toward confirming the usefulness of 3D printing in the field of custom implants. Different demonstrators have been designed, manufactured and assessed biomechanically with highly satisfactory results.

 

INTRODUCTION

Today, medical practice requires implants that are better customized to individual patients. As such, expectations of 3D printing are growing, and it is increasingly common to see news about important clinical advances made thanks to this new technology.

It is important to note that the concept of 3D printing spans a number of additive manufacturing technologies (wire deposition, laser sintering, electron beam melting, etc.), as well as different materials for manufacturing them (plastics like ABS and nylon, metals, etc.). The fields of orthopedic and maxillofacial surgery, where metallic biomaterials (stainless steel, cobalt–chrome alloys and titanium alloys) have traditionally been used, are particularly involved in additive manufacturing technologies using electron beam melting (EBM) and selective laser melting (SLM).

The production flexibility that additive manufacturing brings compared with traditional methods (such as machining parts from forging or casting) seems likely to lend itself to these technologies.

In addition, customized implants allow clinics and hospitals to reduce the volume of products in storage and avoid having to keep all different sizes of implants on hand.

One of the main objectives of the project has been to get manufacturers to offer custom implants while maintaining reasonable unit costs without losing quality and reducing their manufacturing volumes.

The ADDBIO project has helped integrate and automate the processes that support the design and supply of custom implants produced by additive manufacturing technologies, and has helped validate that they are working correctly.

A consortium that includes manufacturers like Surgival Co. S.A.U., AMES S.A. and BTI Biotechnology Institute S.L., as well as companies with extensive experience in healthcare ICT such as Grupo Hospitalario Quirón S.A. and Kanteron Systems S.L.U., has made it possible to conduct this ambitious project. Together with these companies, the Instituto de Biomecánica de Valencia (IBV) has made custom designs based on patients' medical imaging and biomechanical assessment of implants, while the Instituto Tecnológico Metalmecánico (AIMME) has modified the designs to improve functionality and manufacturability, and is responsible for manufacturing implants in association with the companies.

METHODOLOGY

In this context, additive manufacturing by electron beam melting (EBM), the primary manufacturing technology for implants for trauma surgery, has become the best option. It allows custom manufacturing to be done profitably, with acceptable delivery deadlines and a quality equal to that of current implants. EBM also allows for using the same materials that are currently used for the vast majority of implants in the industry (medical-grade metals like titanium alloys and cobalt–chrome alloys).

Customizing implants

In the initial phases of the project, implant models were developed that could be quickly customized to patients. This important requirement was achieved by including two types of design method: implant parameter setting and full anatomical customization using design protocols with highly specialized tools.

Implant parameter setting is done by imposing geometric relationships on a model, which permit proper functional customization. Instead of designing the final geometry for each size individually, the model to be customized is controlled by adjusting a limited set of parameters and dimensions, and thus the relationships imposed during customization allow the final model to retain similar geometric characteristics, whatever its dimensions, and the implant’s functionality is therefore preserved. This methodology makes it possible to customize implants based on the parameters or measurements taken from patients' medical imaging (CT, MRI and X-ray). Figure 1 shows an example of these parameter-based implants, a hip stem made by Surgival.

Figure 1. Parameter-based stem with its main dimensions (above), manufactured using EBM (below) with manufacturing structures typical of the process and a porous part to promote osseointegration.

In more complex cases that cannot be automated by parameter setting, the design will be made into a protocol to provide a quick response with an implant fully customized to the patient's body. Highly specialized tools such as Mimics^® Innovation Suite by Materialise and KDS by Kanteron have been introduced for this purpose. This latest methodology has been used, for instance, to obtain customized plate osteosynthesis for mandibular fractures in the field of craniomaxillofacial surgery (Figure 2). This application is of particular interest to Grupo Hospitalario Quirón.

Figure 2. Customized plate osteosynthesis for mandibular fractures, 3D view of the design to be validated by the doctor.

In addition, to ensure a speedy response and the economic viability of EBM production, serial manufacture of certain volumes of implants using these technologies has been considered. This would include EBM production of standard sizes to provide surgeons with tools for choosing the sizes best customized to each patient's body (Figure 3) from among those featured in the catalog, which would allow companies to manufacture small series.

These were also tested in other fields such as dental implants (BTI Biotechnology Institute S.L.) and in veterinary orthopedics with the new parameter-based prostheses for dogs developed by AMES.

Figure 3. Virtual design for femoral stem placement to let doctors choose the optimal size based on fit with the spinal canal.

Supply chain

Along with these developments, a significant effort has been made to detail the new supply chain that these custom implants will follow, thus completely defining the procedures and processes involved, including certification of additive manufacturing facilities. This supply chain comprises all the phases, from sending patients' medical imaging, measuring and model customization through to manufacture, sterile packaging and delivery of the finished product to specialists.

Here, manufacturers pinpointed a significant competitive advantage. The rapid supply, short production runs and one-off pieces offered by additive manufacturing represent major advantages compared with traditional processes such as forging, a process usually outsourced that requires ordering a large number of units with lengthy delivery periods. The company's production capacity can therefore be maintained, considerably reducing fixed costs and making supply planning much more flexible.

Online platform

One of the project's most significant achievements, after defining the supply chain, has been the development of an online platform that encompasses and streamlines the processes for customizing and manufacturing the personalized implants in the project.

To support these processes, which involve different organizations (hospitals, designers, additive manufacturing producers and manufacturers of the finished implants), a telematic platform (www.addbio.es) has been created that lets all those involved in the supply chain communicate with one another.

The modules required for integrating the specialized tools used in customization were implemented in this platform: Solidworks^®, Mimics^® Innovation Suite, Ansys^® and KDS^® by Kanteron. Of particular importance was the creation of a module that incorporates medical imaging in DICON format using the website and a quick viewer so that doctors can validate implant customization in 3D on the website. The website, along with the customization modes described above (parameter setting and full customization), also allows surgery to be planned by selecting the optimal size or ordering a standard size from a pre-determined catalog (Figure 4).

Figure 4. ADDBIO platform module for ordering standard-sized implants from the catalog for additive manufacturing.

Demonstrators

To complete the project's results, a series of final demonstrators was presented that enabled the supply chain to be validated and the custom implants’ commercial viability to be confirmed, thus showing that EBM manufacturing can compete with traditional manufacturing methods in terms of time and cost.

This project is meant to be the definitive step in applying the innovative technology that is additive manufacturing, known colloquially as metal 3D printing, to develop and manufacture implants for orthopedic surgery and other surgical specialties.

The main demonstrators used in the project were as follows:

♦ Parameter-based tibial tray for knee prosthesis: The main dimensions of this component (medial–lateral width, anterior–posterior width) have been customized to the patient's body. This permits the manufacture of a tibial tray with a better fit than traditional sizes (Figure 5).

Figure 5. Measurement of main parameters of parameter-based tibial tray on the surface created after virtual tibial osteotomy for total knee arthroplasty.

♦ Femoral stem for hip prosthesis (choice of optimal size): This demonstrator used 3D models showing the anatomy of a patient's proximal femur through the use of slides. Candidate stems were placed together with the demonstrator, and the surgeon could view them on the web viewer. Thus the surgeon was able to validate the final choice of femoral stem size (Figure 3).

♦ Maxillofacial plates for mandibular fractures: As a complete customization demonstrator, two plates were made for setting an anterior mandibular fracture. These plates were adapted to the mandible’s anatomy, thus saving time during surgery compared with the osteosynthesis plates traditionally used in maxillofacial surgery (Figure 2), which are deformed for customization and so lose some of their mechanical properties.

In addition, a significant effort was made to ensure the mechanical properties of the implants after they had been customized and manufactured. For this, a series of analyses was conducted using the finite element method (FEM), which enabled the mechanical properties of any adjustments made to the implants to be studied. The results of these analyses were then validated using mechanical tests, including testing the fatigue behavior of a femoral stem made by EBM that had undergone all post-processes, including sterilization (Figure 6).

Figure 6. Femoral stem for modular hip prosthesis manufactured with a medical-grade titanium alloy (Ti4Al4V ELI) as a finished product, packaged in a double blister pack and sterilized.

CONCLUSIONS

This project has made it possible to validate the viability of additive manufacture of surgical implants, in this case by using EBM technology to manufacture implants for orthopedic and maxillofacial surgery. The main ways to extend the use of this technology are to first define the supply chain by implementing a telematic platform to support its use and then put in place the quality-management procedures required to market these implants as custom medical devices. The parameter-based methodology and design have proved useful throughout the project, and the mechanical tests conducted on the implants have made it possible to conclude that the mechanical properties achieved with EBM technology are comparable to those achieved with traditional manufacturing technologies.

ACKNOWLEDGMENTS

The ADDBIO project has been a cooperative R&D project jointly funded by the Centro para Desarrollo Tecnológico Industrial (CDTI) and the Fondo Europeo de Desarrollo Regional (FEDER) through the operational R&D&I program by and for the benefit of the Empresas-Fondo Tecnológico.

Special thanks go to the individuals and businesses involved in this project: Ángel Alberich-Bayarri, coordinator of the Biomedical Engineering Unit of Grupo Hospitalario Quirón; Sergio García David, manager of the R&D&I Department of Surgival Co.; Juan Tatay Galvany, director-general of Kanteron; José Antonio Calero Martinez, R&D manager at AMES; Maria Arroyo Zabala, R&D&I project manager at BTI; Luis Portolés Griñán, manager of strategic marketing and use of R&D at AIMME; José Ramón Blasco Puchades, manager of the New Manufacturing Processes Unit at AIMME.