From the Printer into the Body - Metal 3D Printing in Medicine
While medicine and its associated technologies date back thousands of years, we should also bear in mind that humanity is currently in a Golden Age of progress in this field.
Bloodletting has been replaced by mRNA vaccines and MRI, and progress in medical implants is unrelenting. While early hip prostheses were still made of ivory but not particularly convincing in terms of stability and durability, modern prostheses from 3D printers made with the right materials and composition are nevertheless particularly durable, stable and better accepted by the body.
Hip implants, however, are just one of the many examples proving just how indispensable additive manufacturing has become in the medical industry. While 3D printing is as diverse as its fields of application, additive manufacturing with metals holds a special place. It merges the ability to create shapes no other manufacturing method can with all the benefits of metal implants, medical devices and medical products.
In this whitepaper we take a closer look at the technologies, materials and challenges associated with this manufacturing process.
Multi Talent Metal 3D Printing
To understand additive manufacturing and its benefits for the medical sector and many other industries, one should first take a closer look at the individual manufacturing processes. One in particular is the powder bed process, which has established itself for the industrial fabrication of medical devices made of metal. Additive manufacturing methods for metals and the complementary services offered by manufacturing service providers such as Protolabs should not, however, be ignored in the discussion about precision-fit parts for the medical industry.
1. Additive Manufacturing Processes
In contrast to other manufacturing processes such as CNC machining (subtractive), material is applied layer by layer in additive manufacturing. Depending on the material, different processes are used, the common feature of which is the individual components being machined layer by layer. Unlike 3D printers, which are also found in private use and work with extruders and melted plastics, the technological basis here is provided by different processes serving to solidify the desired materials in the correct location. In stereolithography, for example, thermoset resins are solidified using ultraviolet lasers, while the PolyJet process cures liquid photopolymers layer by layer.
Regardless of the method used, the key advantage of additive manufacturing is that, in contrast to other methods, the layered structure of the components allows for extensive freedom in terms of geometry. This allows the desired components to be flexibly designed with regard to internal channels, voids, or honeycomb structures. The surface can also be shaped without major difficulties to achieve better coalescence and overgrowth with biological material in implants, for example. This offers clear advantages, especially for implants that are individually manufactured and tailored to the respective future wearer. In addition, however, standard manufacturing of implants is now often more cost-effective than conventional methods due to the continuous advancement of continuous advances in additive manufacturing technology.
Orthopaedics, in particular, is focusing on metal 3D printing for the production of implants. A closer look at the underlying technologies and their respective manufacturing processes is therefore certainly worthwhile.
2. Metal 3D Printing
While additive manufacturing still sounds like pure dreams of the future and science fiction to the ears of many, this technology has been established in the medical industry and is now indispensable. Other industries, of course, such as the automotive sector or aerospace, are increasingly using metal additive manufacturing for their own purposes as well. In no other field, however, is it found so close to the human body as with medical technology. In additive manufacturing using metals, both the materials and the printing methods and technology used are vital.
A. Additive Manufacturing with Metals - Basics and Materials
Ti6Al4V – what sounds like a suggestion for a secure password at first is, in fact, the exact designation of a light metal alloy that has excellent mechanical properties, corrosion resistance with a low specific weight and high biocompatibility. This titanium alloy has been used for some time in various industries and is often the material of choice in medical applications when it comes to implants that remain in the body for the long term.
Apart from this alloy, a wide range of other metals and alloys can be processed using additive manufacturing. With regard to the medical industry, this has the enormous advantage that familiar materials that were already used before the invention of additive manufacturing can be processed. As the medical industry is a highly regulated sector, especially in the use of implants, traditional materials such as titanium alloys, cobalt-chrome or stainless steel are relied upon.
In order for the aforementioned metals to be machined using the various additive manufacturing processes, it is crucial that they are used in powder form. At AP&C Powders, a company belonging to GE Additive, metals are atomised as bar stock by means of plasma atomisation. In this process, the metal that is actually available as a solid, such as the titanium alloy Ti6Al4V, is first vaporised using extremely high temperatures generated by a plasma and then cooled down again. This creates a powder that can be processed with metal in the two different forms of additive manufacturing, depending on the grain size.
B. Electron Beam Melting (EBM)
In electron beam melting, the respective metal powder is fused using an electron beam. As with all additive manufacturing processes, the respective components are built up in layers. However, prior to the actual milling process, the appropriate framework conditions for the process must first be created.
To ensure a smooth machining process of the metal powder, the electron beam first heats up the installation space containing the powder bed and the metal powder required for the process. The metal powder is thus brought into a pre-sintered state, thereby simplifying the actual processing by the electron beam. The resulting powder cake provides greater stability and supports the components in the powder bed. This means that the entire installation space can be built up with components (stacking) and fewer
or no support structures need to be planned in the design.
In the next step, this pre-baked powder bed is melted and solidified at the desired points by the electron beam. To ensure that the electron beam hits the powder bed exactly where a layer of the component is to be created, a magnetic field is used to guide it to the correct position. Due to the general conditions, this process can take place at an enormously high speed of up to 8,000 metres per second, which makes the beam look as if it is working on up to 30 melt pools at the same time. Once the processing of a layer is finished, the work plate is lowered by a predefined distance, a squeegee spreads a new thin layer of powder on the work plate and the process is repeated until the desired component has been created. Excess powder is removed from this component after a specified cooling time as part of the finishing process. The excess powder is then sieved, refreshed and returned to the construction process for further processing.
C. Direct Metal Laser Sintering (DMLS)
Another process for the additive manufacturing of metals is direct metal laser sintering. Contrary to the EBM process, no electron beam is used here; instead, the energy required to melt the metal powder is provided by a laser. While the actual printing process then takes place layer by layer, as in the EBM process, by alternately melting and applying a new layer of metal powder, the general conditions are different. Unlike the EBM process, the metal powder is only slightly heated, and work is sometimes carried out in smaller layer thicknesses, with finer-grained powders and a smaller laser focus. This yields more precise contours and surfaces with less roughness. Owing to this circumstance, Protolabs primarily uses the DMLS process.
In order to exclude a spontaneous reaction of the fine-grained powder, the DMLS process generates a protective gas atmosphere, consisting of nitrogen or the noble gas argon, for example. In addition, components are attached to the build plate via support structures in the DMLS process so that they look
exactly as intended in the original design after printing. In addition to stability, the support structures also ensure that the heat generated by the laser can be better distributed within the component. This also prevents distortions that would occur with molten metal.
3. Services and Certificates
“Post-3D-printing” is “pre-secondary operation” – regardless of the additive manufacturing method used. This also applies to medical devices produced using additive manufacturing. Secondary operation involves the removal of support structures, heat treatment to adjust the mechanical properties if necessary, surface treatment and cleaning and marking components.
Manufacturing service providers can comprehensively support medical companies in the supply of implants and other important components for use in the medical environment. For downstream processes, it is also necessary. Service providers such as Protolabs have gained many years of experience and expertise in this area. This service becomes apparent when looking at the process from the first contact to the finished implant.
As with other projects, the collaboration and cooperation between companies that distribute medical devices and manufacturing service providers that rely on additive manufacturing, is not established overnight. Often, those responsible can look back on a wealth of experience built on initial smaller projects and verification parts. While producing such verification parts, companies from the medical sector can recognise whether future cooperation with a manufacturer makes sense and important quality standards and prerequisites for certifications are met. Relevant certificates attesting to Protolab’s expertise include ISO 13485:2016, ISO 9001:2015 and the ROHS & REACH 3D Printing Declaration of Conformity.
Once these crucial certifications and standards have been clarified and a common body of experience has been built up over a certain period of time – which requires a basis of trust – the speed of the manufacturing process is the most important factor in the actual production of implants and other medical devices. This process is best illustrated by looking at the production of an individually manufactured implant. For example, if a patient needs a cranial bone implant that is to remain in the body for the long term, a medical company that specialises in the design and creation of such implants first creates a corresponding printable file. This is then passed on to appropriate manufacturing service providers, who ensure, within a few days, that the required implant arrives at the hospital on time for the operation date. The first step is to prepare for printing by programming the printer accordingly. Once the printing process is complete, secondary operation follows. For this purpose, excess metal powder as well as any supporting structures are removed from the implant.
After detailed measurement of the implant, which guarantees that the exact dimensions that were originally determined are adhered to, the implant can undergo final cleaning and preparation for shipping. All these steps take place within three to four days while guaranteeing that, despite the high speed, the patient receives a functionally flawless implant that meets the highest quality standards and complies with all legal
norms. In addition to these individually manufactured implants, additive manufacturing of metals in other medical fields.
4. Applications of Metal Additive Manufacturing in the Medical Industry
The fact that 3D printing with metal has found a firm place within the medical industry is evidenced by numerous examples and areas of application. This comparatively novel technology certainly does not need to hide behind established fields such as traditional prosthetics or conventional manufacturing methods from the medical environment. Almost unlimited freedom in terms of design and layout of individual parts makes this form of 3D printing highly attractive, which is reflected in series production, one-offs, and the manufacture of other medical devices.
A. Batch Size 1 in Medicine
Implants are art in and of themselves, when custom-fit replacements for individual bones or body parts are required, metal 3D printing excels with all its benefits. Since these are often complex geometries and projects that are difficult to implement using traditional methods, the flexibility and speed of additive manufacturing are crucial. For example, additive manufacturing can be used to produce orbital implants, cranial bones and entire thoracic implants that are precisely tailored to the patient in whose body they will later be used. Another key advantage here is that complex lattice structures that can be produced by additive manufacturing can result in better ingrowth behaviour and thus increased bone growth promotion.
B. Series Production of Implants
In addition to customised products, additive manufacturing with metal has also become increasingly widespread in the production of serial implants in recent years. This category includes, for example, so-called spinal cages, i.e. spinal implants, shoulder and hip implants or crowns, bridges, i.e. implants in dental prosthetics. This form of implant has become increasingly common because 3D printing provides the benefits of near contour manufacturing with adapted surface and internal lattice structures."
Furthermore, metal 3D printing has become increasingly efficient and fast in recent years, rendering it more and more competitive compared to other manufacturing methods. Standard prostheses that differ from each other, for example, by their size or certain dimensions, and of which there are only several dozen variants at the same time, can be manufactured more easily and without tools thanks to additive manufacturing,
while also retaining the benefits such as the wide freedom of design or high production speed. Consequently, 3D printing with metals is taking on an increasingly important role in the series production of implants.
C. From Prototype to Series: Medical Devices
Additive manufacturing with metal is not only used for the production of implants, which comes as no surprise due to the far-reaching flexibility that the manufacturing process offers for companies in the medical industry. Just like the manufacturing industry in general, the medical sector has also discovered the potential benefits of additive manufacturing. Especially with regard to the production of prototypes, yet also in the development of products for series production, metal 3D printing has become an important catalyst for innovation.
While it can often take months or years from the actual product idea to a functioning prototype, this time can be significantly shortened by additive manufacturing and development costs can be considerably reduced. The prevalence of 3D printing in this innovation-driven market is also demonstrated by Pansatori GmbH, an Austrian startup that has launched ForgTin, a medical device to combat tinnitus. As part of the development process of his product, which promises to alleviate discomfort and improve the clinical picture in patients with chronic tinnitus, founder Klaus Grübl relied on additive manufacturing to produce the temple, which is worn behind the ear. When deciding on a manufacturing specialist, he chose Protolabs because he knew about the company’s short manufacturing times and many years of experience in the medical sector. Together with the provider of additive manufacturing services, the entrepreneur is now producing the bracket, the core of this medical device, from 316L stainless steel using GE Additive’s DMLS process.
Besides ForgTin, however, many other metal medical devices are also produced using the 3D printing process. Medical instruments, special tools for the operating theatre and customised devices such as handles for scalpels are just as much a part of the application areas as is the production of implants and prototypes.
5. Technology, Research and Innovations
There is no denying that additive manufacturing has meanwhile become an indispensable standard in the medical sector and in many other industries. While 3D printing is sometimes still being referred to as a “revolution,” many users are already aware that said revolution in the medical industry took place years ago and that people are already fully relying on the possibilities of additive manufacturing with metals and many other materials. Nevertheless, new concepts and possibilities are being explored through technological advancements and research around 3D printing with metals.
The focus of current technological development is primarily the further optimisation of the entire printing process.
For example, GE Additive is working on making the printing process even more efficient, increasing the speed and at the same time further reducing the costs for additive manufacturing and secondary operation. These measures aim to finally move 3D printing away from its beginnings as a niche technology for prototyping through increased cost efficiency and make it a universally applicable, cost-efficient and sustainable manufacturing method.
In addition to this technology aspect, other innovations are currently being explored. Relevant developments are targeting smart prostheses, for example, which can offer additional advantages for the respective wearer through integrated sensors and corresponding intelligent motor functions. Active implants could thus represent a significant medical advance
in the future.
From Metal to Biomaterial – The Future of 3D Printing in Medicine
While it is clear that metal additive manufacturing in the medical industry is one of the most groundbreaking innovations of the 20th century, the future in this field is equally promising. Looking at additive manufacturing as a whole, there are currently already numerous innovative research projects that have the potential in the medium term to represent a quantum leap similar to the step from the ancient theory of humours to MRI. Keywords often mentioned in this context include tissue engineering and the additive processing of organic materials. 3D-printed kidneys and hearts could save lives in the future and defeat currently incurable diseases.
While a lot of development work still needs to be done to realise these technologies and the regulatory framework and ethical issues also need to be clarified, one aspect is already clear today: Additive manufacturing with metals in particular and 3D printing in general have decisively shaped medicine in the past few years.