Medical Applications for Additive Manufacturing

• A. Medical Applications for Additive Manufacturing
  • 1. Additive Manufacturing - Production Processes, Benefits and Materials
    • 1.1 Direct Metal Laser Sintering (DMLS)
    • 1.2 Stereolithography
  • 2. Medical Applications for Additive Manufacturing
    • 2.1 3D Printed Implants
    • 2.2 Medical Equipment and Custom-Made Products
    • 2.3 Prosthetics and Orthoses
    • 2.4 Models for Planning, Research and Training
  • 3. Looking to the Future - Applications of 3D Printing in the Medical Industry
    • 3.1 Current Research into Organic Materials
    • 3.2 Optimisation of Existing Processes
    • 3.3 How will 3D Printing Work with Medical Facilities?
• B. Conclusion: 3D Printing in Medicine - A Technology of Today and Tomorrow

1. Additive manufacturing - production processes, benefits and materials

To get an overview of additive manufacturing applications within the medical sector, it is necessary to understand how the 3D printing process works. Additive manufacturing differs from other manufacturing methods. The material is not cast, as it would be in the manufacture of injection moulded parts, or cut from a larger block, as is the case with CNC machining.

As the term "additive" suggests, the material is added layer-by-layer. Even if the individual additive methods differ in the precise process and materials, the process of layered production is still the same. This enables more freedom for part design and possible geometries compared to other processes.

Since its early days, 3D printing has seen a great deal of differentiation, with a number of manufacturing processes that vary greatly. The most important manufacturing processes used in the production of medical products today are direct metal laser sintering and stereolithography.

1.1 Direct metal laser sintering (DMLS)

In principle, the procedure for printing DMLS parts differs only slightly from other methods of additive manufacturing. Support structures dissipate the heat generated during the process and ensure stability of the components. Without support structures, there would be a risk of wiping away new material during the printing process.

1.2 Stereolithography

Stereolithography is comparable to other additive manufacturing methods. It prints polymers and plastics with complex geometries or very small structures that require a particular rigidity, impact resistance or durability.

As with DMLS, it uses a laser to do the actual printing. Unlike DMLS, however, the raw material is not in powder form, but rather a resin consisting of photopolymers and additives. An ultraviolet laser hardens this resin into a thermosetting plastic. The build platform is lowered at each stage, ensuring that a new layer of resin covers the component, which is then hardened into the required shape by the laser.

After the part is produced, the remaining resin is cleaned off in post-processing and the support structures are removed. Finally, the parts undergo a UV-curing cycle to fully solidify the outer surface of the part.

It’s worth noting a new material called MicroFine™ Green. Using stereolithography it produces particularly fine, high-resolution structures e.g. miniaturised catheters or minimally invasive tools.

 

2. Medical Applications for Additive Manufacturing

The medical sector adopted 3D printing shortly after it appeared. Initially the benefit of being able to easily produce individual parts, such as medical device housings, proved ground-breaking. Shortly after this the industry recognised DMLS' potential and the first production of implants took place.

2.1 3D Printed Implants

Currently implants are the most extensively produced 3D printed parts in the medical industry. They offer a whole range of advantages, particularly when it comes to the replacement of bone material. These parts are printed using CAD files, often generated using medical imaging techniques.

Applications of 3D printed Implants

Since implants are usually custom-made products for a well-defined purpose, additive manufacturing is ideal, due to its ability to produce unique items quickly and cost effectively.
Until recently these types of implants would usually have been mass-produced and then adapted for the patient, often by the surgeon.

It can make simple parts such as femur implants or hip bones tailored to the individual patient, figure joints, zygomatic bones and jawbones, as well as complex implants such as orbital implants, cranial bones and thoracic implants.   And implanting/attachment of artificial teeth is now a standard application for 3D printing.

Due to 3D printing's comparatively fast manufacturing times and the possibility of on-demand production (i.e. implants as and when they are needed), the medical sector is increasingly recognising the benefits of this technology and is using it for both standard implants, such as individual vertebrae in the spine as well as more customised options.

Advantages of 3D Printed implants

The benefits of 3D printing in medicine are similar to those of more industrial sectors. First, there's the wide range of possibilities that 3D printing opens up when designing individual implants. Other manufacturing processes simply cannot create the geometries and shapes that are possible with 3D printing and are therefore less suitable for use. The flexibility additive manufacturing allows in the manufacturing process, also enables the integration of lattice and sponge structures that can drastically improve biocompatibility of implants, helping improve their ability to integrate with endogenous material.

For hospitals and health insurers, there is the advantage that individual specialised implants are more cost-effective than those produced using conventional methods. Other manufacturing processes require significant investment in special tools and equipment geared in each case to the individual implant. In 3D printing, these additional costs are eliminated due to the more flexible manufacturing process. Special implants produced using additive manufacturing do not have to be expensively reworked.

Materials and Legal Requirements for 3D-Printed Implants

By manufacturing parts using DMLS, implants can be printed directly from a material that is suitable for medicine. For implants such as hip bones or orbital implants, in most cases Ti6Al4V is used - an alloy that's main component is titanium. This alloy is characterised by its high-biocompatibility and enormous strength and stability, whilst being comparatively light. Another material used in medical 3D printing is stainless steel 316L.

In contrast, when producing standard implants by milling or casting, the materials used have poorer biocompatibility ratings, which means that in addition to production they need the addition of a titanium coating.

Implant production must observe legal regulations, especially in regard to the selection of materials. For Ti6Al4V, legal requirements include, ISO 5832-3, ASTM F1472 and ASTM B348, which classify the material and chemical components as suitable for use in medicine. Special implants require no CE certification. Ultimately, the responsibility and decision as to whether and how an implant is suitable for use on a patient, rests with the relevant doctor. Another advantage of 3D printing in this area is that many of the materials are familiar to the medical industry. The strict standards and regulations that these materials must meet are not affected by 3D printing. Thus, there is nothing to prevent them from the medical industry using them after the additive manufacturing process.

2.2 Medical Equipment and Custom-Made Products

Another important area where 3D printing is gaining ground in medicine, is for the production of individual medical devices and custom-made products. These devices are often for short-term use to perform specific tasks.

Special templates and individual parts

Surgical aids often need specifically designing for the individual patient and the respective operation e.g. templates help with drilling the cranial bone to millimetre precision. Due to the high-level of accuracy using processes such as DMLS (individual features of less than one millimetre can be achieved - depending on material biocompatibility and intended application), there are huge benefits to using 3D printing for this. Accurate CT scans of a drill section can create precise files that allow the production of parts quickly. The resulting needs-based drilling templates allow for more accurate work and help avoid dangerous errors during the operation.

Another additive manufacturing material used in the production of medical devices and custom-made products is the relatively new MicroFine™ Green. Using this bright green material to create microscopic structures, opens a whole range of possible applications, which were previously not feasible in medical 3D printing. Single parts for pacemakers, only a fraction of a millimetre in size, are just as conceivable as miniaturised catheters or liquid and gas injectors.

By using processes such as DMLS and stereolithography to print complex geometries, there are almost no limits to what additive manufacturing can produce for the medical industry.

Medical Instruments

Besides providing templates for specific operations, which differ from patient to patient, the new manufacturing methods also allow innovations in medical instruments for the operating theatre. 3D printing makes it easier to produce instruments that were previously not economically viable or, in some cases, even impossible.

For example, DMLS can produce surgical devices that allow special drilling or incisions, which can crop up repeatedly in medicine. Additive manufacturing applications also include other specialised medical instruments to better suture surgical wounds or used as tools during the surgery itself. Instruments precisely adapted to an individual surgeon, such as handles for scalpels, are an example. Parts manufactured from special plastics using additive production can also be used, for example as highly specialised brackets or spacers.

Such extensive use of 3D printed parts in the medical industry is possible because the materials and methods combine a whole range of benefits including; mechanical strength, cleanliness and ease of cleaning and sterilisability.   It is also cheaper to produce parts designed for a single task or purpose than by traditional production methods.

2.3 Prosthetics and Orthoses

3D printed components also have many applications for prosthetics.

For a long time, 3D printing has been a useful manufacturing process for specially adapted prostheses and orthoses. Compared with other manufacturing processes, 3D printing allows you to produce individual parts that are specially tailored to an individual patient, inexpensively, quickly and easily.

2.4 Models for Planning, Research and Training

Modern imaging techniques such as CT and MRI give doctors much better insights into the human body than was the case a few years ago. These methods have played an essential role for doctors helping them diagnose diseases in their everyday work. These diagnostic imaging techniques also have a significant impact in their preparation for complicated procedures and operations.

This is another area where additive manufacturing processes can help. Modern imaging techniques are so accurate they can be used to create 3D printed life like models of the relevant organ on which a surgeon can trial the operation before the actual procedure. These models are also suitable for determining optimal approaches or trying out riskier procedures without risk to the patient. Because flexible materials can also be printed using additive manufacturing, the models can also have characteristics that you would expect from the biological material.

Replicas for research and training

Replicas of organs and skeletal parts made of a variety of materials using additive manufacturing also provide universities and colleges with the opportunity to gain a deeper insight into the human body.

While conventional replicas of anatomical parts have often been expensive and of poor resolution and quality, today’s 3D printed replicas present a viable alternative to conventional modelling. Models made for surgical preparation can be used for training medical students, illustrating malfunctions of the human body and displaying disease in realistic examples.

The replicability of examples like these, is a major advantage of 3D printing. Particularly in cases involving a specific body part or organ, you can generate any number of models for medical faculties worldwide.

3. Looking to the Future - Applications of 3D Printing in the Medical Industry

Few new technologies have changed medical research as much in recent years and decades as additive manufacturing. At the moment, the development of additive processes and the possibilities created is still in its infancy. Work is currently in progress on a variety of new, modern applications that could change the medical world and our understanding of healing and care over the coming decades.

3.1 Current Research into Organic Materials

So far, the metals and plastics used for medicine are well-suited to 3D printing. These materials can help with patient care, but quickly reach their limits when it comes to living material. There are, for example, already the first 3D printed prototypes replicating entire organs, such as the heart; but since the material is not organic, not designed to remain permanently in the body and is not designed for the high stresses of everyday life, these are currently only being used for individual prototypes. Developers and researchers are now focusing on innovating/ improving processes for printing organic materials for the future.

Current experiments mainly focus on applying additional tissue from cellulose and organic materials to existing structures, which are then suitable for implantation, leading to functional tissue. The benefits of such a technology, once fully developed and usable, will be enormous. Machines could produce vessels, organs or muscle tissue to be implanted into the human body. Research projects, such as an artificial heart produced via 3D printing, have proven that replicas of entire organs work and can potentially save lives. By extending and improving such systems, the lifespan of the implants could be extended from a few hours to medically useful time intervals.

In addition to this research, other experiments are taking place which may improve medical care in the future. For example, work is currently being carried out to produce human skin in so-called bioprinting processes, to produce biological prostheses such as ears and to print organic material directly onto the patient. 3D printed tissue is also well-suited for trials and testing of new drugs and medical applications. In future, the best-case scenario would be that animal and human trials testing new, active substances would become redundant.

The innovative power of 3D printing in the medical field is almost unlimited. This is because of its flexibility, for example in the production of complex geometries. This is a major benefit, especially when considering the complexity of some medical applications, which typically involve working in difficult to access areas that allow little margin for error.

3.2 Optimisation of Existing Processes

In the near term, applications of 3D printing in medicine will be towards processes that are already possible and how well everyday clinical practice can incorporate them.

Currently no other area produces as much innovation as additive manufacturing. This is due to the fact that constant development of processes and improvements to existing processes always generates new applications for 3D printing. 

Techniques such as stereolithography, direct metal laser sintering and polyJet have gradually emerged and have been constantly evolving to print a wider variety of materials. In future there will be additional 3D printing processes to expand and optimise the range of possible applications. As new processes develop, the choice of materials will continue to expand and provide additional solutions. Subsequent advances in organic materials, new additive methods and results from future research, promise far-reaching innovations.

3.3 How will 3D Printing Work with Medical Facilities?

When it comes to additive manufacturing and medical applications, people have suggested that hospitals and research institutions might need their own machines and be able to use them, problem free. This is currently not the case, specialist companies are the primary manufacturers of implants, orthoses, prostheses etc. which are then sent to hospitals or end-users. Having 3D printers in hospital basements is unlikely to be common anytime soon.

One big reason for this is that the machines used for the production of bone implants made of titanium, for example, are very expensive to buy and use, and the additional post-processing of printed implants incurs additional expense. In addition, the use of additive manufacturing processes and machines requires a considerable amount of specialist knowledge and training. The fact that these procedures will be even more differentiated and that specialist companies have more extensive production options is another argument against its direct use in hospitals.

Instead the cooperation between hospitals and medical professionals and companies specialising in modern manufacturing processes for prototype production and additive manufacturing, will expand and become more interconnected. Since a wide variety of new applications are already emerging, the importance of additive manufacturing within medicine will continue to increase. Doctors in generations to come will wonder how medicine ever managed without 3D printing.