axial3D has created this overview page to aid those in the early stages of investigating 'medical 3D printing' or '3D printing in healthcare' as it's also known. It will also support individuals who want to broaden their understanding of the multifaceted world of medical 3D printing. This combines key information from a range of industry sources, and links to informative and interesting reading.
What is 3D Printing?
3D printing (also referred to as additive manufacturing) is the method of creating physical objects from a digital file by adding multiple layers of a material, or multiple materials to build a single structure. The structure is based on the input of a computer aided design file, in a format compatible with the 3D printing hardware. The technology's origins can be traced back to as early as 1983 when it was first invented by Chuck Hull, co-founder of 3D Systems. Since then this concept has evolved to include 15 methods or technologies of combining these layers, all commonly referred to as 3D printing.
What is 3D Printing in Medicine
3D printing is particularly suited to the medical industry due to the research-based, innovative and fast-moving nature of the field.
The use of 3D printing in medicine has been publicized since the early 1990s and in recent years, there has been a huge rise in the number of applications emerging in the field as a result of the technology becoming more accessible to users.
With major growth in precision and personalized medicine, there is a strong demand for bespoke and patient-specific medical applications, tailored exactly to an individual or their anatomy.
3D printing often wholly or partially drives production of these custom-made products and devices
Examples of actual and potential uses of 3D printing in medicine include:
- Customised prosthetics and implants
- Anatomical models for surgical planning and education
- Pharmaceutical research including drug dosage forms and discovery
- Tissue and organ fabrication
- Personalized medical products and equipment
Figure 1: The process of medical 3D printing
The Market for 3D Printing in Healthcare
3D printing offers ample opportunities in the healthcare industry and as such, the market for 3D printing in the healthcare industry is growing rapidly.
Market research published by Research and Markets predicts the year-on-year growth of 3D printing will be in double digits due to the high demand from North America and Europe, coupled with the rise in awareness about these devices in developing countries.
With an estimated market value of around
$500 million in 2014, there has been a growing body of industry reporting on the 3D printing in healthcare market, with 10 year predictions ranging from $2.4 billion to $17.4 billion according to Frost and Sullivan’s latest market report.
The healthcare sector is expected to be the fastest growing segment of the 3D printing market as innovations are integrated into specialisms such as orthopedics and implants.
As there are continual advancements within 3D printing, regulatory requirements change at rapid pace.
Some organisations exist to advise on regulation, beyond just the scope of 3D printing, to assist in technical standardising and aid product safety and quality including the world-leading International Standards Organization (ISO).
Specifically for 3D Printing (Additive Manufacturing Standards), the ISO and ASTM International (The American Society for Testing and Materials) have collaborated together and developed the Additive Manufacturing Development Structure (AMDS), that will aim to provide technical standards across the board.
Additionally the FDA recently released “leapfrog guidance” on its initial thinking and recommendations for Technical Considerations for Additive Manufactured Medical Devices.
This guidance outlines that manufacturers should also engage with the Center for Devices and Radiological Health (CDRH) or CBER through the Pre-Submission process to obtain more detailed feedback for Additively Manufactured medical devices.
The FDA defines a medical device as "an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including a component part, or accessory which is:
“… intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease”
It could be considered that 3D printed anatomical models used for preoperative planning, might not warrant regulation by FDA if they are not intended for use in any purposes aforementioned.
The main uses for 3D printing in medicine currently are:
Patient-specific anatomical models for preoperative planning
Medical imaging using 2D or 3D onscreen technology provide limitations when radiologists and surgeons are visualizing complex pathologies and abnormalities.
Increasing, both radiology teams and surgeons are using 3D printing to create 3D 1:1 models of anatomical areas, replicated exactly from patients' scans, which can be held in-hand and used for preoperative cutting, planning and collaborative team working.
These anatomical models are often used in patient communication and consultation to show and explain to patients about their medical conditions and what their surgical procedures will involve.
They also have use in surgical education, providing medical students and junior doctors the opportunity to exactly see tumours, fractures, lesions and other abnormalities
Figure 2: Examples of patient-specific anatomical models for surgical planning produced by axial3D
How 3D printed anatomical models are produced
In short, the process of creating patient-specific anatomical models is the conversion of two dimensional medical images to a three dimensional file that can be utilised in 3D printing.
The process begins by utilising raw medical images usually in DICOM® format (Digital Imaging and Communications in Medicine) typically CT, MRi, PET, SPECT.
The images represent a two dimensional cross section of the patient's anatomy, typically taken in the axial plane (XY dimensions depicting left to right and front to back aspects of patient).
The axial slices are ‘stacked’ in processing software to form a volumetric dataset with the space between the scans representing the inter voxel space of the final 3D model (z dimensions, depicting top to bottom of patient). As a general rule, the larger the space between the scans the lower the resolution of the final 3D model that will be produced.
Once data has been stacked within the software, a process of segmentation (also referred as contouring) is carried out on each axial slice to delineate the portions of anatomy which will be 3D printed or not.
This process is typically done with a number of segmentation tools, both manual and semi-automatic, to annotate each image pixel in the dataset.
Once all data is segmented, a volumetric surface of the two-dimensional annotations are created and exported in a three dimensional format (of which the most common are .STL & .OBJ)
Depending on the requirements of the final 3D print, this data can then be further processed (pre-processing of 3D file) by adding in additional features such as pillars to hold anatomy in situ or separating files and colouring for visualisation purposes.
Once the pre-processing has been completed based on model requirements, it is then inputted into a processing software specifically suited to specific printing technology.
This software (usually supplied with a 3D printer) can be used to add support materials (if the print technology requires it) and converted back into two dimensional cross sections called G-code.
This G-code file will guide the printer's system to print consecutive individual layers to create your patient-specific model.
Teaching & Training
There is an increasing body of research on the benefits of using 3D printed anatomic models in an educational setting.
One of the key differences in using 3D models versus standard anatomical models, is the ability to 3D print specific anatomical pathologies leading to more realistic learning.
In contrast to learning though use of cadaver material, 3D printed anatomic regions also ensure each trainee is using the same pathology during instruction therefore standardizing the learning.
Here there are a range of studies looking at the impact of 3D printing as teaching aids:
From medical imaging data to 3D printed anatomical models.
Department of Medical Physics and Biomedical Engineering, University College London, United Kingdom
3D printing materials and their use in medical education: a review of current technology and trends for the future.
Department of Mechanical Engineering, McGill University, Montreal, Québec, Canada
Visualization of Cardiac Anatomy: New Approaches for Medical Education,
Marian University College of Osteopathic Medicine, Indianapolis, IN, USA
Hands-on surgical training of congenital heart surgery using 3-dimensional print models,
Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
3D Custom implants
Models of the patient’s anatomy can be used to support making a standard implant custom, e.g. bending plates, sizing stents. Custom implants, also known as ‘patient specific implants’ or PSIs are used by surgeons in complex cases where a standard implant is not appropriate for the case. These implants are designed and made for an individual patient, tailored to their anatomy and surgical needs.
The advent of 3D printing has enabled these custom implants to be created more quickly and reduce the cost. Read one of a number of papers reviewing the use of custom implants
Medical device prototyping
Used for many years in manufacturing, 3D printing is currently revolutionizing medical device prototyping.
Now, small and large companies alike can rapidly design, test and engineer multiple device prototypes in days or weeks rather than months/years.
The ability for a product designer to see their physical design in hours rather than months has increased the rate of testing, adapting and fine tuning the most effective functions.
This reduced development lifecycle of devices reduces the overall cost, increases the number of test periods, leading to iterative improvements and increased device safety, and ultimately gives the company competitive advantage.
When a design has been finalized - depending on the expectation for future product adaption requirements, tooling can be traditionally manufactured or can be 3D printed.
Custom devices & prosthetics
Over a lifetime, the human body is subject to a huge amount of wear and tear, whether this is a natural occurrence through ageing or disease or brought on by an external force (such as a traumatic collision). At some time in our lives the majority of us will require a custom device to help us regain our normal functions.
One of the most common uses for custom devices is in the creation of individual prosthetics used to replace limbs. In the United States alone, there are over 2 million amputees that all require custom prosthetics.
This matched with the growing availability of 3D printing, has sprouted a number of companies and non-profit organisations, making use of 3D printing to produce parts to improve people's standard of life.
One of earliest was the e-NABLE Community made of a network of volunteers across the world all devoting time and engineering resource to create free 3D printed prosthetics.
This "lower cost approach to a highly valued item" ethos has made its way into a number of commercial entities, with Handsmith & Open Bionics both adding bionic capabilities to their custom devices.
How are they made?
3D printing's role in prosthetics & custom devices are usually at the interface between the human body and the device itself when form and fit is required to be perfect to make a comfortable device.
Usually, traditional manufacturing techniques and materials are used to produce the other structural portions of the devices.
Typically in creating custom devices, laser scanning is carried out on the patient to create a 3D digital surface representation of the anatomy.
This enables the device manufacturers to create direct 'negatives' of the patient's anatomy which can be 3D printed in a number of different materials directly, which would otherwise be created from traditional cumbersome techniques such as plaster casting.
When considering what printing technology and what materials to use for prosthetics design and manufacture there are three main considerations that should be taken into account
Mechanical properties of materials
Custom devices go though a number of extreme forces during day to day wear and appropriate mechanical properties should be taken into account for this. Nylon based materials and tough polymers are commonly used.
Biocompatibility of materials
If the device makes direct contact with the skin for prolonged periods of time ensure that the materials used are biocompatible or bio-inert
3D Printer accuracy
Perfect fit for a patient means a more comfortable device and improved standard of life. Fine detailed anatomy such as maxillofacial reconstruction should use as high an accuracy as possible when choosing technology, for parts with larger tolerances, like prosthetic cups, a slightly lower accuracy may be suitable.
Figure 4: Prosthetic limbs can be customized with the help of 3D printing
Setting up an in-house print lab for medical 3D printing
In his article entitled Considerations for Implementing a 3D Printing Core Service in Your Hospital: A Technical Analysis on 3DHeals.com, Todd Pietila outlines the benefits "By bringing the technology in house, it supports a reduction in 3D printing lead times compared to outsourcing methods, and helps to build knowledge and drive innovation within the hospital."
However, a big challenge is technical expertise and implementation of the innovation in clinical workflows. Choosing a technology that is right for your clinic can be difficult.
With the wide range of technologies on the market, all have pros and cons. When deciding what technology to chose, for either in house printing or when outsourcing these, considerations include but are not limited to: material selection, accuracy, cost of machine & materials, maintenance requirements & post processing requirements.
How will 3D printing be funded.
Charitable donation, fundraising, sponsorship, educational.
Internal skills sets & personnel.
Will new hires be required?
Internal communications & involvement.
How will surgeons request models, what teams will be involved?
3D Printing Workflow software.
Consider cost and if a single or multiple software solution is required.
Image processing & segmentation.
Medical imaging can present some complex challenges in terms of automated segmentation.
3D print post production requirements can include model preparation, cleaning and smoothing.
3D Printing Hardware Technologies
Choosing a technology that is right for your clinic can be difficult. With the wide range of technologies on the market, all have pros and cons. When deciding what technology to chose, for either in house printing or when outsourcing these, considerations include but are not limited to: material selection, accuracy, cost of machine & materials, maintenance requirements & post processing requirements.
When deciding upon a 3D printer for medical models, ascertain first what the model will be used for as this determines the type of printer required - SLA, SLS, FDM, etc.
For example: Surgical Educational, Visualization, Pre-operative planning, Drilling and Cutting.
The intended use of the 3D printed product determines what material should be used.
PLA & ABS is low cost material, good for visualizing and good for rapid prototyping.
Photopolymer resin is suitable for visualization, cutting and drilling. It is highly effective for combining different colours and can print to 25 microns. Materials can be bio-compatible.
Also, materials are available in clear through to black and come in a variety of Shore A hardness.
Gypsum sand is great for creating a visual model in many colours (not including clear). Material can only be used for visual representation as the resulting model is very fragile and will break under pressure
Nylon provides high strength and stiffness and is a great material for prototypes and manufacturing, Material is bio-compatible and is more suitable for 3D printing complex parts.
3Dcreationlab has further advice on choosing the correct materials.
(SLA, DLP, CDLP)
Vendors include 3D Systems, Formlabs, Envisiontec & Carbon.
The first of the technologies to be introduced to the market and still regarded as one of the industry standard for both its accuracy and material capabilities.
The two most common types are Stereolithography (SLA) & Digital Light Processing (DLP). Both use liquid resins as a build material which are placed into a build tank, usually with a clear windowed bottom.
A build platform is then submerged and a light source is introduced, tracing specific patterns, solidifying a single layer at a time, mapped to the design of the final object
For each consecutive layer, the build platform will raise by a small increment, allowing additional resin to be introduced and solidified. This process is repeated until the final object is complete.
SLA & DLP printers are ideal for printing objects that require a high level of detail and an aesthetic surface finish.
This makes them ideal for use in creating intricate medical devices such as hearing aids as well as creating highly detailed anatomical models for preoperative planning.
Vendors include: Stratasys, Ultimaker, Makerbot & Markforged.
FDM (fused deposition modeling) was the first mainstream desktop technology introduced to the market and as a result, is one of the most widely used technologies today.
The technology uses a solid spool of plastic material (typically PLA or ABS) which is uncoiled during the printing process into a heated printer nozzle.
The technology uses a solid spool of plastic material (typically PLA or ABS) which is uncoiled during the printing process into a heated printer nozzle to make it molten.
The nozzle continually extrudes molten plastic onto a flat build platform following a pre-defined path on its XY axis to effectively draw one layer of material at a time matching the CAD model uploaded to the printer.
Due to the relatively low cost of the technology and materials, it has opened the technology up to be used in a wide variety of applications.
Within the medical field, FDM is a good choice when making larger, less complex geometries such as prosthetic fairings & lightweight splints.
Powder Bed Fusion
(SLS, SLM/DMLS, EBM, Multi Jet Fusion)
Vendors include: EOS, 3D Systems, Formlabs & Renishaw.
The process of powder bed fusion is most common in prototyping engineering fields such as automotive or aeronautical.
This is due to the superior mechanical properties of the parts which come straight from the printer, which can be used for functional simulation testing.
The process of SLS (selective laser sintering) works by heating a bed of powdered material (typically Nylon or PEEK materials) to just below its melting point.
A laser is then drawn over the surface of the material in a cross section, matching that of the 3D model uploaded to the system. This laser ‘sinters’ a fine layer of powder while leaving all other material around it still in powder form.
After each layer is sintered, the bed lowers and a roller passes across the top of the bed to deposit a fine layer of additional powder before the sintering process is repeated until a finished part emerges.
One of the technology’s main benefits, aside from its superior mechanical properties, is that supports are not required when using the technology.
This is because unsintered powder within the bed doubles as support material during the print process which can be easily removed and recycled for additional prints.
SLS is mainly used within the industrial engineering space because of the relative size, power requirements and cost of equipment.
However, many lower cost, and office friendly versions of the technology have been emerging recently allowing the technology to be integrated into many other applications.
SLS is a great choice when considering applications where mechanical properties of parts is paramount.
This makes it ideal for uses in medicine when parts are being subject to daily mechanical strain such as lightweight cast design & scoliosis braces and prosthetic applications
Vendors include: 3D Systems, Voxeljet & ExOne.
Binder jetting is the process of dispensing a binding agent onto a powder bed to build a part, one layer at a time. These layers bind to one another to form a solid component.
Binder jetting is a process by which, solid parts are created from a bed of powdered material by binding them together with an adhesive or reagent.
Binder jetting is like SLS technologies as it comprises a bed of powdered material, However instead of a laser sintering each layer, particles are bound together using material that is sprayed over the top of the print bed.
Once the binder is deposited, matching a cross section of the CAD file, a new layer of material is deposited on with a roller system and the process is repeated until there is a fully formed part.
The most common material for this technology is gypsum powder. However larger industrial machines can also manufacture parts in glass or metal powders using the same technique.
When using the common gypsum powder, the binding agent can be integrated within a conventional inkjet printer head to deposit coloured material to make fully coloured finished parts.
Binder jet printing is great for full colour display parts where mechanic functionality and material properties are not required.
This makes it ideal for applications in coloured prototype modelling or in anatomical models when a number of detailed anatomical structures have to be delineated from one another - such as cardiac modelling.
Software used for medical 3D printing
The preparation, storage and design of 3D printed artefacts in the medical space is driven by different types of software. The PACS system is at the heart of the process looking after the storage of the images that are ultimately used to generate models.
Medical images are typically captured in 2D “slices”. These must be converted into a 3D model. The 3D model can then be prepared for printing. There are a number of unique concerns at this stage that separate 3D printing from other applications such as visualization and VR/AR.
Many software packages exist to allow medical professionals to identify the required anatomy in a set of images. The aim of this stage is to identify the boundaries of the anatomy that is required to be printed from the rest of the images.
Once the images have been segmented the volume labeled as the required volume is converted into a 3D mesh. A mesh is the 3D surface of the volume. This mesh is now ready to be processed in preparation for printing. A number of technical issues can occur at this stage that prevent printing.
3D design software is typically used at this stage to identify and rectify these problems.
They involve the application of many geometric algorithms to fix the mesh and make it printable.
Data management and security are important considerations for all healthcare practitioners.
At this stage, it is important to consider how to integrate the request for the creation of a 3D print with the existing workflow of the practitioner.
Many systems still work on manual requests for initiation, therefore care needs to be taken when managing multiple requests.
Some kind of storage system to manage inbound requests and manage load is necessary.
Data minimisation is one technique to ensure only the required amount of information is passed from the PACS system to the 3D printing laboratory for execution of the request.
- PACS integration/management
- Image segmentation
- DICOM convert volume to mesh
- Post-Processing - fixing volume
- Prep for printing
- Print Management
- Data Management
- Quality Control
Figure 5: axial3Dinsight software in use on a tablet device.
It is important to have a dedicated print room that is maintained and kept clean.
A minimum space required for a desktop printer and processing station is 3 meter x 2 meter space, with suitable ventilation.
For a larger printer, a space of 5 x 4 meters would be suitable for one printer and processing station with suitable ventilation.
When including more printers, the required space will not multiply per meters above.
In most cases, added space required is 1 x 2 meters per printer.
For more guidance on managing multiple printers, see advice from Formlabs.
Keep the print room clean. Every surface should be suitable to wipe clean and a lint/dust free environment should be maintained to help keep the printers in optimum working order.
Each printer has specific Personal Protective Equipment (PPE) requirements. However, as standard every print room should have the following:
- Protective eye wear including UV safe eyewear
- Protective latex free gloves
- Eye wash station
- Protective wear for clothing - this could be disposable aprons, lab coats and sleeve protectors
3D printer ownership in a hospital or healthcare institution
How the 3D printer will be (or is being used) will help determine ownership.
Within a manufacturing environment, engineers would be best suited to the role, Similarly, for medical imaging model creation, Biomedical engineers/scientists or persons with an anatomy background should be considered.
Within hospital environments, prosthetics and maxillofacial departments are often early adopters to 3D printing trials and experiments as the technology lends itself effectively to these specialisms.
Especially in USA and Canada, radiologists may lead 3D printing as historically, the radiology department bridges knowledge from medical imaging to physicians.
When deciding upon ownership, consider if multiple departments will share the resource; the process by which 3D printing work would be requested and produced within hospitals; budgets required and how the operation would grow in the future.