Material Selection Guides for 3D Printing in Medical
Choosing the right material is the first step to success in 3D printing. This guide covers the most popular 3D printing materials in medical industry, their advantages, limitations and applications, and provides a framework that help you choose the right one for your project.
Credit: Tom Claes on Unsplash
Table of Contents
1. How medical 3D printing works?
2. 5 types of 3D printing technologies
3. Material selection criteria – By Applications, By Functionality
4. Typical 3D printing materials in medical field
How medical 3D printing works?
Over the past decade, medical 3D printing applications increased significantly in both clinical and research-based healthcare activities.
3D printing, also known as additive manufacturing (AM), is a process of constructing physical objects from a digital 3D model. In clinical settings, 3D printing has been well utilized to create anatomical models of body parts or organs of an individual. The 3D models enable surgeons to visualize, practice and then perform reconstructive surgery while saving time and increasing precision. Medical 3D printing also offers an economic solution for producing tailormade implants, prostheses and surgical tools due to its capacity for prototyping.
Related article: 7 Stunning Use Cases For 3D Printing In Medical Field
5 Common Types of 3D Printing Technologies
Fused Deposition Modeling (FDM)
A diagram illustrating FDM 3D printing process. Credit: Obsessively Geek 3D Printing
Fused deposition modeling (FDM), also known as fused filament fabrication (FFF), is one of the most widely used types of 3D printing due to its simplicity and cost-efficiency. FDM 3D printers work by melting the thermoplastic filaments (such as ABS and PLA) through a heated nozzle, and then applying layer-by-layer until the object is complete. While FDM is user-friendly, it may not be the best option for printing very high quality and detailed products.
Stereolithography (SLA)
Video demonstrating SLA 3D printing process. Credit: Formlabs on Youtube
SLA (Stereolithography) 3D printing is becoming more and more popular due to its ability to produce high-accuracy, isotropic, and watertight prototypes and parts in a range of advanced materials such as ceramics and nanoparticles.
SLA uses UV lasers as a light source to cure photosensitive liquid resins into harden plastic. Due to the high precision of lasers and lasers systems, SLA printed objects have the highest resolution and accuracy, the clearest details, and the smoothest surface among the plastic 3D printing technologies.
SLA resin formulations also offer a wide range of properties as thermoplastics, however, the finished products are more fragile compared to FDM and SLS technology. Besides, the printing process of SLA is much more time consuming than FDM.
Selective Laser Sintering (SLS)
Video demonstrating how SLS 3D printing works. Credit: Protolabs on Youtube
Selective Laser Sintering (SLS) uses a high-power laser to sinter small particles of polymer powder, fusing them to build a solid structure. The materials used in SLS are thermoplastic polymers that come in a granular form.
SLS is a great solution for the rapid prototyping of functional polymers because it offers a very high degree of design freedom and high accuracy. Unlike FDM or SLA 3D printing techniques, SLS produces parts with consistent mechanical properties, meaning the produced parts are very close to end-use quality without the need of post-processing. Although there are many advantages of using SLS, there are also some disadvantages like material recycling is impossible, products are relatively brittle, and the variety of raw material is limited.
Metal 3D printing
ExOne Metal 3D Printing Process. Source: ExOne on Youtube
Metal 3D printing technique combines the design flexibility of 3D printing with the mechanical properties of metal. Selective laser melting (SLM) and direct metal laser sintering (DMLS) are two common metal additive manufacturing processes.
Metal printed parts have higher strength and hardness and are often more flexible than parts that are manufactured using traditional methods.
Support structures are always required in metal printing, due to the extreme high processing temperature and objects are usually built using a lattice pattern. Compared to thermoplastic printing processes, metal 3D printing has unique set of design rules and requires higher set-up and material cost.
Bio-printing
Schematic of 3D bio-printing. Source: Biopharma PEG
Bio-printing is an extension of traditional 3D printing – it prints with a mixture of living cells and biomaterials, also known as bio-inks, to create organ-like structures that let living cells multiply. The starting models can come from anywhere, a CT or MRI scan, a computer-aided design (CAD) program, or a file downloaded from the internet. Bio-printing is a pretty new technology, and it has huge potential to benefit various medical and tissue engineering fields.
Compared with other 3D printing techniques, bio-printing leads to additional complexities, such as the choice of materials, cell types, growth and differentiation factors, and technical challenges related to the sensitivities of living cells and the construction of tissues. Disadvantages include unprecise droplet size and placement and long production time.
Material Selection Criteria
There are so many 3D printing materials with different properties in the market. To choose the one that is most suitable to your project, you should define your project purpose and identify your material requirements.
Two flow charts are shown below to help you select your desirable material.
Selecting a material by application
Selecting a material by functionality
Followings are more detailed material properties you may consider when choosing the right 3D printing materials:
Source: Formlab, IJSRP, Conserve Energy Future, ScienceDirect, Wiki, ResearchGate, Fabbaloo, Reading Plastic
Typical 3D Printing Materials in Medical Field
Polylactic acid (PLA)
FDM printed PLA orthopedic screws, pins and plates. Credit: ResearchGate
PLA is one of the most popular FDM 3D printing material. It is relatively inexpensive, easy to print and biodegradable. During the worldwide pandemic of COVID-19, a group of engineers created working ventilators using PLA plastic, a 3D printer and some off-the-shelf components for hospitals treating Coronavirus patients.
3DP Technology: FDM
Price: USD 25/kg
Pros
Low cost
Easy to print
Rigid, stiff and good strength
Biodegradable
Odorless
Cons
Low heat and chemical resistance
Less durable than ABS or PETG
Not suitable for outdoor (sunlight exposure)
Applications
Personalized prostheses, such as limb sockets
Biodegradable orthopedic devices, such as screws and fixation pins, plates, and suture anchors
Bone scaffolds
Drug delivery system
Acrylonitrile butadiene styrene (ABS)
FDM printed ABS skull. Credit: Sratasys
ABS is another commonly used 3D printing material to date. It is strong, lightweight and allows for easy post-processing. ABS can be melted to form liquid and cooled to form solid, and this process can be repeated many times without any significant degradation in its properties.
However, ABS is slightly more difficult to print – it is prone to warping without an enclosed and heated build chamber. Also, ABS may have odors that could be uncomfortable or irritating for users. Printing shall thus be performed in a well-ventilated area and/or with an enclosure.
3DP Technology: FDM
Price: USD 20 – 35/kg
Pros
Low cost
Tough, durable and light
Good heat resistance
Cons
Heavy warping
Requires heated bed or heated chamber
Parts tend to shrink leading to dimensional inaccuracy
Releases smelly and toxic chemicals during printing
Applications
Surgical planning models
Personalized prostheses
Orthopaedic corset
Polyether ether ketone (PEEK)
3D printed PEEK implants. Credit: 3Dnatives
PEEK (Polyetheretherketone) is considered as one of the world’s highest performing engineering thermoplastics, offering exceptional chemical resistance and excellent mechanical properties. It is often used to replace certain metals. Since PEEK is sterilizable, it can be used for a number of medical applications including custom-made implants and medical devices.
PEEK is available in filament form for all FDM/FFF machines, and is slowly becoming available in powder form for SLS processes. It is the ideal choice for low-volume production and specialist designs where it is difficult to create prototypes using metal and traditional techniques.
3DP Technology: FDM/ SLS
Price: USD 300 – 750/kg
Pros
High impact strength and durability
Superior heat, water and chemical resistance
Greater design freedom
Biocompatible
Facilitate osteointegration, i.e.: bone ingrowth into an artificial implant
Shares similar properties to human bone
Cons
Requires very high printing temperatures
Expensive
Requires measures against warping
Applications
Customized medical devices
Orthopedic implants
Polyetherketoneketone (PEKK)
Customized 3D printed PEKK cranial device. Credit: Oxford Performance Materials
Belonging to the same PAEK family as PEEK, PEKK has superior machinal, thermal, and chemical properties. Thanks to its lower crystallization rate, PEKK is easier to print than PEEK.
PEKK is mainly found in filament form for high temperature FDM printers, but also in powder form for a very limited number of SLS 3D printers.
3DP Technology: FDM/ SLS
Price: USD 80 – 180/kg
Pros
Excellent thermal, chemical and wear resistance
Easier to print than PEEK, less wrapping phenomenon
Better antibacterial properties than PEKK
Does not give out toxic fumes at high temperature
Cons
Expensive
Requires very high printing temperature
Applications
Customized medical devices
Orthopedic implants
Polycarbonate (PC)
FDM printed PC screws. Credit: Plastics Technology
PC is extremely strong and resists deforming at higher temperatures unlike other common 3D printer filaments. PC can be sterilized with various standard processes making it ideal for end-use parts and functional prototypes in the medical industries. However, the 3D printing of PC is more difficult since it requires higher printing temperature than other standard FDM plastics (such as ABS and PLA).
3DP Technology: FDM
Price: USD 30 – 50/kg
Pros
Some of the best impact and thermal resistance of any common FDM plastics
High transparency
Bendable without breaking
Cons
Require high printing temperature
Prone to warping
Absorb moisture from the air which can cause defects
Applications
Medical equipment parts
Polymethyl methacrylate (PMMA)
PMMA finger bones printed with FDM printer.
PMMA, also known as acrylic, is a strong, durable and transparent thermoplastic. PMMA has good impact strength, significantly higher than glass, but lower than some stronger and more expensive materials like polycarbonate (PC). It is applied as a PC substitute when extremely high impact isn’t necessary, but cost is issue. Besides, PMMA is extremely biocompatible with human tissue and has a long history of use in dentures, bone implants and more.
Biotech companies such as Ossfila is working on the development of