3D printers have found homes in hospitals and healthcare facilities by printing custom-fit and durable prosthetics, along with models of organs displaying tumors that will improve surgical outcomes.

The technology known as 3D printing is set to become one of the most useful tools for the medical market. In 2012, the global market for 3D printing in medical applications was $354.5 million. By 2019, that number will jump to almost $1 billion.

The news is filled with stories on the contribution 3D printing delivers:

• Kids developing amateur prosthetic hands
• Surgeons using 3D-printed body parts and systems to guide surgical procedures
• Biodegradable bone and organ support structures implanted into patients

In addition, future applications include:

• Creating custom drugs
• Building skin tissue
• Potentially building organs

3D printing applications also include developing surgical guides and surgical instruments. The 3D printing machines – ranging from desktop to room-size – are used in orthopedic, dental, and especially crani-maxillofacial applications.

How they work

3D printers use a range of technologies and materials to build three-dimensional objects that cannot be built using other technologies. 3D printers generally operate this way: A layer of build material is deposited onto a build tray. In some 3D printers it is exposed to a heat source (such as a laser or UV light) to solidify the deposit; in other systems either a chemical or temperature process creates the bond between layers. Then another layer is deposited on top of that layer, treated in some way to adhere to the previous layer, then another layer is deposited, and so on until the object is complete. This is the layer-by-layer reference often mentioned.

The great advantage of 3D printing is that the machines can build objects with complex geometries, including holes and features that would be impossible to machine using conventional lathes, mills, or injection-molding systems. One example is the human thoracic cavity, with its ribs and organs. A conventional CNC machine would not be able to cut such a model. Injection molding could be used, but the expense would be exorbitant. Some 3D printing machines can even build complex models using different materials and colors to represent all the structures.

The most commonly used 3D printing technologies for medical are:

• Electron Beam Melting (EBM) or Laser Beam Melting (LBM)
• Stereolithography or Digital Light Processing
• Two Photon Polymerization
• Droplet Deposition Manufacturing
• Inkjet Printing
• Fused Deposition Modeling
• Multiphase Jet Solidification

The sidebar below provides for a brief explanation of each.

The most common materials used for medical 3D printing are:

• Metals
• Polymers
• Ceramics
• Biological cells
• Surgical guides

The most frequent use of 3D printing in surgical situations is to print a model of the body parts that will undergo surgery. Such a model helps surgeons plan the operation for a more efficient, less risky procedure. For example, five-year-old Mia Gonzalez suffered from a double aortic arch malformation, in which a vascular ring wrapped around the trachea and esophagus, restricting her airflow. A 3D-printed model of her heart enhanced the planning phase so the surgical team could visualize Mia’s specific cardiac structure.

Dr. Redmond Burke, Director of Pediatric Cardiovascular Surgery at Nicklaus Children’s Hospital, part of Miami Children’s Health System, said, “By making a 3D model of her complex aortic arch vessels, we were able to further visualize which part of her arch should be divided to achieve the best physiological result. It’s powerful when you show a family, ‘This is your baby’s heart and this is how I’m going to repair it.’”

“Once a patient’s scan data from MR or CT imaging is fed into the 3D printer, doctors can create a model of the scan with all its intricacies, specific features, and fine detail. This significantly enhances surgical preparedness, reduces complications, and decreases operating time,” added Scott Rader, GM of Medical Solutions at Stratasys.

Stratasys reseller AdvancedRP supplies 3D anatomical models to Nicklaus Children’s Hospital for surgical planning. The models are produced by a Stratasys Objet500 Connex3 Multi-Material 3D Printer. The 3D printer offers a range of material properties, enabling anatomical models to accurately replicate organs, flesh or mimic the rigidity of bone. Based on the success of recent surgeries, the hospital has now installed its own Stratasys 3D Printer.
Printing a precise implant
In another use, 3D printing is used to create implants. For example, an Argentine patient required a large implant after stroke-related surgery. The implant had to fit as perfectly as possible – a classic requirement of 3D printing applications.

The 3D printer in this application used a laser beam to sinter titanium metal powder into a piece that offered maximum individualization in form and size.

The medical requirements for the implant were that it had to integrate with biological functions and dissipate as little heat as possible into the cerebral tissue. The medical technology experts at Novax DMA and Alphaform worked to develop a porous structure that could be impermeable to tissue fluid from the brain.

The lattice-structured implant with skull-integrated, screw-in fixings allows both the passage of fluids and fusion with the bone of the skull. In addition, such a design has an insulation effect such that the heat dissipation into the cranial cavity is minimized. The dimensions of the pores themselves are approximately 1mm size, while the cell-links are about 0.2mm thick.

For the 3D design of the implant, Novax staff worked with CAD software. As soon as the CAD work was complete, Alphaform took on the manufacture of the implant, using an EOSINT M 280 system from EOS. The build time was just a matter of hours.

The implant’s porosity level reached 95%, so liquids could flow through with the least possible resistance. In addition, the bone tissue was able to penetrate the outer edges of the implant and grow together with it. At the same time, the metal was stable enough to return the patient to the desired level of normality in everyday life. The structure, constructed in the form of a regular lattice, also provided the required level of thermal conductivity – so the patient can even enjoy time in the sun.

War on cancer
Colored, multi-material 3D printing is being successfully used to aid cancer surgeons in treating patients. In one example, physicians use the models during pre-surgery planning of complicated kidney tumor removal, helping to perform precise and successful kidney-sparing surgery and improving patient outcomes. The 3D printed models are also used to improve surgeon training, as well as help physicians better explain the surgery to patients.

The surgical process uses transparent and color 3D-printed models produced on the Objet500 Connex3, Stratasys’ color, multi-material 3D printer, at the Department of Urology and Kidney Transplantation at the University Hospital (CHU) de Bordeaux, in France. According to CHU surgeon Dr. Jean-Christophe Bernhard, this is currently the only hospital in France – and one of the first in the world – to deploy Stratasys’ multi-color, multi-material 3D printing technology for complex kidney tumor removal cases.

“Having a 3D-printed model of the patient’s kidney tumor, main arteries and vessels – each in a different color – provides an accurate picture of what we will see during operations,” said Dr. Bernhard.

“More importantly, the ability to visualize the specific location of a tumor in relation to these other elements, all in three dimensions, greatly facilitates our task and is not something that is easily achievable from a 2D scan,” he added.

According to Dr. Bernhard, the clearer view offered by the 3D-printed model aids in identifying and avoiding damage to the delicate nearby arteries and vessels that can result in complete kidney removal.
The CHU de Bordeaux uses three Stratasys PolyJet materials: transparent VeroClear to show the volume mass of the kidney, red for the arteries and yellow for the excretory tract. The red and yellow is then mixed on the fly – unique to Stratasys multi-material capabilities – to produce the orange for the tumor.

“The transparent material is of fundamental importance, because it allows us to see inside and estimate the depth at which the tumor resides,” said Dr. Bernhard. “It lets us see the arteries and the cavities that collect urine, so we can see if any of the arteries are touching the tumor. We need to remove the tumor, but not at the expense of other vital elements that together enable the kidney to do its job. Finding that balance is much easier to achieve thanks to 3D printing.”

Another major benefit for the CHU of Bordeaux and Dr. Bernhard is the ability to use the 3D printed models to more easily explain procedures to patients prior to surgery, thereby offering increased reassurance.

“Describing kidney tumor removal with 2D scan or a diagram will invariably leave most patients somewhat bewildered,” he explains. “Presenting them with a 3D printed model that clearly shows the tumor puts them at ease and helps the patient grasp exactly what we’re going to do. Indeed, research from patient questionnaires shows that having 3D-printed models increases their understanding of the surgery by more than 50%, so it’s a considerable benefit in terms of overall patient care.”

SIDEBAR: The 3D printing technologies most used in medical applications
There are many ways to additively build an object in 3D printing. The terms used here are not necessarily those accepted by the ASTM organization that monitors terminology. Many names are brand-specific. But here is a brief look at the technologies often used in medical applications.

Electron beam melting (EBM) is an additive manufacturing technique that uses a cathode ray as its heat source to melt metal powder. Because the metal is melted fully, there are no gaps in the finished product, making for dense, heavy parts. For medical applications this technology is used to build surgical instruments and sometimes skull caps, acetabular caps or other joints and bone replacement sections of the human body.

Laser beam melting (also known as laser sintering) is essentially the same as EBM, except that the heat source is a laser beam. In addition to metal powders, this technology can work with polymer powders.
Stereolithography (SL) uses photo-reactive (usually acrylic-based) polymers that instantly harden when exposed to an ultraviolet beam. As with most 3D printing processes, intricate parts or objects are made one layer at a time. SL offers excellent dimensional accuracy and showcases small features well. It is often used in the medical industry to model organs, body cavities and parts for surgical planning needs.

Digital Light Processing is similar to SL, except that the curing mechanism is a digital light projector. Depending on the manufacturer, the projector uses multiple mirrors and lights to cure a photo-reactive material. These printers work quickly, with high resolution and feature accuracy.

Two Photon Polymerization is a three-dimensional fabrication method that uses ultra-short laser pulses to initiate polymerization of a photosensitive material. It is supposed to deliver better resolution and quality than stereolithography. It suits applications that require the development of 3D structures with a resolution of 100 nm or better. The light source is near infrared. This process can be used to develop drug delivery systems, such as micro needles.

Droplet Deposition Manufacturing deposits droplets of material onto a substrate where they solidify to near net shapes. The material is often metal. Part quality depends on droplet size, velocity, and temperature, among other factors. It is often used to develop miniature metal parts.

Inkjet Printing is also known as material deposition. Here, inkjet-type nozzles shoot material onto a build platform, one layer at a time. The material is either a polymer or a type of binder. This method allows building several objects at a time.

Fused Deposition Modeling is a trademarked term by Stratasys, the developer of this 3D printing method. Also known as extrusion, it uses a type of thermoplastic filament that is moved through a heated deposition nozzle head that softens the filament enough to deposit it in layers, one on top of another, to build a part. As the material hardens, it binds to the previous layers. Polymers, like those used in injection molding, are the main materials used. It suits the need to build models of body organs and parts.

Multiphase Jet Solidification is a method developed by the Fraunhofer Institute for Applied Materials Research. It primarily works with metal or ceramic materials. Low-melting metal alloys or a ceramic powder-binder mixture are squeezed through a nozzle, layer by layer. Then the jetted material is sintered to bond the layers together. The benefit for medical with this technology is it is one of the few processes that works with ceramic materials.