The Coalition for Imaging and Bioengineering Research (CIBR) is a dedicated partnership of academic radiology departments, patient advocacy groups, and industry with the mission of enhancing patient care through advances in Biomedical Imaging. My good friend and colleague Dr. Beth Ripley and I recently participated in the sixth annual Medical Technology Showcase at Capitol Hill organized by CIBR, representing the Department of Radiology at the Brigham and Women’s Hospital (BWH) where we emphasized the importance of 3D printing in healthcare.
The annual Medical Technology showcase aims to bring examples of medical breakthroughs in imaging and bioengineering to members of congress and demonstrate how these advances are impacting patient care. In addition to educating policy makers and the public about innovative imaging technology, the event demonstrates the value of NIH funded academic research and the importance of collaborations between academia, industry and patient advocacy groups.
Our display booth comprised of the Department of Radiology at BWH, the Lung Cancer Alliance, and Fujifilm was a hit among attendees and we were pleased to see the level of interest in medical 3D printing. We displayed 3D printed models that have been used for different clinical applications and our booth partners from Fujifilm demonstrated Synapse 3D, a software that allows conversion of 2D image data from CT/MRI into 3D printable files.
Our goal was to demonstrate the importance of 3D printing in pre-surgical planning and how it can benefit patients by allowing surgeons to devise a patient specific treatment strategy and minimize post-surgical complications. Sheila Ross, a lung cancer survivor and patient advocate from the Lung Cancer Alliance emphasized how 3D printed models can give patients and their families a better understanding of the planned procedure.
A lung model from Fujifilm demonstrating a nodule (green) and surrounding bronchioles
The Lung & Brain cookies might have been slightly more popular than our 3D models
It is our hope that more funding and resources will be allocated to investigate innovative medical technologies such as 3D printing, which can then be translated to impact patient care. In order to transform 3D printing from being a fad, to a mainstream tool that fosters precision medicine, evidence based benefits of its different applications will need to be demonstrated in clinical trials which will require funding.
Tatiana Kelil, MD
Purpose of this blog: To create a forum where members of the 3D medical printing community can share problems, solutions and practical advice pertaining to all aspects of the 3D printing pipeline.
Featured problem: Setting up a new printer
Featured printer: Printrbot Metal Plus
Printing type: Fused deposition modeling
Theme: Don’t put the cart in front of the horse
Translation: don’t try to print before you’ve set up the printer
If you are at all like me, you are impatient. When your new printer arrives, you want to rip open the packaging, set the printer on the counter, plug it in and hit “print”. If this sounds like you, keep reading. This first blog is a cautionary tale.
Lesson 1: Make sure that your printer is properly calibrated.
1. Level, Level, Level
While the printer may come “pre-calibrated,” it is always a safe bet to double-check that nothing untoward has happened during shipment.
The printing bed needs to be level in relation to the path of the extruder, and therefore both the bed and the extruder railing should be checked and adjusted if not leveled. The more level you can get the print bed with respect to the extruder, the easier your life will be for all of the following steps. There are many reports of warped print beds on the internet; e.g. some of the printrbot simple models seem to have a dip in the center of the print bed. Using a straight edge rather than just a level may help you detect this type of issue. Getting that print bed straight by whatever means necessary is advised.
2. Determine your negative z-value, or get ready to throw out a lot of failed prints
You need to determine the optimal distance that the hot end of the extruder should be from the print bed when printing.
The number you are determining is the negative z value. Picking your negative z-value is sort of like Goldilocks and the 3 bears: If the negative Z value is too high, your print will look stringy. If the negative Z value is too low, your print will look smashed. So you want it Just Right.
To set the negative z value, you need to modify the G-code.
At this moment, let me digress for those not familiar with G-code. G-code is the language that the printing software uses to communicate with the printer. G-code is, in essence, directions given to the printer on how to drive the motors and turn the heaters on and off. This is akin to postscript for laser printers. Different slicing programs will create different g-code; some will do it better than others, depending on how optimized they are for a given printer, etc. This is also why some slicing programs may result in a faster print, based on more optimized/efficient g-code.
tip: always enter G code in CAPITAL LETTERS
For the Printrbot, you enter the G-code that assigns the negative z-value in Repetier. Go to the manual control tab on the right side of the screen, make sure your printer is connected and then type the following in the G-code line:
M501 (shows you what the current X, Y and Z offsets are; output on the bottom of screen)
M212 Z0 (The number you type after Z is the negative z value that you are assigning. Start with 0 and see where you land, then go negative in small increments e.g. -0.1 to move closer to the print bed, printing a simple object each time and seeing how it turns out. Positive numbers will move the extruder farther from the bed.)
3. Auto-level before every print.
Your printing software should instruct the printer to auto-level before any print. In addition to the basic leveling described in 1., there is an “auto leveling” check designed to determine if the print bed is tilted in any direction. Also referred to as “z probing”, this step is necessary because the quality and success of your print depends on any discrepancies in the distance between the hot end of the extruder and the print bed at a given location being accounted for.
This can be done by probing 3 locations on the print bed.
Don’t believe leveling the bed matters? Well, here are some problems that can arise from a poorly leveled bed:
-Initial print layer does not stick or parts are missing
-The hot end of the extruder scrapes the bed
-The extruder gathers up plastic from the first or second layer
So how does auto-leveling work?
-An auto-leveling probe (aka z end-stop sensor) defines the distance between the extruder hot end and the print bed at any given location.
The auto-leveling probe is to the right of the extruder and has an orange tip in the picture below.
The Printrbot Metal Plus has an “inductive sensor” that detects the print bed via conductivity from the aluminum bed. The theoretical beauty of this design is that the sensor tip can be positioned at a level higher than the tip of hot end of the extruder and thus will not drag through your printing surface the way a touch down sensor would. The potential pitfall is that things that change conductivity (i.e. adjacent metallic objects) may affect the sensor.
It is possible that your z end-stop sensor is faulty- if you are the unlucky soul that receives a malfunctioning sensor, you may be in for some hurt if your printer tries to jam the extruder into the table. Even if your sensor works, you may misjudge the distance from the extruder to the bed- for these reasons, be very close to an off switch or the plug when you are calibrating your negative z value. If the extruder is being jammed into the table, by all means, turn the printer off!
To auto-level before each print, you need to make sure that the printing software contains the autoleveling G-code and adds it to the beginning of any slicing G-code. You need to set up auto-leveling in each slicing/printing program you use. It does not translate between them.
The G code you use in Repetier is:
G28 X0 Y0
Below are some links to setting up auto-leveling in Repetier and Cura.
Setting up auto-leveling in Repetier on Mac: http://help.printrbot.com/Guide/Setting+Up+Your+Auto-Leveling+Probe+and+Your+First+Print+-+Mac/107
Setting up auto-leveling in Repetier on PC: http://www.repetier.com/documentation/repetier-firmware/z-probing/
Setting up auto-leveling with Cura: http://www.instructables.com/id/Use-Printrbots-Autoleveling-Probe-with-Cura/
Beware: Just because your printer auto-levels itself, it doesn’t necessarily mean it won’t plunge through the printer bed in a desperate attempt to follow your every command. In fact, the printrbot metal plus is NOT smart enough to know when to say no. When we accidentally told it to go down 10 mm in the z direction when it was at Z0, it did so, much to our horror (see picture below).
In the background of this picture, a hole in the stage marks the scene of an unfortunate z-axis accident.
In the foreground, the outline of an aorta that did not make it (foreshadowing for the next blog entry).
4. Just how accurate is your model?
You can check to make sure that the printer motors are appropriately calibrated- i.e. they actually travel the correct distance when told to do so. As described above, the printing software communicates with the printer (and thus the motors) using G-code. To make sure nothing is “lost in translation”, you need to make sure that when the software tells the printer head to move, say, 10 mm in the x-direction and 25 mm in the y-direction, the printer head appropriately translates that g-code into the correct movement.
There are 4 motors:
To check the calibration of the x, y and z motors, tell the printer to move 40 mm in the x axis and then measure to determine whether it is accurate. If you measure 40 mm, you are done. If not, you need to do some recalibration (see below). Do the same with the y axis and the z axis.
Appropriate calibration in the x, y and z axis matters a lot for medical modeling…you want to make sure you are creating accurate models!
To check the calibration of the extrusion motor, heat up the extruder to the recommended temperature for the filament. Use tape to mark a few cm up the filament and then measure from the tape to the entrance into the extruder. Tell the printer to extrude 10 mm of filament and measure again.
Rate of extrusion really matters: your printing software assumes it knows the accurate amount of material extruded per given time.
If too much is extruded, your print will have globs; if too little is extruded, you have holes or poor matrix
This is a great primer on motor calibration and how to fix errors: http://www.instructables.com/id/Calibrating-your-3D-printer-using-minimal-filament/
5. More advanced calibration/ “tweaking” to optimize your prints:
A 3D printing manufacturer who goes by “Ville” recently designed and published an STL test file that can be used to troubleshoot calibration issues with any printer. The print has several challenges, including various overhangs, small details, different sized holes and wall-thicknesses, bridging and different surfaces. The idea is that users can share problems and solutions with each other.
Read more at: http://3dprint.com/48922/3d-printer-calibrating-test/
Download this STL test file at: https://www.thingiverse.com/thing:704409
The top picture is what the test model should look like. The bottom picture is what my printer produced. Guess I have some tweaking to do....
In the next post, we will tackle one of the most infamous struggles in 3D printing- getting your model to stick to the print bed.
Until then, happy printing!
An entirely new 3D printing method that prints 25-100x faster than currently available technologies has been introduced. The new process called Continuous Liquid Interface Production Technology (CLIP) works by using light and oxygen to change a photosensitive liquid resin into a three dimensional solid object. The process is similar to Stereolithography (SLA) where liquid photopolymers are cured using ultraviolet light. However instead of depositing material layer by layer, the object is formed at once. CLIP places a pool of liquid resin over a digital projection system which projects an image for how each layer should form. To create an object, bursts of light and oxygen are applied; light hardens the resin while areas exposed to oxygen are kept from hardening.
Proposed advantages of this technology include radically faster processing time and ability to use wide range of materials that make stronger objects.
This technology can potentially be extremely useful in the health care industry if models can be printed within a matter of minutes and enable preoperative planning of surgical procedures that may be time sensitive.
For a summary of other 3D printing technologies, check out my previous post here
Tatiana Kelil, MD
If you are like me and have no real background in engineering or chemistry, keeping the different 3D printing technologies straight may sound daunting. In this post, I will attempt to give a simplified overview of the seven major types of 3D printing technologies and summarize the key advantages and disadvantages for each. I hope this information helps anyone who is interested in acquiring a 3D printer understand the different processes better and direct you to a specific technology that suits your needs the best.
3D printing is an additive process that creates volume by adding material one layer at a time following a predetermined pattern as opposed to milling, where material is removed from a raw block. The American Society for Testing Materials (ATSM) has defined seven major additive manufacturing processes, each represented by one or more commercial technologies.
1) Vat photopolymerization (Stereolithography, SLA)
Invented over 30 years ago, SLA is the foundational technology of 3D printing. In this process an ultraviolet light is applied to a vat (large tub) containing liquid photopolymer (plastic). UV light is used to cure the liquid photopolymer (convert the liquid into a solid state). When a layer is completed, a leveling blade is moved across the surface to smooth it before depositing the next layer. This process is repeated until the model is completed. Support structures are needed which anchor the parts on the build platform and support overhanging structures. Once complete, the part is drained and excess polymer is rinsed off. A final cure in a UV oven is often required to further solidify the object.
Advantage: - High resolution and accuracy
- Allows production of complex geometries
Disadvantages: - Durability; photopolymers are the weakest material
2) Material extrusion (Fused Deposition Modeling, FDM)
This process is analogous to a hot glue gun where a printer melts a cable roll of raw material (usually plastic) and extrudes it through a nozzle. Through the use of a second nozzle, a support structure can be built using a different material. The melted material is laid down on the build platform layer by layer, where it cools and solidifies. Once complete, support material is either mechanically removed or melted away. The majority of commercially available desktop printers are currently of the FDM type.
Advantages: - Multiple materials/colors may be used for both build and support
- Affordable, easy to use, can fit in an office
Disadvantages: - Relatively slow build times
- Limited surface quality, fine details may not be realized
- Care needs to be taken during design to optimize final object strength
3) Material Jetting (Multijet modeling)
This process is analogous to inkjet printing, but instead of jetting drops of ink onto paper, a 3D printer jets drops of liquid photopolymer onto the build tray. Liquid drops are then converted into a solid state using light. Support materials are required which are either mechanically removed or melted away once building is complete. Material jetting can combine different materials within the same 3D printed model, in the same print job. Fully cured models can be handled and used immediately without additional post-curing processes.
Advantage: - High accuracy and surface finishes
- Can combine different materials within the same 3D printed model
Disadvantages: - Durability, Photopolymers are the weakest material
4a) Powder bed fusion (Selective Laser Sintering, SLS)
This process uses laser to selectively sinter (melt and fuse) a thin layer of powdered material. The build platform will then be lowered and the next layer of plastic powder will be laid out on top. By repeating the process of laying out powder and melting where needed, the parts are built up in the powder bed. Unsintered loose powder supports the object during build so no other support structures are needed. The loose powder must be removed from the completed object.
Advantages: - Relatively rapid build time
- No support material is needed
- Can manufacture parts in standard plastics
- Low cost
Disadvantages: - Surface finish can be rough
4b) Powder bed fusion (Electron Beam Melting, EBM)
This process is similar to SLS, but uses electron beam instead of laser to melt and fuse a thin layer of powdered metal into a solid object. Completed object is embedded in a block of loose powder, which must be removed.
Advantages: - Relatively rapid build time
- Material recyclability is often possible, reducing potential waste.
- Useful in settings that require complex internal structures for metal components
Disadvantages: - Relatively high cost for the systems and the knowledgeable operators required to run them
- Surface finish can be rough
5) Binder jetting (Powder bed and inkjet head printing)
In this process a print head moves across a powder bed, laying down a liquid binding agent that glues the particles together to create a solid object. The built parts lie in the bed of loose powder, so no support structure is needed.
Advantages:- Relatively rapid build time
- No support material is needed
- Simple and inexpensive technology
- Can print a wide range of materials in full color
Disadvantages: - Objects are relatively fragile and require post processing to improve durability
6) Sheet lamination
This process stacks sheets of materials using binding agents (adhesives) or other joining processes such as friction welding and then cuts the edges of each layer to create the desired shape.
Advantage: - Does not require a controlled environment and can be run in open air
- Can be used to join dissimilar materials
Disadvantages: - Ability to produce complex objects is limited
7) Directed energy deposition (Laser metal deposition)
In this process material is directly deposited by jetting the build material into the heated zone created by a laser, electron beam or an ionized gas.
Advantage: - Can operate in open air and at large scale
- Multiple materials can be used in the same process
- Good at processing a high volume of material quickly and inexpensively
Disadvantages: - Lower accuracy and reduced ability to create complex objects
Now that you have some idea about the different 3D printing technologies, I hope you will get a 3D printer of your choice and print your heart out!
Tatiana Kelil, MD
Sources: custompart.net, mechanicalengineeringblog.com, additively.com, 3dsystems.com, Deloitte University Press
Enduring the physical and psychological consequences of having a cancer diagnosis is only the beginning of the battle. Cancer patients then have to deal with grueling treatment cycles and associated side effects. The high doses of radiation used to destroy cancer cells can also damage adjacent healthy tissues. Although major improvements in radiation technology such as intensity modulated radiation therapy have led to reduced toxicity, these methods tend to be complex requiring several planning steps and safety checks before the patient can start treatment. 3D printing is promising to solve some of these problems and aid in providing personalized cancer treatment.
One such application of 3D printing is in the production of customized bolus and shields used during radiotherapy. A bolus is an artificial object placed over the treatment area in order to modify dose both at the skin surface and at depth while a shield is used to protect adjacent structures not intended to be exposed to radiation. 3D printing can be used to design customized bolus and shield that fit a patient’s unique anatomy perfectly. Additionally these precise models ensure even distribution of radiation dose to the targeted area while sparing adjacent normal tissues. This technology is especially beneficial to patients with head and neck cancers where susceptible organs such as the eyes and ears are located in close proximity to the target and where surface anatomy of the face is varied among different individuals. Traditional approaches of fabricating shields involve casting of several molds, which are expensive, time consuming and labor intensive. 3D printed shields can be easily and cost effectively created from existing CT/MR images without subjecting sick patients to be present during the fabrication process.
Another application of 3D printing is in Brachytherapy where a radiation source is implanted inside the body next to the area requiring treatment. Under current practice, a one-size-fits-all approach is utilized where standardized implants with internal channels that guide the radiation source are inserted into the body. Standardized implants do not conform to patients’ specific anatomy and precise positioning is often challenging. These implants are also prone to shift during movement resulting in suboptimal dose to the target and unwanted exposure to adjacent organs. Patients are therefore required to remain immobile over the course of a treatment to maintain optimal positioning between the radiation source and treatment target. 3D printed customized implants provide a much better fit and are easier to place thereby increasing patient comfort and reducing shifts due to movement or changes in bladder or bowel distention. Customized implants with curved internal channels can also be used to reach targets that may not be accessible with existing standardized implants.
3D printing appears to provide a rapid, practical and inexpensive approach to deliver homogeneous dose to the target area while minimizing unwanted exposure to adjacent normal tissues. Furthermore this technology minimizes patient discomfort and allows provision of cancer therapy that is tailored to each individual.
Tatiana Kelil, MD
Sources: Garg et al. IEEE.org 2013
Su et al. JACMP.org 2014
Within the past few years, interest in 3D printing and its medical applications has been growing exponentially. 3D printed models have already been used to provide unparalleled pre-surgical planning in complex surgeries such as conjoined twin separation and face transplantation, as well as more common procedures such as fracture fixations and joint replacements. However, the majority of health care providers and recipients are still unaware of this technology and its utility. My hope with this blog is to provide a basic overview of 3D printing and its applications in medicine by answering some of the frequently raised questions. Stay tuned for future blogs where I will attempt to address specific topics in detail!
What is 3D printing?
3D printing is a process of creating 3 dimensional objects from a digital file by using a 3D printer. In the field of medicine, the digital files are comprised of 2 dimensional CT or MR images. 3D printers do not directly recognize these digital files and post processing steps are required to convert these files into a format that is readable by 3D printers. The printer then deposits various materials layer by layer to build a 3 dimensional object.
What are the applications of 3D printing in medicine?
3D models have already been used for presurgical planning in numerous subspecialties including maxillofacial and craniofacial surgery, orthopedic surgery, neurosurgery, cardiovascular surgery, pediatrics and dentistry. Models can also been used to design implants and prosthesis that are customized to each patient. In the field of radiation oncology, 3D models can be used for radiotherapy planning of optimal positioning of radiation beam and creation of personally designed radiation shields. 3D models are also proving to be superb educational tools for teaching anatomy, pathology and surgical techniques. Bioprinting, which involves printing of live cells and viable tissues that can potentially be implanted into human beings is currently an active filed of research.
What are the benefits of 3D printed models that have already been reported?
Currently, 3D printed models are predominantly utilized by surgeons. Preoperatively these models improve diagnosis and evaluation of the complexity of the procedure thereby allowing selection of optimal, patient-specific treatment strategy. The models can be used to plan every step of a complex procedure including surgical point of entry, incision size, precise screw length and trajectory. The models can also serve as a cutting guide for resection and as a template for preoperative bending of reconstruction hardware that would fit the specific patient anatomy perfectly. As a result of this accurate preoperative simulation and preparation, 3D models result in reduced actual operating time and cost associated with the use of surgical rooms. The time that the patient has to remain under general anesthesia, amount of blood loss and other potential complications are subsequently minimized. Shortened hospital stay and decreased need for follow up procedures have also been reported. 3D printed models allow patients who typically don’t have years of medical training, to visualize and better understand the planned procedure and make it easier for surgeons to obtain informed consents from their patients.
What is the purpose of printing models if 3D images can be viewed on a computer screen?
Although a 3 dimensional volume rendered digital models can be created, these digital models are still viewed on a 2 dimensional computer screen, which does not provide the same sensory input as holding a physical model in hand. Surgeons that have used the models report the additional tactile sensory input gained by holding the models and the ability to rotate and view the models from any direction in space greatly enhances their spatial perception of anatomic relationships between adjacent structures. Additionally the models provide the added benefits mentioned above such as serving as a cutting guide and template for pre-surgical bending of reconstruction plates, which cannot be achieved unless these models are printed into tangible objects.
In summary, it is hard to imagine all the ways this technology will impact patient care, but judging from what has already been achieved within a very short period of time, 3D printing will certainly revolutionize the healthcare industry for the better.
Leave a comment or question below regarding topics you would like addressed on the next blog!
Tatiana Kelil, MD
Image credit: Healio.com/orthopedics; John Robert Honiball (University of Stellenbosch).