The Future of 3-D Printing in Medicine | IT Support and Hardware for Clinics | Scoop.it

Today’s 3-D printed plastic models of hearts may one day translate into on-demand printed, functional replacement organs.

 

A 3-D printed model of conjoined twins that was used to help guide surgeons to plan a separation procedure and help navigate the anatomy once in surgery. This case was late-breaking news highlighted at RSNA 2015.

Science fiction offers a lot of ideas for creating new body parts on demand, and the advancement of 3-D printing (also called additive manufacturing) is slowly translating this idea into science fact. Today, the 3-D printed anatomic models created from patient computed tomography (CT), magnetic resonance imaging (MRI) or 3-D ultrasound imaging data-sets are used for education and to plan and navigate difficult procedures. These models are used to teach about complex or rare cardiac or congenital conditions that up until recently could only be seen using examples extracted from cadavers. Today, anatomical models of rare cardiac anatomy can be printed on-demand from CT scans of surviving patients. 

That concept can now be translated into 3-D printing of implantable devices customised to a specific patient using their imaging. Experts at several medical conferences are saying printing functional biological replacement tissues is already in development. Three-dimensional printing has become a topic of discussion in conference sessions and on the expo floors at many medical meetings over the past several years. The topic was covered in a session at the Radiological Society of North America's (RSNA) annual meeting in December, which is detailed in the following sections.

 

 

Early Experience Printing Implantable Devices:

               

            Printed 3-D models are currently used for surgical planning in complex cases, especially in pediatric congenital heart procedures, said Richard G. Ohye, M.D., professor of cardiac surgery, head, section of pediatric cardiovascular surgery, surgical director, pediatric cardiovascular transplant program, co-director, Michigan Congenital Heart Center, C.S. Mott Children's Hospital, Ann Arbor, Mich. However, he explained 3-D printing will soon allow the creation of customised implantable medical devices, including actual tissue or vessel replacements. 

In fact, 3-D printed devices are already being used on a small scale. He presented a case of a three-month-old patient whose airway was underdeveloped and required a splint to hold it open. The patient underwent a CT scan and a 3-D reconstruction of the airway allowed doctors to create a virtual airway splint implant customised to fit into the small anatomy. The design included a “C”-shaped tube that had numerous holes to use as suture anchor points. The shape was designed to allow it to expand outward as the patient grew. They then 3-D printed the splint from bioresorbable plastic and implanted it in the patient. Ohye said the material it was made from is expected to dissolve within three to four years. 

The Finnish dental equipment maker Planmeca recently introduced a 3-D printer that allows dental laboratories and large clinics to create dental splints, models and surgical guides. In the near future, the Planmeca Creo printer will also support the creation of intricate, customised temporary fillings.

The jump to printing full organs to transplant is much more complex, but the groundwork is being laid. Ohye said engineered heart tissue created using cardiac stem cells has already been created, but it is limited to a size of about 200 microns. Anything larger requires blood vessels to keep the cells alive, he explained. 

 

3-D Printing of Biological Tissue Implants:

 

           Research is being conducted to enable 3-D printing of blood vessels, where cells are deposited by the robotically driven printer in patterns that build up layer-by-layer to create a lumen. That same concept is being tested at a few centres to create 3-D print heart valves. Ohye said the process currently being investigated uses a printed matrix of bio compatible material, in which stem cells can then be deposited. If the process can be worked out to create engineered, printed organs, these might be used to create bench-top model organs for new drug testing in the next few years. Implantable 3-D printed living organs for transplant into human patients are also a very real possibility.

“Bio-printing is likely to be a huge field for the future of medicine,” said Roger Markwald, Ph.D., director, Cardiovascular Developmental Biology Center, Medical University of South Carolina. He is involved with The South Carolina Project for Organ Bio-fabrication, one of the groups at the forefront of 3-D bio-printing research. He explained there are too few organ donors to meet demand and there is an even greater need for soft tissues for reconstructive surgeries for things such as injuries, burns, infections, tumor resections and congenital malformations. 

“There are too few organ donors to meet the needs,” Markwald said. “At least 21 people die each day because of the lack of implants.” 

This organ shortage might be solved in the future by bio-printing organs on-demand. Bio-materials can be printed using current technology, but there is a fatal flaw. “The Achilles heel of tissue engineering today is the need to create vascularity in the structure, and that has been the focus of what we have been trying to do,” Markwald said.  

The key to printing vascularizable micro-organs may involve chemical modifications of alginate hydro-gels. Markwald’s lab created an oxidised alginate, which is biodegradable and provides stability for 3-D bio-printing. It also is bio-active, allowing cells to migrate and remodel. They created “plug and play” molds to prepare micro-organ constructs for surgical implantation. These are made with the biodegradable alginate, which contain small molecules to promote host vascular in-growth and suppress inflammatory responses.  

Bio-printing is enabled using a “bio-paper” made of bioresorbable hydro-gels. These allow printing of the cells against gravity and allow the cells to grow, interact and function physiologically. Markwald said research is leading to the development of hydro-gels specific to each type of organ tissue. 

The “bioink” is made from 300 micron diameter spheroids that contain between 8,000-12,000 autologous adipose-derived stem cells. He said it takes about 7 million cells to make 840 spheroids, and it takes thousands of these spheroids to print a 1 mm cube.

Just as 3-D printing allows simultaneous printing of several different colors of materials to build a color 3-D model, bio-printing is being developed to allow use of several different cell types to create complex tissue units. 

“Eventually we will be able to make functional hearts or livers,” Markwald said. “What we can print right now are cardiac patches and small- to medium-sized blood vessels, skin tissue, soft tissue (adipose, muscle) for reconstructive surgery, and vascularized micro-organs that can be grown in a bioreactor and used to supplement the function of a diseased organ like the liver.”

 

 

Creating 3-D Printable Files:

 

Creating files for 3-D printing from medical imaging data-sets starts with good imaging, said Shuai Leng, Ph.D., associate professor of medical physics, Mayo Clinic, Rochester, Minn. “If you start with garbage in, you get garbage out, so you need good image quality,” he stressed.  

To create a usable 3-D file, he suggests using 0.6 mm thin imaging slices. This allows for very smooth surfaces. By comparison, he said use of 6 mm slices will make the printed object very rough and textured, appearing pixelated, when it is printed in 3-D. 

He said dual-energy CT is great for 3-D printing because it can easily exclude bone so only blood vessels or soft tissue remain in the image area. Metal implants commonly cause problems when creating 3-D printing files, but dual-energy systems have metal artifact reduction software to separate the metal and artifacts from the anatomy to allow creation of better models. 

When using 3-D models for procedural planning and navigation, you need to ensure the precision of the model by using U.S. Food and Drug Administration (FDA)-cleared 3-D printing software. The resulting printed models also should be compared to the original images to ensure quality control. Before printing, images should be checked in three planes and approved by a radiologist or the ordering physician. 

The final imaging files are converted into STL/CAD files that can be read by the 3-D printers and translated into the final 3-D object.