HEART TO HEART Using medical imaging, a 3D printer can replicate a human heart in 10 hours or less

Practice before surgery
How do your surgeons currently prepare for procedures? They'll get the medical imaging and view it in consecutive 2D images. But if you have a 3D printout of the entire organ in your hand, you get a real sense of the dimensions and what the best access route is. You can actually hold it, along with the tool that you'll use to fix the organ, so you know whether the tool's the right size and whether it will fit along that access path.

The "printout" is just as it sounds, a virtually identical 3D replica, created slowly, layer by layer, by what looks like an ordinary printer, using medical imaging. The technology, first developed in the 1980s, can now incorporate several printing nozzles and printing materials we can choose from. You can adjust the settings of the printer to make something feel more like tissue or feel more like bone. That replication of texture lets surgeons get a feel for exactly what they'll be dealing with before they operate. With tissue-like material, the surgeon can place needles in the material and actually practice before doing the surgery.

We've done just that here at the Children's National Health System, creating replicas for surgeons who needed to close holes in infants' hearts. A 3D replica of an infant heart takes a couple of hours to print; an adult heart may take up to 10 hours.

Broad applications
The potential applications, if proven beneficial, may be almost limitless, including in outpatient settings. In our group, we've also worked on some spine models where we make the bone out of hard material and the discs out of soft material so you can actually flex the final model.

Could the technology someday be used to create replicas that can function as implants? Absolutely, and that's something several researchers are working on. There are efforts being made, from trying to replicate bone structures right up to printing entire organs of varying complexity. Printing an entire implantable heart is, I think, many years away. It doesn't just need to be an anatomical fit, it also has to be embedded with the functionality of a beating heart, with all its valves and connectivity to the nervous system. It's very complex, and much easier replicating bone structures and parts that have less functionality.

Initial feedback
Still to be resolved is whether the intuitive translates into the actual: Will being able to scrutinize, and rehearse on, lifelike replicas before surgery result in better outcomes?

The initial feedback from surgeons is that it helps them with planning and it increases their confidence. But we'll need to show in clinical trials the actual benefits. So far we've only done a few models and gotten feedback on those. We haven't done the clinical studies that are needed to compare the scientific impact of similar procedures with and without models. That's something that we're aiming to do.

Proponents will also have to ensure that the printers can be operated with sufficient expertise. The printing is very precise, with resolution much, much smaller than a millimeter, but it still depends on imaging, so if you don't do a good job creating the initial image, the printed model won't replicate the real anatomy. It all has to work together — good imaging, good processing of the images, and what we call segmentation — outlining on the digital model what should be printed and what's just noise and should not be printed.

Cost concerns
Expense is bound to be another potential limiting factor, with price tags for high-end 3D printers currently running in the hundreds of thousands of dollars.

Their resolution has gotten significantly better, the materials they use have gotten better and they've gotten faster. Although printer and material costs have gone down, it's still going to be a significant investment for a facility to buy a printer and staff it with the technical people who'll be able to run it. But there may be a viable alternative. You can also outsource it to specialized companies that have both the 3D printers and expert staff. That's a way of integrating the technology without having to have a printer in each facility.

FACIAL RECONSTRUCTION
3D Printing's Potential

LONG ROAD BACK Researchers developed 3D-printed models and implants that surgeons used to reconstruct the face of Stephen Power.

There's been some exciting news coming out of England about the surgical application of 3D printing. A team of investigators from Cardiff Metropolitan University's National Centre for Product Design and Development Research teamed with maxillofacial surgeon Adrian Sugar, MD, to reconstruct the face of Stephen Power, a 29-year-old motorcycle accident victim who suffered significant facial trauma.

After an initial emergency surgery to repair his jaw, cheeks, nose and eye sockets, Mr. Power underwent a second procedure in an attempt to restore his pre-accident appearance. It wouldn't be easy — Dr. Sugar would have to cut and move bones around delicate anatomy.

Enter the Cardiff researchers. Led by engineer Sean Peel, the team used CT scans to create a virtual model of Mr. Power's face with 3D printing techniques. They then worked closely with the surgical team to plot precise locations of cuts that would free up facial bones. To apply the model in the OR, the researchers printed a saw guide that fit securely around the 3D model.

Before surgery, the researchers and clinical team removed bone segments from the model and repositioned them to replicate the desired anatomy. The team then created custom 3D-printed titanium implants and a repositioning guide to hold bone segments in place while the implants were placed.

"It was a very complex injury and correcting it involved bones having to be re-cut into several fragments," Dr. Sugar told the Daily Mail (tinyurl.com/loqtmnb). "It made sense to plan it in three dimensions."

He was able to plot his course on a 3D model before every stage of the operation. "The results are in a different league from anything we've done before," he says.

A British surgeon also recently used 3D printing technology to recreate half a pelvis for a patient in whom bone cancer took a segment of the original, according to a published report in the Telegraph (tinyurl.com/lfyl54p).

CT and MRI scans determined the amount and shape of the bone lost. The 3D printer then created successive layers of titanium, fused together by a laser, into the shape of the missing pelvis segment, which was mineral-coated to allow bone ingrowth. The surgeon implanted the segment, which reportedly fit perfectly, and performed a standard hip replacement to insert the new joint implant into the printed titanium socket.

— Daniel Cook