Dec.12, 2013

In an age where 3D printers are becoming a common tool to make custom designed objects, some researchers are using the technology for 3D printing metals, ceramics and other materials to create custom medical implants designed to fix complicated injuries.

A husband and wife duo - materials scientist Susmita Bose and materials engineer Amit Bandyopadhyay - are leading a team of researchers at Washington State University to create implants that more closely mimic the properties of human bone, and can be custom-designed for unusual injuries or anatomy.

"In the majority of cases, results are fantastic with off-the-shelf implants," Bandyopadhyay says. "However, physicians come across many patients in which the anatomy or injury is so unique they can't take a part off the shelf. In these unique situations, the surgeon becomes a carpenter."

Using a technology called Laser Engineered Net Shaping (LENS), researchers create new implants which could integrate into the body more effectively. In the LENS process, tiny particles are blown into the path of a laser and melted. The material cools and hardens as soon as it is out of the laser beam, and custom parts can be quickly built up layer by layer. The process is so precise that parts can be used straight off the printer without the polishing or finishing needed.

Parts on demand

Using this technology, implant manufacturers could simply start with a CT scan or MRI to make a 3D model of the injury. According to Bandyopadhyay, "the most exciting part is it doesn't take months. Within a few hours the first iteration of a design can be done. It then takes another five to six hours to manufacture it. As long as the physician is connected to the Internet, within three days he or she can have a custom, patient-specific implant in hand."

Making parts out of many different materials

Not every implant needs to be custom manufactured. In most cases, surgeons can choose a standard-size implant based on the anatomy of the patient.

The standard materials for weight-bearing implants--titanium or stainless steel--are well-tolerated by the human body. Nevertheless, these metals have different properties from the bone they replace. Although bone seems stiff and solid, it in fact has some "spring" and millions of microscopic pores.

Because a metal implant is much stiffer, the surrounding bone doesn't have to support as much weight as it normally would. This is a significant problem with today's implants. Bones weaken and break down when they aren't properly exercised.

LENS allows different kinds of materials, such as metals and ceramics, to be easily combined into a single part. The heating and cooling processes are so fast that the component materials don't react with one another to create unexpected materials or properties.

Researchers have been testing materials that were difficult to manufacture, like tantalum. Tantalum is non-irritating and can directly bond to hard tissue like bone. This gives researchers greater control over how implants interact with the body. "We can make a tantalum implant or coating in less than 15 minutes, even though its melting temperature is over 3000 degrees Celsius," Bandyopadhyay says.

A metal core can then be coated with a thin ceramic layer so that new bone is more likely to grow and bond with the implant. With 3D printing, implants can be manufactured with structures and have pores in the center but be solid at the edges, or have texture on the surface to help bond with bone or other biological materials.

Porous structures

Porous structures are particularly challenging to make using traditional manufacturing, yet they are potentially critical in making implants that more closely mimic natural bone. The LENS process allows implants to be manufactured with microscopic holes for bone to grow into and attach. The holes have the added benefit of making the metal part less stiff and more like the bone it replaces, also helping the bone grow.

When bone grows into an implant, it forms a strong bond between the two and makes the bone less likely to degrade. The less the bone degrades, the less chance a replacement might be needed.

Wave of the future

In the early development the greatest challenge for the researchers was to show that the material produced using the LENS process showed similar mechanical and physical properties compared to standard implants. Over time, the technology has matured to a level where it is reliable enough to become commercially feasible.

Bandyopadhyay expects that by 2020 custom-designed and manufactured implants will become commonplace.

This research is funded by the National Science Foundation. According to Bandyopadhyay, "Biomedical device companies have invested heavily in this research and are setting up 3-D printing facilities. The FDA approved its first 3-D printed device last year."


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