Nurse, print me out another plaster cast!

5. September 2013
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Researchers agree: Three-dimensional printing technologies are revolutionising orthopaedics. In a few years tailor-made exoskeletons could already be replacing ancient plaster bandaging. In addition, many laboratories are working on bone made-to-measure.

A remnant from the past: since 1851 orthopaedic surgeons have been using plaster casts to set fractures. A presumed innovation of the present is the synthetic cast. They have higher strength with less weight, faster curing, and do not swell in the presence of water. This is offset by higher costs and disposing of not entirely unproblematic materials. What’s more, synthetic casts have even worse water vapour and air permeability than the plaster version. That page of the story is now being turned.

Welcome to the 21st Century

Jake Evill, a graduate of Victoria University in Wellington, New Zealand, knows the problem only too well. After the media and industrial designer broke his hand, he was given a plaster cast. Evill was surprised at just how little patient-friendliness this procedure offers – having two kilograms of itchy “plaster” on his arm really seemed to him somewhat archaic. During warmer months patients sweat immensely, which quickly leads to unpleasant odours. In view of the absence of better alternatives, Evill set himself a task. The result: Cortex, an exoskeleton with honeycomb-like structures and large open spaces. Polyamides such as nylon are used as base material. Possessing excellent strength and toughness, the material proves to be very light. This can be explained by its intermolecular hydrogen bonds, similar to proteins.

From the data to the piece of work

With Cortex as well, it all starts with an X-ray image, in order to determine the exact position of the fracture. In addition, three-dimensional scans of the affected limb are made. Evill works here with Kinect, a hardware controller for the Xbox 360. His colleague the computer then enters the picture: From this data, the geometry can be calculated which the exoskeleton needs to have in order for it to fit well and provide support where needed. For three-dimensional modeling the creator uses  ZBrush, a graphics program from Pixologic. In the final step, all data was transferred to the Netherlands. Using this, Shapeways, specialists in three-dimensional prints, produced one exoskeleton – less than 500 grams in weight and three millimetres thick.

Great benefits, high costs

Viewed critically, the new creation carries two serious disadvantages: compared to plaster casts or synthetic casts, significantly higher costs are to be expected. This relates to both hardware and software as well as the material itself. In addition Evill calculates about three hours to get an exemplar finished – compared to a maximum of ten minutes for the classical method. After the work is performed however Cortex functions immediately, whereas plaster is only fully cured after one day. Doctors otherwise immediately see several advantages: the exact geometry, low weight, the aesthetic quality. Patients can shower or bathe as normal, and their skin is well ventilated. Long-sleeved shirts, blouses or long pants? No problem. There is also the environmental aspect: to achieve a bracing effect, very little synthetic material is generally required. All polymers used can be recycled by remelting after successful healing.

Stable, and a perfect fit

Whereas this exoskeleton is yet to be perfected before hospitals and clinics can benefit from it, other 3D technologies in orthopaedics have already been clearly further developed. Professor Jules Poukens, Belgium, faced the challenge of treating an elderly female patient with chronic inflammatory processes in the lower jaw. Because of her age, he viewed bone-building measures, including its long operating times, critically. His alternative: following three-dimensional measuring, a tailor-made titanium implant emerged. Using powerful lasers, titanium powder was put into a final form using millimetre-scale precision. Before the surgery Poukens also plated his piece of work with bioceramic coatings. British doctors were faced with similar problems. With one patient they had to remove large areas of a patient’s cranial bone. On the basis of various CT scans, they made a 3D reconstruction. The piece of bone itself consisted of polyetherketoneketone (PEKK).

Bone to order

In the future there remains the possibility of using 3D printers to produce implants that can be integrated by the body. In Germany, Cynthia M. Gomes is working at the Federal Institute for Materials Research and Testing (BAM) on ceramic units. Her vision: during the operation, surgeons scan bone defects – and promptly obtain matching implants. Pores make up 60 percent of their material, so that cells can grow into them well. Eventually, the body absorbs the inorganic components. Gomes is confident that in five years the first implants could come into use. At Washington State University professor Amit Bandyopadhyay has put a lot of energy into the three-dimensional printer. His prototype produces ceramic bone substitutes that resemble biological replacement models. Initial tests on rats and rabbits have been successful. It will still take according to his estimate at least ten years before people will benefit from the new technology. Professor Kevin Shakesheff from the University of Nottingham is pursuing a different strategy: he is building artificial bones using a bioprinter. CT scans are used as an information base in order to generate a template. Then the bioprinter applies stem cells. In the body, this base structure is subsequently replaced by the body’s own bone. Shakesheff recently presented his method at the Royal Society’s Annual Summer Science Exhibition in London.

Doctors are coming on board

Whereas engineers have been using three-dimensional scanning and printing processes for some time to create such products, medicine was initially rather skeptical. Meanwhile, working groups around the world have been trying to explore possible applications for patients. For artificial bone and exoskeletons, things look promising. Beyond orthopaedics, laboratories are also working on livers, kidneys and hearts produced by the 3D bioprinter – something with long-term perspectives in view of an increasing demand alongside decreasing willingness to donate organs.

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Medicine, Ortopedics, Research

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