As a nurse in Denmark, Casper Slots got used to seeing the pain that ill-fitting artificial bone implants caused in patients. Some were left in permanent discomfort, or had their faces disfigured by “one size fits all” models.
In 2012, he enrolled in a masters course in medical technology and welfare, where he met Martin B Jensen. They began work on a better solution, and in 2017 founded Particle3D, a startup with a single mission: printing bone.
Customised implants generally use non-degradable materials such as polymer or titanium that don’t behave like organic matter. In their research, Slots and Jensen found a material that would not only replace damaged bone, but encourage new bone to grow back. “I would like to help patients and push for not using foreign materials anymore,” says Slots. “We’re using something that could be part of the patient.”
At their laboratory in Odense, the company has a 3D printer with a nozzle specially crafted for the job. It uses “bio-ink” made from tricalcium phosphate (TCP) – a material that has been used in reconstruction for 30 years, but normally comes in blocks that surgeons have to manually carve into implants for patients.
Particle3D’s method is far more accurate: surgeons use computer models to create a customised implant for a patient, which is printed at the Particle3D lab. The finished product is then sent back to the hospital, ready for surgery.
Combining TCP with 3D printing means that the implants are far less dense than usual – so they not only function to replace bone, but actually fuse with it. They are designed to degrade, allowing new bone to grow. In trials on pigs and mice, new bone marrow and blood vessels developed in the implants after eight weeks. “We are just making a scaffold that uses the unique power of the human body to regenerate itself,” says Slots. “Maybe within a couple of years you will have your full bone back.”
To prevent infection, some companies coat their polymer and titanium implants with antibiotics, but these are active for only a few days after surgery. Because Particle3D’s implants degrade like real bone, medicines can be stored within the fatty acids of the material, allowing a slower, prolonged release.
CEO Thea Wulff Olesen says she hopes to see the product being used in humans from 2022. At first the implants are likely to be used to fill in gaps where the stability of the bone is not affected, in the face and jaw. As David Hamilton, a research fellow in orthopaedics at the University of Edinburgh, says: “If you’re dealing with issues in the lower limbs, then the loading tolerances become really important.”
Load tests show that the material’s compressive strength is only one twentieth of the average human thigh bone. To ensure stability in such a load-bearing bone, Slots suspects that titanium plates would need to be added.
Researchers are currently looking at “scaffold plates” printed from Particle3D bio-ink to test how they react with human cells. Olesen hopes that approval from the US and European regulators will follow. “I think that a lot of people will really benefit,” she says.
Maria Mellor is a writer for WIRED. She tweets from @Maria_mellor
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