3D–printed implants shown to help grow ‘real bone’

Modeled after the bone pieces they are meant to help replace, the implants were assembled onsite using three-dimensional robotic printing, a technology that uses a fine-point print head to push out a gel-like ink material.

The material is printed onto a platform, and the printer repeats the process until two-dimensional layers stack up into a three-dimensional object, which is then superheated into its final ceramic form. Available for more than a decade, the technology has only of late been applied in medicine to print out replacement ears, skin, and heart valves.

“Our three-dimensional scaffold represents the best implant in development because of its ability to regenerate real bone,” said study senior investigator and biomedical engineer Paulo G. Coelho, DDS, PhD.

“Our latest study results move us closer to clinical trials and potential bone implants for children living with skull deformations since birth, as well as for veterans seeking to repair damaged limbs,” added Dr. Coelho, who is the Dr. Leonard I. Linkow Professor at NYU Dentistry and a professor of plastic surgery at NYU School of Medicine.

The scientists say their novel ceramics more closely resemble real bone shape and composition than other experimental bone implants in which plastic elasticisers are added to make the implant flex. Although the ability to flex offers some advantages, the plastic does not have the same healing ability as the NYU scaffold.

An important feature of the ceramic devices is that they are made of beta tricalcium phosphate, a compound of the same chemicals found in natural bone that makes the implants resorbable.

One of the secrets to the rapid growth of native bone with the NYU devices is a coating of dipyridamole, a blood thinner shown in other experiments to speed up bone formation by more than 50%.

The chemical also attracts bone stem cells, which spur the formation of nourishing blood vessels and bone marrow within the newly grown bone. These soft tissues, researchers say, lend to their scaffold-grown bone the same flexibility as natural bone.

“Dipyridamole has proven to be key to the implant’s success,” said study co-investigator Bruce N. Cronstein, MD, the Dr. Paul R. Esserman Professor of Medicine at NYU School of Medicine, who perfected the drug’s use during device testing.

Used for more than a half-century to prevent blood clots and treat stroke, dipyridamole has a long-standing safety record, said Dr. Cronstein, who also serves as the director of the Clinical and Translational Science Institute, and chief of the Division of Translational Medicine at NYU Langone Health.

“And because the implant is gradually resorbed, the drug is released a little at a time and locally into the bone, not into the whole body, thereby minimising risks of abnormal bone growth, bleeding, or other side effects.”

In the latest experiments, researchers used the test scaffolds to repair small holes surgically made in the skulls of mice and missing bone pieces as long as 1.2cm in rabbit limbs and jaws.

The scientists found that on average 77% of each scaffold was resorbed by the mammal’s body 6 months after implantation. They also found that new bone grows into the lattice-like structural supports of the scaffold, which then dissolves.

Some CT scans of the implant sites showed almost no trace of beta tricalcium phosphate, the three-dimensional–printed material of which the original implants were made.

Subsequent weight-bearing tests showed that the new bone was of equivalent strength as original, undamaged bone. The investigators say their next studies will test the scaffolds, for which they have a patent pending, in larger animals. They caution that clinical trials are still several years away.