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Researchers from Sungkyunkwan University have developed a handheld 3D printing device that can create biodegradable bone implants directly at the site of an injury.
Led by Professor Jung Seung Lee of Sungkyunkwan University, the approach was tested in rabbits with large bone defects and showed that it provided structural support while also encouraging stronger and more natural bone growth, though adhesion and long-term strength still require improvement.
Much like a glue gun, the device extrudes a warm mixture of polycaprolactone (PCL), a biodegradable polymer, and hydroxyapatite (HA), a mineral found in natural bone. Surgeons can guide the nozzle to fill irregular gaps, and the material quickly hardens into a scaffold that fits the defect.
As described in Device, this scaffold holds the bone in place and gradually breaks down as the body replaces it with new tissue. Unlike prefabricated implants or bone cement, which must be shaped in advance and may not match the defect precisely, the printed material forms directly in place, adapting to the unique geometry of each injury.
Alongside Sungkyunkwan University, the study also included contributions from Harvard Medical School (HMS), Incheon National University (INU), Korea Advanced Institute of Science and Technology (KAIST), Korea University (KU), Massachusetts Institute of Technology (MIT), and Seoul National University (SNU).
Tailoring strength with mineral content
To understand how the composition influenced performance, the researchers varied the amount of HA in the mix. Increasing HA made the scaffolds stronger and slower to degrade, while also stimulating bone-forming cells.
In laboratory experiments, human stem cells grown on HA-rich scaffolds deposited more calcium and showed significantly higher expression of genes linked to bone growth, such as osteopontin and osteocalcin, compared with scaffolds without HA. These findings suggested that the material could do more than fill space, actively supporting the process of regeneration.
Testing also focused on how well the material could withstand physical stress. The printed scaffolds endured physiologically relevant pressures and remained stable under simulated cyclic loading, such as those created by walking, without breaking down.
Because infection is one of the most common reasons for implant failure, the researchers explored whether the scaffolds could also deliver antibiotics. By mixing gentamicin or vancomycin into the material, they created implants that released the drugs slowly over several weeks.
When tested against bacteria, gentamicin-loaded scaffolds prevented the growth of Escherichia coli (E. coli) and Staphylococcus aureus. Against E. coli, the zone of inhibition measured 38.8 ± 3.4 mm for gentamicin-loaded scaffolds, nearly three times larger than the 14.0 ± 0.9 mm seen with vancomycin-loaded scaffolds, showing that the implants could help protect against complications during healing. Similarly for S. aureus, only gentamicin-loaded scaffolds were effective, producing an inhibition zone of 22.63 ± 0.75 mm, while vancomycin showed little to no activity.
The approach was then evaluated in rabbits with femoral defects about 1 cm long, which are too large to heal naturally. Some animals received printed scaffolds while others were treated with commercial bone cement. After 12 weeks, both groups showed integration with surrounding bone, but the outcomes differed.
Rabbits treated with printed scaffolds developed denser tissue and more organized collagen structures. Imaging confirmed that bone volume and surface area were significantly higher in the printed group compared to the cement group. Mechanical stability was also enhanced, with measures such as the polar moment of inertia and radius of gyration also higher in the printed group.
Importantly, the implants did not trigger abnormal inflammation or tissue damage.
Although the scaffolds did not completely heal the defects within three months, they showed clear advantages by combining strength, biodegradability, and biological activity. Adjusting the ratio of PCL and HA allows the material to be tailored for different needs, and adding antibiotics offers protection against infection.
The authors note that improvements in adhesion, printing precision, and larger animal studies are still required, but the findings point to a future where surgeons could use a portable printer in the operating room to create implants directly inside damaged bone, providing stability while guiding natural repair.
3D printing in bone generation
Bone implants have advanced with 3D printing, allowing patient-specific designs that promote natural regeneration while reducing surgeries, complications and costs, and using biocompatible materials that safely degrade over time.
In partnership with Maastricht University Medical Centre (UMC+) Osteopore created a bioresorbable implant designed to prevent lower leg amputations. Using Osteopore’s 3D printing technology combined with CT imaging, the team produced a personalized cage-like scaffold made from FDA-approved polycaprolactone (PCL).
The material mimics the structure of trabecular bone and gradually degrades into water and carbon dioxide, all while encouraging new bone to form. This implant was reportedly placed in a patient in the Netherlands, where early results were said to be encouraging.
Elsewhere at the University of New South Wales (UNSW), Associate Professor Kristopher Kilian and Dr. Iman Roohani developed a technique to 3D print bone-like structures containing living cells. Using a ceramic-based ink, they were able to print directly into damaged areas at room temperature, which made it possible to support cartilage and bone repair while also creating new opportunities for tissue engineering, disease modeling, and drug testing.
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Featured image shows preparation of PCL/HA composites and their application in a printing device. Image via Sungkyunkwan University.
