Korean 3D ‘glue gun’ prints custom bone repairs directly onto fractures

By Stephen Beech

A new 3D printing “glue gun” can generate bone grafts directly onto fractures.

The revolutionary device has already been tested in animals.

Now, researchers in South Korea are preparing for human trials.

They developed a tool made from a modified glue gun that can 3D print bone grafts directly onto fractures and defects during surgery.

It has already been tested in rabbits to quickly create complex bone implants without the need to make them in advance.

The researchers "optimized" the 3D-printed grafts for high structural flexibility, release of anti-inflammatory antibiotics, and promotion of natural bone regrowth at the grafting site.

Bone implants have previously been made of metal, donor bone, or even more recently, 3D-printed material.

But in cases involving more complex fractures, the implants must be designed and produced prior to surgery to allow for appropriate fitting.

Study co-author Professor Jung Seung Lee, of Sungkyunkwan University, said: “Our proposed technology offers a distinct approach by developing an in situ printing system that enables a real-time fabrication and application of a scaffold directly at the surgical site.

“This allows for highly accurate anatomical matching even in irregular or complex defects without the need for preoperative preparation such as imaging, modelling, and trimming processes.”

He explained that the material fed into the glue gun is a filament comprised of two major components: a feature of natural bone known to promote healing called hydroxyapatite (HA) and a biocompatible thermoplastic called polycaprolactone (PCL).

PCL can liquify in temperatures as low as 60 °C, which, when applied with a heat-modified glue gun, is cool enough to prevent tissue damage during surgical application while being able to conform to the jagged grooves of fractured bone.

By adjusting the proportion of HA to PCL within the filament, the researchers can customize the hardness and strength of the grafts to fit different anatomical needs.

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Lee said, “Because the device is compact and manually operated, the surgeon can adjust the printing direction, angle, and depth during the procedure in real time.

“Also, we demonstrated that this process could be completed in a matter of minutes.

"This highlights a significant advantage in terms of reducing operative time and improving procedural efficiency under real surgical conditions.”

Since infection is a common concern with surgical implants, the researchers incorporated vancomycin and gentamicin, two anti-bacterial compounds, into the filament.

The research, published in the journal Device, showed, in both petri dish culture and liquid medium, the filament scaffold successfully inhibited the growth of E. coli and S. aureas, two common bacteria prone to cause post-surgery infections.

Due to the physical properties of HA and PCL within the filament, the drugs are released slowly and are able to diffuse directly onto the surgical site over several weeks.

Lee said: "This localized delivery approach offers meaningful clinical advantages over systemic antibiotic administration by potentially reducing side effects and limiting the development of antibiotic resistance, while still effectively protecting against postoperative infection."

As a proof of concept, the device was tested on severe femoral bone fractures in rabbits.

Within 12 weeks of surgery, the team found no signs of infection or necrosis and greater bone regeneration when compared to rabbits grafted with bone cement - a sealing compound commonly used for treating defects.

Lee said: “The scaffold was designed not only to integrate biologically with surrounding bone tissue but also to gradually degrade over time and be replaced by newly formed bone.

“The results showed that the printing group exhibited superior outcomes in key structural parameters such as bone surface area, cortical thickness, and polar moment of inertia, suggesting more effective bone healing and integration.”

The researchers have now set their sights on optimising the anti-bacterial potential of the scaffold further and preparing the procedure for human trials.

Lee said: “Clinical adoption will require standardised manufacturing processes, validated sterilisation protocols, and preclinical studies in large animal models to meet regulatory approval standards."

Lee added: “If these steps are successfully achieved, we envision this approach becoming a practical and immediate solution for bone repair directly in the operating room.”