A pen-like 3D printer for orthopedic surgeons could help address the increasingly problematic global issues of antimicrobial resistance and bacterial bone infections specific to medical implants.

Researchers introduced their unique use of the portable, handheld device in a study published March 8 in Acta Biomaterialia. They modified a commercially available 3D-printing pen to print biomaterials as scaffolds directly into a bone defect or fracture, and said that dosing the 3D-printed scaffolds with zinc oxide made them resistant to infections.

"We used zinc oxide, which is very well known to be antibacterial, and some have demonstrated that it is also antiviral," said coauthor Ali Tamayol, an assistant professor at the University of Nebraska's Department of Mechanical and Materials Engineering.

The engineered nanoparticles were shown to effectively inhibit the growth of Methicillin-resistant Staphylococcus, a type of bacteria resistant to several antibiotics, on the surface of the 3D-printed scaffolds when compared with a control group of scaffolds that were not dosed with zinc oxide.

Examinations of the potential of 3D-printing implant devices to inhibit bacterial growth have increased in recent years, and the new study is an example of how regenerative medicine can benefit from 3D printing, particularly in pen form. 3D-printing pens have been around since the early 2010s.

The latest results arrive amid a growing global public health emergency of antimicrobial resistance. The World Health Organization declared antimicrobial resistance as one of the top 10 global public health threats facing humanity and has issued a global action plan for an integrated approach to combating it.

The portable 3D printer is the size and weight of a normal pen and as easy to use as medical instruments such as scalpels. By lending itself to flexible designs, it can be quickly modified as needed to meet patient needs depending on their condition; for example, to be bigger or smaller. 

The project was driven by interactions that researchers had with caregivers and clinicians who explained concerns with conventional regenerative treatments, Tamayol and coauthor Adnan Memic, a professor at King Abdulaziz University in Saudi Arabia, told The Academic Times. 

They spoke about adverse outcomes in treating bone defects and fractures. These require two surgeries, at minimum, in addition to the high rate of surgical revisions associated with bone implants. Bone defects can be caused by trauma, tumor or infection, including the increasingly prevalent osteomyelitis bone infection, which was assessed as part of the project. 

The study comes on the heels of another that revealed a new bone cell type dubbed osteomorphs, which could advance thinking on skeletal disease therapy, as others looked to improve metallic alloys for medical implants through 3D printing. Producing biomaterials using eggshell membranes to help with bone regeneration was recently touted, also. 

Traumatic injuries and tumor removal usually lead to bone defects that tend to require medical intervention, with a small window for action that creates urgency to prevent morbidity and mortality. Trauma-related injuries are the third-leading cause of death in the U.S., according to the Centers for Disease Control and Prevention. 

But current implant designs hamper infection control. In this light, some researchers take issue with current strategies in regenerative orthopedics, such as the two most common types of bone graft, auto and allografts, the former of which uses bone from inside the patient's own body and the latter, bone from a donor.

In the study, researchers opted for polycaprolactone, a biodegradable polyester with a low melting point of around 60 degrees Celsius, to design the materials that would then form 3D-printed scaffolds.

"Temperature was important," Tamayol said. That's because if the temperature of the implant is too high, it could damage surrounding tissue, a complication in procedures for reconstructing bone defects. 

"So, we went through iterations of 3D printers to ensure that the material when touching the tissue isn't warm or hot," Tamayol continued. "And the version that we eventually used is a low-melting-temperature device, so you can even print on the back of your hand without even sensing it." 

The paper checked multiple boxes addressing a variety of persisting challenges in treating bone defects. The 3D-printed scaffolds promote infection control and prevention, as they can immediately address the affected site, Memic and Tamayol further noted. The scaffolds also showed improved biocompatibility and adhesion to the bone, even in wet conditions.  

Memic added that the researchers plan to pursue additional studies using the 3D bioprinter. 

"If we want to compete with the other technologies more head-on, I'm sure that we can think about making filaments that are going to be almost patient-specific," Memic said.  

The study, "In situ printing of scaffolds for reconstruction of bone defects," published March 8 in Acta Biomaterialia, was authored by Ali Tamayol, University of Nebraska-Lincoln and University of Connecticut; Azadeh Mostafavi, Carina S. Russell, Tyrell J. Williams and Seth Harris, University of Nebraska-Lincoln; Tuerdimaimaiti Abudula, Numan Salah, Ahmed Alshahrie and Adnan Memic, King Abdulaziz University; Ebrahim Mostafavi and Thomas J. Webster, Northeastern University; Seyed Masoud Moosavi Basri, American University of Sharjah; and Yogendra K. Mishra, University of Southern Denmark.