Laser Surface Modification Aims to Reduce Infection from Implants

To help prevent infections caused by orthopedic implants, Purdue University researchers developed a laser-assisted surface modification process that may improve the efficacy of the implanted device.

Most ortho device-related infections occur because the surface of the implant has poor antibacterial and osteo-inductive properties. The laser-assisted process immobilizes silver onto the titanium surfaces of the device that have been laser-nanotextured to boost bone cell mineralization and the antimicrobial properties of the device.

“The first step of the two-step process creates a hierarchical nanostructure onto the titanium implant surface to enhance the bone cells’ attachment,” professor Rahim Rahimi said. “The second step immobilizes silver with antibacterial properties onto the titanium implant surface.”

The researchers determined the threshold laser processing power required for effective nanotexturing and osseointegration using the level of osteoblast cells mineralized on the laser-nanotextured titanium surface. They used a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with a wavelength of 1.06 μm.

Titanium orthopedic screws shown with and without antimicrobial silver nanoparticle coatings. Inset shows an electron microscopy image of the nanoparticle coating applied using a laser-assisted immobilization process. Courtesy of Rahim Rahimi.

The immobilization of silver nanoparticles onto the laser-nanotextured titanium surface was achieved by an initial dip coating in an aqueous silver ionic solution, followed by a low-power, laser-assisted photocatalytic reduction process to allow the conversion to silver nanoparticles.

The researchers performed a structural and surface morphology analysis using x-ray diffraction and scanning electron microscopy. The analysis revealed a uniform distribution of silver and the formation of a silver-titanium-alloy interface on the titanium surface.

The antibacterial efficacy of the laser-nanotextured titanium surface with laser-immobilized silver was tested against both gram-positive and gram-negative bacteria. The titanium surface was found to maintain efficient, stable antimicrobial properties for more than six days.

The researchers further found that laser processing powers above 24 W resulted in the formation of hierarchical nanoporous structures on the titanium surface, with a 2.5-fold increase in osseointegration, compared to the pristine titanium implant surface.

“The technology allows us to not only immobilize antibacterial silver compounds onto the surface of the titanium implants, but also provide a unique surface nanotexturing that allows better settle attachment mineralization,” Rahimi said.

Infections caused by implanted orthopedic devices are typically addressed through antibiotics or other surface modifications. These approaches invite complications, according to Rahimi.

“Long-term antibacterial protection is not possible with these traditional drug coatings because a large portion of the loaded drug is released in a short time,” Rahimi said. “There also is often a mixture of microbes that are found in implant-associated infection; it is essential to choose a bactericidal agent that covers a broad spectrum.”

The next steps for Rahimi and his team will be to implement the laser-assisted process and validate the efficacy of the technology on standard orthopedic devices. After that, the team plans to seek FDA approval for the technology and license it to companies working in the orthopedic sector. The Purdue Research Foundation Office of Technology Commercialization has applied for a patent on the laser-assisted nanotexturing and silver immobilization technology.

The process to immobilize silver onto the implant surfaces of titanium orthopedic devices, to improve antibacterial properties and cellular integration, can be implemented onto many of the metal implant surfaces that are currently in use. According to Rahimi, the technique’s “unique characteristics will allow improving implant outcomes, including less risk of infection and fewer complications like device failure.”

The research was published in Langmuir: The ACS Journal of Fundamental Interface Science (www.pubs.acs.org/doi/full/10.1021/acs.langmuir.2c00008).