New laser surface modification process with silver provides antimicrobial defense to titanium orthopedic devices

Process to create nanostructures on implant surfaces also enhances bone cells’ attachment

WEST LAFAYETTE, Ind. – A patent-pending process developed by Purdue University engineers could improve the quality of life for the more than 6 million people who undergo orthopedic and trauma surgery annually, according to a paper published in Langmuir: The ACS Journal of Fundamental Interface Science.

Infection is a major complication when rods, plates, screws and other devices are embedded into people during procedures like joint replacement surgery and spinal fusion surgery. Most infections occur because the devices’ titanium implant surfaces have poor antibacterial and osteoinductive properties; osteoinduction is the process that prompts bone formation.

Rahim Rahimi, a Purdue University assistant professor in the School of Materials Engineering, has created a process that immobilizes silver onto the implant surfaces of titanium orthopedic devices to improve antibacterial properties and cellular integration. The process can be implemented onto many currently utilized metal implant surfaces.

The antibacterial efficacy of laser-nanotextured titanium surfaces with laser-immobilized silver was tested against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The surfaces were observed to have efficient and stable antimicrobial properties for more than six days. The laser-nanotextured titanium surfaces also provided a 2.5-fold increase in osseointegration properties as compared to the pristine titanium implant surface.

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

“These unique characteristics will allow improving implant outcomes, including less risk of infection and fewer complications like device failure.”

Rahimi said the traditional method to address infections caused by implanted orthopedic devices often utilizes antibiotics or other surface modifications that have their own associated complications.

“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.”

Rahimi disclosed the innovation to the Purdue Research Foundation Office of Technology Commercialization, which has applied for a patent on the intellectual property. Industry partners seeking to further develop this innovation should contact Patrick Finnerty, pwfinnerty@prf.org, about reference number 2022-RAHI-69768.

Rahimi said the next steps to develop the laser process to texturize and immobilize silver onto orthopedic devices are to implement it onto standard orthopedic fixtures, validate the technology to get approval from the U.S. Food and Drug Administration, and license it to companies working in the orthopedic sector.

Rahimi’s research was funded by Purdue’s School of Materials Engineering.

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About Purdue Research Foundation Office of Technology Commercialization

The Purdue Research Foundation Office of Technology Commercialization operates one of the most comprehensive technology transfer programs among leading research universities in the U.S. Services provided by this office support the economic development initiatives of Purdue University and benefit the university’s academic activities through commercializing, licensing and protecting Purdue intellectual property. In fiscal year 2021, the office reported 159 deals finalized with 236 technologies signed, 394 disclosures received and 187 issued U.S. patents. The office is managed by the Purdue Research Foundation, which received the 2019 Innovation and Economic Prosperity Universities Award for Place from the Association of Public and Land-grant Universities. In 2020, IPWatchdog Institute ranked Purdue third nationally in startup creation and in the top 20 for patents. The Purdue Research Foundation is a private, nonprofit foundation created to advance the mission of Purdue University. Contact otcip@prf.org for more information.

Writer: Steve Martin, sgmartin@prf.org

Source: Rahim Rahimi, rrahimi@purdue.edu

ABSTRACT

Laser-Assisted Nanotexturing and Silver Immobilization on Titanium Implant Surfaces to Enhance Bone Cell Mineralization and Antimicrobial Properties

Vidhya Selvamani, Sachin Kadian, David A. Detwiler, Amin Zareei, Ian Woodhouse, Zhimin Qi, Samuel Peana, Alejandro M. Alcaraz, Haiyan Wang, Rahim Rahimi

Despite the great advancement and wide use of Titanium (Ti) and Ti-based alloys in different orthopedic implants, device-related infections remain the major complication in modern orthopedic and trauma surgery. Most of these infections are often caused by both poor antibacterial and osteoinductive properties of the implant surface. Here, we have demonstrated a facile two-step laser nanotexturing and immobilization of silver onto the titanium implants to improve both cellular integration and antibacterial properties of Ti surfaces. The required threshold laser processing power for effective nanotexturing and osseointegration was systematically determined by the level of osteoblast cells mineralized on the laser nanotextured Ti (LN-Ti) surfaces using a Neodymium-doped yttrium aluminum garnet laser (Nd-YAG, wavelength of 1.06 μm). Laser processing powers above 24 W resulted in the formation of hierarchical nanoporous structures (average pore 190 nm) on the Ti surface with a 2.5-fold increase in osseointegration as compared to the pristine Ti surface. Immobilization of silver nanoparticles onto the LN-Ti surface was conducted by dip coating in an aqueous silver ionic solution and subsequently converted to silver nanoparticles (AgNPs) by using a low power laser-assisted photocatalytic reduction process. Structural and surface morphology analysis via XRD and SEM revealed a uniform distribution of Ag and the formation of an AgTi-alloy interface on the Ti surface. The antibacterial efficacy of the LN-Ti with laser immobilized silver (LN-Ti/LI-Ag) was tested against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The LN-Ti/LI-Ag surface was observed to have efficient and stable antimicrobial properties for over 6 days. In addition, it was found that the LN-Ti/LI-Ag maintained a cytocompatibility and bone cell mineralization property similar to the LN-Ti surface. The differential toxicity of the LN-Ti/LI-Ag between bacterial and cellular species qualifies this approach as a promising candidate for novel rapid surface modification of biomedical metal implants.