Laser-Assisted Surface Alloying to Enhance Antibacterial Properties and Bone-Cell Mineralization of Titanium Implants

Orthopedic implants are commonly used to improve the patient’s quality of life. Titanium-based alloys are widely employed in surgical implants due to their cytocompatibility and appropriate mechanical properties. However, the most common perspective problem that orthopedists face is implant-associated infection (IAI), which can lead to serious impacts such as the need for complex revision procedures, patient suffering, and even death. These complications that arise from the poor antibacterial property of titanium implants can be addressed by introducing antibacterial components such as silver. While researchers show the application of silver particles as an efficient anti-infection agent for Ti-based orthopedic implants, most of the developed products suffer from complicated and long fabrication/modification techniques, multi-step processing, high cost, unintended alteration in mechanical properties, unstable antibacterial effect, and leaching of the silver ions. Here we offer a simple and fast two-step technique for surface modification of the Ti-based implants using laser-assisted alloying (LAA). In this work, a nanosecond Nd:Yag laser was applied via optimized laser power for alloying of the coated Ag-ink film on the Ti surface. Besides, this prompt laser processing developed a micro/nano roughness on the Ti surface which was beneficial for osseointegration and cell mineralization. The Ti-Ag LAA samples prepared using a range of laser powers (8, 16, 24, 32, and 40 W) were characterized via various techniques. The scanning electron microscopy (SEM) images showed a developed hierarchical micro/nanostructure on the LAA surfaces. Energy-dispersive X-ray mapping and X-ray diffraction (XRD) results demonstrated enhanced oxygen level and Ag-Ti alloying. The Rockwell hardness tests of the Ti-Ag showed preserved bulk hardness of the samples with an average hardness of about 31 ± 1 HRC. This observation revealed a superficial alloying of the laser-assisted method which is essential for the Ti-based implant modification. The optimized Ti-Ag LAA sample (prepared with 32 W laser power) showed over 6-fold enhancement in antibacterial effect compared to the pristine Ti sample. This antibacterial property was shown to be effective on both gram-negative (E. coli) and gram-positive (S. aureus) bacteria during the test period of 12 days. On the other hand, the cell mineralization test showed over 2-fold increase in cell mineralization of the Ti-Ag LAA as compared to the pristine Ti sample which is due to the developed micro/nano features that provide active sites for cell attachment and growth. Moreover, the antibacterial effect of the developed surface helps the natural body cells to succeed in the competition on the implant surface toward the bacterial cell. The long-lasting antibacterial properties of the prepared Ti-Ag LAA samples along with cytotoxicity as low as 5- 10 % originated from the properly anchored Ag inside the Ti structure originated from the efficient laser surface alloying.