Characterization and Evaluation of Submicron Femtosecond Laser-Induced Periodic Surface Structures on Titanium to Improve Osseointegration of Dental and Orthopaedic Implants

Abstract

Surface properties such as topography and wettability play a pivotal role in controlling the cellular behavior on dental and orthopaedic implants and eventually their clinical success. The implementation of more advanced cell-targeted surface modification approaches has opened up additional possibilities for improving osseointegration to further increase the success rate of bone implants. In this thesis, the potential of employing femtosecond laser-induced periodic surface structures with submicron spatial periodicities of 300 nm, 600 nm and 760 nm on titanium to improve osseointegration of dental and orthopaedic implants was explored. Uniform submicron femtosecond laser-induced periodic surface structures with consistent periodicity, roughness and oxide thickness were generated over large areas (10 x 10 mm^2) on titanium substrates and characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), electron energy loss spectroscopy (EELS), and Auger electron microscopy (AES). In vitro experiments using osteosarcoma Saos-2 cells showed the same level of cell metabolism on the laser textured and unmodified (control) surfaces along with statistically significant alkaline phosphatase activity after 14 days of cell seeding for the laser patterned surface with periodicity of 620 nm compared to the control surface. Average circularity along with nuclear area factor of cells fixed onto the laser textured and unmodified titanium surfaces were acquired from SEM images using ImageJ. The lower circularity and higher nuclear area factor of cells was observed on all laser textured surfaces as compared to the control, and are indicative of healthier cells on the laser textured surfaces. The cells appeared to align perpendicularly to the periodic laser generated structures and showed a more elongated shape on laser patterned surfaces as compared with the control surface, with the cell’s filopodia appearing to be attached to the peaks of the laser-textured pattern. In the second part of the thesis, the mechanism underlying the wettability transition from superhydrophilic to superhydrophobic on femtosecond laser generated periodic surface structures on titanium was investigated. The time-dependent wettability of the laser treated surfaces was assessed by the sessile drop method. The samples exhibited superhydrophilic behavior immediately after laser texturing and became superhydrophobic over time. Detailed surface chemical analyses by X-ray photoelectron spectroscopy revealed that the unique electronic structures of Ti2O3 and TiO2, which resulted in hydrophilic and hydrophobic hydration structures, respectively, played a crucial role in the observed wettability transition. This study demonstrates the prospect of using femtosecond laser-induced periodic surface structures as a promising surface modification strategy to potentially manipulate cellular behavior and improve dental and orthopaedic implants’ clinical success rate.