Impact of Femtosecond Laser Treatment Accompanied with Anodization of Titanium Alloy on Fibroblast Cell Growth

Abstract

Herein, Ti6Al4V alloy is surface modified by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples (laser‐induced periodic surface structures). To make the surface hydrophilic, anodization is performed resulting in further smoothness of microstructure and a final thickness of 35 ± 4 nm is estimated for oxide produced after anodization at 10 V (scan rate = 0.1 V s−1) versus standard hydrogen electrode. The obtained electrochemically active surface area (ECSA) is approximately 8 times larger compared with flat mirror polished Ti6Al4V surface. Combined chemical analysis by Pourbaix diagram and X‐ray photoelectron spectroscopy (XPS) analyses reveal that titanium and aluminum are passivating into TiO2 and Al2O3, but the dissolution of aluminum in the form of solvated ion is inevitable. Finally, cell seeding experiments on anodized and laser‐treated titanium alloy samples show that the growth of murine fibroblast cells is significantly suppressed due to unique surface texture of the laser‐treated and anodized titanium alloy sample.

Repellent rings at titanium cylinders against overgrowth by fibroblasts

“…Oxidized Ti surfaces are well known for their colorful appearance, which is often used for medical implants to guide the users. The brownish color of the regions (3) in Figure 6 can be attributed to oxide-layer thickness in the order of 100 nm [15,16]. The effective thickness of the oxide-layer in femtosecondlaser and anodized area (4) is probably considerably larger [17], considering that the irradiation process takes place in air environment with a combination of (i) high energy deposited by the laser that increases strongly the sample surface temperature and (ii) an increase of the effective surface induced by the topography inherent of the spike structures.…”

Quo Vadis LIPSS?—Recent and Future Trends on Laser-Induced Periodic Surface Structures

“… Combined processing strategies: Currently, several research groups are exploring the combination of LIPSS with additional surface treatment techniques—either “in situ” during the laser processing, or “ex situ” after the laser-processing. Examples are: (i) combined laser processing strategies (such as in situ double-pulse treatments [ 20 , 73 , 74 ] or ex situ LIPSS + DLIP, see Section 3.3 ), or a two-step laser processing of microstructures (e.g., lines, grids, or more complex microfluidic channels) patterned additionally with nanostructures (LIPSS) [ 59 , 75 ]; (ii) the combination of LIPSS processing with thermal heat during [ 76 , 77 ] or after [ 78 , 79 ] laser irradiation; (iii) electrochemical post-processing, such as anodization [ 67 , 80 ]; or (iv) ion beam post-processing for altering the electrical conductivity [ 81 ]. Improved regularity of LIPSS through surface overlayers: On dielectrics, the generation of large surface areas covered homogeneously with LIPSS is often very difficult when the single photon energy is significantly smaller than the band gap energy, i.e., when nonlinear absorption is required to couple the laser beam energy with the solid.…”

Femtosecond Laser-Processing of Pre-Anodized Ti-Based Bone Implants for Cell-Repellent Functionalization

“…Both treatments, anodization and femtosecond laser-processing, lead to a considerable increase of the native oxide layer on Ti-based materials, resulting in layers with a thickness in the order of 100 nm [10,11,16]. However, the characteristic of both oxides is different.…”

“…The anodization leads to much denser oxides with less defects, while the oxide layers induced by the femtosecond laser-processing in air results in more porous not perfect layers. For this reason, it is possible to further oxidize laser-processed areas by anodization, as described by Lone et al in [10]. On the other hand, the femtosecond laser-processing results in material removal and structural and topographical reorganization of the surface on a 10 to 15 µm scale.…”

“…Here, the exact geometry of the combined microstructures and nanostructures seems to be of great relevance, as adherent cells can grow well on certain nanostructured materials, which can even be used as functional substrates [8,9]. Another important feature for the cellsubstrate interaction is the oxide layer on top of the Ti or Ti alloy, which can be thickened in a controlled manner by electrochemical anodization [10]. This treatment is applied to many Ti-based medical implants due to the chemical inertness, corrosion resistance, and mechanical stability of the resulting layers and also due to the colorful appearance of these layers, which are often employed for marking and decoration purposes [11].…”