Surface analysis and electrochemical characterization on micro-patterns of biomedical Nitinol after nanosecond laser irradiating

Highlights

• Three novel micro-patterns on Nitinol were fabricated with nanosecond laser.

• Detailed and comprehensive surface characterizations were conducted.

• The wettability and anti-corrosion of micro-patterns were respectively investigated.

• Interface corrosion behavior between micro-pattern and simulated body fluid solution was studied.

Abstract

In the present work, micro-pattern surfaces of Nitinol after a novel nanosecond laser irradiating were accurately and efficiently characterized. Fruitful 2D/3D images illustrate surface topography and roughness of micro/nanostructures. Energy dispersive spectrometer and X-ray photoelectron spectrometry was utilized to reveal surface compositions. Most importantly, the results of electrochemical corrosion experiments present the donuts-like micro-pattern surface performs the best anti-corrosion performance compared with other samples. All of the preliminary results clearly demonstrate the effects of nanosecond laser micro-processing on the surface state and the resultant corrosion behavior of Nitinol. The findings would provide a potential path way to simultaneously improve the corrosion resistance and biocompatibility of biomedical alloys by laser one-step manufacturing.

Introduction

The combination of shape memory effects, superelasticity and apparent biocompatibility makes Nitinol especially suitable for the biomedical industry, where in devices such as dental wires, intravascular stents, orthopedic implants and other surgical supplies are manufactured [1]. Usually, the materials surface performs a pivotal position to interact with the human micro-environment or injured tissues once biomaterials are implanted into the human body. Therefore, it is necessary to improve the relevant properties of biomaterials surface including Nitinol.

Surface functionalization of metals has become increasingly popular in recent years. This technology is applied to nickel-titanium alloy directly leading to significant improvement of its surface properties. For biomedical applications, surface functionalization of NiTi alloys may promote surface biocompatibility and enhance the stability and durability of materials, meanwhile, may also produce anti-bacterial, anti-friction and corrosion resistant properties, etc. [2]. Various methods have been developed to fabricate functional metal surface, such as coatings [3,4], sandblasting [5], acid treatment [6], electrochemical methods [7] and laser texturing technology [[8], [9], [10]].

Among these manufacturing methods, laser processing has attracted a great deal of attention due to its briefness, rapidness and effectiveness. Many investigations have concentrated on laser processing of Nitinol. Liang et al. improved the biocompatibility of NiTi alloy by femtosecond laser inducing micro-patterns [11]. Wang et al. enhanced the bioactivity of Ti under SBF solution by femtosecond laser ablation [12]. Kosuke Nozaki et al. created hierarchical periodic micro/nano-structures on Nitinol and investigated the influence of micro/nanostructures on endothelialization and anti-thrombosis [13]. Chan et al. investigated the responses of mesenchymal stem cell on shape memory NiTi alloy after laser treatment [14]. C.H. Ng et al. produced TiN on NiTi by laser nitriding for improving surface wear resistance [15].

In summary, considerable attention has been paid to laser-processed biomedical Nitinol surface. Moreover, it is worth noting that a key feature of these literatures is micro-patterns have been created on Nitinol for improving surface biocompatibility. Indeed, topography (including micro-patterns/micro/nanostructures) plays a key role in surface properties of materials. By using laser processing, various micro-patterns can be constructed on surface, and further produce various functions such as superhydrophilicity, optical absorbance and enhanced biocompatibility. In the field of biomedicine, topography can be manufactured for promoting mechanical locking force between cell and materials. During laser one-step scanning, a variety of researches only pay attention to the improvement of cell compatibility, but rarely pay attention to that the generation of surface patterns that will, to a certain extent, affect the corrosion resistance of materials.

Hence, in the current study, we designed and manufactured three novel surface micro-patterns on NiTi alloys. Afterwards, electrochemical characterization and surface analysis were conducted. Through comparison, it can be obtained and analyzed that the generation of micro-patterns affects surface wettability and corrosion resistance. And the interface corrosion behavior between micro-patterns and simulated body fluid (SBF) solution was correspondingly analyzed. This paper was aimed to understand the interfacial reaction between surface micro/nanostructures (laser one-step preparation) and SBF solution. In the meantime, this study provides a solid foundation for the simultaneous improvement of biocompatibility and corrosion resistance of biomaterials.