Surface analysis and electrochemical characterization on micro-patterns of biomedical Nitinol after nanosecond laser irradiating
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.
Section snippets
Nanosecond laser system
Biomedical Nitinol sheets (Ti-55.72wt.%Ni) with the size of 100 mm × 100 mm × 2 mm and negligible roughness were treated with a semiconductor-pumped solid-state DPSS nanosecond (ns) laser system. The specific framework of laser system is shown in Fig. 1. The laser beam with energy was transported to beam expander and then delivered through mirror to galvanometer. Finally, the laser beam was focused on materials by f-theta lens. Computer controlled the output of laser beam and the scanning
Surface morphology and roughness
In order to explain the formation of surface micro-patterns, it is necessary to strictly analyze the interaction mechanism of nanosecond lasers and materials. In case of the duration of laser pulse is on the order of nanosecond pulses, there would be the processes of material melting and ablation. It is worth mentioning that the energy density distribution of the Gaussian beam exhibits uneven spatial distribution. And the energy density of the laser determines the specific impact of the two
Conclusions
In conclusion, three micro-patterns (including DLS, HLS and BLS) were manufactured on biomedical Nitinol after ns laser scanning. The LSCM measurement shows that the appearance of the surface micro/nanostructures also brings a certain degree of roughness, of which the HLS surface is the roughest. EDS mapping analysis proves the generation of oxidation. The WCA results demonstrate that micro-pattern surfaces produce different wetting properties. It is worth noting that DLS surface exhibits best
CRediT authorship contribution statement
Zeqin Cui:Investigation, Funding acquisition, Supervision, Writing - original draft.Shang Li:Investigation, Writing - original draft, Methodology, Visualization.Jun Zhou:Supervision, Investigation.Zhihao Ma:Visualization, Investigation.Wei Zhang:Methodology.Yuancheng Li:Methodology.Peng Dong:Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by National Natural Science Foundation of China (No. 51675365) and the Basic Application Research Project of Shanxi Province (No. 201701D221138).
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