Effect of superhydrophobicity/superhydrophilicity of titanium surface on hemocompatibility

• ¹ Colorado State University, Mechanical Engineering, United States
• ² Colorado State University, School of Biomedical Engineering, United States

Introduction: Titanium has been commonly used for implantable devices due to its excellent biocompatibility with many different tissues in the body^[1]. However, in contact of the blood, occurrence of the incidents such as platelet and leukocyte adhesion and activation leads to further thrombosis and sometimes failure of these implants^[2][3]. It is well known that the functionality of the platelets can be modulated by the chemistry and the texture of the surfaces^[4][5]. To the best of our knowledge, there are very few studies that have been investigated the effect of superhydrophobicity/superhydrophilicty on surface hemocompatibility. Superhydrophobic surfaces are extremely repellent to water (contact angle for water is greater than 150˚) and water droplets easily roll off from such surfaces. Superhydrophilic surfaces are completely wet by water (contact angle for water is less than 10˚) and the wetting is almost instantaneous. In this study, we have developed surfaces with different nanotextures that were modified with fluorinated silane and PEG silane to make them superhydrophobic and superhydrophilic, respectively. The surfaces were characterized using contact angle goniometry and X-ray photoelectron spectroscopy (XPS) and platelet adhesion and activation was investigated using fluorescence microscopy and scanning electron microscopy (SEM).

Methods and Materials: In this study, as the two different textured surfaces, titania nanotubes and titania nanoflowers were used. Un-textured titanium with native oxide surface was used as control. Titania nanotubes were fabricated by an anodization technique, and titania nanoflowers were fabricated by a chemical etching method. The textured and un-textured surfaces were modified with fluorinated silane and PEG silane to create superhydrophobic and superhydrophilic surfaces, respectively. The surface wettability and chemical composition were investigated by contact angle measurements with both water and plasma, and XPS analysis respectively. The platelets adhesion/activation were investigated by incubation the samples in the whole blood plasma for 2hrs and imaging the cells.

Results and Discussion: For un-textured surfaces, the results indicate that the fluorinated and PEGylated treatments leads to a significant decrease in the number of adhered platelets and platelets activation in compare to the unmodified surface.

For the titania nanotubes, there are less adhered and activated platelets in the fluorinated surfaces that are in the Cassie-Baxter^[6] state (a composite liquid-air-solid interface) of wettability in comparison to the unmodified and the PEGylated surfaces that are in the Wenzel^[7] state (complete wetting). For the fluorinated titania nanoflowers, although the most parts of the surface is in the Cassie-Baxter state, the locally micro-Wenzel parts result in higher number of adhered platelets as compared to the fluorinated titania nanotubes.

Conclusion: In the current study, a hemocompatibility was investigated for textured surfaces that were either superhydrophoic or superhydrophilic. By comparing the platelet adhesion and activation, it can be concluded that hemocompatibility of the fluorinated and PEGylated un-textured surface is significantly better than the unmodified one. Furthermore, fluorinated titania nanotubes are completely in Cassie-Baxter wettability state resulting in lower number of platelets adhesion and activation.

References:
[1] Farrell, Brad J., et al. "Effects of pore size, implantation time, and nano‐surface properties on rat skin ingrowth into percutaneous porous titanium implants." Journal of Biomedical Materials Research Part A 102.5 (2014): 1305-1315.
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[4] Smith, Barbara S., and Ketul C. Popat. "Titania nanotube arrays as interfaces for blood-contacting implantable devices: a study evaluating the nanotopography-associated activation and expression of blood plasma components." Journal of biomedical nanotechnology 8.4 (2012): 642-658.
[5] Sun, Taolei, et al. "No platelet can adhere—largely improved blood compatibility on nanostructured superhydrophobic surfaces." Small 1.10 (2005): 959-963.
[6] Cassie, A. B. D., and S. Baxter. "Wettability of porous surfaces." Transactions of the Faraday Society 40 (1944): 546-551.
[7] Wenzel, Robert N. "Resistance of solid surfaces to wetting by water." Industrial & Engineering Chemistry 28.8 (1936): 988-994.