Surface Modification of Biomedical Titanium for Bacterial Proliferation Regulation and Characterization with Non-Leaching Mechanisms

生物醫用鈦表面改性及其對細菌生長非浸出性調控的研究

Student thesis: Doctoral Thesis

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Award date19 Jul 2021

Abstract

Surface modification is an efficient method to make a balance between the introduction of new properties to the surface and maintenance of intrinsic performances of the bulk. Titanium is a kind of desirable candidate in the biomedical fields thanks to its appropriate mechanical properties and biocompatibility. However, the titanium surface shows inertness in the interaction with bacteria, which gets in the way of further applications. In this work, surface modification techniques are utilized to treat biomedical titanium. Besides, the behaviors of the modification layers in the co-culture with bacteria were characterized. What’s more, the corresponding mechanisms of these interactions were explored. Specifically, this thesis consists of five parts except for the introduction and conclusion parts.

Firstly, titanium nitride nanowire coating is synthesized by liquid-phase oxidation process and nitridation. On the one hand, the topography of the nanowires can exert mechanical stress on the bacteria, which can inhibit only 70% of bacteria. On the other hand, their capacitive property helped the realization of a higher antibacterial rate after the charging process. The charged samples can not only enhance a closer attachment with negatively charged bacteria and relevant piercing effects, but it can also create a potential difference with bacteria and speed up the bacterial death by triggering the electron transfer.

Secondly, titanium surface is modified via a hydrothermal process and the following magnetron deposition. Gold nanoparticles decorated zinc oxide nanorods were constructed on the substrate surface. Different from conventional ion releasing of Zn2+ and photo-induced ROS production, electron transfer (ET) between bacteria and materials is the main factor for rapid bactericidal effects in a short time under dark conditions. When the bacteria and materials contact directly, the transferred electrons produce a saturation current that varies linearly with the bacteria number, semi-logarithmically, which becomes the basis of counting bacteria quantitatively in real-time. The results reveal the capability of real-time detection of bacteria based on ET and provide information about the antibacterial behavior of ZnO-based materials, especially in the early stage.

Thirdly, titanium surface is modified with Berlin Green (BG) coating. The Berlin Green crystalline layer inactivates both E. coli and S. aureus without light illumination. The bactericidal behaviors depend on the bacterial electron exhaust caused by the electron transfer rather than the ion-releasing process. BG coating is reduced during the antibacterial period with a noticeable color change, which provides the basis for the visual characterization and detection of live bacteria.

In the next section, titanium hydride layer is prepared on the titanium surface via a simple hot phosphorus acid treatment. The hydride coating does not change the microenvironment during bacterial cultivation. While the introduction of hydrogen elements reduces the water contact angle, surface hardness, and elastic modulus of the substrate's surface, which promote the adhesion and proliferation of Gram-negative bacteria such as E. coli and P. aeruginosa.

In addition, vapor phase hydrothermal (VPH) process is introduced to explore the in-situ formation of modification coatings on the Ti surface. Molybdenum disulfide is selected to be the example. Compared to the traditional liquid-phase hydrothermal (LPH) process, the controllable growth of MoS2 nanosheets with distinctive morphology is achieved on the titanium surface. The formation mechanisms are analyzed from the perspective of in situ nucleation in the VPH process versus dissolution-nucleation-coagulation in the LPH process.

In summary, modification layers could be constructed on the biomedical titanium surface through several different methods. The original substrate will be activated in interaction with bacterial cells through the non-leaching process. The works in this thesis demonstrated the possibility of the in-situ modification with different materials systems and the potential of the coatings to regulate the bacterial metabolism positively or negatively. They could provide new insights into the preparation advancement and offer references for the design and multi-functionalization of other materials.