Ti6Al4V (TC4) titanium alloy is widely used in orthopedic and cardiovascular implant fields, but it suffers from critical limitations, such as poor osseointegration, high propensity for thrombosis upon blood contact, and elevated risk of bacterial infection post-surgery. To address these challenges, the work aims to carry out surface modification on TC4 titanium alloy to improve its biocompatibility and endow it with efficient antibacterial properties.
TC4 titanium alloy surfaces were ground with sandpaper and ultrasonically cleaned in acetone and ethanol to ensure surface purity. After alkaline pretreatment of the TC4 surface, dopamine (PDA) and copper ions (Cu2+) were sequentially introduced for surface functionalization, resulting in the fabrication of the TC4/PDA-Cu composite. Notably, the composite achieved synergistic and controllable antibacterial activity through photothermal regulation.
A series of characterization and evaluation methods were employed to systematically analyze the composite. Scanning electron microscopy (SEM) was used to observe the surface microstructure and morphological characteristics of the composite. Fourier transform infrared spectroscopy (FTIR) was applied to identify the surface functional groups. Inductively coupled plasma mass spectrometry (ICP-MS) was utilized to determine the release concentration of copper ions. A contact angle measuring instrument was employed to assess the hydrophilicity of the composite. Additionally, the photothermal performance and stability of the composite were evaluated under irradiation with an 808 nm near-infrared (NIR) laser. The antibacterial properties and underlying mechanisms were verified with E. coli and S. aureus, while osteoblast cells (MC3T3-E1) were used to evaluate the biocompatibility of the TC4/PDA-Cu composite under NIR irradiation (TC4/PDA-Cu+NIR group).
The experimental results indicated that the TC4/PDA-Cu composite exhibited a stable surface microstructure, with PDA and Cu2+ successfully and firmly immobilized on the TC4 surface. The Cu2+ loading amount was measured to be 16 μg/cm2, and its release profile presented a typical "initial burst release followed by sustained slow release" pattern, while the cumulative release of Cu2+ remained within the biosafety range. Compared with pristine TC4, the water contact angle of TC4/PDA-Cu decreased to 48°, indicating a significant enhancement in surface hydrophilicity. This improved hydrophilicity was favorable for protein adsorption and subsequent cell adhesion. Under irradiation with an 808 nm laser, the interaction between PDA and Cu2+ generated a prominent thermionic effect, raising the surface temperature of TC4/PDA-Cu to 56 ℃ within 4 min, which demonstrated excellent photothermal performance and stability. The plate counting method and bacterial live/dead staining assay confirmed that the TC4/PDA-Cu+NIR system achieved highly efficient antibacterial activity against both E. coli and S. aureus, with an antibacterial rate of up to 97.3%. This robust antibacterial effect was primarily attributed to the synergistic action of the photothermal effect and reactive oxygen species (ROS) generated by the composite. Cell experiment results showed that the cell proliferation rate in the TC4/PDA-Cu+NIR group increased progressively with the prolonged culture time. Moreover, osteoblasts adhered tightly to the implant surface and extended numerous pseudopodia, indicating good cellular compatibility. This favorable cellular response was mainly ascribed to two factors: firstly, the hydrophilic nature of PDA promoted the adsorption of extracellular matrix proteins, thereby facilitating cell adhesion, proliferation, and differentiation; secondly, copper ions upregulated the expression of osteogenesis-related genes, which further enhanced osteogenic differentiation. Collectively, these results confirmed that the TC4/PDA-Cu composite exhibited excellent biocompatibility.
In conclusion, this work provides experimental basis and theoretical support for the development of medical titanium alloy implants with controllable antibacterial activity, low toxicity, and excellent biocompatibility, which is expected to promote the clinical translation of multifunctional biomaterials in the field of implantology.
Key words
Ti6Al4V titanium alloy /
surface modification /
photothermal property /
antibacterial activity /
biocompatibility
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Funding
Shanxi Province Basic Research Program (Free Exploration Category) Youth Project (202303021222264); Shanxi Province Higher Education Science and Technology Innovation Project (2023L318); Jinzhong University Research Funds for Doctor (JUD2023014); Jinzhong University Technology Innovation Team Research Project (jzxyjscxtd202416)
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