Abstract
Titanium and Ti-based alloys are widely applied in the orthopedic implants due to their qualified biocompatibility, mechanical properties, corrosion resistance and so on. However, the elastic modulus of commercial pure Ti (cp-Ti, ~105 GPa) and Ti-6Al-4V (Ti64, ~112 GPa) are still far larger than that of real bone (4-40 GPa), which easily causes stress-shielding effect and subsequently leads to the bone or implant failure. To avoid this problem, Ti-28Nb-11Ta-8Zr alloy (TNTZ) with a low elastic modulus (49 GPa) is utilized in this study to meet the bone-mimetic condition with improved biocompatibility and corrosion resistance in the environment of simulated body fluid, Hank’s solution. Additionally, to mimic bone extracellular matrix (ECM), the nano-sized porous structure for sturdy cell interlocks was carried out by anodic oxidation (AO). The as-prepared amorphous nanoporous oxides exhibit the characteristics of highly adhesive coatings, chemical inertness and rough surface morphology to serve as the study platform. Concerning with infection issues before and after the surgery, we also proposed an antibacterial agent, Ag nanoparticles (AgNPs), incorporated into the cavities of oxide coatings to assist in surgery success and rapid healing rate. Firstly, the mechanical properties of TNTZ were evaluated by measuring Young’s modulus, impact strength, yield and tensile strength. Subsequently, material characteristics of Nanoporous TNTZ oxide coatings (NPTNTZO) with AgNPs were analyzed, including surface morphologies by scanning electron microscopy (SEM) and chemical compositions by X-ray photoelectron spectroscopy (XPS). Thirdly, potentiodynamic polarization method was conducted to test corrosion resistance of TNTZ and AO TNTZ coatings, compared with that of cp-Ti. Finally, in-vitro bacteria tests were practiced to observe the antimicrobial efficacy of as-prepared NPTNTZO/ AgNPs and in-vitro cell tests were utilized to determine the cell viability and proliferation. Experimental results indicated that TNTZ possesses lower elastic modulus (49 GPa) than cp-Ti and T64 implants and it still remains high impact strength, yield strength and tensile strength compared with other commonly used bone metals, like stainless steels. Besides, TNTZ and its oxide coatings also improve corrosion resistance compared with titanium and titania coatings. In aspect of surface modification through anodization, different applied voltages can lead to different pore diameters. During the osteoblast culture, size effect is obvious that smaller diameter (<30 nm) is beneficial for cell proliferation and larger diameter (>70 nm) gives the opposite results. Here we chose 65 nm nanopores as reservoir to store AgNPs to precede in-vitro bacteria tests and osteoblast culture, which still maintained certain degrees of cell proliferation and viability (MTT assay and Live/Dead Staining). As for antibacterial tests, qualitative Kirby-Bauer test, inhibited zone observation, reveals that NPTNTZO/ AgNPs effectively inactivate both gram-negative bacteria strains (Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa)) and gram-positive bacteria (Staphylococcus aereus (S. aereus) and Methicillin-resistant Staphylococcus aureus (MRSA)). Quantitative test of antibacterial efficiency was presented by growth curve of P. aeruginosa and MRSA. The efficiency at least reaches 24h and 12h respectively in such a strict environment (high volume of bacteria solution). The final MTT assay and Live/Dead Staining show that silver-containing samples (NPTNTZO/ AgNPs) have little cytotoxicity on osteoblast culture under 2.5 mM silver concentration. This study successfully investigates the comprehensive evaluations of material characteristics, in vitro antibacterial tests and cellular activities on the bases of β-Ti-28Nb-11Ta-8Zr bone implant.