Enhanced in vitro immersion behavior and antibacterial activity of NiTi orthopedic biomaterial by HAp-Nb2O5 composite deposits

Abstract

NiTi is a class of metallic biomaterials, benefit from superelastic behavior, high biocompatibility, and favorable mechanical properties close to that of bone. However, the Ni ion leaching, poor bioactivity, and antibacterial activity limit its clinical applications. In this study, HAp-Nb₂O₅ composite layers were PC electrodeposited from aqueous electrolytes containing different concentrations of the Nb₂O₅ particles, i.e., 0-1 g/L, to evaluate the influence of the applied surface engineering strategy on in vitro immersion behavior, Ni²⁺ ion leaching level, and antibacterial activity of the bare NiTi. Surface characteristics of the electrodeposited layers were analyzed using SEM, TEM, XPS, and AFM. The immersion behavior of the samples was comprehensively investigated through SBF and long-term PBS soaking. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) infective reference bacteria were employed to address the antibacterial activity of the samples. The results illustrated that the included particles led to more compact and smoother layers. Unlike bare NiTi, composite layers stimulated apatite formation upon immersion in both SBF and PBS media. The concentration of the released Ni²⁺ ion from the composite layer, containing 0.50 g/L Nb₂O₅ was ≈ 60% less than that of bare NiTi within 30 days of immersion in the corrosive PBS solution. The Nb₂O₅-reinforced layers exhibited high anti-adhesive activity against both types of pathogenic bacteria. The hybrid metallic-ceramic system comprising HAp-Nb₂O₅-coated NiTi offers the prospect of a potential solution for clinical challenges facing the orthopedic application of NiTi.

Figure 1

The surface morphology of the electroplated coatings: (a) HANb0, (b) HANb1, (c) HANb2, and (d) HANb3.

Figure 2

Bright-field TEM micrographs of (a) HANb0 and (b) HANb2 layers. Scale bars are 200 nm.

Figure 3

XPS survey spectra of outermost layer of the electrodeposited coatings.

Figure 4

Representative high-resolution XPS spectra of Ca 2p, P 2p, O 1s, and Nb 3d regions for sample HANb3.

Figure 5

3D topographic AFM micrographs of the electrodeposits: (a) HANb0, (b) HANb1, (c) HANb2, and (d) HANb3.

Figure 6

The contact angle values of the studied samples. The measurements were carried out using PBS drop.

Figure 7

FESEM micrographs of the bare and coated samples after soaking in SBF for 7 days: (a) NiTi, (b) HANb0, (c) HANb1, (d) HANb2, and (e) HANb3.

Figure 8

Mass change of the coatings after 7 days of immersion in SBF.

Figure 9

The FESEM images of the specimens soaked in PBS for 30 days: (a,b) NiTi, (c,d) HANb0, (e,f) HANb1, (g,h) HANb2, and (i,j) HANb3.

Figure 10

XRD patterns of the electrodeposited layers upon immersion in PBS for 30 days.

Figure 11

Concentration of the: (a) released Ni²⁺ (**p < 0.0001 with respect to bare NiTi) and (b) Ca²⁺ ions (*p = 0.0001 and **p < 0.0001 with respect to HANb0) upon 30 of immersion in PBS at 37 °C. The windowed images at top right corner show the total concentration of the corresponding ion after 30 days.

Figure 12

The quantitative results of plate-counting assay against both E. coli and S. aureus bacteria (*p < 0.0001 with respect to bare NiTi), and optical images of the formed (b) E. coli and (c) S. aureus bacterial colonies on agar plates.

Figure 13

(a) MTT results of the antibacterial activity of HANb0 and HANb2 layers against planktonic adherent E. coli and S. aureus; E. coli bacteria morphology on (b) HANb0 and (c) HANb2; and S. aureus bacteria morphology on (d) HANb0 and (e) HANb2.