Abstract
New TiNb-based alloys, such as Ti–6Al–7Nb, are currently being studied around the world as an alternative to other Ti alloys, e.g., instead of Ti–6Al–4V. We conducted a pilot study where thin (approximately 1.2 micron) CaP coatings containing low doses of Zn2+ (0.4–0.8 wt.%) were prepared by the radio frequency magnetron sputtering (RFMS) of Zn-hydroxyapatite (HA) target on Ti–6Al–4V and Ti–6Al–7Nb substrates and investigated their physicochemical properties, in vitro solubility, cytotoxicity, and antibacterial and osteogenic activities. The thickness of the obtained coatings was approximately 1.2–1.3 microns. Zn substitution did not result in roughness or structural or surface changes in the amorphous CaP coatings. The distributions of Ca, P, and Zn were homogeneous across the film thickness as shown by the EDX mapping of these elements. Zn doping of CaP coatings on both types of Ti-based alloys statistically influenced the results of the scratch-test. However, obtained values are satisfactory to use Zn-CaP coatings on biomedical implants. Increased Zn2+ release vs. tapered output of Ca and phosphate ions occurred during 5 weeks of an in vitro immersion test in 0.9% NaCl solution. Ti–6Al–7Nb alloy, unlike Ti–6Al–4V, promoted more linear biodegradation of CaP coatings in vitro. As a result, CaP-based surfaces on Ti–6Al–7Nb, compared with on Ti–6Al–4V alloy, augmented the total areas of Alizarin red staining in a 21-day culture of human adipose-derived mesenchymal stem cells in a statistically significant manner. Moreover, Zn–CaP coatings statistically reduced leukemic Jurkat T cell survival within 48 h of in vitro culture. Along with the higher solubility of the Zn–CaP surface, a greater reduction (4- to 5.5-fold) in Staphylococcus aureus growth was observed in vitro when 7-day extracts of the coatings were added into the microbial culture. Hence, Zn–CaP-coated Ti–6Al–7Nb alloy with controllable biodegradation as prepared by RFMS is a prospective material suitable for bone applications in cases where there is a risk of bacterial contamination with severe consequences, for example, in leukemic patients. Further research is needed to closely investigate the mechanical features and pathways of their solubility and antimicrobial, antitumor, and osteogenic activities.
Highlights
One of the main research directions of modern medical materials science is in the field of new materials for use in the treatment of bone fractures and defects [1]
We describe a method for producing thin calcium phosphate (CaP) coatings containing low doses of Zn doped by radio frequency magnetron sputtering (RFMS) of Zn-HA target on Ti–6Al–4V alloy and a novel Ti–6Al–7Nb substrate and study their physicochemical properties, in vitro solubility, cytotoxicity, and antibacterial and osteogenic activities as a first approximation
The surface morphology of the coatings deposited from Zn-HA did not differ significantly from CaP surface deposited from stoichiometric HA
Summary
One of the main research directions of modern medical materials science is in the field of new materials for use in the treatment of bone fractures and defects [1]. Due to their excellent mechanical properties, metallic materials are widely used in many clinical cases [2]. Among many other metallic materials, titanium (Ti)-based alloys are primarily used due to their low weight, good fatigue properties, toughness, and biological inertness. The most commonly used alloy was Ti–6Al–4V (grade 5). Some studies show that Ti–6Al–4V can release toxic elements, such as vanadium, during a prolonged post-surgery period [3]. New Ti-based alloys have been introduced, including Ti–6Al–7Nb, Ti–13Nb–13Zr, and Ti–12Mo–6Zr [4]
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