Flexible antibacterial Zr-Cu-N thin films resistant to cracking

Abstract

This study investigates how the Cu concentration in Zr-Cu-N films affects the films' antibacterial capacity and mechanical properties. Zr-Cu-N films were prepared by reactive magnetron sputtering from composed Zr/Cu targets using a dual magnetron in an Ar + N2 mixture. The antibacterial capacity of Zr-Cu-N films was tested on Escherichia coli (E. coli) bacteria. The mechanical properties of Zr-Cu-N films were determined from the load vs. displacement curves measured using a Fisherscope H 100 microhardness tester. The antibacterial capacity was modulated by the amount of Cu added to the Zr-Cu-N film. The mechanical properties were varied based on the energy Ei delivered to the growing film by bombarding ions. It was found that it is possible to form Zr-Cu-N films with Cu concentrations ≥10 at. % that simultaneously exhibit (1) 100% killing efficiency Ek for E. coli bacteria on their surfaces, and (2) (1) high hardness H of about 25 GPa, (2) high ratio H/E* ≥ 0.1, (3) high elastic recovery We ≥ 60% and (4) compressive macrostress (σ < 0). The Zr-Cu-N films with these parameters are flexible/antibacterial films that exhibit enhanced resistance to cracking. This enhanced resistance was tested by (1) bending the Mo and Ti strip coated by sputtered Zr-Cu-N films (bending test) and (2) loading the surface of the Zr-Cu-N sputtered on a Si substrate by a diamond indenter at high loads up to 1 N (indentation test). Physical, mechanical, and antibacterial properties of Zr-Cu-N films are described in detail. In summary, it can be concluded that Zr-Cu-N is a promising new material for creating flexible antibacterial coatings on contact surfaces.

Antimicrobial Nanostructured Coatings: A Gas Phase Deposition and Magnetron Sputtering Perspective

“…Moreover, when such coatings are deposited on flexible substrates, they easily crack and/or delaminate due to the residual stress resulting from the growth mode (for some reviews on thin film growth modes and on the effect on surfaces, see for instance [119,120]). This issue has recently been investigated for antibacterial films prepared by reactive magnetron sputtering for Cr-Cu-O [44,118], Al-Cu-N [44,114] and Zr-Cu-N [121], where the influence of Cu content on the mechanical and bactericidal properties of the film have been measured. The mechanical characteristics measured through Vickers tests were the film hardness H, defined as its resistance to local plastic deformation [122], the elastic recovery We, defined as the fraction of a given deformation of a solid which behaves elastically [123], the Young's modulus E and the effective Young's modulus E* = E(1 − ν 2 ), where ν = Poisson ratio has been obtained by mechanical indentation.…”

“…The Zr-Cu-N coatings exhibit a ratio H/E* ≥ 0.1, a value indicating an enhanced resistance to cracking for all Cu contents ranging from 0 to 19 at.% Cu. [121] Moreover, the hardness H ranging from~25 to~17 GPa is quite high and it makes it possible to prevent the coating from being removed from the surface of a substrate by fretting (wear). The region of Cu content in which the coatings exhibit a killing of the E. coli bacteria of 100% is marked by dashed lines and in light gray, setting the limit for the minimum Cu concentration in such films [121].…”

“…[121] Moreover, the hardness H ranging from~25 to~17 GPa is quite high and it makes it possible to prevent the coating from being removed from the surface of a substrate by fretting (wear). The region of Cu content in which the coatings exhibit a killing of the E. coli bacteria of 100% is marked by dashed lines and in light gray, setting the limit for the minimum Cu concentration in such films [121]. The good mechanical properties obtained for such films have been obtained thanks to a deposition substrate temperature of 450 • C, and this might be a major drawback when the same behavior is needed to form films on flexible substrates that would melt at that temperature.…”

Flexible Antibacterial Coatings

“…For antibacterial coatings, a long lifetime is a key requirement in many practical applications when these coatings are deposited on contact surfaces of rigid or flexible substrates and must simultaneously exhibit two functions: antibacterial and protective. Recently, it has been shown that flexible antibacterial coatings can provide good mechanical protection of substrates [ 34 , 35 , 36 , 37 , 38 ]. The formation of antibacterial coatings with a high efficiency of killing of bacteria that simultaneously demonstrates good mechanical properties is, however, quite a difficult task [ 13 , 24 , 39 , 40 , 41 ].…”

Recent Developments in Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces under Indoor Visible Light

“…The drastic effect of extremely low amounts of Cu released during the bacterial inactivation can be rationalized by the high toxicity of Cu(Cu(I)/Cu(II) species/oxides on the bacteria and cannot be ascribed to any doping of the TiO 2 by Cu, which requires much higher Cu-amounts. Recent developments on flexible antibacterial sputtered coatings have been reported using Cu as a bactericide agent in the composite films [182][183][184].…”