Copper-containing glass ceramic with high antimicrobial efficacy

Abstract

Hospital acquired infections (HAIs) and the emergence of antibiotic resistant strains are major threats to human health. Copper is well known for its high antimicrobial efficacy, including the ability to kill superbugs and the notorious ESKAPE group of pathogens. We sought a material that maintains the antimicrobial efficacy of copper while minimizing the downsides - cost, appearance and metallic properties - that limit application. Here we describe a copper-glass ceramic powder as an additive for antimicrobial surfaces; its mechanism is based on the controlled release of copper (I) ions (Cu¹⁺) from cuprite nanocrystals that form in situ in the water labile phase of the biphasic glass ceramic. Latex paints containing copper-glass ceramic powder exhibit ≥99.9% reduction in S. aureus, P. aeruginosa, K. aerogenes and E. Coli colony counts when evaluated by the US EPA test method for efficacy of copper-alloy surfaces as sanitizer, approaching that of benchmark metallic copper.

Fig. 1

Structures of two model glass compositions by molecular dynamics simulations a Model glass with composition of 60SiO₂−20Al₂O₃−20Cu₂O (in mol%). The model shows a tightly packed glass network structure surrounding small, high-field strength copper (I) ions. b Model glass with composition of 60SiO₂−20Al₂O₃−20K₂O (in mol%). The model reveals a more open glass network structure surrounding larger, lower-field strength K⁺ ions. The high oxygen packing density of glass networks formed around small radius, high ionic field strength modifier ions (as in a) reduces the capability for ion exchange with charged water species

Fig. 2

Scanning electron microscope (SEM)  images of copper–glass ceramic cross-section before and after exposure to water a Cross-section of the copper–glass ceramic shown prior to water exposure reveals a continuous glassy phase, a discontinuous glassy phase, and a cuprite crystalline phase trapped in the discontinuous phase. Inset is X-ray diffraction (XRD) data collected on copper–glass ceramic powder which shows that the crystalline species present is cuprite. b Cross-section of the copper–glass ceramic shows the formation of cavities following water exposure (~120 min) due to dissolution of the discontinuous glassy phase that lead to the release of cuprite crystals into solution

Fig. 3

Elemental mapping of chemical species in microstructure of copper–glass ceramic Energy-dispersive X-ray spectroscopy (EDS) using a scanning transmission electron microscope was used for elemental mapping. a A microstructural view of the copper–glass ceramic highlighting the three phases present. Some smaller cuprite crystals are also observed in the continuous phase. b EDS elemental mapping shows that the high durability, continuous matrix phase is enriched in silicon, the lower durability, discontinuous phase in enriched in phosphorous, and the crystals are composed of copper. c EDS elemental mapping also reveals that the lower durability phase is enriched in potassium. Although boron is a major element in the composition, it was not included in the analysis due to the difficulty of measuring light elements via EDS

Fig. 4

Bacterial reduction kinetics on paint coupons containing copper glass ceramic particles. Plot of S. aureus reduction as a function of exposure time shows a steady decrease in S. aureus colony counts over 2.5 h, at which point bacterial colonies reduced down to limit of detection. EPA-prescribed 3-log kill (99.9% reduction) was observed in about 1 h. Data and error bars represent mean and standard deviation from two experiments with samples in triplicate. The inset table showcases the high bactericidal efficacy of copper–glass ceramic particles against S. aureus, P. aeruginosa, E. coli and K. aerogenes. ≥4-log kill (≥99.99% reduction) was measured against all bacteria following 2-h exposure to test coupons. Bacterial growth on each test and control coupon was measured in triplicate—data shown are geometric mean of values

Fig. 5

Efficacy of copper–glass ceramic particles after simulated wear. Plot of antimicrobial potency following washing and abrasion that illustrates longevity of copper–glass ceramic particles. Test paint coatings maintain bactericidal efficacy (>99.9%) even after 4 years of simulated wear (“Methods”). Each wear cycle represents 4× washing and abrasion every month. Log reduction calculations are differences in S. aureus colony counts between control and test coupons (both subjected to wear cycles). Data and error bars represent mean and standard deviation from n = 2 replicates