Science Advisory Board and Copper Research

Supported by leading researchers in the fields of polymer science, nanotechnology, and "contact-killing."

Dr. Ávila-Orta

Carlos Alberto Ávila Orta, PhD

PhD in Polymer Technology (CIQA, 2001) and postdoctoral fellow the State University of New York (Stony Brook, 2002-2004). National researcher SNI level II since 2013. CIQA employee since 2004, currently Principal Investigator Level C. Chair of the Department of Advanced Materials (2007-2014, 2017-to date), A Schulman/Polynnova for Sabbatical leave (2014-2015). Professor of the MSc and PhD program in Polymer Technology (CIQA), member of the ACS from 2004 to 2010 and the MRS from 2010 to date. Among the lines of research is the preparation of polymeric nanocomposites (semicrystalline polymers/metallic nanoparticles, carbon, graphene, among others) and their physical and chemical characterization, aimed at their application in the automotive industry, food packaging, health care, textiles and in the area of semiconductor materials.

Other important data: Currently there 90+ scientific publications with more than 2100 citations, h index 26, more than 50 papers at international conferences, 3 book chapters, 30+ national patent applications, 1 patent granted in Mexico, China and Japan; also in the training of human resources with 6 undergraduate, 2 specialty, 9 master's and 14 doctoral students. He has participated as technical manager in the direction of more than 10 scientific projects approved by the private initiative and government agencies, among which stand out those supported by the Ministry of Economy, the Secretariat of Public Education, the Energy Secretariat, the European Union, Innovate UK through CONACYT.

Selected Research Papers

Synthesis of Copper Nanoparticles by Thermal Decomposition and Their Antimicrobial Properties (65 citations)

Abstract: Copper nanoparticles were synthesized by thermal decomposition using copper chloride, sodium oleate, and phenyl ether as solvent agents. The formation of nanoparticles was evidenced by the X-ray diffraction and transmission electron microscopy. The peaks in the XRD pattern correspond to the standard values of the face centered cubic (fcc) structure of metallic copper and no peaks of other impurity crystalline phases were detected. TEM analysis showed spherical nanoparticles with sizes in the range of 4 to 18 nm. The antibacterial properties of copper nanoparticles were evaluated in vitro against strains of Staphylococcus aureus and Pseudomonas aeruginosa. The antibacterial activity of copper nanoparticles synthesized by thermal decomposition showed significant inhibitory effect against these highly multidrug-resistant bacterial strains.

Enhanced Antibacterial Activity of Melt Processed Poly(propylene) Ag and Cu Nanocomposites by Argon Plasma Treatment (26 citations)

Abstract: Argon surface plasma treatment (APT) of poly(propylene)/silver (PP/Ag) and poly(propylene)/copper (PP/Cu) nanocomposite improves their antibacterial properties against pathogenic bacteria. Dispersions of PP/Ag and PP/Cu nanocomposites were prepared by sonication assisted melt mixing 0.05, 0.5, and 5 w/w% metal nanoparticle/polymer compositions, and then melt casted to form films that were surface treated with argon plasma. Scanning electron and atomic force microscopy showed that APT increase the surface roughness and the exposed nanoparticles. Also, APT produced implanted oxygen and nitrogen species as demonstrated by XPS analysis and enhanced the surface wettability. Antibacterial activity (AA) against S. aureus and P. aeruginosa of the plasma treated NC films was significantly increased in all conditions tested such as NP loading and interaction time; copper NCs were more effective than silver NCs. Surface activation of the PP/Ag and PP/Cu NC films by APT is a viable technique to increase the antibacterial activity of nanocomposites, an important issue in medical and health care applications.

 

Dr. Nagarajan


 Selected Research Papers

Enhanced bioactivity of ZnO nanoparticles—an antimicrobial study (1099 citations)

Abstract: In this study, we investigate the antibacterial activity of ZnO nanoparticles with various particle sizes. ZnO was prepared by the base hydrolysis of zinc acetate in a 2-propanol medium and also by a precipitation method using Zn(NO3)2 and NaOH. The products were characterized by x-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. Bacteriological tests such as minimum inhibitory concentration (MIC) and disk diffusion were performed in Luria-Bertani and nutrient agar media on solid agar plates and in liquid broth systems using different concentrations of ZnO by a standard microbial method for the first time. Our bacteriological study showed the enhanced biocidal activity of ZnO nanoparticles compared with bulk ZnO in repeated experiments. This demonstrated that the bactericidal efficacy of ZnO nanoparticles increases with decreasing particle size. It is proposed that both the abrasiveness and the surface oxygen species of ZnO nanoparticles promote the biocidal properties of ZnO nanoparticles.

Understanding the pathway of antibacterial activity of copper oxide nanoparticles (151 citations)

Abstract: This work investigates the role of oxidation state in the antibacterial activity of copper oxide nanoparticles (NPs). The findings add strong support to a contact killing mechanism of copper oxides (CuO and Cu2O) through which bacteria initially suffer severe damage to the cell envelope. Then further damage ensues by an independent pathway of each copper oxide nanoparticle. Formation of copper(I)–peptide complex from cuprous oxide (Cu2O) and free radical generation from cupric oxide (CuO) were identified as key sources of toxicity towards E.coli. Cu2O rapidly inactivated Fumarase A, an iron sulphur cluster enzyme suggesting the cuprous state of copper binding to the proteins. This inactivation was not noticed in CuO. The percentage of biocidal/bacteriostatic activity is closely related to the oxidation state of the copper oxides. In the case of E.coli, Cu2O nanoparticles showed more efficient antibacterial activity and higher affinity to the bacterial cells. CuO nanoparticles produced significant ROS in terms of super oxides while Cu2O did not. The diminishing defective emission peaks of Cu2O after incubation with microbes strongly suggest the formation of protein complexes. This work is carried out to enable better understanding of the mechanistic pathways of copper oxide nanoparticles.

 Dr. Palza

Toward Tailor‐Made Biocide Materials Based on Poly(propylene)/Copper Nanoparticles (105 citations)

Abstract: A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X‐ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.

Antimicrobial Polymers with Metal Nanoparticles (388 citations)

Abstract: Metals, such as copper and silver, can be extremely toxic to bacteria at exceptionally low concentrations. Because of this biocidal activity, metals have been widely used as antimicrobial agents in a multitude of applications related with agriculture, healthcare, and the industry in general. Unlike other antimicrobial agents, metals are stable under conditions currently found in the industry allowing their use as additives. Today these metal based additives are found as: particles, ions absorbed/exchanged in different carriers, salts, hybrid structures, etc. One recent route to further extend the antimicrobial applications of these metals is by their incorporation as nanoparticles into polymer matrices. These polymer/metal nanocomposites can be prepared by several routes such as in situ synthesis of the nanoparticle within a hydrogel or direct addition of the metal nanofiller into a thermoplastic matrix. The objective of the present review is to show examples of polymer/metal composites designed to have antimicrobial activities, with a special focus on copper and silver metal nanoparticles and their mechanisms.

Robert McLean, PhD

Bio: I have over 36 years’ experience (30 years as an independent PI) working with various aspects of bacterial biofilms. In addition, I became interested in polymicrobial interactions within biofilms and other microbial communities particularly since 2007. During my training and early career in Canada, my focus was on urinary biofilm infections due to Proteus mirabilis including a study involving deposition of thin metal coatings on catheter materials to reduce biofilm growth. Since moving to Texas State in 1993, I shifted my research focus to understanding the basic biology of biofilm formation. While our graduate program here is predominately at the MS level until recently, my students and I have made some notable finds, including the first description of quorum-signaling in natural (1997) and clinically relevant (1998) biofilms, the first description of the essential role of rpoS in biofilms (1999), and the first illustration of biofilm formation in microgravity (2001). In 2007, I shifted my primary research focus to the study of mixed culture interactions, as this field represented an important yet largely unknown aspect of microbiology. Currently, we are studying the growth and disinfectant susceptibility of biofilms under microgravity conditions. Throughout my academic career, I have been privileged to work with a number of outstanding students and collaborators.

Antibacterial activity of multilayer silver-copper surface films on catheter material. (127 Citations)

The antimicrobial activity of Ag, Cu, and layered Ag-Cu surface films, sputter-coated onto several types of catheter material, against clinical isolates of Staphylococcus epidermidis and Staphylococcus aureus was evaluated. When 20 microL of a suspension of S. epidermidis or S. aureus (2.68 x 10(6) colony-forming units/mL) was applied onto Ag-Cu- or Cu-coated butyl rubber, bacterial numbers were greatly reduced within 10 h, and eliminated within 24 h. In contrast, antibacterial activity was significantly less on uncoated or Ag-coated surfaces. Ag-Cu- or Cu-coated silicon rubber, polyvinylchloride, and teflon were even more effective than Ag-Cu- or Cu-coated butyl rubber. Ag-Cu layered surface films also showed antibacterial activity against Pseudomonas aeruginosa biofilm formation. Multiple metal surface film combinations show great promise in lowering the incidence of device-associated nosocomial infections.

Additional Research:

Synthesis and Antimicrobial Activity of Copper Nanomaterials

Abstract: Bioactive copper nanomaterials are an emerging class of nano-antimicrobials providing complimentary effects and characteristics, as compared to other nano-sized metals, such as silver or zinc oxide nanoparticles. In this chapter, copper nano-antimicrobials are reviewed and classified firstly as a function of the preparation methods, and secondly as a function of the target microorganism used for testing their antimicrobial activity. The antimicrobial activity of copper-based nanostructures depends on the microbial species and on the experimental set-up. As a consequence, in this chapter details are provided on methods, as well as on experimental details such as contact time, microorganism strain, concentration of the interacting species, etc. Finally, real-life applications of copper-based nanoantimicrobials are briefly discussed.

Copper-polymer nanocomposites: An excellent and cost-effective biocide for use on antibacterial surfaces

Abstract: The development of polymer nanocomposites with antimicrobial properties has been a key factor for controlling or inhibiting the growth of microorganisms and preventing foodborne diseases and nosocomial infections. Commercially available antibacterial products based on silver-polymer are the most widely used despite the fact that copper is considerably less expensive. The incorporation of copper nanoparticles as antibacterial agents in polymeric matrices to generate copper-polymer nanocomposites have presented excellent results in inhibiting the growth of a broad spectrum of microorganisms. The potential applications in food packaging, medical devices, textiles and pharmaceuticals and water treatment have generated an increasing number of investigations on preparing copper based nanocomposites and alternative polymeric matrices, as potential hosts of nano-modifiers. This review presents a comprehensive compilation of previous published work on the subject, mainly related to the antimicrobial activity of copper polymer nanocomposites. Within all the phenomenology associated to antibacterial effects we highlight the possible mechanisms of action. We discuss the differences in the susceptibility of Gram negative and positive bacteria to the antibacterial activity of nanocomposites, and influencing factors. As well, the main applications of copper polymer-metal nanocomposites are described, considering their physical and chemical characteristics. Finally, some commercially available copper-polymer nanocomposites are described.

Nanomaterial with High Antimicrobial Efficacy—Copper/Polyaniline Nanocomposite

Abstract: This study explores different mechanisms of antimicrobial action by designing hybrid nanomaterials that provide a new approach in the fight against resistant microbes. Here, we present a cheap copper–polyaniline (Cu–PANI) nanocomposite material with enhanced antimicrobial properties, prepared by simple in situ polymerization method, when polymer and metal nanoparticles are produced simultaneously. The copper nanoparticles (CuNPs) are uniformly dispersed in the polymer and have a narrow size distribution (dav = 6 nm). We found that CuNPs and PANI act synergistically against three strains, Escherichia coliStaphylococcus aureus, and Candida albicans, and resulting nanocomposite exhibits higher antimicrobial activity than any component acting alone. Before using the colony counting method to quantify its time and concentration antimicrobial activity, different techniques (UV–visible spectroscopy, transmission electron microscopy, scanning electron microscope, field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrophotometry, and inductively coupled plasma optical emission spectrometry) were used to identify the optical, structural, and chemical aspects of the formed Cu–PANI nanocomposite. The antimicrobial activity of this nanocomposite shows that the microbial growth has been fully inhibited; moreover, some of the tested microbes were killed. Atomic force microscopy revealed dramatic changes in morphology of tested cells due to disruption of their cell wall integrity after incubation with Cu–PANI nanocomposite.

Long-term antimicrobial polyamide 6/silver-nanocomposites

Abstract: Elemental silver nanoparticles were generated in polyamide 6 (PA6) by the thermal reduction of silver ions during the melt processing of a PA6/silver acetate mixture. The silver ion release from PA6 filled with 2 wt% nanosilver obeys a zero-order rate law for at least 100 days. During this time about 17 μg silver per day, per litre immersion liquid and per cm2 sample surface are released. The PA6/Ag-nanocomposite was shown to be active against Escherichia coli whereas the pure PA6 did not show any antimicrobial efficacy. Immersion of a nanocomposite containing 2 wt% silver in water for 100 days does not reduce its antimicrobial efficacy against Escherichia coli. Thus PA6 filled with 2 wt% nanosilver is an effective antimicrobial material for long-term applications.

Kinetic aspects of the silver ion release from antimicrobial polyamide/silver nanocomposites

Abstract: Spherical silver nanoparticles were grown in situ in different polyamides by a thermal reduction of silver acetate during melt processing of the polymers. Most of the particles have a diameter of about 20 nm. The absolute amount as well as the kinetics of the silver ion release from the various polyamide/silver nanocomposites differ strongly, although the filler content in all materials is the same (1.5 wt. %) and the morphologies of the silver particles are not very different. One result of the investigations was that the absolute amount of the long-term silver ion release increases exponentially with the maximum water absorption of the polymers used as matrix materials, because silver ions are formed from elemental silver particles in the presence of water, only. Moreover, it was also found that the long-term silver ion release increases with a growing diffusion coefficient of water in the polymer. The water absorption properties of the polymers govern the kinetics of the silver ion release, too: for strong hydrophilic polyamides like PA6 or PA6.6, which are plasticized by water, the silver ion release is a zero-order process. For nanocomposites with less hydrophilic polyamides like a cycloaliphatic polyamide or a P12 modified with polytetrahydrofurane (PA12-poly-THF), the silver ion release is governed by diffusion. As expected from the efficacy of the silver ion release, PA6, PA6.6, PA12 and PA12 modified with polytetrahydrofurane and a cycloaliphatic polyamide filled with 1.5 wt. % of silver nanoparticles are active against Escherichia coli. But, only nanocomposites with PA6, PA6.6 and P12-poly-THF as matrix materials are suitable as long-term biocidal materials.

Dendrimer−Silver Complexes and Nanocomposites as Antimicrobial Agents

Abstract: Silver complexes of poly(amidoamine) (PAMAM) dendrimers as well as different {silver−PAMAM} dendrimer nanocomposite solutions have been tested in vitro against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli bacteria, using the standard agar overlay method. Both PAMAM silver salts and nanocomposites displayed considerable antimicrobial activity without the loss of solubility and activity, even in the presence of sulfate or chloride ions.

Antibacterial Composites of Cuprous Oxide Nanoparticles and Polyethylene

Abstract: Cuprous oxide nanoparticles (Cu2ONPs) were used for preparing composites with linear low-density polyethylene (LLDPE) by co-extrusion, thermal adhesion, and attachment using ethyl cyanoacrylate, trimethoxyvinylsilane, and epoxy resin. The composites were examined by Scanning electron microscope and tested for their antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. All of these composites—except for the one obtained by extrusion—eradicated cells of both bacteria within half an hour. The composite prepared by thermal adhesion of Cu2ONPs on LLDPE had the highest external exposure of nanoparticles and exhibited the highest activity against the bacteria. This composite and the one obtained using ethyl cyanoacrylate showed no leaching of copper ions into the aqueous phase. Copper ion leaching from composites prepared with trimethoxyvinylsilane and epoxy resin was very low. The antibacterial activity of the composites can be rated as follows: obtained by thermal adhesion > obtained using ethyl cyanoacrylate > obtained using trimethoxyvinylsilane > obtained using epoxy resin > obtained by extrusion. The composites with the highest activity are potential materials for tap water and wastewater disinfection.

 

Synthesis of cuprous oxide epoxy nanocomposite as an environmentally antimicrobial coating

Abstract: Cuprous oxide is commonly used as a pigment; paint manufacturers begin to employ cuprous oxide as booster biocides in their formulations, to replace the banned organotins as the principal antifouling compounds. Epoxy coating was reinforced with cuprous oxide nanoparticles (Cu2O NPs). The antibacterial as well as antifungal activity of Cu2O epoxy nanocomposite (Cu2O EN) coating films was investigated. Cu2O NPs were also experimented for antibiofilm and time—kill assay. The thermal stability and the mechanical properties of Cu2O EN coating films were also investigated. The antimicrobial activity results showed slowdown, the growth of organisms on the Cu2O EN coating surface. TGA results showed that incorporating Cu2O NPs into epoxy coating considerably enhanced the thermal stability and increased the char residue. The addition of Cu2O NPs at lower concentration into epoxy coating also led to an improvement in the mechanical resistance such as scratch and abrasion. Cu2O NPs purity was confirmed by XRD. The TEM photograph demonstrated that the synthesized Cu2O NPs were of cubic shape and the average diameter of the crystals was around 25 nm. The resulting perfect dispersion of Cu2O NPs in epoxy coating revealed by SEM ensured white particles embedded in the epoxy matrix.

Long-term antibacterial stable reduced graphene oxide nanocomposites loaded with cuprous oxide nanoparticles

Abstract: Stable reduced graphene oxide-cuprous oxide (rGO-Cu2O) nanocomposites with long-term antibacterial activities were prepared by reducing copper sulfate supported on GO using ascorbic acid as reducing agent in the presence of polyethylene glycol (PEG) and sodium hydroxide at room temperature. The rGO provided a protective barrier for Cu2O, preventing Cu2O from reacting with external solution to leach copper ions too quickly. Meanwhile, the rGO also promoted the separation of photoexcited charge carriers of Cu2O nanoparticles to enhance the oxidative stress reactive and protected Cu2O from falling apart in the phosphate buffered solution (PBS) solution to prolong the generation time of reactive oxygen species (ROS). More importantly, the large specific surface area of rGO improved the dispersibility of Cu2O by electrostatic interaction. The synergistic effect of sustained release of copper ions, elevated ROS production ability and uniform dispersion of rGO-Cu2O nanocomposites resulted in the excellent antibacterial activities of rGO-Cu2O nanocomposites against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) which were maintained around 70% and 65% and were increased by 40% and 35% compared with free Cu2O after immersing 30 days in PBS solutions.

Antimicrobial active silver nanoparticles and silver/polystyrene core-shell nanoparticles prepared in room-temperature ionic liquid

Abstract: Uniform silver nanoparticles and silver/polystyrene core-shell nanoparticles were successfully synthesized in a room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]·BF4). [BMIM]·BF4 plays a protective role to prevent the nanoparticles from aggregation during the preparation process. Transmission electron micrographs confirm that both silver nanoparticles and core-shell nanoparticles are regular spheres with the sizes in the range of 5–15 nm and 15–25 nm, respectively. The X-ray diffraction analysis reveals the face-centered cubic geometry of silver nanoparticles. The as-prepared nanoparticles were also characterized by Fourier transform infrared spectroscopyRaman spectroscopyUV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. In addition, antimicrobial activities against E. coli and S. aureus were studied and the results show that both silver nanoparticles and core-shell nanoparticles possess excellent antimicrobial activities. The antimicrobial mechanism of the as-prepared nanoparticles was discussed.

Physicochemical properties of copper important for its antibacterial activity and development of a unified model

Abstract: Contact killing is a novel term describing the killing of bacteria when they come in contact with metallic copper or copper-containing alloys. In recent years, the mechanism of contact killing has received much attention and many mechanistic details are available. The authors here review some of these mechanistic aspects with a focus on the critical physicochemical properties of copper which make it antibacterial. Known mechanisms of contact killing are set in context to ionic, corrosive, and physical properties of copper. The analysis reveals that the oxidation behavior of copper, paired with the solubility properties of copper oxides, are the key factors which make metallic copper antibacterial. The concept advanced here explains the unique position of copper as an antibacterial metal. Based on our model, novel design criteria for metallic antibacterial materials may be derived.

Copper Reduction and Contact Killing of Bacteria by Iron Surfaces

Abstract: The well-established killing of bacteria by copper surfaces, also called contact killing, is currently 34 believed to be a combined effect of bacterial contact with the copper surface and the dissolution of 35 copper, resulting in lethal bacterial damage. Iron can similarly be released in ionic form from iron 36 surfaces and would thus be expected to also exhibit contact killing, though essentially no contact killing is 37 observed by iron surfaces. However, we here show that exposure of bacteria to iron surfaces in the presence of copper ions results in efficient contact killing. The process involves reduction of Cu2+ to Cu + 38 by iron; Cu + has been shown to be considerably more toxic to cells than Cu2+. The specific Cu + 39 chelator, bicinchoninic acid, suppresses contact killing by chelating the Cu + 40 ions. These findings underline the importance of Cu + 41 ions in the contact killing process and infer that iron-based alloys containing copper 42 could provide novel antimicrobial materials.

Inactivation of Norovirus on Dry Copper Alloy Surfaces

Abstract: Noroviruses (family Caliciviridae) are the primary cause of viral gastroenteritis worldwide. The virus is highly infectious and touching contaminated surfaces can contribute to infection spread. Although the virus was identified over 40 years ago the lack of methods to assess infectivity has hampered the study of the human pathogen. Recently the murine virus, MNV-1, has successfully been used as a close surrogate. Copper alloys have previously been shown to be effective antimicrobial surfaces against a range of bacteria and fungi. We now report rapid inactivation of murine norovirus on alloys, containing over 60% copper, at room temperature but no reduction of infectivity on stainless steel dry surfaces in simulated wet fomite and dry touch contamination. The rate of inactivation was initially very rapid and proportional to copper content of alloy tested. Viral inactivation was not as rapid on brass as previously observed for bacteria but copper-nickel alloy was very effective. The use of chelators and quenchers of reactive oxygen species (ROS) determined that Cu(II) and especially Cu(I) ions are still the primary effectors of toxicity but quenching superoxide and hydroxyl radicals did not confer protection. This suggests Fenton generation of ROS is not important for the inactivation mechanism. One of the targets of copper toxicity was the viral genome and a reduced copy number of the gene for a viral encoded protein, VPg (viral-protein-genome-linked), which is essential for infectivity, was observed following contact with copper and brass dry surfaces. The use of antimicrobial surfaces containing copper in high risk closed environments such as cruise ships and care facilities could help to reduce the spread of this highly infectious and costly pathogen.

Inactivation of Influenza A Virus on Copper versus Stainless Steel Surfaces

 Abstract: Influenza A virus particles (2 × 106) were inoculated onto copper or stainless steel and incubated at 22°C at 50 to 60% relative humidity. Infectivity of survivors was determined by utilizing a defined monolayer with fluorescent microscopy analysis. After incubation for 24 h on stainless steel, 500,000 virus particles were still infectious. After incubation for 6 h on copper, only 500 particles were active.

Effectiveness of Nanomaterial Copper Cold Spray Surfaces on Inactivation of Influenza A Virus

Abstract: Bacterial and viral contamination of touch surfaces allows for transmission of pathogens leading to increased risk of infection. Previous work has demonstrated the antimicrobial properties of copper for contact-killing of microbes for use in hospitals. Less research exists on copper as an antiviral surface and on the effects of nanomaterial copper surfaces in the contact-killing of viruses. Nano agglomerate and conventional copper powder feedstock is used in the cold spray process to form copper coatings on aluminum substrates. The nano and conventional copper surfaces formed are tested for antiviral contact-killing of influenza A virus. After a two hour exposure to the surfaces, the surviving influenza A virus was assayed and the results compared. The differences in the powder feedstock used to produce the test surfaces were examined in order to explain the mechanism that caused the observed differences in influenza A virus killing efficiency. Results showed that the nano copper surface was antiviral, but less effective than a study on antimicrobial killing of MRSA on copper surfaces. The nano copper surface was more effective at percent reduction of influenza A virus than that of conventional copper. It was determined that the work hardening caused by the cold spray process in combination with the high number of grain boundaries results in a copper microstructure that enhances ionic diffusion. Copper ion diffusion is the principle mechanism for microbial and viral destruction on copper surfaces. Testing determined significant microbiologic differences between nano- and conventional Cu surfaces and demonstrates the importance of nano copper surfaces as an antiviral agent. The nano agglomerate powder shows superior antiviral effectiveness to that of conventional Cu due to an increase in grain boundaries at the nano level. Further research is needed to determine the effects of nano and conventional copper surface roughness on the contact-killing rate of viruses versus microbes on both a micro and nano-scale.

Role of Copper Oxides in Contact Killing of Bacteria

Abstract: The potential of metallic copper as an intrinsically antibacterial material is gaining increasing attention in the face of growing antibiotics resistance of bacteria. However, the mechanism of the so-called “contact killing” of bacteria by copper surfaces is poorly understood and requires further investigation. In particular, the influences of bacteria−metal interaction, media composition, and copper surface chemistry on contact killing are not fully understood. In this study, copper oxide formation on copper during standard antimicrobial testing was measured in situ by spectroscopic ellipsometry. In parallel, contact killing under these conditions was assessed with bacteria in phosphate buffered saline (PBS) or Tris-Cl. For comparison, defined Cu2O and CuO layers were thermally generated and characterized by grazing incidence X-ray diffraction. The antibacterial properties of these copper oxides were tested under the conditions used above. Finally, copper ion release was recorded for both buffer systems by inductively coupled plasma atomic absorption spectroscopy, and exposed copper samples were analyzed for topographical surface alterations. It was found that there was a fairly even growth of CuO under wet plating conditions, reaching 4−10 nm in 300 min, but no measurable Cu2O was formed during this time. CuO was found to significantly inhibit contact killing, compared to pure copper. In contrast, thermally generated Cu2O was essentially as effective in contact killing as pure copper. Copper ion release from the different surfaces roughly correlated with their antibacterial efficacy and was highest for pure copper, followed by Cu2O and CuO. Tris-Cl induced a 10−50-fold faster copper ion release compared to PBS. Since the Cu2O that primarily forms on copper under ambient conditions is as active in contact killing as pure copper, antimicrobial objects will retain their antimicrobial properties even after oxide formation.