Publications by authors named "Elena P Ivanova"

167 Publications

Antibacterial Action of Nanoparticles by Lethal Stretching of Bacterial Cell Membranes.

Adv Mater 2020 Dec 12;32(52):e2005679. Epub 2020 Nov 12.

School of Science, RMIT University, P.O. Box 2476, Melbourne, Victoria, 3001, Australia.

It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. It is demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP-membrane interactions is presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon is demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram-positive and Gram-negative bacteria. Hydrophilic and hydrophobic quasi-spherical and star-shaped gold (Au)NPs are synthesized to explore the antibacterial mechanism of non-translocating AuNPs. Direct observation of nanoparticle-induced membrane tension and squeezing is demonstrated using a custom-designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi-spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques are used to characterize the NP-bacterial-membrane interactions. This combination of experimental and theoretical results confirm the proposed mechanism of membrane-tension-induced (mechanical) killing of bacterial cells by non-translocating NPs.
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http://dx.doi.org/10.1002/adma.202005679DOI Listing
December 2020

Mechano-Bactericidal Titanium Surfaces for Bone Tissue Engineering.

ACS Appl Mater Interfaces 2020 Oct 15;12(43):48272-48283. Epub 2020 Oct 15.

Cancer Target and Experimental Therapeutics, Institute for Advanced Biosciences, INSERM U1209, UMR CNRS 5309, Grenoble Alpes University, Site Santé, Allée des Alpes, 38700 La Tronche, France.

Despite advances in the development of bone substitutes and strict aseptic procedures, the majority of failures in bone grafting surgery are related to nosocomial infections. Development of biomaterials combining both osteogenic and antibiotic activity is, therefore, a crucial public health issue. Herein, two types of intrinsically bactericidal titanium supports were fabricated by using commercially scalable techniques: plasma etching or hydrothermal treatment, which display two separate mechanisms of mechano-bactericidal action. Hydrothermal etching produces a randomly nanostructured surface with sharp nanosheet protrusions killing bacteria via cutting of the cell membrane, whereas plasma etching of titanium produces a microscale two-tier hierarchical topography that both reduce bacterial attachment and rupture those bacteria that encounter the surface. The adhesion, growth, and proliferation of human adipose-derived stem cells (hASCs) on the two mechano-bactericidal topographies were assessed. Both types of supports allowed the growth and proliferation of the hASCs in the same manner and cells retained their stemness and osteogenic potential. Furthermore, these supports induced osteogenic differentiation of hASCs without the need of differentiation factors, demonstrating their osteoinductive properties. This study proves that these innovative mechano-bactericidal titanium surfaces with both regenerative and bactericidal properties are a promising solution to improve the success rate of reconstructive surgery.
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http://dx.doi.org/10.1021/acsami.0c11502DOI Listing
October 2020

Electrospun Nanodiamond-Silk Fibroin Membranes: A Multifunctional Platform for Biosensing and Wound-Healing Applications.

ACS Appl Mater Interfaces 2020 Oct 13;12(43):48408-48419. Epub 2020 Oct 13.

School of Science, RMIT University, Melbourne, Victoria 3001, Australia.

Next generation wound care technology capable of diagnosing wound parameters, promoting healthy cell growth, and reducing pathogenic infections noninvasively would provide patients with an improved standard of care and accelerated wound repair. Temperature is one of the indicating biomarkers specific to chronic wounds. This work reports a hybrid, multifunctional optical material platform-nanodiamond (ND)-silk membranes as biopolymer dressings capable of temperature sensing and promoting wound healing. The hybrid structure was fabricated through electrospinning, and 3D submicron fibrous membranes with high porosity were formed. Silk fibers are capable of compensating for the lack of an extracellular matrix at the wound site, supporting the wound-healing process. Negatively charged nitrogen vacancy (NV) color centers in NDs exhibit optically detected magnetic resonance (ODMR) and act as nanoscale thermometers. This can be exploited to sense temperature variations associated with the presence of infection or inflammation in a wound, without physically removing the dressing. Our results show that the presence of NDs in the hybrid ND-silk membranes improves the thermal stability of silk fibers. NV color centers in NDs embedded in silk fibers exhibit well-retained fluorescence and ODMR. Using the NV centers as fluorescent nanoscale thermometers, we achieved temperature sensing in 25-50 °C, including the biologically relevant temperature window, for cell-grown ND-silk membranes. An enhancement (∼1.5× on average) in the temperature sensitivity of the NV centers was observed for the hybrid materials. The hybrid membranes were further tested in a murine wound-healing model and demonstrated biocompatibility and equivalent wound closure rates as the control wounds. Additionally, the hybrid ND-silk membranes exhibited selective antifouling and biocidal propensity toward Gram-negative and , while no effect was observed on Gram-positive .
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http://dx.doi.org/10.1021/acsami.0c15612DOI Listing
October 2020

Use of Synergistic Interactions to Fabricate Transparent and Mechanically Robust Nanohybrids Based on Starch, Non-Isocyanate Polyurethanes, and Cellulose Nanocrystals.

ACS Appl Mater Interfaces 2020 Oct 12;12(42):47865-47878. Epub 2020 Oct 12.

School of Science, College of Science, Engineering & Health, RMIT University, Melbourne, Victoria 3000, Australia.

Materials based on petroleum-based resources have aroused widespread concern because of their environmental and healthcare footprints. Cellulose nanocrystals (CNCs) are at the cutting edge of current research because of their great promise in developing sustainable and high-performance materials. To establish a comprehensive understanding of the synergistic reinforcement effect of CNCs, we introduced a new method to fabricate all-green, transparent, and mechanically robust nanohybrid materials using CNCs in conjunction with gelatinized starch (GS) and polyhydroxyurethanes (PHUs). The synergistic interaction between the CNC skeleton and the GS/PHU network enabled us to span exceptionally stiff nanohybrids that could withstand up to 8.5 MPa tensile strength. The tunable mechanical properties and enhanced thermal stability in these nanohybrids primarily arise from the presence of dense hydroxyl groups on the CNCs' surface, which offer a robust scaffold for fortified hydrogen bonds to form with GS/PHU domains. The multiple intramolecular hydrogen bonds synergistically served as highly stable associations and concurrently facilitated energy dissipation and transferred the stress across the interfacial region. The rational design of the molecular interactions presented in this work provided increased opportunities to build nanohybrids with outstanding mechanical performance. More broadly, the insights afforded by this study not only delivered a better understanding on the molecular-level interactions in the CNC/GS/PHU system but also enriched the potential for the commercial exploration of tunable cellulosic nanohybrid materials.
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http://dx.doi.org/10.1021/acsami.0c14525DOI Listing
October 2020

Mechano-bactericidal actions of nanostructured surfaces.

Nat Rev Microbiol 2021 01 17;19(1):8-22. Epub 2020 Aug 17.

ARC Industrial Transformation Training Centre in Surface Engineering for Advanced Materials, School of Science, Swinburne University of Technology, Hawthorn, VIC, Australia.

Antibiotic resistance is a global human health threat, causing routine treatments of bacterial infections to become increasingly difficult. The problem is exacerbated by biofilm formation by bacterial pathogens on the surfaces of indwelling medical and dental devices that facilitate high levels of tolerance to antibiotics. The development of new antibacterial nanostructured surfaces shows excellent prospects for application in medicine as next-generation biomaterials. The physico-mechanical interactions between these nanostructured surfaces and bacteria lead to bacterial killing or prevention of bacterial attachment and subsequent biofilm formation, and thus are promising in circumventing bacterial infections. This Review explores the impact of surface roughness on the nanoscale in preventing bacterial colonization of synthetic materials and categorizes the different mechanisms by which various surface nanopatterns exert the necessary physico-mechanical forces on the bacterial cell membrane that will ultimately result in cell death.
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http://dx.doi.org/10.1038/s41579-020-0414-zDOI Listing
January 2021

Single shot multispectral multidimensional imaging using chaotic waves.

Sci Rep 2020 Aug 17;10(1):13902. Epub 2020 Aug 17.

Center for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia.

Multispectral imaging technology is a valuable scientific tool for various applications in astronomy, remote sensing, molecular fingerprinting, and fluorescence imaging. In this study, we demonstrate a single camera shot, lensless, interferenceless, motionless, non-scanning, space, spectrum, and time resolved five-dimensional incoherent imaging technique using tailored chaotic waves with quasi-random intensity and phase distributions. Chaotic waves can distinctly encode spatial and spectral information of an object in single self-interference intensity distribution. In this study, a tailored chaotic wave with a nearly pure phase function and lowest correlation noise is generated using a quasi-random array of pinholes. A unique sequence of signal processing techniques is applied to extract all possible spatial and spectral channels with the least entropy. The depth-wavelength reciprocity is exploited to see colour from depth and depth from colour and the physics of beam propagation is exploited to see at one depth by calibrating at another.
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http://dx.doi.org/10.1038/s41598-020-70849-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7431426PMC
August 2020

Direct Measurement of Temperature Diffusivity of Nanocellulose-Doped Biodegradable Composite Films.

Micromachines (Basel) 2020 Jul 29;11(8). Epub 2020 Jul 29.

CREST-JST and School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8550, Japan.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of nanocellulose-doped starch-polyurethane nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2 wt%. of nanocellulose were synthesised by a simple chemical process and are biodegradable. Films of a high optical transmittance T≈80% (for a 200 μm thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on (1) a resistance change and (2) micro-thermocouple detected voltage modulation caused by the heat wave, were used for the polymer films with cross sections of ∼100 μm thickness. Twice different in-plane α‖ and out-of-plane α⟂ temperature diffusivities were directly determined with high fidelity: α‖=2.12×10-7 m2/s and α⟂=1.13×10-7 m2/s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite biodegradable polymer films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this polymer nanocomposite.
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http://dx.doi.org/10.3390/mi11080738DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464088PMC
July 2020

Assessment of interfacial interactions between starch and non-isocyanate polyurethanes in their hybrids.

Carbohydr Polym 2020 Oct 17;246:116656. Epub 2020 Jun 17.

School of Science, College of Science, Engineering & Health, RMIT University, Melbourne, VIC, 3000, Australia. Electronic address:

Manufacturing of multifunctional materials through blending is a promising route for improving performance of biopolymers including starch. Non-isocyanate polyurethanes (NIPUs) are an emerging group of green materials. Understanding the mechanism of interaction between starch and NIPU not only highlights underlying chemistry but also offers an opportunity to tailor the properties and functions of starch-NIPU hybrids. We investigated the interfacial interactions between starch and NIPU to pave the way towards development of high-performance green materials. Multiple analyses revealed that NIPU interacted effectively with starch chains via intermolecular hydrogen bonds. We showed that NIPU domains can efficiently interact with the small portion of starch skeleton at interfacial region and they are only moderately miscible. Incorporation of either component above certain ratio resulted in a phase separation. This work contributes towards understanding of interfacial chemistry between starch and NIPUs and enables tailoring the interface for facile engineering of starch-NIPU hybrids.
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http://dx.doi.org/10.1016/j.carbpol.2020.116656DOI Listing
October 2020

Tilted black-Si: ∼0.45 form-birefringence from sub-wavelength needles.

Opt Express 2020 May;28(11):16012-16026

The self-organised conical needles produced by plasma etching of silicon (Si), known as black silicon (b-Si), create a form-birefringent surface texture when etching of Si orientated at angles of θ < 50 - 70 (angle between the Si surface and vertical plasma E-field). The height of the needles in the form-birefringent region following 15 min etching was d ∼ 200 nm and had a 100 μm width of the optical retardance/birefringence, characterised using polariscopy. The height of the b-Si needles corresponds closely to the skin-depth of Si ∼λ/4 for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance Δn × d/λ ≈ 0.15 of the region with tilted b-Si needles. The quantified form birefringence of Δn = -0.45 over λ = 400 - 700 nm spectral window was obtained. Such high values of Δn at visible wavelengths can only be observed in the most birefringence calcite or barium borate as well as in liquid crystals. The replication of b-Si into Ni-shim with high fidelity was also demonstrated and can be used for imprinting of the b-Si nanopattern into other materials.
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http://dx.doi.org/10.1364/OE.392646DOI Listing
May 2020

Roadmap for naming uncultivated Archaea and Bacteria.

Nat Microbiol 2020 08 8;5(8):987-994. Epub 2020 Jun 8.

National Museum of Natural Sciences, CSIC, Madrid, Spain.

The assembly of single-amplified genomes (SAGs) and metagenome-assembled genomes (MAGs) has led to a surge in genome-based discoveries of members affiliated with Archaea and Bacteria, bringing with it a need to develop guidelines for nomenclature of uncultivated microorganisms. The International Code of Nomenclature of Prokaryotes (ICNP) only recognizes cultures as 'type material', thereby preventing the naming of uncultivated organisms. In this Consensus Statement, we propose two potential paths to solve this nomenclatural conundrum. One option is the adoption of previously proposed modifications to the ICNP to recognize DNA sequences as acceptable type material; the other option creates a nomenclatural code for uncultivated Archaea and Bacteria that could eventually be merged with the ICNP in the future. Regardless of the path taken, we believe that action is needed now within the scientific community to develop consistent rules for nomenclature of uncultivated taxa in order to provide clarity and stability, and to effectively communicate microbial diversity.
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http://dx.doi.org/10.1038/s41564-020-0733-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7381421PMC
August 2020

The multi-faceted mechano-bactericidal mechanism of nanostructured surfaces.

Proc Natl Acad Sci U S A 2020 06 26;117(23):12598-12605. Epub 2020 May 26.

School of Science, College of Science, Engineering and Health, RMIT University, Melbourne, VIC 3000, Australia.

The mechano-bactericidal activity of nanostructured surfaces has become the focus of intensive research toward the development of a new generation of antibacterial surfaces, particularly in the current era of emerging antibiotic resistance. This work demonstrates the effects of an incremental increase of nanopillar height on nanostructure-induced bacterial cell death. We propose that the mechanical lysis of bacterial cells can be influenced by the degree of elasticity and clustering of highly ordered silicon nanopillar arrays. Herein, silicon nanopillar arrays with diameter 35 nm, periodicity 90 nm and increasing heights of 220, 360, and 420 nm were fabricated using deep UV immersion lithography. Nanoarrays of 360-nm-height pillars exhibited the highest degree of bactericidal activity toward both Gram stain-negative and Gram stain-positive bacteria, inducing 95 ± 5% and 83 ± 12% cell death, respectively. At heights of 360 nm, increased nanopillar elasticity contributes to the onset of pillar deformation in response to bacterial adhesion to the surface. Theoretical analyses of pillar elasticity confirm that deflection, deformation force, and mechanical energies are more significant for the substrata possessing more flexible pillars. Increased storage and release of mechanical energy may explain the enhanced bactericidal action of these nanopillar arrays toward bacterial cells contacting the surface; however, with further increase of nanopillar height (420 nm), the forces (and tensions) can be partially compensated by irreversible interpillar adhesion that reduces their bactericidal effect. These findings can be used to inform the design of next-generation mechano-responsive surfaces with tuneable bactericidal characteristics for antimicrobial surface technologies.
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http://dx.doi.org/10.1073/pnas.1916680117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293705PMC
June 2020

Black-Si as a Photoelectrode.

Nanomaterials (Basel) 2020 May 1;10(5). Epub 2020 May 1.

Center for Physical Sciences and Technology, Saulėtekio ave. 3, LT-10257 Vilnius, Lithuania.

The fabrication and characterization of photoanodes based on black-Si (b-Si) are presented using a photoelectrochemical cell in NaOH solution. B-Si was fabricated by maskless dry plasma etching and was conformally coated by tens-of-nm of TiO using atomic layer deposition (ALD) with a top layer of CoO x cocatalyst deposited by pulsed laser deposition (PLD). Low reflectivity R < 5 % of b-Si over the entire visible and near-IR ( λ < 2   μ m) spectral range was favorable for the better absorption of light, while an increased surface area facilitated larger current densities. The photoelectrochemical performance of the heterostructured b-Si photoanode is discussed in terms of the n-n junction between b-Si and TiO.
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http://dx.doi.org/10.3390/nano10050873DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7279502PMC
May 2020

Three-Dimensional Hierarchical Wrinkles on Polymer Films: From Chaotic to Ordered Antimicrobial Topographies.

Trends Biotechnol 2020 05 28;38(5):558-571. Epub 2020 Feb 28.

School of Science, College of Science, Engineering and Health, RMIT University, Melbourne 3000, VIC, Australia. Electronic address:

Microbial contamination of polymer surfaces has become a significant challenge in domestic, industrial, and biomedical applications. Recent progress in our understanding of how topographical features of different length scales can be used to effectively and selectively control the attachment and proliferation of different cell types has provided an alternative strategy for imparting antibacterial activity to these surfaces. Among the well-recognized engineered models of antibacterial surface topographies, self-organized wrinkles have shown particular promise with respect to their antimicrobial characteristics. Here, we critically review the mechanisms by which wrinkles form on the surface of different types of polymer material and how they interact with various biomolecules and cell types. We also discuss the feasibility of using this antimicrobial strategy in real-life biomedical applications.
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http://dx.doi.org/10.1016/j.tibtech.2019.12.004DOI Listing
May 2020

Synthesis of green hybrid materials using starch and non-isocyanate polyurethanes.

Carbohydr Polym 2020 Feb 6;229:115535. Epub 2019 Nov 6.

School of Science, RMIT University, Melbourne, VIC 3083, Australia. Electronic address:

Green and environment-friendly polymers with comparable thermal and mechanical performance can be suitable alternatives of synthetic polymers. This paper documents the synthesis of crystallizable polyhydroxyurethanes (PHUs) through a facile, non-isocyanate and catalyst-free route with step growth polymerization of ethylene carbonate and three different diamines (1,2-ethanediamine, 1,4-butanediamine and 1,6-hexanediamine). The PHU monomers were interacted with gelatinized starch (HAGS) to synthesize HAGS/PHU hybrid materials. Both PHU monomers and hybrid materials were characterized by FT-IR, H NMR, C NMR, DSC and XRD. Hydroxyl groups of HAGS and PHUs were found to predominantly contribute to the intermolecular hydrogen bonding. The films produced using HAGS/PHU hybrid materials exhibited tuneable mechanical properties with tensile strength ranging between 1.7 MPa and 3.2 MPa and a breaking strain varying between 45% and 121%. These findings underscore the potential of non-isocyanate polyurethanes as environmentally sustainable materials and provide facile route for synthesis of HAGS/PHU hybrid materials.
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http://dx.doi.org/10.1016/j.carbpol.2019.115535DOI Listing
February 2020

Polymerization-Induced Phase Segregation and Self-Assembly of Siloxane Additives to Provide Thermoset Coatings with a Defined Surface Topology and Biocidal and Self-Cleaning Properties.

Nanomaterials (Basel) 2019 Nov 13;9(11). Epub 2019 Nov 13.

UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, University of New South Wales, Sydney, NSW 2052, Australia.

In this work, we report on the incorporation of a siloxane copolymer additive, poly((2-phenylethyl) methylsiloxane)-co(1-phenylethyl) methylsiloxane)-co-dimethylsiloxane), which is fully soluble at room temperature, in a rapid-cure thermoset polyester coating formulation. The additive undergoes polymerization-induced phase segregation (PIPS) to self-assemble on the coating surface as discrete discoid nanofeatures during the resin cure process. Moreover, the copolymer facilitates surface co-segregation of titanium dioxide pigment microparticulate present in the coating. Depending on the composition, the coatings can display persistent superhydrophobicity and self-cleaning properties and, surprisingly, the titanium dioxide pigmented coatings that include the siloxane copolymer additive display high levels of antibacterial performance against Gram-positive ( and Gram-negative () bacteria. This antibacterial performance is believed to be associated with the unique surface topology of these coatings, which comprise stimuli-responsive discoid nanofeatures. This paper provides details of the surface morphology of the coatings and how these relates to the antimicrobial properties of the coating.
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http://dx.doi.org/10.3390/nano9111610DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6915580PMC
November 2019

Tunable morphological changes of asymmetric titanium nanosheets with bactericidal properties.

J Colloid Interface Sci 2020 Feb 19;560:572-580. Epub 2019 Oct 19.

School of Science, College of Science, Engineering & Health, RMIT, Melbourne, Vic 3000, Australia. Electronic address:

Hypothesis: Titanium and titanium alloys are often the most popular choice of material for the manufacture of medical implants; however, they remain susceptible to the risk of device-related infection caused by the presence of pathogenic bacteria. Hydrothermal etching of titanium surfaces, to produce random nanosheet topologies, has shown remarkable ability to inactivate pathogenic bacteria via a physical mechanism. We expect that systematic tuning of the nanosheet morphology by controlling fabrication parameters, such as etching time, will allow for optimisation of the surface pattern for superior antibacterial efficacy.

Experiments: Using time-dependent hydrothermal processing of bulk titanium, we fabricated bactericidal nanosheets with variable nanoedge morphologies according to a function of etching time. A systematic study was performed to compare the bactericidal efficiency of nanostructured titanium surfaces produced at 0.5, 1, 2, 3, 4, 5, 6, 24 and 60 h of hydrothermal etching.

Findings: Titanium surfaces hydrothermally treated for a period of 6 h were found to achieve maximal antibacterial efficiency of 99 ± 3% against Gram-negative Pseudomonas aeruginosa and 90 ± 9% against Gram-positive Staphylococcus aureus bacteria, two common human pathogens. These surfaces exhibited nanosheets with sharp edges of approximately 10 nm. The nanotopographies presented in this work exhibit the most efficient mechano-bactericidal activity against both Gram-negative and Gram-positive bacteria of any nanostructured titanium topography reported thus far.
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http://dx.doi.org/10.1016/j.jcis.2019.10.067DOI Listing
February 2020

The idiosyncratic self-cleaning cycle of bacteria on regularly arrayed mechano-bactericidal nanostructures.

Nanoscale 2019 Sep 27;11(35):16455-16462. Epub 2019 Aug 27.

School of Science, College of Science, Engineering and Health, RMIT University, Melbourne, VIC 3001, Australia.

Nanostructured mechano-bactericidal surfaces represent a promising technology to prevent the incidence of microbial contamination on a variety of surfaces and to avoid bacterial infection, particularly with antibiotic resistant strains. In this work, a regular array of silicon nanopillars of 380 nm height and 35 nm diameter was used to study the release of bacterial cell debris off the surface, following inactivation of the cell due to nanostructure-induced rupture. It was confirmed that substantial bactericidal activity was achieved against Gram-negative Pseudomonas aeruginosa (85% non-viable cells) and only modest antibacterial activity towards Staphylococcus aureus (8% non-viable cells), as estimated by measuring the proportions of viable and non-viable cells via fluorescence imaging. In situ time-lapse AFM scans of the bacteria-nanopillar interface confirmed the removal rate of the dead P. aeruginosa cells from the surface to be approximately 19 minutes per cell, and approximately 11 minutes per cell for dead S. aureus cells. These results highlight that the killing and dead cell detachment cycle for bacteria on these substrata are dependant on the bacterial species and the surface architecture studied and will vary when these two parameters are altered. The outcomes of this work will enhance the current understanding of antibacterial nanostructures, and impact upon the development and implementation of next-generation implants and medical devices.
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http://dx.doi.org/10.1039/c9nr05923gDOI Listing
September 2019

Engineering the Interface: Nanodiamond Coating on 3D-Printed Titanium Promotes Mammalian Cell Growth and Inhibits Colonization.

ACS Appl Mater Interfaces 2019 Jul 28;11(27):24588-24597. Epub 2019 Jun 28.

National Institutes for Quantum and Radiological Science and Technology , Takasaki , Gunma 370-1292 , Japan.

Additively manufactured selective laser melted titanium (SLM-Ti) opens the possibility of tailored medical implants for patients. Despite orthopedic implant advancements, significant problems remain with regard to suboptimal osseointegration at the interface between the implant and the surrounding tissue. Here, we show that applying a nanodiamond (ND) coating onto SLM-Ti scaffolds provides an improved surface for mammalian cell growth while inhibiting colonization of bacteria. Owing to the simplicity of our methodology, the approach is suitable for coating SLM-Ti geometries. The ND coating achieved 32 and 29% increases in cell density of human dermal fibroblasts and osteoblasts, respectively, after 3 days of incubation compared with the uncoated SLM-Ti substratum. This increase in cell density complements an 88% reduction in detected on the ND-coated SLM-Ti substrata. This study paves a way to create facile antifouling SLM-Ti structures for biomedical implants.
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http://dx.doi.org/10.1021/acsami.9b07064DOI Listing
July 2019

Switchable Dual-Function and Bioresponsive Materials to Control Bacterial Infections.

ACS Appl Mater Interfaces 2019 Jul 19;11(26):22897-22914. Epub 2019 Jun 19.

Center for Humanities and Sciences, Department of Food and Nutrition, Bionanocomposite Research Center , Kyung Hee University , 26 Kyungheedae-ro, Dongdaemun-gu , Seoul 02447 , Republic of Korea.

The colonization of undesired bacteria on the surface of devices used in biomedical and clinical applications has become a persistent problem. Different types of single-function (cell resistance or bactericidal) bioresponsive materials have been developed to cope with this problem. Even though these materials meet the basic requirements of many biomedical and clinical applications, dual-function (cell resistance and biocidal) bioresponsive materials with superior design and function could be better suited for these applications. The past few years have witnessed the emergence of a new class of dual-function materials that can reversibly switch between cell-resistance and biocidal functions in response to external stimuli. These materials are finding increased applications in biomedical devices, tissue engineering, and drug-delivery systems. This review highlights the recent advances in design, structure, and fabrication of dual-function bioresponsive materials and discusses translational challenges and future prospects for research involving these materials.
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http://dx.doi.org/10.1021/acsami.9b05901DOI Listing
July 2019

Nanoscale optical and structural characterisation of silk.

Beilstein J Nanotechnol 2019 23;10:922-929. Epub 2019 Apr 23.

Swinburne University of Technology, John st., Hawthorn, 3122 Vic, Australia.

The nanoscale composition of silk defining its unique properties via a hierarchial structural anisotropy needs to be analysed at the highest spatial resolution of tens of nanometers corresponding to the size of fibrils made of β-sheets, which are the crystalline building blocks of silk. Nanoscale optical and structural properties of silk have been measured from 100 nm thick longitudinal slices of silk fibers with ca. 10 nm resolution, the highest so far. Optical sub-wavelength resolution in hyperspectral mapping of absorbance and molecular orientation were carried out for comparison at IR wavelengths of 2-10 μm using synchrotron radiation. A reliable distinction of transmission changes by only 1-2% as the anisotropy of amide bands was obtained from nanometer-thin slices of silk.
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http://dx.doi.org/10.3762/bjnano.10.93DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6541335PMC
April 2019

The Fate of Osteoblast-Like MG-63 Cells on Pre-Infected Bactericidal Nanostructured Titanium Surfaces.

Materials (Basel) 2019 May 14;12(10). Epub 2019 May 14.

School of Science, College of Science, Engineering and Health, RMIT University, Melbourne, VIC 3000, Australia.

Biomaterials that have been newly implanted inside the body are the substratum targets for a "race for the surface", in which bacterial cells compete against eukaryotic cells for the opportunity to colonize the surface. A victory by the former often results in biomaterial-associated infections, which can be a serious threat to patient health and can undermine the function and performance of the implant. Moreover, bacteria can often have a 'head start' if implant contamination has taken place either prior to or during the surgery. Current prevention and treatment strategies often rely on systemic antibiotic therapies, which are becoming increasingly ineffective due to a growing prevalence of antibiotic-resistant bacteria. Nanostructured surfaces that kill bacteria by physically rupturing bacterial cells upon contact have recently emerged as a promising solution for the mitigation of bacterial colonization of implants. Furthermore, these nanoscale features have been shown to enhance the adhesion and proliferation of eukaryotic cells, which is a key to, for example, the successful osseointegration of load-bearing titanium implants. The bactericidal activity and biocompatibility of such nanostructured surfaces are often, however, examined separately, and it is not clear to what extent bacterial cell-surface interactions would affect the subsequent outcomes of host-cell attachment and osseointegration processes. In this study, we investigated the ability of bactericidal nanostructured titanium surfaces to support the attachment and growth of osteoblast-like MG-63 human osteosarcoma cells, despite them having been pre-infected with pathogenic bacteria. MG-63 is a commonly used osteoblastic model to study bone cell viability, adhesion, and proliferation on the surfaces of load-bearing biomaterials, such as titanium. The nanostructured titanium surfaces used here were observed to kill the pathogenic bacteria, whilst simultaneously enhancing the growth of MG-63 cells in vitro when compared to that occurring on sterile, flat titanium surfaces. These results provide further evidence in support of nanostructured bactericidal surfaces being used as a strategy to help eukaryotic cells win the "race for the surface" against bacterial cells on implant materials.
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http://dx.doi.org/10.3390/ma12101575DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6567816PMC
May 2019

Simulations of Protein Adsorption on Nanostructured Surfaces.

Sci Rep 2019 03 18;9(1):4694. Epub 2019 Mar 18.

Universitat Rovira i Virgili, Departament d'Enginyeria Quimica, Tarragona, 43007, Spain.

Recent technological advances have allowed the development of a new generation of nanostructured materials, such as those displaying both mechano-bactericidal activity and substrata that favor the growth of mammalian cells. Nanomaterials that come into contact with biological media such as blood first interact with proteins, hence understanding the process of adsorption of proteins onto these surfaces is highly important. The Random Sequential Adsorption (RSA) model for protein adsorption on flat surfaces was modified to account for nanostructured surfaces. Phenomena related to the nanofeature geometry have been revealed during the modelling process; e.g., convex geometries can lead to lower steric hindrance between particles, and hence higher degrees of surface coverage per unit area. These properties become more pronounced when a decrease in the size mismatch between the proteins and the surface nanostructures occurs. This model has been used to analyse the adsorption of human serum albumin (HSA) on a nano-structured black silicon (bSi) surface. This allowed the Blocking Function (the rate of adsorption) to be evaluated. The probability of the protein to adsorb as a function of the occupancy was also calculated.
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http://dx.doi.org/10.1038/s41598-019-40920-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6423022PMC
March 2019

Computational prediction of microRNAs in marine bacteria of the genus Thalassospira.

PLoS One 2019 12;14(3):e0212996. Epub 2019 Mar 12.

Swinburne University of Technology, Hawthorn, Australia.

MicroRNAs (miRNAs) are key players in regulation of gene expression at post-transcription level in eukaryotic cells. MiRNAs have been intensively studied in plants, animals and viruses. The investigations of bacterial miRNAs have gained less attention, except for the recent studies on miRNAs derived from Streptococcus mutans ATCC 25175 and Escherichia coli DH10B. In this study, high-throughput sequencing approach was employed to investigate the miRNA population in bacteria of the genus Thalassospira using both the miRDeep2 and CID-miRNA methods. A total of 984 putative miRNAs were identified in 9 species of the genus Thalassospira using both miRDeep and CID-miRNA analyses. Fifty seven conserved putative miRNAs were found in different species of the genus Thalassospira, and up to 6 miRNAs were found to be present at different locations in the T. alkalitolerans JCM 18968T, T. lucentensis QMT2T and T. xianhensis P-4T. None of the putative miRNAs was found to share sequence to the reported miRNAs in E. coli DH10B and S. mutans ATCC 25175. The findings provide a comprehensive list of computationally identified miRNAs in 9 bacterial species of the genus Thalassospira and addressed the existing knowledge gap on the presence of miRNAs in the Thalassospira genomes.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212996PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6413936PMC
December 2019

PC 12 Pheochromocytoma Cell Response to Super High Frequency Terahertz Radiation from Synchrotron Source.

Cancers (Basel) 2019 Jan 31;11(2). Epub 2019 Jan 31.

School of Science, RMIT University, P.O. Box 2476, Melbourne, VIC 3001, Australia.

High frequency (HF) electromagnetic fields (EMFs) have been widely used in many wireless communication devices, yet within the terahertz (THz) range, their effects on biological systems are poorly understood. In this study, electromagnetic radiation in the range of 0.3⁻19.5 × 10 Hz, generated using a synchrotron light source, was used to investigate the response of PC 12 neuron-like pheochromocytoma cells to THz irradiation. The PC 12 cells remained viable and physiologically healthy, as confirmed by a panel of biological assays; however, exposure to THz radiation for 10 min at 25.2 ± 0.4 °C was sufficient to induce a temporary increase in their cell membrane permeability. High-resolution transmission electron microscopy (TEM) confirmed cell membrane permeabilization via visualisation of the translocation of silica nanospheres ( = 23.5 ± 0.2 nm) and their clusters ( = 63 nm) into the PC 12 cells. Analysis of scanning electron microscopy (SEM) micrographs revealed the formation of atypically large (up to 1 µm) blebs on the surface of PC 12 cells when exposed to THz radiation. Long-term analysis showed no substantial differences in metabolic activity between the PC 12 cells exposed to THz radiation and untreated cells; however, a higher population of the THz-treated PC 12 cells responded to the nerve growth factor (NGF) by extending longer neurites (up to 0⁻20 µm) compared to the untreated PC12 cells (up to 20 µm). These findings present implications for the development of nanoparticle-mediated drug delivery and gene therapy strategies since THz irradiation can promote nanoparticle uptake by cells without causing apoptosis, necrosis or physiological damage, as well as provide a deeper fundamental insight into the biological effects of environmental exposure of cells to electromagnetic radiation of super high frequencies.
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http://dx.doi.org/10.3390/cancers11020162DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6406661PMC
January 2019

Interaction of Giant Unilamellar Vesicles with the Surface Nanostructures on Dragonfly Wings.

Langmuir 2019 02 25;35(6):2422-2430. Epub 2019 Jan 25.

School of Science, College of Science, Engineering and Health , RMIT University , GPO Box 2476, Melbourne , Victoria 3001 , Australia.

The waxy epicuticle of dragonfly wings contains a unique nanostructured pattern that exhibits bactericidal properties. In light of emerging concerns of antibiotic resistance, these mechano-bactericidal surfaces represent a particularly novel solution by which bacterial colonization and the formation of biofilms on biomedical devices can be prevented. Pathogenic bacterial biofilms on medical implant surfaces cause a significant number of human deaths every year. The proposed mechanism of bactericidal activity is through mechanical cell rupture; however, this is not yet well understood and has not been well characterized. In this study, we used giant unilamellar vesicles (GUVs) as a simplified cell membrane model to investigate the nature of their interaction with the surface of the wings of two dragonfly species, Austrothemis nigrescens and Trithemis annulata, sourced from Victoria, Australia, and the Baix Ebre and Terra Alta regions of Catalonia, Spain. Confocal laser scanning microscopy and cryo-scanning electron microscopy techniques were used to visualize the interactions between the GUVs and the wing surfaces. When exposed to both natural and gold-coated wing surfaces, the GUVs were adsorbed on the surface, exhibiting significant deformation, in the process of membrane rupture. Differences between the tensile rupture limit of GUVs composed of 1,2-dioleoyl- sn-glycero-3-phosphocholine and the isotropic tension generated from the internal osmotic pressure were used to indirectly determine the membrane tensions, generated by the nanostructures present on the wing surfaces. These were estimated as being in excess of 6.8 mN m, the first experimental estimate of such mechano-bactericidal surfaces. This simple model provides a convenient bottom-up approach toward understanding and characterizing the bactericidal properties of nanostructured surfaces.
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http://dx.doi.org/10.1021/acs.langmuir.8b03470DOI Listing
February 2019

Exposure to high-frequency electromagnetic field triggers rapid uptake of large nanosphere clusters by pheochromocytoma cells.

Int J Nanomedicine 2018 10;13:8429-8442. Epub 2018 Dec 10.

School of Science, RMIT University, Melbourne, VIC, Australia,

Background: Effects of man-made electromagnetic fields (EMF) on living organisms potentially include transient and permanent changes in cell behaviour, physiology and morphology. At present, these EMF-induced effects are poorly defined, yet their understanding may provide important insights into consequences of uncontrolled (, environmental) as well as intentional (, therapeutic or diagnostic) exposure of biota to EMFs. In this work, for the first time, we study mechanisms by which a high frequency (18 GHz) EMF radiation affects the physiology of membrane transport in pheochromocytoma PC 12, a convenient model system for neurotoxicological and membrane transport studies.

Methods And Results: Suspensions of the PC 12 cells were subjected to three consecutive cycles of 30s EMF treatment with a specific absorption rate (SAR) of 1.17 kW kg, with cells cooled between exposures to reduce bulk dielectric heating. The EMF exposure resulted in a transient increase in membrane permeability for 9 min in up to 90 % of the treated cells, as demonstrated by rapid internalisation of silica nanospheres (diameter ≈ 23.5 nm) and their clusters ( ≈ 63 nm). In contrast, the PC 12 cells that received an equivalent bulk heat treatment behaved similar to the untreated controls, showing lack to minimal nanosphere uptake of approximately 1-2 %. Morphology and growth of the EMF treated cells were not altered, indicating that the PC 12 cells were able to remain viable after the EMF exposure. The metabolic activity of EMF treated PC 12 cells was similar to that of the heat treated and control samples, with no difference in the total protein concentration and lactate dehydrogenase (LDH) release between these groups.

Conclusion: These results provide new insights into the mechanisms of EMF-induced biological activity in mammalian cells, suggesting a possible use of EMFs to facilitate efficient transport of biomolecules, dyes and tracers, and genetic material across cell membrane in drug delivery and gene therapy, where permanent permeabilisation or cell death is undesirable.
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http://dx.doi.org/10.2147/IJN.S183767DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6294056PMC
February 2019

Subtle Variations in Surface Properties of Black Silicon Surfaces Influence the Degree of Bactericidal Efficiency.

Nanomicro Lett 2018 6;10(2):36. Epub 2018 Feb 6.

1School of Science, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122 Australia.

One of the major challenges faced by the biomedical industry is the development of robust synthetic surfaces that can resist bacterial colonization. Much inspiration has been drawn recently from naturally occurring mechano-bactericidal surfaces such as the wings of cicada () and dragonfly () species in fabricating their synthetic analogs. However, the bactericidal activity of nanostructured surfaces is observed in a particular range of parameters reflecting the geometry of nanostructures and surface wettability. Here, several of the nanometer-scale characteristics of black silicon (bSi) surfaces including the density and height of the nanopillars that have the potential to influence the bactericidal efficiency of these nanostructured surfaces have been investigated. The results provide important evidence that minor variations in the nanoarchitecture of substrata can substantially alter their performance as bactericidal surfaces.
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http://dx.doi.org/10.1007/s40820-017-0186-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6199077PMC
February 2018

Imaging the air-water interface: Characterising biomimetic and natural hydrophobic surfaces using in situ atomic force microscopy.

J Colloid Interface Sci 2019 Feb 20;536:363-371. Epub 2018 Oct 20.

School of Science, College of Science, Engineering and Health, RMIT University, Melbourne VIC 3000, Australia. Electronic address:

The interface between water and a textured hydrophobic surface can exist in two regimes; either the Wenzel (surface-engulfed) or Cassie-Baxter (water-suspended) state. Better understanding of the influence of pattern geometry and spacing is crucial for the design of functional (super)hydrophobic surfaces, as inspired by numerous examples in nature. In this work, we have employed amplitude modulated - atomic force microscopy to visualize the air-water interface with an unprecedented degree of clarity on a superhydrophobic and a highly hydrophobic nanostructured surface. The images obtained provide the first real-time experimental visualization of the Cassie-Baxter wetting on the surface of biomimetic silicon nanopillars and a naturally superhydrophobic cicada wing. For both surfaces, the air-water interface was found to be remarkably well-defined, revealing a distinctly nanostructured air-water interface in the interstitial spacing. The degree of interfacial texture differed as a function of surface geometry. These results reveal that the air-water interface is heterogeneous in its structure and confirmed the presence of short-range interfacial ordering. Additionally, the overpressure values for each point on the interface were calculated, quantifying the difference in wetting behavior for the biomimetic and natural surface. Results suggest that highly-ordered, closely spaced nanofeatures facilitate robust Cassie-Baxter wetting states and therefore, can enhance the stability of (super)hydrophobic surfaces.
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http://dx.doi.org/10.1016/j.jcis.2018.10.059DOI Listing
February 2019

Pillars of Life: Is There a Relationship between Lifestyle Factors and the Surface Characteristics of Dragonfly Wings?

ACS Omega 2018 Jun 5;3(6):6039-6046. Epub 2018 Jun 5.

School of Science, College of Science, Engineering and Health, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.

Dragonfly wings are of great interest to researchers investigating biomimetic designs for antiwetting and antibacterial surfaces. The waxy epicuticular layer on the membrane of dragonfly wings possesses a unique surface nanoarchitecture that consists of irregular arrays of nanoscale pillars. This architecture confers superhydrophobic, self-cleaning, antiwetting, and antibiofouling behaviors. There is some evidence available that suggests that lifestyle factors may have influenced the evolution of the wing nanostructures and, therefore, the resulting properties of the wings; however, it appears that no systematic studies have been performed that have compared the wing surface features across a range of dragonfly species. Here, we provided a comparison of relevant wing surface characteristics, including chemical composition, wettability, and nanoarchitecture, of seven species of dragonfly from three families including , , and . The characteristic nanopillar arrays were found to be present, and the chemical composition and the resultant wing surface superhydrophobicity were found to be well-conserved across all of the species studied. However, subtle differences were observed between the height, width, and density of nanofeatures and water droplet bouncing behavior on the wing surfaces. The results of this research will contribute to an understanding of the physical and chemical surface features that are optimal for the design of antiwetting and antibacterial surfaces.
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http://dx.doi.org/10.1021/acsomega.8b00776DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6130794PMC
June 2018