Trends in Colloid and Interface Science XXIII, 2010
The bacterial attachment response on titanium surfaces with various degrees of nano-roughness in ... more The bacterial attachment response on titanium surfaces with various degrees of nano-roughness in the range of 14 nm to 0.6 nm has been investigated. Titanium surfaces were fabricated from commercial purity grade 2 (as-received) titanium, titanium modified by equal channel angular pressing (modified titanium) and titanium thin film of 12 nm and 150 nm obtained using a magnetron sputtering system. The chemical composition, wettability and surface architecture of Ti surfaces were characterised using X-ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy. Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025 were found to respond differently to each of the tested surfaces. The results indicate that bacteria can differentiate between surfaces with the fine (less than 1 nm) change of topographic characteristics, the number of retained cells differing by a factor of up to 2.
The nanometer scale surface topography of a solid substrate is known to influence the extent of b... more The nanometer scale surface topography of a solid substrate is known to influence the extent of bacterial attachment and their subsequent proliferation to form biofilms. As an extension of our previous work on the development of a novel organic polymer coating for the prevention of growth of medically significant bacteria on three-dimensional solid surfaces, this study examines the effect of surface coating on the adhesion and proliferation tendencies of Staphylococcus aureus and compares to those previously investigated tendencies of Pseudomonas aeruginosa on similar coatings. Radio frequency plasma enhanced chemical vapor deposition was used to coat the surface of the substrate with thin film of terpinen-4-ol, a constituent of tea-tree oil known to inhibit the growth of a broad range of bacteria. The presence of the coating decreased the substrate surface roughness from approximately 2.1 nm to 0.4 nm. Similar to P. aeruginosa, S. aureus presented notably different patterns of attachment in response to the presence of the surface film, where the amount of attachment, extracellular polymeric substance production, and cell proliferation on the coated surface was found to be greatly reduced compared to that obtained on the unmodified surface. This work suggests that the antimicrobial and antifouling coating used in this study could be effectively integrated into
The effect of sub-nano-metric surface roughness of Ti thin films surfaces on the attachment of tw... more The effect of sub-nano-metric surface roughness of Ti thin films surfaces on the attachment of two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025, was studied. A magnetron sputtering thin film deposition system was used to control the titanium thin film thicknesses of 3 nm, 12 nm and 150 nm on silicon wafers with the correspondent surface roughness parameters of Rq 0.14 nm, 0.38 nm and 5.55 nm (1 m 1 m scanning area). Analysis of bacterial retention profiles showed that the bacteria responded differently to a less than 1 nm change in the Ra and Rq (Ti thin film) surface roughness parameters, with up to 2 -3 times more cells being retained on the surface, and elevated levels of extracellular polymeric substances being secreted on the Ti thin films, in particular on the surfaces with 0.14 nm (Rq) roughness.
Two-tier micro-and nanoscale quasi-periodic self-organized structures, mimicking the surface of a... more Two-tier micro-and nanoscale quasi-periodic self-organized structures, mimicking the surface of a lotus Nelumbo nucifera leaf, were fabricated on titanium surfaces using femtosecond laser ablation. The first tier consisted of large grainlike convex features between 10 and 20 μm in size. The second tier existed on the surface of these grains, where 200 nm (or less) wide irregular undulations were present. The introduction of the biomimetic surface patterns significantly transformed the surface wettabilty of the titanium surface. The original surface possessed a water contact angle of θ W 73 ( 3°, whereas the laser-treated titanium surface became superhydrophobic, with a water contact angle of θ W 166 ( 4°. Investigations of the interaction of S. aureus and P. aeruginosa with these superhydrophobic surfaces at the surface-liquid interface revealed a highly selective retention pattern for two pathogenic bacteria. While S. aureus cells were able to successfully colonize the superhydrophobic titanium surfaces, no P. aeruginosa cells were able to attach to the surface (i.e., any attached bacterial cells were below the estimated lower detection limit).
Magnetron sputtering techniques were used to prepare molecularly smooth titanium thin films posse... more Magnetron sputtering techniques were used to prepare molecularly smooth titanium thin films possessing an average roughness between 0.18 nm and 0.52 nm over 5 mm 3 5 mm AFM scanning areas. Films with an average roughness of 0.52 nm or lower were found to restrict the extent of P. aeruginosa cell attachment, with less than 0.5% of all available cells being retained on the surface. The attachment of S. aureus cells was also limited on films with an average surface roughness of 0.52 nm, however they exhibited a remarkable propensity for attachment on the nano-smoother 0.18 nm average surface roughness films, with the attachment density being almost twice as great as that observed on the nano-rougher film. The difference in attachment behaviour can be attributed to the difference in morphology of the rod-shaped P. aeruginosa compared to the spherical S. aureus cells. SUBJECT AREAS: NANOBIOTECHNOLOGY CELLULAR MICROBIOLOGY BIOPHYSICS CELL BIOLOGY How to cite this article: Ivanova, E.P. et al. Differential attraction and repulsion of Staphylococcus aureus and Pseudomonas aeruginosa on molecularly smooth titanium films.
Numerous insects have evolved to possess superhydrophobic surfaces, which are thought to limit ba... more Numerous insects have evolved to possess superhydrophobic surfaces, which are thought to limit bacterial contamination through a self-cleaning action. While investigating the adhesion of Pseudomonas aeruginosa on the wings of a species of cicada (Psaltoda claripennis), we discovered that the wing surfaces were actually deadly to the cells. Electron microscopy showed nanopillars on the surface penetrating the cells, which was confirmed to be lethal through viability experiments. The effect was very fast, with individual bacterial ...
The nanoarchitecture and surface roughness of metallic thin films prepared by magnetron sputterin... more The nanoarchitecture and surface roughness of metallic thin films prepared by magnetron sputtering were analyzed to determine the topographical statistics that give the optimum description of their nanoarchitechture. Nanoscale topographical profiles were generated by performing atomic force microscopy (AFM) scans of 1 μm × 1 μm areas of titanium and silver films of three different thicknesses (3 nm, 12 nm, and 150 nm). Of the titanium films, the 150-nm film had the highest average roughness (R a = 2.63 nm), more than four times that of the 3-nm and 12-nm titanium films. When silver films were coated on top of 150-nm titanium films, the average roughness increased further; the 3-nm (R a = 4.96 nm) and 150-nm (R a = 4.65 nm) silver films average roughnesses were approximately twice that of the 150-nm titanium film. For topographical analysis, seven statistical parameters were calculated. These parameters included commonly used roughness measurements, as well as some less commonly used measurements, in order to determine which combination of parameters gave the best overall description of the nanoarchitecture of the films presented. Skewness (R skw ), surface area increase (R sa ), and peak counts (R pc ) provided the best description of horizontal surface dimensions, and in conjunction with vertical descriptors R a and R q gave the best characterization of surface architecture. The five roughness parameters R a , R q , R skw , R sa , and R pc are proposed as a new standard for describing surface nanoarchitecture.
Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 902... more Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025, were adsorbed onto surfaces containing Ti thin films of varying thickness to determine the extent to which nanoscale surface roughness influences the extent of bacterial attachment. A magnetron sputter thin film system was used to deposit titanium films with thicknesses of 3, 12, and 150 nm on glass substrata with corresponding surface roughness parameters of R q 1.6, 1.2, and 0.7 nm (on a 4 μm  4 μm scanning area). The chemical composition, wettability, and surface architecture of titanium thin films were characterized using X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, three-dimensional interactive visualization, and statistical approximation of the topographic profiles. Investigation of the dynamic evolution of the Ti thin film topographic parameters indicated that three commonly used parameters, R a , R q , and R max , were insufficient to effectively characterize the nanoscale rough/smooth surfaces. Two additional parameters, R skw and R kur , which describe the statistical distributions of roughness character, were found to be useful for evaluating the surface architecture. Analysis of bacterial retention profiles indicated that bacteria responded differently to the surfaces on a scale of less than 1 nm change in the R a and R q Ti thin film surface roughness parameters by (i) an increased number of retained cells by a factor of 2-3, and (ii) an elevated level of secretion of extracellular polymeric substances.
Self-cleaning surfaces found in nature show great potential for application in many fields, rangi... more Self-cleaning surfaces found in nature show great potential for application in many fields, ranging from industry to medicine. The ability for a surface to self-clean is intimately related to the wetting properties of the surface; for a surface to possess self-cleaning ability it must exhibit extremely high water contact angles and low water adhesion. While investigating the self-cleaning properties of damselfly wings, significant spatial variations in surface wettability were observed. Within an area of 100 μm × 100 μm of the wing surface the water contact angle was found to vary up to 17.8°, while remaining consistently superhydrophobic. The contributions of both surface chemistry and topography to the hydrophobicity of the wings were assessed in an effort to explain these variations. Synchrotron-sourced Fourier-transform infrared microspectroscopy revealed that some of the major components of the wing were aliphatic hydrocarbons and esters, which are attributable to epicuticular lipids. The wing topography, as determined by optical profilometry and atomic force microscopy (AFM), also showed only minor levels of heterogeneity arising from irregular ordering of surface nanostructures. The measured contact angle of a single droplet of water was also found to decrease over time as it evaporated, reaching a minimum of 107°. This is well below the threshold value for superhydrophobicity (i.e., 150°), demonstrating that when the surface is in contact with water for a prolonged period, the damselfly wings lose their superhydrophobicity and subsequently their ability to self-clean. This decrease in hydrophobicity over time can be attributed to the surface undergoing a transition from the Cassie-Baxter wettability state toward the Wenzel wettability state.
Atomic force microscopy (AFM) is a technique that has long been employed in materials science, bu... more Atomic force microscopy (AFM) is a technique that has long been employed in materials science, but is now increasingly being used in the biological sciences. AFM provides excellent topographical information on prokaryotic and eukaryotic cell surfaces, and the extracellular material produced by the cells. It helps to generate important data on the mechanical properties of cells, such as hardness and elasticity. AFM can also be used to measure the strength of adhesion, attraction, and repulsion forces between cells and surfaces or even between individual molecules. Additionally, by combining AFM with other complementary techniques such as fluorescence microscopy or Raman spectroscopy, the chemistry of given surface structures can be identified. This review aims to provide an update on the AFM techniques currently used in cell biology studies, along with a description of the range of recently developed research methodologies in which AFM plays a key role.
Attachment tendencies of Escherichia coli K12, Pseudomonas aeruginosa ATCC 9027, and Staphylococc... more Attachment tendencies of Escherichia coli K12, Pseudomonas aeruginosa ATCC 9027, and Staphylococcus aureus CIP 68.5 onto glass surfaces of different degrees of nanometer-scale roughness have been studied. Contact-angle and surface-charge measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM) were employed to characterize substrata and bacterial surfaces. Modification of the glass surface resulted in nanometer-scale changes in the surface topography, whereas the physicochemical characteristics of the surfaces remained almost constant. AFM analysis indicated that the overall surface roughness parameters were reduced by 60-70%. SEM, CLSM, and AFM analysis clearly demonstrates that although E. coli, P. aeruginosa and S. aureus present significantly different patterns of attachment, all of the species exhibited a greater propensity for adhesion to the ''nano-smooth'' surface. The bacteria responded to the surface modification with a remarkable change in cellular metabolic activity, as shown by the characteristic cell morphologies, production of extracellular polymeric substances, and an increase in the number of bacterial cells undergoing attachment.
Untreated recycled water, such as sewage and graywater, will almost always contain a wide range o... more Untreated recycled water, such as sewage and graywater, will almost always contain a wide range of agents that are likely to present risks to human health, including chemicals and pathogenic microorganisms. The microbial hazards, such as large numbers of enteric pathogens that can cause gastroenteric illness if ingested, are the main cause of concern for human health. The presence of the enteropathogenic Escherichia coli (EPEC) serotype is of particular concern, as this group of bacteria is responsible for causing severe infant and travelers' diarrhea, gastroenteritis and hemolytic uremic syndrome. A biosensing system based on an optical Fabry-Pérot (FP) cavity, capable of directly detecting the presence of EPEC within 5 min, has been developed using a simple micro-thin double-sided adhesive tape and two semitransparent FP mirror plates. The system utilizes a poly(methyl methacrylate) (PMMA) or glass substrates sputtered by 40-nm-thick gold thin films serving as FP mirrors. Mirrors have been activated using 0.1 M mercaptopropionic acid, influencing an immobilization density of the translocated intimin receptor (TIR) of 100 ng/cm 2 . The specificity of recognition was confirmed by exposing TIR functionalized surfaces to four taxonomically related and/or distantly related bacterial strains. It was found that the TIR-functionalized surfaces did not show any bacterial capture for these other bacterial strains within a 15 min incubation period.
The nano-pattern on the surface of the Clanger cicada (Psaltoda claripennis) wings represents the... more The nano-pattern on the surface of the Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. They provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and the cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. This was experimentally confirmed by decreasing the rigidity of 'surface-resistant' strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. These findings demonstrate the potential benefits of incorporating cicada wing nano-patterns into the design of antibacterial nanomaterials.
We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, ... more We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, Grade-2) on bacterial attachment to the mechano-chemically polished surfaces of the material. The ultrafine crystallinity of the bulk was achieved by severe plastic deformation by means of equal channel angular pressing (ECAP). The chemical composition, wettability, surface topography and roughness of titanium surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements, as well as atomic force microscopy (AFM) with 3D interactive visualization of the titanium surface morphology. It was found that physico-chemical surface characteristics of the as-received and the ECAP-modified CP titanium did not differ in any significant way, while the surface roughness at the nano-scale did. Optical profilometry performed on large scanning areas of approximately 225 mm  300 mm showed that there was no significant difference between the roughness parameters R a and R q for surfaces in the two conditions, the overall level of roughness being lower for the ECAPprocessed one. By contrast, topographic profile analysis at the nano-scale by AFM did reveal a difference in these parameters. This difference was sensitive to the size of the scanned surface area. A further two surface roughness parameters, skewness (R skw ) and kurtosis (R kur ), were also used to describe the morphology of titanium surfaces. It was found that the bacterial strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 65.8 and Pseudomonas aeruginosa ATCC 9025, showed preference for surfaces of ECAP-processed titanium. S. aureus cells were found to have a greater propensity for attachment to surfaces of ECAP-modified titanium, while the attachment of P. aeruginosa, while also showing some preference for the ECAP-processed material, was less sensitive to the ECAP processing.
Optical fibres have received considerable attention as high-density sensor arrays suitable for bo... more Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 mm in diameter and 2.5 mm deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R q ¼ 273 nm), non-etched fibre surfaces (water contact angle, y ¼ 1068 + 48). In comparison, the surfaces of the etched optical fibres (water contact angle, y ¼ 968 + 108) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.
The retention patterns of five taxonomically different marine bacteria after attachment on two ty... more The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a *1 nm decrease in the average surface roughness (R a ) and the root-mean-squared roughness (R q ) and in a *8 nm decrease in the surface height and the peak-to-peak (R max ) and the 10-point average roughness (R z ). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.
Trends in Colloid and Interface Science XXIII, 2010
The bacterial attachment response on titanium surfaces with various degrees of nano-roughness in ... more The bacterial attachment response on titanium surfaces with various degrees of nano-roughness in the range of 14 nm to 0.6 nm has been investigated. Titanium surfaces were fabricated from commercial purity grade 2 (as-received) titanium, titanium modified by equal channel angular pressing (modified titanium) and titanium thin film of 12 nm and 150 nm obtained using a magnetron sputtering system. The chemical composition, wettability and surface architecture of Ti surfaces were characterised using X-ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy. Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025 were found to respond differently to each of the tested surfaces. The results indicate that bacteria can differentiate between surfaces with the fine (less than 1 nm) change of topographic characteristics, the number of retained cells differing by a factor of up to 2.
The nanometer scale surface topography of a solid substrate is known to influence the extent of b... more The nanometer scale surface topography of a solid substrate is known to influence the extent of bacterial attachment and their subsequent proliferation to form biofilms. As an extension of our previous work on the development of a novel organic polymer coating for the prevention of growth of medically significant bacteria on three-dimensional solid surfaces, this study examines the effect of surface coating on the adhesion and proliferation tendencies of Staphylococcus aureus and compares to those previously investigated tendencies of Pseudomonas aeruginosa on similar coatings. Radio frequency plasma enhanced chemical vapor deposition was used to coat the surface of the substrate with thin film of terpinen-4-ol, a constituent of tea-tree oil known to inhibit the growth of a broad range of bacteria. The presence of the coating decreased the substrate surface roughness from approximately 2.1 nm to 0.4 nm. Similar to P. aeruginosa, S. aureus presented notably different patterns of attachment in response to the presence of the surface film, where the amount of attachment, extracellular polymeric substance production, and cell proliferation on the coated surface was found to be greatly reduced compared to that obtained on the unmodified surface. This work suggests that the antimicrobial and antifouling coating used in this study could be effectively integrated into
The effect of sub-nano-metric surface roughness of Ti thin films surfaces on the attachment of tw... more The effect of sub-nano-metric surface roughness of Ti thin films surfaces on the attachment of two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025, was studied. A magnetron sputtering thin film deposition system was used to control the titanium thin film thicknesses of 3 nm, 12 nm and 150 nm on silicon wafers with the correspondent surface roughness parameters of Rq 0.14 nm, 0.38 nm and 5.55 nm (1 m 1 m scanning area). Analysis of bacterial retention profiles showed that the bacteria responded differently to a less than 1 nm change in the Ra and Rq (Ti thin film) surface roughness parameters, with up to 2 -3 times more cells being retained on the surface, and elevated levels of extracellular polymeric substances being secreted on the Ti thin films, in particular on the surfaces with 0.14 nm (Rq) roughness.
Two-tier micro-and nanoscale quasi-periodic self-organized structures, mimicking the surface of a... more Two-tier micro-and nanoscale quasi-periodic self-organized structures, mimicking the surface of a lotus Nelumbo nucifera leaf, were fabricated on titanium surfaces using femtosecond laser ablation. The first tier consisted of large grainlike convex features between 10 and 20 μm in size. The second tier existed on the surface of these grains, where 200 nm (or less) wide irregular undulations were present. The introduction of the biomimetic surface patterns significantly transformed the surface wettabilty of the titanium surface. The original surface possessed a water contact angle of θ W 73 ( 3°, whereas the laser-treated titanium surface became superhydrophobic, with a water contact angle of θ W 166 ( 4°. Investigations of the interaction of S. aureus and P. aeruginosa with these superhydrophobic surfaces at the surface-liquid interface revealed a highly selective retention pattern for two pathogenic bacteria. While S. aureus cells were able to successfully colonize the superhydrophobic titanium surfaces, no P. aeruginosa cells were able to attach to the surface (i.e., any attached bacterial cells were below the estimated lower detection limit).
Magnetron sputtering techniques were used to prepare molecularly smooth titanium thin films posse... more Magnetron sputtering techniques were used to prepare molecularly smooth titanium thin films possessing an average roughness between 0.18 nm and 0.52 nm over 5 mm 3 5 mm AFM scanning areas. Films with an average roughness of 0.52 nm or lower were found to restrict the extent of P. aeruginosa cell attachment, with less than 0.5% of all available cells being retained on the surface. The attachment of S. aureus cells was also limited on films with an average surface roughness of 0.52 nm, however they exhibited a remarkable propensity for attachment on the nano-smoother 0.18 nm average surface roughness films, with the attachment density being almost twice as great as that observed on the nano-rougher film. The difference in attachment behaviour can be attributed to the difference in morphology of the rod-shaped P. aeruginosa compared to the spherical S. aureus cells. SUBJECT AREAS: NANOBIOTECHNOLOGY CELLULAR MICROBIOLOGY BIOPHYSICS CELL BIOLOGY How to cite this article: Ivanova, E.P. et al. Differential attraction and repulsion of Staphylococcus aureus and Pseudomonas aeruginosa on molecularly smooth titanium films.
Numerous insects have evolved to possess superhydrophobic surfaces, which are thought to limit ba... more Numerous insects have evolved to possess superhydrophobic surfaces, which are thought to limit bacterial contamination through a self-cleaning action. While investigating the adhesion of Pseudomonas aeruginosa on the wings of a species of cicada (Psaltoda claripennis), we discovered that the wing surfaces were actually deadly to the cells. Electron microscopy showed nanopillars on the surface penetrating the cells, which was confirmed to be lethal through viability experiments. The effect was very fast, with individual bacterial ...
The nanoarchitecture and surface roughness of metallic thin films prepared by magnetron sputterin... more The nanoarchitecture and surface roughness of metallic thin films prepared by magnetron sputtering were analyzed to determine the topographical statistics that give the optimum description of their nanoarchitechture. Nanoscale topographical profiles were generated by performing atomic force microscopy (AFM) scans of 1 μm × 1 μm areas of titanium and silver films of three different thicknesses (3 nm, 12 nm, and 150 nm). Of the titanium films, the 150-nm film had the highest average roughness (R a = 2.63 nm), more than four times that of the 3-nm and 12-nm titanium films. When silver films were coated on top of 150-nm titanium films, the average roughness increased further; the 3-nm (R a = 4.96 nm) and 150-nm (R a = 4.65 nm) silver films average roughnesses were approximately twice that of the 150-nm titanium film. For topographical analysis, seven statistical parameters were calculated. These parameters included commonly used roughness measurements, as well as some less commonly used measurements, in order to determine which combination of parameters gave the best overall description of the nanoarchitecture of the films presented. Skewness (R skw ), surface area increase (R sa ), and peak counts (R pc ) provided the best description of horizontal surface dimensions, and in conjunction with vertical descriptors R a and R q gave the best characterization of surface architecture. The five roughness parameters R a , R q , R skw , R sa , and R pc are proposed as a new standard for describing surface nanoarchitecture.
Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 902... more Two human pathogenic bacteria, Staphylococcus aureus CIP 68.5 and Pseudomonas aeruginosa ATCC 9025, were adsorbed onto surfaces containing Ti thin films of varying thickness to determine the extent to which nanoscale surface roughness influences the extent of bacterial attachment. A magnetron sputter thin film system was used to deposit titanium films with thicknesses of 3, 12, and 150 nm on glass substrata with corresponding surface roughness parameters of R q 1.6, 1.2, and 0.7 nm (on a 4 μm  4 μm scanning area). The chemical composition, wettability, and surface architecture of titanium thin films were characterized using X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, three-dimensional interactive visualization, and statistical approximation of the topographic profiles. Investigation of the dynamic evolution of the Ti thin film topographic parameters indicated that three commonly used parameters, R a , R q , and R max , were insufficient to effectively characterize the nanoscale rough/smooth surfaces. Two additional parameters, R skw and R kur , which describe the statistical distributions of roughness character, were found to be useful for evaluating the surface architecture. Analysis of bacterial retention profiles indicated that bacteria responded differently to the surfaces on a scale of less than 1 nm change in the R a and R q Ti thin film surface roughness parameters by (i) an increased number of retained cells by a factor of 2-3, and (ii) an elevated level of secretion of extracellular polymeric substances.
Self-cleaning surfaces found in nature show great potential for application in many fields, rangi... more Self-cleaning surfaces found in nature show great potential for application in many fields, ranging from industry to medicine. The ability for a surface to self-clean is intimately related to the wetting properties of the surface; for a surface to possess self-cleaning ability it must exhibit extremely high water contact angles and low water adhesion. While investigating the self-cleaning properties of damselfly wings, significant spatial variations in surface wettability were observed. Within an area of 100 μm × 100 μm of the wing surface the water contact angle was found to vary up to 17.8°, while remaining consistently superhydrophobic. The contributions of both surface chemistry and topography to the hydrophobicity of the wings were assessed in an effort to explain these variations. Synchrotron-sourced Fourier-transform infrared microspectroscopy revealed that some of the major components of the wing were aliphatic hydrocarbons and esters, which are attributable to epicuticular lipids. The wing topography, as determined by optical profilometry and atomic force microscopy (AFM), also showed only minor levels of heterogeneity arising from irregular ordering of surface nanostructures. The measured contact angle of a single droplet of water was also found to decrease over time as it evaporated, reaching a minimum of 107°. This is well below the threshold value for superhydrophobicity (i.e., 150°), demonstrating that when the surface is in contact with water for a prolonged period, the damselfly wings lose their superhydrophobicity and subsequently their ability to self-clean. This decrease in hydrophobicity over time can be attributed to the surface undergoing a transition from the Cassie-Baxter wettability state toward the Wenzel wettability state.
Atomic force microscopy (AFM) is a technique that has long been employed in materials science, bu... more Atomic force microscopy (AFM) is a technique that has long been employed in materials science, but is now increasingly being used in the biological sciences. AFM provides excellent topographical information on prokaryotic and eukaryotic cell surfaces, and the extracellular material produced by the cells. It helps to generate important data on the mechanical properties of cells, such as hardness and elasticity. AFM can also be used to measure the strength of adhesion, attraction, and repulsion forces between cells and surfaces or even between individual molecules. Additionally, by combining AFM with other complementary techniques such as fluorescence microscopy or Raman spectroscopy, the chemistry of given surface structures can be identified. This review aims to provide an update on the AFM techniques currently used in cell biology studies, along with a description of the range of recently developed research methodologies in which AFM plays a key role.
Attachment tendencies of Escherichia coli K12, Pseudomonas aeruginosa ATCC 9027, and Staphylococc... more Attachment tendencies of Escherichia coli K12, Pseudomonas aeruginosa ATCC 9027, and Staphylococcus aureus CIP 68.5 onto glass surfaces of different degrees of nanometer-scale roughness have been studied. Contact-angle and surface-charge measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM) were employed to characterize substrata and bacterial surfaces. Modification of the glass surface resulted in nanometer-scale changes in the surface topography, whereas the physicochemical characteristics of the surfaces remained almost constant. AFM analysis indicated that the overall surface roughness parameters were reduced by 60-70%. SEM, CLSM, and AFM analysis clearly demonstrates that although E. coli, P. aeruginosa and S. aureus present significantly different patterns of attachment, all of the species exhibited a greater propensity for adhesion to the ''nano-smooth'' surface. The bacteria responded to the surface modification with a remarkable change in cellular metabolic activity, as shown by the characteristic cell morphologies, production of extracellular polymeric substances, and an increase in the number of bacterial cells undergoing attachment.
Untreated recycled water, such as sewage and graywater, will almost always contain a wide range o... more Untreated recycled water, such as sewage and graywater, will almost always contain a wide range of agents that are likely to present risks to human health, including chemicals and pathogenic microorganisms. The microbial hazards, such as large numbers of enteric pathogens that can cause gastroenteric illness if ingested, are the main cause of concern for human health. The presence of the enteropathogenic Escherichia coli (EPEC) serotype is of particular concern, as this group of bacteria is responsible for causing severe infant and travelers' diarrhea, gastroenteritis and hemolytic uremic syndrome. A biosensing system based on an optical Fabry-Pérot (FP) cavity, capable of directly detecting the presence of EPEC within 5 min, has been developed using a simple micro-thin double-sided adhesive tape and two semitransparent FP mirror plates. The system utilizes a poly(methyl methacrylate) (PMMA) or glass substrates sputtered by 40-nm-thick gold thin films serving as FP mirrors. Mirrors have been activated using 0.1 M mercaptopropionic acid, influencing an immobilization density of the translocated intimin receptor (TIR) of 100 ng/cm 2 . The specificity of recognition was confirmed by exposing TIR functionalized surfaces to four taxonomically related and/or distantly related bacterial strains. It was found that the TIR-functionalized surfaces did not show any bacterial capture for these other bacterial strains within a 15 min incubation period.
The nano-pattern on the surface of the Clanger cicada (Psaltoda claripennis) wings represents the... more The nano-pattern on the surface of the Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. They provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and the cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. This was experimentally confirmed by decreasing the rigidity of 'surface-resistant' strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. These findings demonstrate the potential benefits of incorporating cicada wing nano-patterns into the design of antibacterial nanomaterials.
We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, ... more We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, Grade-2) on bacterial attachment to the mechano-chemically polished surfaces of the material. The ultrafine crystallinity of the bulk was achieved by severe plastic deformation by means of equal channel angular pressing (ECAP). The chemical composition, wettability, surface topography and roughness of titanium surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements, as well as atomic force microscopy (AFM) with 3D interactive visualization of the titanium surface morphology. It was found that physico-chemical surface characteristics of the as-received and the ECAP-modified CP titanium did not differ in any significant way, while the surface roughness at the nano-scale did. Optical profilometry performed on large scanning areas of approximately 225 mm  300 mm showed that there was no significant difference between the roughness parameters R a and R q for surfaces in the two conditions, the overall level of roughness being lower for the ECAPprocessed one. By contrast, topographic profile analysis at the nano-scale by AFM did reveal a difference in these parameters. This difference was sensitive to the size of the scanned surface area. A further two surface roughness parameters, skewness (R skw ) and kurtosis (R kur ), were also used to describe the morphology of titanium surfaces. It was found that the bacterial strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 65.8 and Pseudomonas aeruginosa ATCC 9025, showed preference for surfaces of ECAP-processed titanium. S. aureus cells were found to have a greater propensity for attachment to surfaces of ECAP-modified titanium, while the attachment of P. aeruginosa, while also showing some preference for the ECAP-processed material, was less sensitive to the ECAP processing.
Optical fibres have received considerable attention as high-density sensor arrays suitable for bo... more Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 mm in diameter and 2.5 mm deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R q ¼ 273 nm), non-etched fibre surfaces (water contact angle, y ¼ 1068 + 48). In comparison, the surfaces of the etched optical fibres (water contact angle, y ¼ 968 + 108) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.
The retention patterns of five taxonomically different marine bacteria after attachment on two ty... more The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a *1 nm decrease in the average surface roughness (R a ) and the root-mean-squared roughness (R q ) and in a *8 nm decrease in the surface height and the peak-to-peak (R max ) and the 10-point average roughness (R z ). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.
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Papers by V. Truong