Patricia L. Schilardi

Spontaneous adsorption of silver nanoparticles on Ti/TiO2 surfaces. Antibacterial effect on Pseudomonas aeruginosa

Titanium is a corrosion-resistant and biocompatible material widely used in medical and dental implants. Titanium surfaces, however, are prone to bacterial colonization that could lead to infection, inflammation, and finally to implant failure. Silver nanoparticles (AgNPs) have demonstrated an excellent performance as biocides, and thus their integration to titanium surfaces is an attractive strategy to decrease the risk of implant failure. In this work a simple and efficient method is described to modify Ti/TiO(2) surfaces with citrate-capped AgNPs. These nanoparticles spontaneously adsorb on Ti/TiO(2), forming nanometer-sized aggregates consisting of individual AgNPs that homogeneously cover the surface. The modified AgNP-Ti/TiO(2) surface exhibits a good resistance to colonization by Pseudomonas aeruginosa, a model system for biofilm formation.

Citrate-Capped Silver Nanoparticles Showing Good Bactericidal Effect against Both Planktonic and Sessile Bacteria and a Low Cytotoxicity to Osteoblastic Cells

A common problem with implants is that bacteria can form biofilms on their surfaces, which can lead to infection and, eventually, to implant rejection. An interesting strategy to inhibit bacterial colonization is the immobilization of silver (Ag) species on the surface of the devices. The aim of this paper is to investigate the action of citrate-capped silver nanoparticles (AgNPs) on clinically relevant Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria in two different situations: (i) dispersed AgNPs (to assess the effect of AgNPs against planktonic bacteria) and (ii) adsorbed AgNPs on titanium (Ti) substrates, a material widely used for implants (to test their effect against sessile bacteria). In both cases, the number of surviving cells was quantified. The small amount of Ag on the surface of Ti has an antimicrobial effect similar to that of pure Ag surfaces. We have also investigated the capability of AgNPs to kill planktonic bacteria and their cytotoxic effect on UMR-106 osteoblastic cells. The minimum bactericidal concentration found for both strains is much lower than the AgNP concentration that leads to cytotoxicity to osteoblasts. Planktonic P. aeruginosa show a higher susceptibility to Ag than S. aureus, which can be caused by the different wall structures, while for sessile bacteria, similar results are obtained for both strains. This can be explained by the presence of extracellular polymeric substances in the early stages of P. aeruginosa biofilm formation. Our findings can be important to improving the performance of Ti-based implants because a good bactericidal action is obtained with very small quantities of Ag, which are not detrimental to the cells involved in the osseointegration process.

Influence of the nano-micro structure of the surface on bacterial adhesion

Biomaterials failures are frequently associated to the formation of bacterial biofilms on the surface. The aim of this work is to study the adhesion of non motile bacteria streptococci consortium and motile Pseudomonas fluorescens. Substrates with micro and nanopatterned topography were used. The influence of surface characteristics on bacterial adhesion was investigated using optical and epifluorescence microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results showed an important influence of the substratum nature. On microrough surfaces, initial bacterial adhesion was less significant than on smooth surfaces. In contrast, nanopatterned samples showed more bacterial attachment than the smooth control. It was also noted a remarkable difference in morphology, orientation and distribution of bacteria between the smooth and the nanostructured substrate. The results show the important effect of substratum nature and topography on bacterial adhesion which depended on the relation between roughness characteristics dimensions and bacterial size.

Submicron trenches reduce the Pseudomonas fluorescens colonization rate on solid surfaces.

Bacterial adhesion and spreading on biomaterials are considered key features of pathogenicity. Roughness and topography of the substrate have been reported to affect bacterial adhesion, but little is known about their effect on spreading. Submicron row and channel tuning with bacterial diameter (S2) were designed to test bacterial motility on these surfaces. Random nanometer-sized structures (S1) were used as controls. Optical microscopy and AFM were employed to detect biological and surface pattern details in the micro- and nanoscale, respectively. Results showed that motility strategies (flagella orientation, elongation, aggregation in rafts, formation of network structures, and development of a bacterial frontier) were affected by the presence of submicropatterns. Importantly, the rate of bacterial spreading on S2 was significantly reduced and influenced by the orientation of the submicropatterns. Consequently, submicroengineered substrates could be employed as a tool to downgrade bacterial colonization. Such patterns could impact on the design of proper engineered structures to control biofilm spreading on solid surfaces.

Metal electrodeposition on self-assembled monolayers: a versatile tool for pattern transfer on metal thin films

Self-assembled monolayers (SAMs) of thiols on metals have attracted considerable scientific interest because their wide range of applications including their potential use for serial fabrication of nano/microstructures. Different methods have been proposed involving SAM patterning by different techniques. The patterned SAM is then used as a resist for etching, deposition on the uncovered regions or for self-assembly on the patterned SAM surface. In this work new applications of SAM-covered metals based on their excellent anti-adherent properties and their ability to allow pattern transfer from a metallic substrate to metal or alloy electrodeposits are presented. We have used electrodeposition on SAM-covered electrodes to prepare thin standing-free metal or alloy films, for patterning metal and alloy surfaces in the micro- and meso- scale, and to fabricate metallic molds and replicas of metallic masters. The SAM-covered molds produced by this technique can also be used for patterning soft and rigid polymeric films. The method is fast, inexpensive and requires only basic instrumentation available at any chemical laboratory.

Have flagella a preferred orientation during early stages of biofilm formation?: AFM study using patterned substrates

Biofilm development involves several stages and flagellar expression of bacteria is considered an important factor in this process. However, its role in the earliest stage of biofilm development is not yet clear. In order to analyse this topic, Pseudomonas fluorescens samples were trapped on a patterned gold surface with sub-microtrenches (ST) so as to hinder their motility, and nanostructured gold with random orientation (SR) was used as control substrate. Atomic force microscopic (AFM) observations were made on untreated samples. Initially, ca. 75% of the flagella on ST and 85% of flagella on SR are oriented towards the neighbouring bacteria. Some of them made contact and surrounded the cells. Subsequently, 2-D raft structures formed on SR inert substrates with lateral curly flagella, while those at the poles of the rafts turned towards the nearest cell group. A few flagella and the formation of 3-D bacterial structures were observed on toxic substrates like copper. Results showed that patterned substrates are suitable tools to detect the orientation of flagella in the earliest stage of biofilm formation on solid opaque surfaces avoiding sample pre-treatment.

Organization of Pseudomonas fluorescens on Chemically Different Nano/Microstructured Surfaces

This paper describes bacterial organization on nano/micropatterned surfaces with different chemical properties, which show different interactions with the biological systems (inert, biocompatible, and bactericide). These surfaces were prepared by molding techniques and exposed to Pseudomonas fluorescens (P. fluorescens) cultures. Results from atomic force microscopy and optical imaging demonstrate that the structure of P. fluorescens aggregates is strongly dependent on the surface topography while there is no clear linking with the physical-chemical surface properties (charge and contact angle) of the substrate immersed in abiotic culture media. We observe that regardless of the material when the surface pattern matches the bacterial size, bacterial assemblages involved in surface colonization are disorganized. The fact there is not a relationship between surface chemistry and bacterial organization can be explained by the coverage of the surfaces by adsorbed organic species coming from the culture medium. Viability assays indicate that copper behaves as a toxic substrate despite the presence of adsorbed molecules. The combination of surface traps and biocidal activity could act synergistically as a suitable strategy to limit bacterial spreading on implant materials.

Extrinsic origin of ferromagnetism in single crystalline LaAlO3 substrates and oxide films

Commercial LaAlO3 substrates were thermally cycled simulating a procedure similar to those followed during TiO2 and SnO2 dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO2 films is of extrinsic origin.

Templated electrodeposition of patterned soft magnetic films

Fabrication of patterned magnetic CoNiFe films by the thiol-assisted templated electrodeposition method is described. This method involves electrodeposition of the alloy components from their ionic species in solution on a dodecanethiol-covered Cu template. The ultrathin alkanethiol layer enables nano/micrometer pattern transfer and easy detachment of the magnetic film from the template. This method opens the possibility of fabricating nano/micropatterned chemically complex alloy structures in an extremely easy way with very few intermediate steps.

Influence of Surface Sub‐micropattern on the Adhesion of Pioneer Bacteria on Metals

Most of the implantable medical devices are prone to infection caused by microorganisms that form biofilms. Pseudomonads are frequently used as model species for studying bacterial adhesion. The initial stages of biofilm formation are influenced by different factors including, among others, the chemistry of the surface, the roughness, and topography. The aim of this work was to assess the early stages of Pseudomonas fluorescens biofilm formation on sub-microstructured surfaces (SMS) that are in tune with bacterial size. Copper and gold were used as the substrata. It was concluded that SMS influenced bacterial length, alignment, and distribution, whereas the chemistry of the surfaces affected bacterial length and distribution. However, the effect of the SMS was the most significant. The shape of the bacterial colonies and the polymeric substances production were also influenced by SMS and the chemistry of the surface and both factors may be considered to reduce the susceptibility of a surface to biofilm formation.