Cells flowing to attain functionality.

Unraveling the fundamental biological processes underpinning cell functions and behavior remains a key challenge. Researchers working on cell biological processes might want to take a look at microscale cell flow as functionality genesis. This Commentary provides an outlook on how cell-microcirculation interplay promises to lead to exciting insights into the cell biology complexity.

Toward droplets displaying life-like interaction behaviors.

Developments in synthetic biology usually bring the conception of individual artificial cells. A key feature of living systems is, however, the interaction between individuals, in which living units can interact autonomously and display a role differentiation such as the case of entities chasing each other. On the other hand, droplets have become a very useful and exciting medium for modern microengineering and biomedical technologies. In this Perspective, we show a brief discussion-outlook of different approaches to recreate predator-prey interactions in both swimmer and crawling droplet systems toward a new generation of synthetic life with impact in both fundamental insights and relevant applications.

Droplets in underlying chemical communication recreate cell interaction behaviors.

The sensory-motor interaction is a hallmark of living systems. However, developing inanimate systems with "recognize and attack" abilities remains challenging. On the other hand, controlling the inter-droplet dynamics on surfaces is key in microengineering and biomedical applications. We show here that a pair of droplets can become intelligently interactive (chemospecific stimulus-response inter-droplet autonomous operation) when placed on a nanoporous thin film surface. We find an attacker-victim-like non-reciprocal interaction between spatially separated droplets leading to an only-in-one shape instability that triggers a drop projection to selectively couple, resembling cellular phenomenologies such as pseudopod emission and phagocytic-like functions. The nanopore-driven underlying communication and associated chemical activity are the main physical ingredients behind the observed behavior. Our results reveal that basic features found in many living cell types can emerge from a simple two-droplet framework. This work is a promising step towards the design of microfluidic smart robotics and for origin-of-life protocell models.

Determination of Antibacterial Activity of Film Coatings Against Four Clinically Relevant Bacterial Strains.

Antibacterial coatings have currently gained great importance in biomedical technology investigations. Because of the spatial arrangement of the film coatings, evaluation of antibacterial activity presents a new challenge regarding traditional bacterial counting methods. In this protocol, four clinically relevant pathogens, Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were incubated on titania mesostructured thin film coatings for 24 h. Then, cell viability was studied considering three methods: counting of the number of colony forming units (CFU), live/dead staining, and quantification of extracellular DNA in suspension. Firstly, bacterial count was determined by the standard plate-count technique. Secondly, bacteria membrane integrity was evaluated by utilization of two fluorescent dyes, which allow distinction between live (membrane intact) and dead (membrane disrupted) bacteria. Lastly, extracellular DNA was quantified by spectrophotometry. In this manner, the three aforementioned techniques enabled the study of bacterial viability by qualitative and quantitative analyses.

Nanopore-Mediated Spontaneous Dilution of Droplets: When Evaporation Turns to a Dilutor.

Droplet evaporation on surfaces is ubiquitous and affects areas as diverse as climate, microbiology, the chemical industry, and materials science. While solute concentration is the universally taken-for-granted behavior in drop evaporation, the present work shows that saline droplets evaporating on nanoporous thin-film surfaces can get diluted rather than concentrated. The driving mechanism of this phenomenon is attributed to the flow drawn from the drop through the nanopores by an annular peripheral evaporation. This fluid transport can continuously collect the salt solution from a concentrated region of the droplet, which is induced by radial microflows during drop evaporation. The coupling of these processes leads to the overall drop dilution effect. The influence of substrate temperature and drop volume was also investigated. This study opens up new perspectives on many natural phenomena and offers alternatives for physicochemical applications in small dimensions as well as for water desalination technologies.

Antibiofilm effect of mesoporous titania coatings on Pseudomonas aeruginosa biofilms.

Activation of photocatalytic titania by ultraviolet-A (UVA) radiation has been proposed as a good approach for combating bacteria. Titania powder, in solution or immobilized on a surface, has excellent UVA-assisted killing properties on several microorganisms. However, these properties could not be demonstrated in biofilms of Pseudomonas aeruginosa, a resistant opportunistic human pathogen that can cause severe complications in patients who are immunocompromised or have burn wounds or cystic fibrosis. P. aeruginosa biofilms have detrimental effects on health and industry, causing serious economic damage. In this study, the effect of titania photocatalysis for controlling P. aeruginosa biofilms was investigated by employing different coatings obtained through sol-gel and evaporation-induced self-assembly. Biofilms were grown on non-mesoporous and mesoporous titania surfaces with different pore sizes, which were achieved based on the use of surfactants Brij-58 and Pluronics-F127. In addition, two structural forms of titania were assayed: amorphous and anatase. As well as inhibiting biofilm formation, these coatings significantly enhanced the bactericidal effect of UVA on P. aeruginosa biofilms. The most efficient surface with regard to total antibacterial effect was the mesoporous Brij-58-templated anatase film, which, compared to control biofilms, decreased the number of viable bacteria by about 5 orders, demonstrating the efficacy of this methodology as a disinfection system.

Transforming an inert nanopolymer into broad-spectrum bactericidal by superstructure tuning.

Poloxamer block copolymers (also known as Pluronic®) are particularly useful for drug delivery and self-assembly techniques. These nanopolymers are generally considered to be biologically inert and they were used to generate only bacteria repellent surfaces but keeps bacteria alive and as a latent threat. However, the inherent capabilities of these nanopolymers to kill bacteria have been largely overlooked. Here, we report that Pluronic shaped as superstructures (self-organized array of micelles) in fact possess a broad-spectrum bactericidal activity (capability of killing bacteria) similar to that shown for some antibiotics. This further represents the first report that shows that appropriate control of superstructured mesophase architecture is a key parameter for bactericidal efficacy. Based on this finding, we have developed a highly bactericidal coating (>99.9% kill) against all tested Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Salmonella typhimurium LT2, Escherichia coli K12 and Pseudomonas aeruginosa PAO1) bacteria which moreover allows the adhesion and proliferation of mammalian cells. The inexpensiveness and ease of production make these versatile nanopolymer structures a powerful tool for the development of a new generation of highly effective antimicrobial coatings.

Spontaneous water adsorption-desorption oscillations in mesoporous thin films.

Understanding fluid transport and phase changes in nanopore structures is of great interest to many application fields, from energy conversion to water harvesting. This work discusses the spontaneous oscillations of the water saturation of mesoporous thin films, in the zone adjacent to a sessile water drop, at ambient conditions. The wetting-front dynamics onto the film is described by considering three coexisting phenomena: infiltration from the water drop, condensation from air vapor, and evaporation to the ambient. It was found that the oscillations follow spontaneous condensation-evaporation imbalances, which are governed by the hysteretic character of the adsorption-desorption behavior of the mesoporous material. The outcomes of this work provide insights on the complex interplay between water and nanopore structures, which has practical implications for the handling of humid microenvironments in lab-on-a-chip technology, as well as for many processes that take part of the cycle of water in nature.

An Open Pit Nanofluidic Tool: Localized Chemistry Assisted by Mesoporous Thin Film Infiltration.

Nanofluidics based on nanoscopic porous structures has emerged as the next evolutionary milestone in the construction of versatile nanodevices with unprecedented applications. However, the straightforward development of nanofluidically interconnected systems is crucial for the production of practical devices. Here, we demonstrate that spontaneous infiltration into supramolecularly templated mesoporous oxide films at the edge of a sessile drop in open air can be used to connect pairs of landmarks. The liquids from the drops can then join through the nanoporous network to guide a localized chemical reaction at the nanofluid-front interface. This method, here named "open-pit" nanofluidics, allows mixing reagents from nanofluidically connected droplet reservoirs that can be used as reactors to conduct reactions and precipitation processes. From the fundamental point of view, the work contributes to unveiling subtle phenomena during spontaneous infiltration of fluids in bodies with nanoscale dimensions such as the front broadening effect and the oscillatory behavior of the infiltration-evaporation front. The approach has distinctive advantages such as easy fabrication, low cost, and facility of scaling up for future development of ultrasensitive detection, controlled nanomaterial synthesis, and novel patterning methods.

Antibiofilm effect of supramolecularly templated mesoporous silica coatings.

Bacteria attached to solid surfaces and encased in a self-synthesized matrix, so-called biofilms, are highly difficult to eradicate and present negative impact on industry and human health. The ability of supramolecularly templated mesoporous silica coatings to inhibit biofilm formation in Pseudomonas aeruginosa is shown here. Assays employing submerged and air-liquid interface biofilms demonstrated that mesoporous coatings with tuned pore size significantly reduce the number of attached bacteria and matrix production. Given its versatility, scalability, robustness and low cost, our proposal is attractive for the production of transparent, inert and permanent antibiofilm coatings that could be applied on multiple surfaces.

Modeling the abnormally slow infiltration rate in mesoporous films.

Mesoporous films have been shown to exhibit striking behaviors in capillary-driven infiltration experiments. The process has been shown to follow classical Lucas-Washburn dynamics, but the effective pore radius has been calculated from hydrodynamic resistance considerations to be orders of magnitude lower than measured pore dimensions. In addition, the infiltration rate has been observed to decrease with increasing pore diameter, in contrast to the expected trend for capillary-like pores. Here, we present a simple model accounting for the mechanism behind these anomalous effects. We found the infiltration rate to be inversely proportional to the cubed ratio of pore to neck size. This physical scaling correctly modeled both the magnitude of the infiltration rate and its variation with pore diameters, for a wide range of experimental data. The model established a connection between capillary filling dynamics and nanoscale pore structure, which is of practical interest for the design and characterization of mesoporous films.

Complex Filling Dynamics in Mesoporous Thin Films.

The fluid-front dynamics resulting from the coexisting infiltration and evaporation phenomena in nanofluidic systems has been investigated. More precisely, water infiltration in both titania and silica mesoporous films was studied through a simple experiment: a sessile drop was deposited over the film and the advancement of the fluid front into the porous structure was optically followed and recorded in time. In the case of titania mesoporous films, capillary infiltration was arrested at a given distance, and a steady annular region of the wetted material was formed. A simple model that combines Lucas-Washburn infiltration and surface evaporation was derived, which appropriately describes the observed filling dynamics and the annulus width in dissimilar mesoporous morphologies. In the case of wormlike mesoporous morphologies, a remarkable phenomenon was found: instead of reaching a steady infiltration-evaporation balance, the fluid front exhibits an oscillating behavior. This complex filling dynamics opens interesting possibilities to study the unusual nanofluidic phenomena and to discover novel applications.

Full solution processed mesostructured optical resonators integrating colloidal semiconductor quantum dots.

Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure.

Wired enzymes in mesoporous materials: A benchmark for fabricating biofuel cells.

Evolution of fuel cells using metallic inorganic catalysts has led to the development of biofuel cells with potential applications in implantable devices. However, the main disadvantages in real world applications of enzymatic biofuel cells are short lifetime and low power density. Many efforts have been devoted to immobilize redox enzymes on surfaces to allow efficient electrical communication with electrodes and to provide an adequate habitat for biochemical activity. In this context, nanocavities of mesoporous materials offer a tailored environment for protein immobilization. Mesostructured platforms with high surface area and stability have been developed to enhance mass transport, charge transfer from biocatalysts to electrodes and enzyme stability, leading to biofuel cells with improved power density (up to 602 µW cm(-2) at physiological conditions) and overall performance (high stability after 30 h of continuous operation and after 10 days of storage). This review discusses recent developments using mesoporous materials as novel platforms for effective electronic charge transfer in the context of current and emerging technologies in enzymatic fuel cell research, emphasizing their practical implications and potential improvements leading to a major impact on medical science and portable electronics.

The redox-active nanomaterial toolbox for cancer therapy.

Advances in nanomaterials science contributed in recent years to develop new devices and systems in the micro and nanoscale for improving the diagnosis and treatment of cancer. Substantial evidences associate cancer cells and tumor microenvironment with reactive oxygen species (ROS), while conventional cancer treatments and particularly radiotherapy, are often mediated by ROS increase. However, the poor selectivity and the toxicity of these therapies encourage researchers to focus efforts in order to enhance delivery and to decrease side effects. Thus, the development of redox-active nanomaterials is an interesting approach to improve selectivity and outcome of cancer treatments. Herein, we describe an overview of recent advances in redox nanomaterials in the context of current and emerging strategies for cancer therapy based on ROS modulation.

Nano-designed enzyme-functionalized hierarchical metal-oxide mesoporous thin films: en route to versatile biofuel cells.

A versatile bioelectronic system is presented, based on Ag nanoparticle assemblies embedded into hierarchically mesoporous titania thin films on which electroactive enzymes are simply immobilized by a fast adsorption process. This strategy enables straightforward, cost effective, high-performance, thin-film enzymatic fuel cell technology with foreseeable applications in self-powered microfluidic and electronic devices.

Controlled adhesion and proliferation of a human osteoblastic cell line by tuning the nanoporosity of titania and silica coatings.

The engineering of surfaces to control cell adhesion represents an active area of biomaterials research. Herein, we demonstrate that it is possible to tune the adhesion and proliferation of a human osteoblastic cell line (Saos-2) by tailoring the nanopore size of an oxide film coating.

Electrical conductivity in patterned silver-mesoporous titania nanocomposite thin films: towards robust 3D nano-electrodes.

The space-resolved electrical conductivity of patterned silver nanoparticle (NP) arrays embedded in mesoporous TiO(2) thin films was locally evaluated using a conductive-tip AFM. A remarkable conductivity dependence on the film mesostructure and metal NP loading was observed, confirming a three-dimensional current flow throughout the nanocomposite.

Amylase-functionalized mesoporous silica thin films as robust biocatalyst platforms.

A robust biocatalyst was produced by immobilization of alpha-amylase into mesoporous silica thin films with local order pore structure and 11 nm pore diameter, supported on glass stripes. The activity of this novel catalyst was evaluated for direct starch degradation. The catalyst films show excellent activity, and enhanced stability with respect to free enzyme at extreme conditions of pH and temperature. In addition, they can be easily separated from the reaction media and reused several times.