Experimental and theoretical studies of the self-propelled motional dynamics of a new genre of catalytic sphere dimer, which comprises a non-catalytic silica sphere connected to a catalytic platinum sphere, are reported for the first time. Using aqueous hydrogen peroxide as the fuel to effect catalytic propulsion of the sphere dimers, both quasi-linear and quasi-circular trajectories are observed in the solution phase and analyzed for different dimensions of the platinum component. In addition, well-defined rotational motion of these sphere dimers is observed at the solution-substrate interface. The nature of the interaction between the sphere dimer and the substrate in the aqueous hydrogen peroxide phase is discussed. In computer simulations of the sphere dimer in solution and the solution-substrate interface, sphere-dimer dynamics are simulated using molecular-dynamics methods and solvent dynamics are modeled by mesoscopic multiparticle collision methods taking hydrodynamic interactions into account. The rotational and translational dynamics of the sphere dimer are found to be in good accord with the predictions of computer simulations.

As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities. By simply varying the flow rate of charged species passing through an electrospun material during spray-assisted layer-by-layer deposition, individual fibres within the matrix can be conformally functionalized for ultrahigh-surface-area catalysis, or bridged to form a networked sublayer with complimentary properties. Exemplified here by the creation of selectively reactive gas purification membranes, the myriad applications of this technology also include self-cleaning fabrics, water purification and protein functionalization of scaffolds for tissue engineering.

Half a century ago, Richard Feynman envisioned tiny machines able to perform chemistry by mechanical manipulation of atoms. While this vision has not yet been realized in practice, researchers have recently discovered how to use chemistry to drive tiny engines and to operate tiny machines in the liquid phase, in much the same way Nature uses biochemistry to power a myriad of biological motors and machines. Herein, we provide a brief Perspective on the rapidly growing research activity in the emerging field of chemically powered nanomotors and nanomachines, consider some of the challenges facing its continued rapid development, and imagine a future in which these tiny motors and machines can get down to doing some serious work.

Nature's nanomachines, built of dynamically integrated biochemical components, powered by energy-rich biochemical processes, and designed to perform a useful task, have evolved over millions of years. They provide the foundation of all living systems on our planet today. Yet synthetic nanomotors, driven by simple chemical reactions and which could function as building blocks for synthetic nanomachines that can perform useful tasks, have been discovered only in the last few years. Why did it take so long to power-up a myriad of synthetic nanostructures from their well-known static states to new and exciting dynamic ones of the kind that abound in nature? This article will delve into this disconnect between the world of biological and abiological nanomotors, then take a look at some recent developments involving chemically powered nanoscale motors and rotors, and finally try to imagine: what's next for nanolocomotion?

We present the fabrication of nanoscale electroactive thin films that can be engineered to undergo remotely controlled dissolution in the presence of a small applied voltage (؉1.25 V) to release precise quantities of chemical agents. These films, which are assembled by using a nontoxic, FDA-approved, electroactive material known as Prussian Blue, are stable enough to release a fraction of their contents after the application of a voltage and then to restabilize upon its removal. As a result, it is possible to externally trigger agent release, exert control over the relative quantity of agents released from a film, and release multiple doses from one or more films in a single solution. These electroactive systems may be rapidly and conformally coated onto a wide range of substrates without regard to size, shape, or chemical composition, and as such they may find use in a host of new applications in drug delivery as well as the related fields of tissue engineering, medical diagnostics, and chemical detection.drug delivery ͉ layer-by-layer thin film ͉ polymer ͉ responsive materials ͉ Prussian Blue

The electrostatic layer-by-layer (LbL) assembly approach offers large potential in the area of drug delivery from thin films; however, because the processing technique is aqueous-based, there have been few strategies proposed to incorporate hydrophobic molecules into these films. Here we create an LbL film that is capable of incorporating hydrophobic drug at high loadings via encapsulation with lineardendritic block copolymer micelles and demonstrate for the first time release times of a hydrophobic antibacterial agent over a period of several weekssa significant improvement over reports of other micelleencapsulated thin films with release times of several minutes. The amphiphilic linear-dendritic block copolymer is composed of poly(propylene oxide) (PPO), which forms the hydrophobic core creating the compartment for hydrophobic drug encapsulation, and poly(amidoamine) (PAMAM), which forms the outer corona of the micelle. The PAMAM is polycationic, enabling LbL deposition with negatively charged poly(acrylic acid) (PAA). The stable PPO-PAMAM micelles incorporated into the LbL films encapsulated a hydrophobic bactericide, triclosan, which have loading capacities as high as 80-90%. Film thickness and UV-vis measurements confirm the formation of the LbL film and incorporation of triclosan into the film. Fluorescence measurements of PPO-PAMAM/PAA films with pyrene indicated the presence of hydrophobic domains in the film. GISAXS revealed regular spacing of approximately 10.5 nm in the direction parallel to the film substrate, which is approximately the same size as the PPO-PAMAM micelles in aqueous solution. Volume fraction measurements based on elemental analysis and TGA confirm the GISAXS data. An in vitro release study revealed long release times of triclosan on the order of weeks, and a Kirby Bauer test was performed on Staphylococcus aureus, demonstrating that the drug released was still active to inhibit the growth of bacteria.

Omniphobic and slippery coatings from lubricant-infused, textured surfaces have recently been shown to have superior properties including low contact angle hysteresis and low sliding angles. Here, we present an omniphobic slippery surface prepared by infusing a fluorinated lubricant into a porous polyelectrolyte multilayer. These surfaces repel water and decane with sliding angles as low as 3°. One advantage of polyelectrolyte multilayers is the ease with which they can coat nonplanar surfaces, demonstrated here.

One promising aspect of the electrostatic multilayer assembly techniques is the ability to consistently and predictably create controlled heterostructures that may be of interest for active devices, designed biomaterials, membranes, or other composite thin film structures. This promise is mitigated by the challenge of controlling diffusion and exchange processes that can take place in certain layer-by-layer assembled film systems and cause unanticipated or unwanted materials distributions and in extreme cases completely disrupt the assembly. To further understanding toward prediction and control of these processes, we investigate a series of polyamines and their interdiffusion and exchange within preassembled multilayer films to explore the role of polyion degree of ionization, hydrophobicity/hydrophilicity of the backbone, basicity of amine groups, and polyion topology in a polyelectrolyte interdiffusion and exchange process. Interdiffusion of these polyamines will be examined within a polyhexylviologen (PXV)/poly(acrylic acid) multilayer model system in which conditions favor exchange of the polyamine with PXV, a strong polycation containing quarternary ammonium groups along the backbone. Four aminecontaining polycations were examined: linear and branched polyethylene imine (LPEI and BPEI), polyamidoamine (PAMAM) dendrimer, and poly(allylamine hydrochloride) (PAH). It was found that fully charged polycations in dilute aqueous solution are unable to diffuse through the multilayer film whereas partially charged polycations have the necessary mobility. Remarkably, despite strong differences in the nature of the polycation, as in the case of PAH, LPEI, and BPEI, for every polyamine there existed the same critical degree of ionization in solution below which interdiffusion was possible, which was seen to be near 70% in these exchange experiments with PXV. Only for the highly branched PAMAM dendrimer was this value different; the critical degree of ionization for PAMAM was observed to be 55%. Kinetics of the interdiffusion were significantly impacted by the polyion degree of ionization and molecular weight.