Scientific publications

Biomaterials have evolved from inert materials that lack interaction with the body to biologically active, instructive materials that host and provide signals to surrounding cells and tissues. Engineered living materials contain living cells (responsive function) and polymeric matrices (scaffolding function) and, thus, can be designed as active and response biomaterials. In this Review, we discuss engineered living materials that incorporate microorganisms as the living, bioactive component. Microorganisms can provide complex responses to environmental stimuli, and they can be genetically engineered to allow user control over responses and integration of numerous inputs. The engineered microorganisms can either generate their own matrix, such as in biofilms, or they can be incorporated in matrices using various technologies, such as coating, 3D printing, spinning and microencapsulation. We highlight biomedical applications of such engineered living materials, including biosensing, wound healing, stem-cell-based tissue engineering and drug delivery, and provide an outlook to the challenges and future applications of engineered living materials.

Progress in our understanding of mechanotransduction events requires noninvasive methods for the manipulation of forces at molecular scale in physiological environments. Inspired by cellular mechanisms for force application (i.e. motor proteins pulling on cytoskeletal fibers), we present a unique molecular machine that can apply forces at cell-matrix and cell-cell junctions using light as an energy source. The key actuator is a light-driven rotatory molecular motor linked to polymer chains, which is intercalated between a membrane receptor and an engineered biointerface. The light-driven actuation of the molecular motor is converted in mechanical twisting of the entangled polymer chains, which will in turn effectively “pull” on engaged cell membrane receptors (e.g., integrins, T cell receptors) within the illuminated area. Applied forces have physiologically-relevant magnitude and occur at time scales within the relevant ranges for mechanotransduction at cell-friendly exposure conditions, as demonstrated in force-dependent focal adhesion maturation and T cell activation experiments. Our results reveal the potential of nanomotors for the manipulation of living cells at the molecular scale and demonstrate a functionality which at the moment cannot be achieved by other technologies for force application.

The considerable growth of the world population, concomitant with an increase in environmental pollution, aggravates the antinomy between supply and demand for drinking water. Various desalination technologies have been developed to address this issue, allowing for abundant saltwater as a source for drinking water. Electrochemical desalination attracts more and more attention due to its high energy efficiency, facile operation, and low cost. Especially within the last decade, tremendous scientific progress on electrochemical desalination technologies has been made. This paper reviews the development of electrochemical desalination technologies and introduces a facile classification into three generations according to the different working principles. The cell architecture, metrics, advantages, and disadvantages of other electrochemical desalination technologies are introduced and compared.

The viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity v at small v and a pronounced maximum at intermediate v. Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding.

Manufactured nanomaterials have the potential to impact an exceedingly wide number of industries and markets ranging from energy storage, electronic and optical devices, light-weight construction to innovative medical approaches for diagnostics and therapy. In order to foster the development of safer nanomaterial-containing products, two main aspects are of major interest: their functional performance as well as their safety towards human health and the environment. In this paper a first proposal for a strategy is presented to link the functionality of nanomaterials with safety aspects. This strategy first combines information on the functionality and safety early during the innovation process and onwards, and then identifies Safe-by-Design (SbD) actions that allow for optimisation of both aspects throughout the innovation process. The strategy encompasses suggestions for the type of information needed to balance functionality and safety to support decision making in the innovation process. The applicability of the strategy is illustrated using a literature-based case study on carbon nanotube-based transparent conductive films. This is a first attempt to identify information that can be used for balancing functionality and safety in a structured way during innovation processes.

In order to investigate the effect of grain boundaries on the mechanical response in the micrometer and submicrometer levels, complementary experiments and molecular dynamics simulations were conducted on a model bcc metal, tantalum. Microscale pillar experiments (diameters of 1 and 2 μm) with a grain size of ∼ 100-200 nm revealed a mechanical response characterized by a yield stress of ∼1,500 MPa. The hardening of the structure is reflected in the increase in the flow stress to 1,700 MPa at a strain of ∼0.35. Molecular dynamics simulations were conducted for nanocrystalline tantalum with grain sizes in the range of 20-50 nm and pillar diameters in the same range. The yield stress was approximately 6,000 MPa for all specimens and the maximum of the stress-strain curves occurred at a strain of 0.07. Beyond that strain, the material softened because of its inability to store dislocations. The experimental results did not show a significant size dependence of yield stress on pillar diameter (equal to 1 and 2 um), which is attributed to the high ratio between pillar diameter and grain size (∼10-20). This behavior is quite different from that in monocrystalline specimens where dislocation ‘starvation’ leads to a significant size dependence of strength. The ultrafine grains exhibit clear ‘pancaking’ upon being plastically deformed, with an increase in dislocation density. The plastic deformation is much more localized for the single crystals than for the nanocrystalline specimens, an observation made in both modeling and experiments. In the molecular dynamics simulations, the ratio of pillar diameter (20-50 nm) to grain size was in the range 0.2 to 2, and a much greater dependence of yield stress to pillar diameter was observed. A critical result from this work is the demonstration that the important parameter in establishing the overall deformation is the ratio between the grain size and pillar diameter; it governs the deformation mode as well as surface sources and sinks, which are only important when the grain size is of the same order as the pillar diameter.

Human respiratory mucus lining the airway epithelium forms a challenging barrier to inhalation therapeutics. Therefore, structural elucidation of hydrated mucus is essential for an efficient drug delivery development. The structure of mucus has been primarily investigated by conventional electron microscopy techniques, which operate under vacuum conditions and require sample preparation steps that might alter the structure of mucus. In this study we investigated the impact of dehydration on mucus and analyzed the structure of mucus in its hydrated state. Cryo-scanning electron microscopy (Cryo-SEM) analysis of mucus showed, that during the process of sublimation, non-porous structure of mucus is transformed into a porous network. Similarly, images acquired by environmental scanning electron microscopy (ESEM), revealed a non-porous structure of hydrated mucus, while further observation at decreasing pressure demonstrated the strong influence of dehydration on mucus structure. We could successfully visualize the structural organization of the major gel forming mucin MUC5B in its hydrated state by employing stimulated emission depletion (STED) microscopy, which allowed resolving the nano-scale patterns of mucin macromolecules within the essentially pore-free mucus structure. The general structural organization of mucus components was addressed by confocal laser scanning microscopy (CLSM), which revealed the heterogeneous and composite structure of mucus. These results provide a novel view on the native structure of mucus and will affect drug delivery development.

We report on the dilution-induced agglomeration of ultrathin gold nanowires (AuNWs) into regular bundles. Wires with a metal core diameter of 1.6–1.7 nm surrounded by a ligand shell of oleylamine formed stable colloids in n-hexane and cyclohexane. Dilution with pure solvent induced the self-assembly into bundles with a regular, hexagonal cross-section. Small-angle X-ray scattering and thermogravimetric analysis indicated that bundles formed only if the ligand shell was sufficiently sparse. Dilution with pure solvent shifts the chemical equilibrium and reduces the ligand density, thus enabling agglomeration. We show that agglomeration is driven not by van der Waals forces but by the depletion forces of linearly shaped molecules. Linear solvent molecules or small amounts of unbound ligand align normal to the nanowire if the ligand shell is sparse. The resulting reduction in entropy creates a driving force for the AuNWs to bundle such that the low-entropy domains overlap and the overall entropy is increased. Dilution-induced nanowire bundling is thus explained as a combined effect of ligand desorption and destabilization by depletion.

Abstract A new type of hybrid core–shell nanoparticle dielectric that is suitable for inkjet printing is introduced. Gold cores (dcore ≈ 4.5 nm diameter) are covalently grafted with thiol-terminated polystyrene (Mn = 11000 Da and Mn = 5000 Da) and used as inks to spin-coat and inkjet-print dielectric films. The dielectric layers have metal volume fractions of 5 to 21 vol% with either random or face-centered-cubic structures depending on the polymer length and grafting density. Films with 21 vol% metal have dielectric constants of 50@1 Hz. Structural and electrical characterization using transmission electron microscopy, small-angle X-ray scattering, and impedance spectroscopy indicates that classical random capacitor–resistor network models partially describe this hybrid material but fail at high metal fractions, where the covalently attached shell prevents percolation and ensures high dielectric constants without the risk of dielectric breakdown. A comparison of disordered to ordered films indicates that the network structure affects dielectric properties less than the metal content. The applicability of the new dielectric material is demonstrated by formulating inkjet inks and printing devices. An inkjet-printed capacitor with an area of 0.79 mm2 and a 17 nm thick dielectric had a capacitance of 2.2±0.1 nF@1 kHz.

We examine network formation and percolation of carbon black by means of Monte Carlo simulations and experiments. In the simulation, we model carbon black by rigid aggregates of impenetrable spheres, which we obtain by diffusion-limited aggregation. To determine the input parameters for the simulation, we experimentally characterize the micro-structure and size distribution of carbon black aggregates. We then simulate suspensions of aggregates and determine the percolation threshold as a function of the aggregate size distribution. We observe a quasi-universal relation between the percolation threshold and a weighted average radius of gyration of the aggregate ensemble. Higher order moments of the size distribution do not have an effect on the percolation threshold. We conclude further that the concentration of large carbon black aggregates has a stronger influence on the percolation threshold than the concentration of small aggregates. In the experiment, we disperse the carbon black in a polymer matrix and measure the conductivity of the composite. We successfully test the hypotheses drawn from simulation by comparing composites prepared with the same type of carbon black before and after ball milling, i.e., on changing only the distribution of aggregate sizes in the composites.