Elevated humidity levels in medical, food, and pharmaceutical products may reduce the products' shelf life, trigger bacterial growth, and even lead to complete spoilage. In this study, we report a humidity indicator that mechanically bends and rolls itself irreversibly upon exposure to high humidity conditions. The indicator is made of two food-grade polymer films with distinct ratios of a milk protein, casein, and a plasticizer, glycerol, that are physically attached to each other. Based on the thermogravimetric analysis and microstructural characterization, we hypothesize that the bending mechanism is a result of hygroscopic swelling and consequent counter diffusion of water and glycerol. Guided by this mechanism, we demonstrate that the rolling behavior, including response time and final curvature, can be tuned by the geometric dimensions of the indicator. As the proposed indicator is made of food-grade ingredients, it can be placed directly in contact with perishable products to report exposure to undesirable humidity inside the package, without the risk of contaminating the product or causing oral toxicity in case of accidental digestion, features that commercial inedible electronic and chemo-chromatic sensors cannot provide presently.

Properties such as shear modulus, gelation time, structure of supramolecular hydrogels are strongly dependent on self-assembly, gelation triggering mechanism and processes used to form the gel. In our work we extend reported rheology analysis methodologies to pH-triggered supramolecular gels to understand structural insight using a model system based on N−N’ Dibenzoyl-L-Cystine pH-triggered hydrogelator and Glucono-δ-Lactone as the trigger. We observed that Avrami growth model when applied to time-sweep rheological data of gels formed at lower trigger concentrations provide estimates of fractal dimension which agree well compared with visualization of the microstructure as seen via Confocal Laser Scanning Microscopy, for a range of gelator concentrations.

This work describes a facile approach allowing Dibenzoyl-L-Cystine (DBC) based hydrogel controlled deposition and controlled detachments over a conducting support. The method itself is an electrochemically assisted approach, where the water oxidation at the electrode surface results in a local pH drop inducing DBC gelation and hydrogel formation. We have comprehensively described the possibility of the hydrogel shaping by alternating the anodic deposition potential, DBC concentration and finally the working electrode geometry. The latter includes macro-electrodes in a form of platinum discs having diameter equal to 200 and 500 μm; hexagonal arrays of circular platinum microelectrodes with a diameter of a single electrode equal to 5 or 10 μm and custom made platinum microelectrodes, having the shape of circles, triangles and squares, that are used to shape the microgels. Over the course of our work we were able to define the conditions to form a number of different hydrogel shapes such as: (i) flat and planar deposits; (ii) hemispherical deposits with an oxygen bubble pocket; (iii) spongy hydrogel structures or (iv) hemispherical micro-cups build from radially oriented DBC fibres directionally growing from the support. Furthermore, we were also able to remotely form and then detach the hydrogel deposit in the initial formulation solution using only an electrochemical trigger. Our work represents a solid proof of concept and opens a number of new avenues for the electrochemically assisted soft matter fabrication down to micrometre scale.

Signal transduction in living systems is the conversion of information into a chemical change, and is the principal process by which cells communicate. In nature, these functions are encoded in non-equilibrium (bio)chemical reaction networks (CRNs) controlled by enzymes. However, man-made catalytically controlled networks are rare. We incorporated catalysis into an artificial fuel-driven out-of-equilibrium CRN, where the forward (ester formation) and backward (ester hydrolysis) reactions are controlled by varying the ratio of two organocatalysts: pyridine and imidazole. This catalytic regulation enables full control over ester yield and lifetime. This fuel-driven strategy was expanded to a responsive polymer system, where transient polymer conformation and aggregation are controlled through fuel and catalyst levels. Altogether, we show that organocatalysis can be used to control a man-made fuel-driven system and induce a change in a macromolecular superstructure, as in natural non-equilibrium systems.

Here, transient supramolecular hydrogels that are formed through simple aging-induced seeded self-assembly of molecular gelators are reported. In the involved molecular self-assembly system, multicomponent gelators are formed from a mixture of precursor molecules and, typically, can spontaneously self-assemble into thermodynamically more stable hydrogels through a multilevel self-sorting process. In the present work, it is surprisingly found that one of the precursor molecules is capable of self-assembling into nano-sized aggregates upon a gentle aging treatment. Importantly, these tiny aggregates can serve as seeds to force the self-assembly of gelators along a kinetically controlled pathway, leading to transient hydrogels that eventually spontaneously convert into thermodynamically more stable hydrogels over time. Such an aging-induced seeded self-assembly process is not only a new route toward synthetic out-of-equilibrium supramolecular systems, but also suggests the necessity of reporting the age of self-assembling building block solutions in other self-assembly systems.

Reported here is a 2D, interfacial microcompartmentalization strategy governed by 3D phase separation. In aqueous polyethylene glycol (PEG) solutions doped with biotinylated polymers, the polymers spontaneously accumulate in the interfacial layer between the oil-surfactant-water interface and the adjacent polymer phase. In aqueous two-phase systems, these polymers first accumulated in the interfacial layer separating two polymer solutions and then selectively migrated to the oil-PEG interfacial layer. By using polymers with varying photopolymerizable groups and crosslinking rates, kinetic control and capture of spatial organisation in a variety of compartmentalized macroscopic structures, without the need of creating barrier layers, was achieved. This selective interfacial accumulation provides an extension of 3D phase separation towards synthetic compartmentalization, and is also relevant for understanding intracellular organisation.

Supramolecular assemblies are promising building blocks for the fabrication of functional soft devices for high-tech applications. However, there is a lack of effective methods for large-scale manipulation and integration of nano-sized supramolecular structures on soft substrate. Now, functional soft devices composed of micellar filaments and hydrogels can be created through a versatile approach involving guided dewetting, transfer-printing, and laser-assisted patterning. Such an approach enables unprecedented control over the location and alignment of the micellar filaments on hydrogel substrates. As examples, freely suspended micellar fishnets immobilized on hydrogels are formed, showing the capability of trapping and releasing micro-objects and the piconewton force sensitivity. By incorporating responsive moieties into hydrogels, shape-morphing actuators with micelle-controlled rolling directionality are constructed.

Supramolecular structures with strain-stiffening properties are ubiquitous in nature but remain rare in the lab. Herein, we report on strain-stiffening supramolecular hydrogels that are entirely produced through the self-assembly of synthetic molecular gelators. The involved gelators self-assemble into semi-flexible fibers, which thereby crosslink into hydrogels. Interestingly, these hydrogels are capable of stiffening in response to applied stress, resembling biological intermediate filaments system. Furthermore, strain-stiffening hydrogel networks embedded with liposomes are constructed through orthogonal self-assembly of gelators and phospholipids, mimicking biological tissues in both architecture and mechanical properties. This work furthers the development of biomimetic soft materials with mechanical responsiveness and presents potentially enticing applications in diverse fields, such as tissue engineering, artificial life, and strain sensors.

This study investigates the stabilization of oil/water emulsions as a function of addition of a biopolymer (scleroglucan) which acts as an emulsion stabilizer. Rheological characterization in the form of controlled stress creep measurements has been carried out and it reveals the colloidal gel exhibiting a delayed yielding in a certain applied stress window. The delay time and stresses that an emulsion can withstand depend strongly on the concentration of added scleroglucan. Increasing polymer concentration, however, is limited to a maximum value, above which a limited effect on the delay time is observed. Investigating of the emulsion under study was visualized by means of cryo transmission electron microscopy which shows adsorption of scleroglucan onto the surface of the oil particles and a gel-like structure that connects the oil phases. The results mentioned in this study support that scleroglucan-surfactant interactions play a key role in the stabilization of the oil/water emulsion.

Controlled localization of platinum nanoparticles (Pt NPs) at a solid support assisted by a polarized liquid-liquid interface is reported. Electrocatalytic water oxidation resulted in local pH modulation followed by the directed self-assembly of a dibenzoyl-l-cystine hydrogelator forming a structured hydrogel retaining the shape of the Pt NP deposit.

Polymer nanowire-related research has shown considerable progress over the last decade. The wide variety of materials and the multitude of well-established chemical modifications have made polymer nanowires interesting as a functional part of a diagnostic biosensing device. This review provides an overview of relevant publications addressing the needs for a nanowire-based sensor for biomolecules. Working our way towards the detection methods itself, we review different nanowire fabrication methods and materials. Especially for an electrical signal read-out, the nanowire should persist in a single-wire configuration with well-defined positioning. Thus, the possibility of the alignment of nanowires is discussed. While some fabrication methods immanently yield an aligned single wire, other methods result in disordered structures and have to be manipulated into the desired configuration.

Hydrogel microparticles are important in materials engineering, but their applications remain limited owing to the difficulties associated with their manipulation. Herein, we report the self-orientation of crescent-shaped hydrogel microparticles and elucidate its mechanism. Additionally, the microparticles were used, for the first time, as micro-buckets to carry living cells. In aqueous solution, the microparticles spontaneously rotated to a preferred orientation with the cavity facing up. We developed a geometric model that explains the self-orienting behavior of crescent-shaped particles by minimizing the potential energy of this specific morphology. Finally, we selectively modified the particles’ cavities with RGD peptide and exploited their preferred orientation to load them with living cells. Cells could adhere, proliferate, and be transported and released in vitro. These micro-buckets hold a great potential for applications in smart materials, cell therapy, and biological engineering.

In this study, we investigated the Stabilization of bitumen emulsions by scleroglucan, a rigid triple-helix forming biopolymer, in combination with a pH-sensitive cationic surfactant. Various aspects of the emulsification process and the final composition influence the Stabilization. We examined two different methods to add scleroglucan to the emulsion: either by adding it to the aqueous surfactant solution before emulsification, denoted ‘pre-emulsification addition’ (pre-EA), or by addition to the emulsion after emulsification (post-EA). We investigated scleroglucan concentrations in the aqueous phase ranging between 0.017 and 0.07 w/w%. The emulsions were evaluated according to the European EN 13808 standard used for cationic bituminous emulsions, as well as by rheological analysis. We observed an improvement of the storage stability upon pre-EA at a biopolymer concentration as low as 0.017 w/w% in combination with an increased particle size, whereas the breaking index (characterising breaking of the emulsion in presence of ‘aggregates’ = stones) was not influenced. The rheological data show a minor viscosity increase by scleroglucan in the pre-EA formulation at low scleroglucan concentrations (0.017–0.05 wt.%) where Stabilization already improved dramatically. This indicates that the stabilization mechanism is not only governed by a viscosity increase but also by interfacial stabilisation effects were polymer is adsorbed onto the adsorbed surfactant. In a separate experiment we changed the conformation of scleroglucan by subjecting it to extreme pH values and by dissolution in DMSO, in order to study the role of the triple helix conformation in the stabilization mechanism. Scleroglucan becomes less effective in a denatured and hydrolysed state confirming the crucial role of the triple helix conformation in the Stabilization of bitumen emulsions.

The last decade has witnessed great progress in understanding and manipulating self-assembly of block copolymers in solution. A wide variety of micellar structures can be created and many promising applications in bioscience have been reported. In particular, nano-fibrous micelles provide a great platform to mimic the filamentous structure of native extracellular matrix (ECM). However, the evaluation of this kind of filomicellar system with potential use in tissue engineering is virtually unexplored. The question behind it, such as if the block copolymer nano-fibrous micelles can regulate cellular response, has lingered for many years because of the difficulties in preparation and 3D manipulation of these tiny objects. Here, by using a combination approach of self-assembly of block copolymers and soft lithography, we establish a novel and unique nano-fibrous 2D platform of organized micelles and demonstrate that patterned micelles enable control over the cellular alignment behavior. The area density and orientation of fibrous micelles determine the alignment degree and directionality of cells, respectively. Furthermore, when cells were cultured on multi-directionally aligned micelles, a competitive response was observed. Due to the virtually infinite possibilities of functionalization of the micelle corona, our work opens a new route to further mimic the native fibrous networks with artificial micelles containing various functionalities.

By combining a surfactant, an organic pore expander, a silane, and poly(ethylene glycol) (PEG), we have observed the formation of a previously unknown set of ultrasmall silica structures in aqueous solutions. At appropriate concentrations of reagents, â2 nm primary silica clusters arrange around surfactant micelles to form ultrasmall silica rings, which can further evolve into cage-like structures. With increasing concentration, these rings line up into segmented worm-like one-dimensional (1D) structures, an effect that can be dramatically enhanced by PEG addition. PEG adsorbed 1D striped cylinders further arrange into higher order assemblies in the form of two-dimensional (2D) sheets or three-dimensional (3D) helical structures. Results provide insights into synergies between deformable noncovalent organic molecule assemblies and covalent inorganic network formation as well as early transformation pathways from spherical soft materials into 1D, 2D, and 3D silica solution structures, hallmarks of mesoporous silica materials formation. The ultrasmall silica ring and cage structures may prove useful in nanomedicine and other nanotechnology based applications.

Pluronics P94 are block-copolymer showing prolonged circulation time and tumor-cell internalization in vitro, suggesting a potential for tumor accumulation and as a drug carrier. Here we report the results of the radiolabeled-P94 unimers (P94-¹¹¹In-DTPA) on tumor uptake/retention and biodistribution after intravenous and intratumoral injection to tumor-bearing mice. Intravenous administration results in a high radioactive signal in the liver; while in tumor and other healthy tissues only low levels of radioactivity could be measured. In contrast, the intratumoral injection of P94 resulted in elevated levels of radioactivity in the tumor and low levels in other organs, including the liver. Independently from the injection route, the tumor tissue presented long retention of radioactivity. The minimal involvement of off-target tissues of P94, together with the excellent tracer retention over-time in the tumor designates Pluronic P94 copolymer as a highly promising carrier for anti-tumor drugs.

A generic method is used for compartmentalization of supramolecular hydrogels by using water-in-water emulsions based on aqueous multi-phase systems (AMPS). By forming the low-molecular-weight hydrogel throughout all phases of all-aqueous emulsions, distinct, micro-compartmentalized materials were created. This structuring approach offers control over the composition of each type of the compartments by directing the partitioning of objects to be encapsulated. Moreover, this method allows for barrier-less, dynamic exchange of even large hydrophilic solutes (MW≈60kDa) between separate aqueous compartments. These features are expected to find use in the fields of, for instance, micro-structured catalysts, templating, and tissue engineering.

Electroactive materials and their applications are enjoying renewed attention, in no small part motivated by the advent of nanoscale tools for their preparation and study. While the fundamentals of charge and mass transport in electrolytes on this scale are by and large well understood, their interplay can have subtle manifestations in the more complex situations typical of, for example, integrated microfluidics-based applications. In particular, the role of faradaic processes is often overlooked or, at best, purposefully suppressed via experimental design. In this introductory article we discuss, using simple illustrations from our laboratories, some of the manifestations of electrochemistry in electroactive materials.