Active camouflage is widely recognized as a soft-tissue feature, and yet the ability to integrate adaptive coloration and tissuelike mechanical properties into synthetic materials remains elusive. We provide a solution to this problem by uniting these functions in moldable elastomers through the self-assembly of linear-bottlebrush-linear triblock copolymers. Microphase separation of the architecturally distinct blocks results in physically cross-linked networks that display vibrant color, extreme softness, and intense strain stiffening on par with that of skin tissue. Each of these functional properties is regulated by the structure of one macromolecule, without the need for chemical cross-linking or additives. These materials remain stable under conditions characteristic of internal bodily environments and under ambient conditions, neither swelling in bodily fluids nor drying when exposed to air.

This contribution provides a comprehensive mechanistic picture of the gold nanoparticle synthesis by citrate reduction of HAuCl4, known as Turkevich method, by addressing five key questions. The synthesis leads to monodisperse final particles as a result of a seed-mediated growth mechanism. In the initial phase of the synthesis, seed particles are formed onto which the residual gold is distributed during the course of reaction. It is shown that this mechanism is a fortunate coincidence created by a favorable interplay of several chemical and physicochemical processes which initiate but also terminate the formation of seed particles and prevent the formation of further particles at later stages of reaction. Since no further particles are formed after seed particle formation, the number of seeds defines the final total particle number and therefore the final size. The gained understanding allows illustrating the influence of reaction conditions on the growth process and thus the final size distribution.

Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature’s demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials.

Macromolecular crowding in biological media is an essential factor for cellular function. The interplay of intermolecular interactions at multiple time and length scales governs a fine-tuned system of reaction and transport processes, including particularly protein diffusion as a limiting or driving factor. Using quasielastic neutron backscattering, we probe the protein self-diffusion in crowded aqueous solutions of bovine serum albumin on nanosecond time and nanometer length scales employing the same protein as crowding agent. The measured diffusion coefficient DðφÞ strongly decreases with increasing protein volume fraction φ explored within 7% ≤ φ ≤ 30%. With an ellipsoidal protein model and an analytical framework involving colloid diffusion theory, we separate the rotational D r ðφÞ and translational D t ðφÞ contributions to DðφÞ. The resulting D t ðφÞ is described by short-time self-diffusion of effective spheres. Protein self-diffusion at biological volume fractions is found to be slowed down to 20% of the dilute limit solely due to hydrodynamic interactions. macromolecular crowding | quasi-elastic neutron scattering | globular proteins T he interior of biological cells is a medium with a macromolecular volume fraction of up to 40%. This crowding crucially affects reaction kinetics and equilibria in the cell (1, 2). Cellular function and structure thus cannot be understood without a systematic understanding of both phase behavior and transport processes in crowded media. Diffusion is the main transport process for systems at low Reynolds numbers, governing many dynamic processes in nature (3). From the perspective of a single tracer molecule, all other molecules act as obstacles. In vivo diffusion coefficients for globular proteins in living cells (4-7) are strongly decreased compared to the in vitro diffusion coefficient in dilute buffer solutions. Systematic measurements of the tracer diffusion of proteins dissolved in concentrated suspensions of crowding agents, i.e., other proteins or polymers, reveal a complex dependence of the slowing down on the combination of tracer molecule and crowding agent (8-10). Furthermore, macromolecular crowding is found to induce subdiffusive behavior in several cases (11,12), being suggested as a slower but more reliable diffusive search process inside the cell (13). This anomalous diffusion process has been found also in theory and simulations (12-15) suggesting a crossover from subdiffusive behavior at small times to diffusive behavior at larger times.Proteins are macromolecules generally with a nonspherical shape and a nonhomogeneous surface charge, showing specific interactions with ligands. Furthermore, proteins not only show global motions like translational and rotational diffusion but also internal and interdomain motions. Therefore, proteins pose a challenge to colloid theory (16,17). In a recent simulation study Ando and Skolnick (4) revealed that using an equivalent-sphere model for macromolecules is a reasonable approximation to describe diffusion. Moreover, ...

The relevance of anisotropic interactions in colloidal systems has recently emerged in the context of the rational design of new soft materials. Patchy colloids of different shapes, patterns and functionalities are considered the new building blocks of a bottom-up approach toward the realization of self-assembled bulk materials with predefined properties. The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and micro-scales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies suggest that the phase diagram of patchy colloids can be significantly altered by limiting the particle coordination number (that is, valence). New concepts such as empty liquids—liquid states with vanishing density—and equilibrium gels—arrested networks of bonded particles, which do not require an underlying phase separation to form—have been formulated. Yet no experimental evidence of these predictions has been provided. Here we report the first observation of empty liquids and equilibrium gels in a complex colloidal clay, and support the experimental findings with numerical simulations.