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Here we present a method to extract thermodynamic quantities for nanoparticle dispersions in solvents. The method is based on the study of tomograms obtained from cryogenic electron tomography (cryoET). The approach is demonstrated for gold nanoparticles (diameter < 5 nm). Tomograms are reconstructed from tilt-series 2D images. Once the three-dimensional (3D) coordinates for the centres of mass of all of the particles in the sample are determined, we calculate the pair distribution function g(r) and the potential of mean force U(r) without any assumption. Importantly, we show that further quantitative information from 3D tomograms is readily available as the spatial fluctuation in the particles’ position can be efficiently determined. This in turn allows for the prompt derivation of the Kirkwood–Buff integrals with all their associated quantities such as the second virial coefficient. Finally, the structure factor and the agglomeration states of the particles are evaluated directly. These thermodynamic quantities provide key insights into the dispersion properties of the particles. The method works well both for dispersed systems containing isolated particles and for systems with varying degrees of agglomerations., Nanoparticle dispersions were studied by cryogenic electron tomography, which was found to allow extraction of key thermodynamic quantities.

The billion tons of synthetic-polymer-based materials (i.e. plastics) produced yearly are a great challenge for humanity. Nature produces even more natural polymers, yet they are sustainable. Proteins are sequence-defined natural polymers that are constantly recycled when living systems feed. Digestion is the protein depolymerization into amino acids (the monomers) followed by their re-assembly into new proteins of arbitrarily different sequence and function. This breaks a common recycling paradigm where a material is recycled into itself. Organisms feed off of random protein mixtures that are "recycled" into new proteins whose identity depends on the cell's specific needs. In this study, mixtures of several peptides and/or proteins are depolymerized into their amino acid constituents, and these amino acids are used to synthesize new fluorescent, and bioactive proteins extracellularly by using an amino-acid-free, cell-free transcription-translation (TX-TL) system. Specifically, three peptides (magainin II, glucagon, and somatostatin 28) are digested using thermolysin first and then using leucine aminopeptidase. The amino acids so produced are added to a commercial TX-TL system to produce fluorescent proteins. Furthermore, proteins with high relevance in materials engineering (beta-lactoglobulin films, used for water filtration, or silk fibroin solutions) are successfully recycled into biotechnologically relevant proteins (fluorescent proteins, catechol 2,3-dioxygenase)., Advanced Materials, 33 (44), ISSN:0935-9648, ISSN:1521-4095

The billion tons of synthetic polymer-based materials (i.e. plastics) produced every year are one of the greatest challenges that humanity has to face. Nature produces even more natural polymers, yet they are sustainable. For example, proteins are sequence-defined natural polymers, that are constantly recycled when living systems feed. Indeed, digestion is the protein depolymerization into amino acids (i.e. the monomers) followed by their re-assembly into new proteins of arbitrarily different sequence and function. This process breaks a common recycling paradigm where a material is recycled into itself. Organisms feed of random protein mixtures that are ‘recycled’ into new proteins whose identity depends on the cell’s needs at the time of protein synthesis. Currently, advanced materials are increasingly made of proteins, but the abovementioned ideal recyclability of such materials has yet to be recognized and established. In this study mixtures of several (up to >30) peptides and/or proteins were depolymerized into their amino acid constituents, and these amino acids were used to synthesize new fluorescent, and bio-active proteins extra-cellularly by using an amino acid-free cell-free transcription-translation system. Proteins with high relevance in materials engineering (β-lactoglobulin films, used for water filtration, or silk fibroin solutions) were successfully recycled into biotechnologically relevant proteins (green, and red fluorescent proteins, catechol 2,3-dioxygenase). The potential long-term impact of this approach to recycling lies in its compatibility with circular-economy models where raw materials remain in use as long as possible, thus reducing the burden on the planet.

Significance Every folded protein presents an interface with water that is composed of domains of varying hydrophilicity/-phobicity. Many simulation studies have highlighted the nonadditivity in the wetting of such nanostructured surfaces in contrast with the accepted theoretical formula that is additive. We present here an experimental study on surfaces of identical composition but different organization of hydrophobic and hydrophilic domains. We prove that the interfacial energy of such surfaces differs by ∼20% and that a significant difference in the interfacial water H-bonding structure can be measured. As a result, in combination with molecular-dynamics simulations, we propose a model that captures the wetting of molecularly heterogeneous surfaces, showing the importance of local structure (first-nearest neighbors) in determining the wetting properties., The interface between water and folded proteins is very complex. Proteins have “patchy” solvent-accessible areas composed of domains of varying hydrophobicity. The textbook understanding is that these domains contribute additively to interfacial properties (Cassie’s equation, CE). An ever-growing number of modeling papers question the validity of CE at molecular length scales, but there is no conclusive experiment to support this and no proposed new theoretical framework. Here, we study the wetting of model compounds with patchy surfaces differing solely in patchiness but not in composition. Were CE to be correct, these materials would have had the same solid–liquid work of adhesion (WSL) and time-averaged structure of interfacial water. We find considerable differences in WSL, and sum-frequency generation measurements of the interfacial water structure show distinctively different spectral features. Molecular-dynamics simulations of water on patchy surfaces capture the observed behaviors and point toward significant nonadditivity in water density and average orientation. They show that a description of the molecular arrangement on the surface is needed to predict its wetting properties. We propose a predictive model that considers, for every molecule, the contributions of its first-nearest neighbors as a descriptor to determine the wetting properties of the surface. The model is validated by measurements of WSL in multiple solvents, where large differences are observed for solvents whose effective diameter is smaller than ∼6 Å. The experiments and theoretical model proposed here provide a starting point to develop a comprehensive understanding of complex biological interfaces as well as for the engineering of synthetic ones.

Calcium carbonate (CaCO

Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

Understanding nanostructured materials - cell interactions is essential for the development of innovative substrates for cell culture, differentiation and precise electrical stimulation. In this framework, silicon nanowires (SiNWs), characterized by high aspect ratio and a broad range of mechanical, optical and electrical properties, are interesting nanomaterials for innovative cellular engineering. We investigated and quantified, using single cell force spectroscopy (SCFS), the interaction of murine embryonic fibroblast with two mechanically different SiNW substrates, and two reference substrates, collagen gel which is generally used for cell culture, and flat glass which has the same chemical reactivity of SiNWs. We observed comparable adhesion values on SiNWs substrates and on gel substrate, while flat glass generate a 10-times weaker interaction. A closer analysis of the adhesion curves revealed significant differences between soft and hard SiNW, suggesting that a different cell membrane organization is developed depending on the mechanical and geometrical properties of the substrate. In conclusion SiNW substrates are compatible with cell engineering and thanks to their high range of mechanical and geometric properties, a fine tuning of cellular response can be achieved.Figure 1: representative SCFS curves for rigid NWs, flexible NWs and collagen-coated coverslips.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Calcium carbonate (CaCO3) is one of the most abundant biominerals that is prevalent in rocks and often used as a structural material in marine animals. Many of these natural CaCO3-based materials display excellent mechanical properties that are difficult to reproduce by man-made counterparts. This difficulty arises from the incomplete understanding of the influence of processing conditions on the structure and composition of CaCO3. To gain a better understanding of the evolution of the structure and composition of amorphous CaCO3 (ACC) particles during early stages, we introduce a new, organic solvent-free method that quenches this process with a high temporal resolution. We produce ACC particles inside small airborne drops that are formed with a microfluidic spray-dryer. These drops dry within 100 ms to 10 s and thereby arrest the formation of CaCO3 particles on that time scale. Using the microfluidic spray-dryer, we demonstrate that the amount of mobile water contained in ACC particles increases with increasing formation time and hence with increasing particle size. As a result of the higher concentration of mobile water, larger particles are less stable against temperature-induced solid-state crystallization and electron beam-induced decomposition than smaller counterparts. The amount of mobile water contained in ACC can be substantially reduced, and hence their kinetic stability against solid-state transformations increased, if certain organic additives, such as poly(acrylic acid) (PAA), are incorporated. These insights might open up new opportunities to fabricate biomimetic CaCO3-based materials with tunable structures and hence with properties that can be adapted to the needs of specific applications.