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.

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 (β‐lactoglobulin films, used for water filtration, or silk fibroin solutions) are successfully recycled into biotechnologically relevant proteins (fluorescent proteins, catechol 2,3‐dioxygenase).

SignificanceEvery 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.

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.

In 2070, 1012 Kg of polymer-based materials (i.e. plastics) might be produced yearly, posing one of the greatest challenges that humanity has to face. Even though natural polymers, such as proteins and nucleic acids, are more abundant than synthetic ones, they are sustainable. The key property of such natural polymers is that they are sequence-defined. This allows for recycling to start with depolymerization into monomers, and end in the re-assembly of new polymers of arbitrarily different sequence. This process breaks a common recycling paradigm that a material is recycled only into itself. An organism digests proteins into amino acids. These are re-assembled into new proteins whose identity depends on the cell’s needs at the time of protein synthesis. Here we show that the process described above is achievable extra-cellularly. Specifically, we depolymerized a mixture of different peptides and/or proteins into their amino acid constituents and used these amino acids to synthesize fluorescent proteins using an amino acid-free cell-free transcription-translation system. We were successful in recycling proteins with high relevance in materials engineering (β-lactoglobulin films, used for water filtration, or silk fibroin solutions) into a biotechnologically relevant protein (green fluorescent protein). 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.