Independent Blue and Red Light Triggered Narcissistic Self‐Sorting Self‐Assembly of Colloidal Particles

The ability of living systems to self‐sort different cells into separate assemblies and the ability to independently regulate different structures are one ingredient that gives rise to their spatiotemporal complexity. Here, this self‐sorting behavior is replicated in a synthetic system with two types of colloidal particles; where each particle type independently self‐assembles either under blue or red light into distinct clusters, known as narcissistic self‐sorting. For this purpose, each particle type is functionalized either with the light‐switchable protein VVDHigh or Cph1, which homodimerize under blue and red light, respectively. The response to different wavelengths of light and the high specificity of the protein interactions allows for the independent self‐assembly of each particle type with blue or red light and narcissistic self‐sorting. Moreover, as both of the photoswitchable protein interactions are reversible in the dark; also, the self‐sorting is reversible and dynamic. Overall, the independent blue and red light controlled self‐sorting in a synthetic system opens new possibilities to assemble adaptable, smart, and advanced materials similar to the complexity observed in tissues.     

Bottom‐Up Assembly of Functional Intracellular Synthetic Organelles by Droplet‐Based Microfluidics

Bottom‐up synthetic biology has directed most efforts toward the construction of artificial compartmentalized systems that recreate living cell functions in their mechanical, morphological, or metabolic characteristics. However, bottom‐up synthetic biology also offers great potential to study subcellular structures like organelles. Because of their intricate and complex structure, these key elements of eukaryotic life forms remain poorly understood. Here, the controlled assembly of lipid enclosed, organelle‐like architectures is explored by droplet‐based microfluidics. Three types of giant unilamellar vesicles (GUVs)‐based synthetic organelles (SOs) functioning within natural living cells are procedured: (A) synthetic peroxisomes supporting cellular stress‐management, mimicking an organelle innate to the host cell by using analogous enzymatic modules; (B) synthetic endoplasmic reticulum (ER) as intracellular light‐responsive calcium stores involved in intercellular calcium signalling, mimicking an organelle innate to the host cell but utilizing a fundamentally different mechanism; and (C) synthetic magnetosomes providing eukaryotic cells with a magnetotactic sense, mimicking an organelle that is not natural to the host cell but transplanting its functionality from other branches of the phylogenetic tree. Microfluidic assembly of functional SOs paves the way for high‐throughput generation of versatile intracellular structures implantable into living cells. This in‐droplet SO design may support or expand cellular functionalities in translational nanomedicine.     

A Self‐Assembled Protein Nanotube with High Aspect Ratio

Production of a self‐assembled protein nanotube achieved through engineering of the 11mer ring protein trp RNA‐binding attenuation protein is described. The produced mutant protein is able to stack in solution to produce an extremely narrow, uniform nanotube apparently stabilized by a mixture of disulfide bonds and hydrophobic interactions. Assembly is reversible and the length of tube can potentially be controlled. Large quantities of hollow tubes 8.5 nm in overall diameter with lengths varying from 7 nm to over 1 µm are produced. The structure is analyzed using transmission electron microscopy, atomic force microscopy, mass spectrometry, and single‐particle analysis and it is found that component rings stack in a head‐to‐head fashion. The internal diameter of the tube is 2.5 nm, and the amino acid residues lining the central cavity can be mutated, raising the possibility that the tube can be filled with a variety of conducting or semiconducting materials.     

Self‐Propelled Micro/Nanomotors for Sensing and Environmental Remediation

Self‐propelled micro/nanomotors have gained attention for successful application in cargo delivery, therapeutic treatments, sensing, and environmental remediation. Unique characteristics such as high speed, motion control, selectivity, and functionability promote the application of micro/nanomotors in analytical sciences. Here, the recent advancements and main challenges regarding the application of self‐propelled micro/nanomotors in sensing and environmental remediation are discussed. The current state of micro/nanomotors is reviewed, emphasizing the period of the last five years, then their developments into the future applications for enhanced sensing and efficient purification of water resources are extrapolated.     

Self‐Assembly of Perovskite for Fabrication of Semitransparent Perovskite Solar Cells

This work reports on the preparation of semitransparent perovskite solar cells. The cells transparency is achieved through a unique wet deposition technique that creates perovskite grids with various dimensions. The perovskite grid is deposited on a mesoporous TiO₂ layer, followed by hole transport material deposition and evaporation of a semitransparent gold film. Control of the transparency of the solar cells is achieved by changing the perovskite solution concentration and the mesh openings. The semitransparent cells demonstrate 20–70% transparency with a power conversion efficiency of 5% at 20% transparency. This is the first demonstration of the possibility to create a controlled perovskite pattern using a direct mesh‐assisted assembly deposition method for fabrication of a semitransparent perovskite‐based solar cell.     

Self‐Assembling Proteins as High‐Performance Substrates for Embryonic Stem Cell Self‐Renewal

The development of extracellular matrix mimetics that imitate niche stem cell microenvironments and support cell growth for technological applications is intensely pursued. Specifically, mimetics are sought that can enact control over the self‐renewal and directed differentiation of human pluripotent stem cells (hPSCs) for clinical use. Despite considerable progress in the field, a major impediment to the clinical translation of hPSCs is the difficulty and high cost of large‐scale cell production under xeno‐free culture conditions using current matrices. Here, a bioactive, recombinant, protein‐based polymer, termed ZT^Fn, is presented that closely mimics human plasma fibronectin and serves as an economical, xeno‐free, biodegradable, and functionally adaptable cell substrate. The ZT^Fn substrate supports with high performance the propagation and long‐term self‐renewal of human embryonic stem cells while preserving their pluripotency. The ZT^Fn polymer can, therefore, be proposed as an efficient and affordable replacement for fibronectin in clinical grade cell culturing. Further, it can be postulated that the ZT polymer has significant engineering potential for further orthogonal functionalization in complex cell applications.     

A Generic Self‐Assembly Process in Microcompartments and Synthetic Protein Nanotubes

Bacterial microcompartments enclose a biochemical pathway and reactive intermediate within a protein envelope formed by the shell proteins. Herein, the orientation of the propanediol‐utilization (Pdu) microcompartment shell protein PduA in bacterial microcompartments and in synthetic nanotubes, and the orientation of PduB in synthetic nanotubes are revealed. When produced individually, PduA hexamers and PduB trimers, tessellate to form flat sheets in the crystal, or they can self‐assemble to form synthetic protein nanotubes in solution. Modelling the orientation of PduA in the 20 nm nanotube so as to preserve the shape complementarity and key interactions seen in the crystal structure suggests that the concave surface of the PduA hexamer faces out. This orientation is confirmed experimentally in synthetic nanotubes and in the bacterial microcompartment produced in vivo. The PduB nanotubes described here have a larger diameter, 63 nm, with the concave surface of the trimer again facing out. The conserved concave surface out characteristic of these nano‐structures reveals a generic assembly process that causes the interface between adjacent subunits to bend in a common direction that optimizes shape complementarity and minimizes steric clashes. This understanding underpins engineering strategies for the biotechnological application of protein nanotubes.     

Piezoresistivity,Strain, and Damage Self‐Sensing of Polymer Composites Filled with Carbon Nanostructures

Previous and current research on piezoresistivity of polymer composites filled with carbon nanostructures is reviewed. The review covers the use of the coupled electro‐mechanical response of these materials to self‐sense their strain and damage during mechanical loading. The mechanisms yielding changes in electrical resistance upon mechanical loading in polymer composites filled with carbon nanostructures are first discussed. Published knowledge is then summarized, starting with framework literature on carbon black and graphite and then moving to more recent research on carbon nanotubes, exfoliated graphite, and few‐layer graphene sheets. Piezoresistive studies of polymer nanocomposites with aligned carbon fillers are also reviewed. It is aimed that this review contributes in collecting, organizing, and summarizing the knowledge, foundations, and state of the art on the piezoresistive response of polymer composites filled with different carbon allotropes, providing new perspectives and advancing towards the fast development of smart self‐sensing carbon filled nanocomposites.

     

Shaping Giant Membrane Vesicles in 3D‐Printed Protein Hydrogel Cages

Giant unilamellar phospholipid vesicles are attractive starting points for constructing minimal living cells from the bottom‐up. Their membranes are compatible with many physiologically functional modules and act as selective barriers, while retaining a high morphological flexibility. However, their spherical shape renders them rather inappropriate to study phenomena that are based on distinct cell shape and polarity, such as cell division. Here, a microscale device based on 3D printed protein hydrogel is introduced to induce pH‐stimulated reversible shape changes in trapped vesicles without compromising their free‐standing membranes. Deformations of spheres to at least twice their aspect ratio, but also toward unusual quadratic or triangular shapes can be accomplished. Mechanical force induced by the cages to phase‐separated membrane vesicles can lead to spontaneous shape deformations, from the recurrent formation of dumbbells with curved necks between domains to full budding of membrane domains as separate vesicles. Moreover, shape‐tunable vesicles are particularly desirable when reconstituting geometry‐sensitive protein networks, such as reaction‐diffusion systems. In particular, vesicle shape changes allow to switch between different modes of self‐organized protein oscillations within, and thus, to influence reaction networks directly by external mechanical cues.