Programmable active matter (PAM) combines information processing and energy transduction. The physical embodiment of information could be the direction of magnetic spins, a sequence of molecules, the concentrations of ions, or the shape of materials. Energy transduction involves the transformation of chemical, magnetic, or electrical energies into mechanical energy. A major class of PAM consists of material systems with many interacting units. These units could be molecules, colloids, microorganisms, droplets, or robots. Because the interaction among units determines the properties and functions of PAMs, the programmability of PAMs is largely due to the programmable interactions. Here, we review PAMs across scales, from supramolecular systems to macroscopic robotic swarms. We focus on the interactions at different scales and describe how these (often local) interactions give rise to global properties and functions. The research on PAMs will contribute to the pursuit of generalised crystallography and the study of complexity and emergence. Finally, we ponder on the opportunities and challenges in using PAM to build a soft-matter brain.

Nucleobases are nitrogenous bases composed of monomers that are a major constituent of RNA and DNA, which are an essential part of any cellular life on the Earth. The search for nucleobases in the interstellar medium remains a major challenge, however, the recent detection of nucleobases in meteorite samples and laboratory synthesis in simulated analogue experiments have confirmed their abiotic origin and a possible route for their delivery to the Earth. Nevertheless, cellular life is based on the interacting network of complex structures, and there is substantial lack of information on the possible routes by which such ordered structures may be formed in the prebiotic environment. In the current study, we present the evidence for the synthesis of complex structures due to shock processing of nucleobases. The nucleobases were subjected to the reflected shock temperature of 3500–7000 K (estimated) and pressure of about 15–34 bar for over ~2 ms timescale. Under such extreme thermodynamic conditions, the nucleobases sample experiences superheating and subsequent cooling. Electron microscopic studies of shock processed residue show that nucleobases result in spontaneous formation of complex structures when subjected to extreme conditions of shock. These results suggest that impact shock processes might have contributed to the self-assembly of biologically relevant structures and the origin of life.

The purpose of this study was to construct a glycyrrhetinic acid (GA)-mediated, breakable, intracellular, nanoscale drug-delivery carrier via amide and esterification reactions. The structures were identified by Fourier-transformed infrared (FTIR) and 1H-nuclear magnetic resonance (1H-NMR) spectrophotometry. The compatibility and safety of the carrier were evaluated using hemolysis and cytotoxicity tests. The GA-copolymer micelle was prepared using the solvent evaporation method. FTIR and 1H-NMR detection demonstrated the successful construction of the polymer. No hemolysis occurred in any concentration of polymer within 3 h, and the hemolysis rate was less than 5%. 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) experimental results showed that the novel polymer reduced the cell survival rate and had significant cytotoxic effects. The blank nanoparticles were liquid with light blue opalescence. Transmission electron microscopy revealed that the empty micelles were uniform spheres, with an average size of 62 nm and a zeta potential of −13 mV. The novel GA-mediated polymeric carrier material developed here has the potential to effectively kill human SMMC-7721 cancer cells within 3 days when the dose is above 500 ug/mL.

RNA delivery into deep tissues with dense extracellular matrix (ECM) has been challenging. For example, cartilage is a major barrier for RNA and drug delivery due to its avascular structure, low cell density and strong negative surface charge. Cartilage ECM is comprised of collagens, proteoglycans, and various other noncollagneous proteins with a spacing of 20nm. Conventional nanoparticles are usually spherical with a diameter larger than 50-60nm (after cargo loading). Therefore, they presented limited success for RNA delivery into cartilage. Here, we developed Janus base nanotubes (JBNTs, self-assembled nanotubes inspired from DNA base pairs) to assemble with small RNAs to form nano-rod delivery vehicles (termed as “Nanopieces”). Nanopieces have a diameter of ∼20nm (smallest delivery vehicles after cargo loading) and a length of ∼100nm. They present a novel breakthrough in ECM penetration due to the reduced size and adjustable characteristics to encourage ECM and intracellular penetration.

Achieving control over the morphology of conjugated polymer (CP) blends at nanoscale is crucial for enhancing their performances in diverse organic optoelectronic devices, including thin film transistors, photovoltaics, and light emitting diodes. However, the complex CP chemical structures and intramolecular interactions often make such control difficult to implement. We demonstrate here that cooperative combination of non-covalent interactions, including hydrogen bonding, coordination interactions, and π-π interactions, etc., can be used to effectively define the morphology of CP blend films, in particular being able to achieve accurate spatial arrangement of nanoparticles within CP nanostructures. Through UV-vis absorption spectroscopy and transmission electron microscopy, we show strong attachment of fullerene molecules, CdSe quantum dots, and iron oxide nanoparticles, onto well-defined CP nanofibers. The resulting core/shell hybrid nanofibers exhibit well-defined donor/acceptor interface when employed in photovoltaic devices, which also contributes to enhanced charge separation and transport. These findings provide a facile new methodology of improving CP/nanoparticle interfacial properties and controlling blend morphology. The generality of this methodology demonstrated in current studies points to a new way of designing hybrid materials based on organic polymers and inorganic nanoparticles towards applications in modern electronic devices.

α-Synuclein (α-syn) is an intrinsically disordered protein with a highly asymmetric charge distribution, whose aggregation is linked to Parkinson’s disease. The effect of ionic strength was investigated at mildly acidic pH (5.5) in the presence of catalytic surfaces in the form of α-syn seeds or anionic lipid vesicles using thioflavin T fluorescence measurements. Similar trends were observed with both surfaces: increasing ionic strength reduced the rate of α-syn aggregation although the surfaces as well as α-syn have a net negative charge at pH 5.5. This anomalous salt dependence implies that short-range attractive electrostatic interactions are critical for secondary nucleation as well as heterogeneous primary nucleation. Such interactions were confirmed in Monte Carlo simulations of α-syn monomers interacting with surface-grafted C-terminal tails, and found to be weakened in the presence of salt. Thus, nucleation of α-syn aggregation depends critically on an attractive electrostatic component that is screened by salt to the extent that it outweighs the screening of the long-range repulsion between negatively charged monomers and negative surfaces. Interactions between the positively charged N-termini of α-syn monomers on the one hand, and the negatively C-termini of α-syn on fibrils or vesicles surfaces on the other hand, are thus critical for nucleation.

We report a simple and feasible technique for the formation of well-distributed nickel nanodot arrays on both oxidized and unoxidized silicon substrate by a conventional annealing process. The shape and distribution of nickel nanodots were maintained by adjusting annealing temperature, time and the SiO2 buffer layer thickness in between nickel film and the silicon substrate. The diffusion of nickel into the silicon is significantly reduced when the nickel film on the oxidized silicon substrate is annealed at high temperature. From this conventional annealing technique, we achieve a maximum nickel nanodots density up to (7.94±1.92) nanodot counts/µm2 on the oxidized silicon substrate with a well-defined spherical shape by adjusting the thickness of nickel film as well as buffer SiO2 layer. In the next experiment, the surface charge distribution on the nickel nanodot arrays were characterized through the Kelvin probe force microscope (KPFM) on tapping mode. It is found that the nickel nanodots can store and release the electric charges under an applied bias voltage.

Bio-composite materials with optimal mechanical and structural properties and capability of cell differentiation are crucial for tissue engineering. Synthetic collagen proteins with lengths of approximately 10 nanometers, along with natural spider silk proteins provide an opportunity for development of an optimal biomaterial for scaffolding applications in tissue engineering. This combines unique mechanical, structural and biological properties of two of the nature’s best polymer proteins, albeit the collagen used in the present work is of the synthetic nature, it mimics the properties and advantages of natural collagen itself. In the present work, we study the binding capability of these proteins at a molecular level via molecular dynamics modeling. Spider silk and synthetic collagen protein molecular models in biophysical saline conditions under standard pressure and temperature are investigated to understand if natural binding occurs between the two without any other external factors. An initial minimum separation of 10 angstroms between the proteins was used. Binding was observed between the two proteins throughout the dynamic simulation of 100 nanoseconds. The radius of gyration and minimum distance between the proteins shows a decreasing separation between the two proteins until a stable distance of 2.5 nanometers and 0.2 nanometers respectively, is achieved. Binding is further observed between the proteins via formation of strong and stable hydrogen bonds. A hydrogen bond between collagen Proline-31 and silk Serine-96 was observed to be the most stable and frequent bond between the single collagen and silk system. Results clearly indicate a self-assembly behavior of these two systems illustrating their potential as a biomaterial for tissue engineering.

Oriented attachment (OA) is a particle-based crystallization pathway in which nanocrystals self-assemble in solution and attach along certain crystallographic direction often forming highly organized three-dimensional crystal morphologies. The pathway offers the potential for a general synthetic approach of hierarchical nanomaterials, in which multiscale structural control is achieved by manipulating the interfacial nucleation and self-assembly of nanoscale building blocks. Here, the current status of the development of a predictive theoretical framework for modeling crystallization by OA is reviewed. A particular emphasis is made on recent developments in understanding the microscopic details of solvent-mediated forces that drive nanocrystal reorientation and alignment for face-selective attachment. Interactions arising from the correlated solvent dynamics at particle interfaces emerge as the main sources of long-range face-specific interparticle forces and short-range torque for fine particle alignment into lattice matching configuration. These findings shift the focus of the experimental and theoretical research of OA onto the detailed study of interfacial solvent structure and dynamics.

Porphyrin, as a planar macrocyclic molecule, extensively exists naturally in plants and animals and plays an important role in life activities. Normally, porphyrin exists in the form of nanostructures/aggregations through molecular self-assembly. Thus, it is of great interest for tuning nanostructures, understanding mechanisms, and exploring the diverse applications. In this issue, we present articles covering the synthesis and formation mechanisms of porphyrin nanostructures by self-assembly methods and their applications in solar-energy harvesting, water splitting, environmental pollutant reduction, and nanomedicine for tumor therapy. These articles present the recent developments and potential research directions of this field, and we hope they will interest and inspire readers to enter this growing field.

There has been widespread recent interest in self-assembly and synthesis of porphyrin and its derivatives-based ordered arrays aiming to emulate natural light-harvesting processes and energy storage. However, technologies that leverage the structural advantages of individual porphyrins have not been fully realized and have been limited by available synthesis methods. This article provides general perspectives on porphyrin and derivative chemistry, and discussions on surfactant-assisted cooperative self-assembly using amphiphilic surfactants and functional porphyrins and derivatives. The cooperative self-assembly amplifies the intrinsic advantages of individual porphyrins by engineering them into well-defined one-dimensional–three-dimensional (1D–3D) nanostructures. Surfactant-assisted self-assembly of amphiphilic surfactants and porphyrins has been utilized to form well-defined “micelle-like” nanostructures. Driven by intermolecular interactions, subsequent nucleation and growth confined within these nanostructures lead to the formation of 1D–3D ordered optically and electrically active nanomaterials with structure and function on multiple length scales.

The design and engineering of the size and shapes of photoactive building blocks enable the fabrication of functional nanocrystals, especially for applications in light harvesting, photocatalytic synthesis, water splitting, and photodegradation. Synthesis of such nanocrystals has been demonstrated recently through noncovalent interactions such as π–π stacking and ligand coordination using optically active porphyrin as a functional building block. Depending on the kinetic conditions, the resulting nanocrystals exhibit well-defined one- to three-dimensional shapes such as spheres, nanowires, and nano-octahedra. These well-defined porphyrin nanocrystals show interesting size- and shape-dependent photocatalytic activity. This article reviews the synthesis and formation of porphyrin nanocrystals with controlled size and shape. Important photocatalytic processes such as photodegradation of organic pollutants, photocatalytic water splitting and hydrogen production, and photosynthesis of metallic fuel-cell catalysts are highlighted. Insights on size- and shape-dependent properties are discussed.

Porphyrins are a class of conjugated molecules that structurally and functionally resemble natural photosynthetic and enzymatic chromophores. Crystalline solids self-assembled from anionic and cationic porphyrins yield a new class of multifunctional optoelectronic micro- and nanomaterials. In this article, we provide details on the concept of binary ionic self-assembly (ISA) and ionized forms of porphyrins, as well as formation of hierarchical structures, including nanotubes, rods and ribbons, sheets, and three-dimensional clover-like shapes, spheres, and sheaf-like structures. We summarize key physical properties from ultraviolet–visible characterizations of J-aggregate, exciton delocalization and extended π–π stacking, and related electronic and light-harvesting properties of the structures. Depending on the molecular subunits, the functionalities of the ISA materials are altered. These ISA nanostructures possess attractive light-harvesting and charge- and energy-transport functionalities and allow access to a novel class of nanomaterials with potential for applications in sensors, photovoltaics, photocatalysis, and solar power.

Nature’s optical nanomaterials are poised to form the platform for future optical devices with unprecedented functionality. The brilliant colors of many animals arise from the physical interaction of light with nanostructured, multifunctional materials. While their length scale is typically in the 100-nm range, the morphology of these structures can vary strongly. These biological nanostructures are obtained in a controlled manner, using biomaterials under ambient conditions. The formation processes nature employs use elements of both equilibrium self-assembly and far-from-equilibrium and growth processes. This renders not only the colors themselves, but also the formation processes technologically and ecologically highly relevant. Yet, for many biological nanostructured materials, little is known about the formation mechanisms—partially due to a lack of in vivo imaging methods. Here, we present the toolbox of natural multifunctional nanostructures and the current knowledge about the understanding of their far-from-equilibrium assembly processes.

Far-from-equilibrium systems are ubiquitous in nature. They are also rich in terms of diversity and complexity. Therefore, it is an intellectual challenge to be able to understand the physics of far-from-equilibrium phenomena. In this article, we revisit a standard tabletop experiment, the Rayleigh–Bénard convection, to explore some fundamental questions and present a new perspective from a first-principles point of view. We address how nonequilibrium fluctuations differ from equilibrium fluctuations, how emergence of order out of equilibrium breaks symmetries in the system, and how free energy of a system gets locally bifurcated to operate a Carnot-like engine to maintain order. The exploration and investigation of these nontrivial questions are the focus of this article.

Materials can be endowed with unique properties by the integration of molecular motors. Molecular motors can have a biological origin or can be chemically synthesized and produce work from chemical energy or light. Their ability to access large internal or external reservoirs of energy enables a wide range of nonequilibrium behaviors, including the production of force, changes in shape, internal reorganization, and dynamic changes in mechanical properties—muscle tissue is one illustration of the possibilities. Current research efforts advance our experimental capabilities to create such “active matter” by using either biomolecular or synthetic motors, and also advance our theoretical understanding of these materials systems. Here, we introduce this exciting research field and highlight a few of the recent advances as well as open questions.

Searching for materials with improved or perhaps completely novel properties involves an iterative process intended to successively narrow the gap between some initial starting point and the desired design target. This can be viewed as an optimization problem in a high-dimensional search space, often with many dozens of material parameters that need to be tuned. To tackle this, the evolutionary process in biology has been a source of inspiration in developing effective search algorithms. However, reaping the full benefits of bioinspired searches for materials design requires some thought. Here, we go beyond traditional black box algorithms and take a broader view of computational evolution strategies. We discuss recent strategies that exploit knowledge about the material configuration statistics and we highlight the advantages when time-varying environments are considered. Throughout, we emphasize that the search strategies themselves can be viewed as a nonequilibrium dynamical process in design space.

Traditional approaches to materials synthesis have largely relied on uniform, equilibrated phases leading to static “condensed-matter” structures (e.g., monolithic single crystals). Departures from these modes of materials design are pervasive in biology. From the folding of proteins to the reorganization of self-regulating cytoskeletal networks, biological materials reflect a major shift in emphasis from equilibrium thermodynamic regimes to out-of-equilibrium regimes. Here, equilibrium structures, determined by global free-energy minima, are replaced by highly structured dynamical states that are out of equilibrium, calling into question the utility of global thermodynamic energy minimization as a first-principles approach. Thus, the creation of new materials capable of performing life-like functions such as complex and cooperative processes, self-replication, and self-repair, will ultimately rely upon incorporating biological principles of spatiotemporal modes of self-assembly. Elucidating fundamental principles for the design of such out-of-equilibrium dynamic self-assembling materials systems is the focus of this issue of MRS Bulletin.

Biological entities are capable of amazing material feats, such as self-organization, self-repair, self-replication, and self-immolation. Indeed, the most intriguing feature of living biomaterials, whether they are tissues, cells, or intracellular structures, is their ability to autonomously sense, decide, and perform work without the need of a project manager. The effect is multiscale—from enzymes to full organisms, each level is capable of such autonomous activities. Further, each scale has similar energy-using units that work together to compose the larger-scale material. For instance, autonomous cells work together to create tissues. In this article, we will discuss some of the outstanding and desirable properties of active biological materials that we might consider mimicking in future materials. We will discuss how such active materials are powered and explore some fundamental lessons we can learn to direct future fundamental scientific inquiries to begin to understand and use these properties to make synthetic, autonomous materials of the future.