Metamaterials are artificial substances that are structurally engineered to have properties not typically found in nature. To date, almost all metamaterials have been made from inorganic materials such as silicon and copper, which have unusual electromagnetic or acoustic properties that allow them to be used, for example, as invisible cloaks, superlenses or super absorbers for sound. Here, we show that metamaterials with unusual mechanical properties can be prepared using DNA as a building block. We used a polymerase enzyme to elongate DNA chains and weave them non-covalently into a hydrogel. The resulting material, which we term a meta-hydrogel, has liquid-like properties when taken out of water and solid-like properties when in water. Moreover, upon the addition of water, and after complete deformation, the hydrogel can be made to return to its original shape. The meta-hydrogel has a hierarchical internal structure and, as an example of its potential applications, we use it to create an electric circuit that uses water as a switch.

This Communication demonstrates a method that generates parallel fibers via electrospinning (ES) magnetic-particledoped polymers in a magnetic field. ES is a simple method for generating ultrathin fibers with diameters ranging from tens of nanometers to tens of micrometers. [1][2][3][4][5] ES possesses several attractive features: comparatively low-cost, relatively high production rate, the ability to generate materials with large surface area-to-volume ratios, and applicability to many types of materials. These features have enabled many applications. [6][7][8][9][10] During electrospinning, the fibers deposited on the collector are typically randomly oriented in the form of nonwoven mats. It is desirable to generate periodic structures to broaden the applications of ES. For example, in the fabrication of electronic and photonic devices, well-aligned and highly ordered architectures are often required. [11,12] For application of fiber-reinforced polymer composites, the alignment of fibers can improve mechanical properties. [13] Well-ordered fibers may also be suitable for many applications in tissue engineering. [8,14] There have been a few approaches to improving the orderliness of electrospun fibers. [15][16][17][18][19][20][21][22][23][24][25][26][27] Matthews et al. [25] used a rotating mandrel as a ground target to collect fibers. By controlling the rotation speed of the mandrel, they obtained collagen fibers aligned along the axis of rotation. Katta et al. [16] employed a macroscopic copper wireframed rotating drum as the collector, and the electrospun fibers collected on the drum as it rotated were parallel to each other. Theron et al. [26] described an electrostatic field-assisted assembly technique using a tapered and grounded wheel-like bobbin to position and align individual nanofibers into parallel arrays. Because the edge of the bobbin was relatively sharp, this technique could not fabricate well-aligned nanofibers over large areas. Li et al. [15,17] fabricated parallel arrays made of polymeric and ceramic nanofibers using a collector consisting of two pieces of electrically conductive substrate separated by a gap. To sum up, existing strategies for making parallel electrospun fibers include modifying the collectors and manipulating the electrical field. These methods can fabricate more or less aligned fibers; however, they still have some drawbacks. Modifying the collectors, such as rotating drums, is a time-and energy-consuming method; moreover fibers fabricated by this method are poorly aligned and cannot be conveniently transferred to different types of substrates. Methods based on electrical fields do not seem to achieve the fabrication of aligned fibers over large areas. It is therefore necessary to explore new and more reliable methods that generate wellaligned electrospun polymeric fibers over large areas. Herein, we report a facile and effective approach to fabricating well-aligned arrays and multilayer grids by a technique called magnetic electrospinning (MES; Scheme 1), where magnetized f...

DNA is traditionally known as a central genetic biomolecule in living systems. From an alternative perspective, DNA is a versatile molecular building-block for the construction of functional materials, in particular biomaterials, due to its intrinsic biological attributes, molecular recognition capability, sequence programmability, and biocompatibility. The topologies of DNA building-blocks mainly include linear, circular, and branched types. Branched DNA recently has been extensively employed as a versatile building-block to synthesize new biomaterials, and an assortment of promising applications have been explored. In this review, we discuss the progress on DNA functional materials assembled from branched DNA. We first briefly introduce the background information on DNA molecules and sketch the development history of DNA functional materials constructed from branched DNA. In the second part, the synthetic strategies of branched DNA as building-blocks are categorized into base-pairing assembly and chemical bonding. In the third part, construction strategies for the branched DNA-based functional materials are comprehensively summarized including tile-mediated assembly, DNA origami, dynamic assembly, and hybrid assembly. In the fourth part, applications including diagnostics, protein engineering, drug and gene delivery, therapeutics, and cell engineering are demonstrated. In the end, an insight into the challenges and future perspectives is provided. We envision that branched DNA functional materials can not only enrich the DNA nanotechnology by ingenious design and synthesis but also promote the development of interdisciplinary fields in chemistry, biology, medicine, and engineering, ultimately addressing the growing demands on biological and medical-related applications in the real world.

CONSPECTUS: In recent decades, DNA has taken on an assortment of diverse roles, not only as the central genetic molecule in biological systems but also as a generic material for nanoscale engineering. DNA possesses many exceptional properties, including its biological function, biocompatibility, molecular recognition ability, and nanoscale controllability. Taking advantage of these unique attributes, a variety of DNA materials have been created with properties derived both from the biological functions and from the structural characteristics of DNA molecules. These novel DNA materials provide a natural bridge between nanotechnology and biotechnology, leading to far-ranging real-world applications. In this Account, we describe our work on the design and construction of DNA materials. Based on the role of DNA in the construction, we categorize DNA materials into two classes: substrate and linker. As a substrate, DNA interfaces with enzymes in biochemical reactions, making use of molecular biology's "enzymatic toolkit". For example, employing DNA as a substrate, we utilized enzymatic ligation to prepare the first bulk hydrogel made entirely of DNA. Using this DNA hydrogel as a structural scaffold, we created a protein-producing DNA hydrogel via linking plasmid DNA onto the hydrogel matrix through enzymatic ligation. Furthermore, to fully make use of the advantages of both DNA materials and polymerase chain reaction (PCR), we prepared thermostable branched DNA that could remain intact even under denaturing conditions, allowing for their use as modular primers for PCR. Moreover, via enzymatic polymerization, we have recently constructed a physical DNA hydrogel with unique internal structure and mechanical properties. As a linker, we have used DNA to interface with other functional moieties, including gold nanoparticles, clay minerals, proteins, and lipids, allowing for hybrid materials with unique properties for desired applications. For example, we recently designed a DNA-protein conjugate as a universal adapter for protein detection. We further demonstrate a diverse assortment of applications for these DNA materials including diagnostics, protein production, controlled drug release systems, the exploration of life evolution, and plasmonics. Although DNA has shown great potential as both substrate and linker in the construction of DNA materials, it is still in the initial stages of becoming a well-established and widely used material. Important challenges include the ease of design and fabrication, scaling-up, and minimizing cost. We envision that DNA materials will continue to bridge the gap between nanotechnology and biotechnology and will ultimately be employed for many real-world applications.