DNA has received considerable attention as a promising building material owing to its ability to form predictable secondary structures through sequence-directed hybridization. [ 1 , 2 ] It has been shown that DNA can be precisely designed with specifi c sequences and self-assemble into two-or three-dimensional nanostructures, [3][4][5][6][7][8][9] fabricated to nanomachines or motors, [10][11][12][13] or used as a programmable template to direct the assembly of nanoparticles. [14][15][16][17] Recently, the concept of DNA assembly has been expanded to construct "DNA hydrogels", which are crosslinked networks swollen in an aqueous phase. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] Though hydrogels have great potential in biological and medical applications, [32][33][34][35][36] such as drug and gene delivery, biosensing, and tissue engineering, studying the preparation of DNA hydrogels with designable properties is still in its early stages. In the past, several methods have been reported to prepare DNA hydrogels, for example, DNA directly extracted from the nucleus in nature, behaves like a long linear polymer and forms a hydrogel via physical entanglement or by chemical crosslinking of small molecules. [ 18 − 20] Similarly, DNA can be used as a negatively charged polymer and form a complex with cationic (poly)electrolytes through electrostatic interactions. [ 21 , 22 ] However, both methods treated DNA as a polymer and did not take advantage of the self-assembly of DNA into ordered structures, therefore, the resulting hydrogels lacked precise structural control and specifi c responses. Instead of using physical interactions, DNA can be covalently grafted onto synthetic polymers and serve as a cross-linker, the recognition of complementary DNA strands leads to crosslinking of polymer chains and causes hydrogel formation. [ 23 − 28] In general, the preparation of a DNA-polymer hybrid requires laborious modifi cation steps, and an easy and fast strategy to build tailored DNA hydrogels is desired. Luo and his coworkers have developed a new approach to construct pure DNA hydrogels: using well-designed DNA sequences, selfassembled DNA building blocks with more than two branches could be prepared and further enzymatic ligation between the building blocks led to DNA hydrogel formation. [ 29 ] These DNA hydrogels have been demonstrated for potential applications in controllable drug release [ 29 ] and cell-free protein-producing systems, [ 30 ] however, the enzymatic ligation is rather slow and the preparation is time-consuming. More recently, we have reported that pure DNA hydrogels could be made based on duplex formation and intermolecular i-motif structures. The DNA hydrogels showed a fast sol-gel transition upon changes in the pH, that is, within minutes, and released cargoes in a pH-controlled manner. [ 31 ] However, these DNA hydrogels were not stable under physiological conditions, which limited their in-vivo applications.Herein, we propose a new and general platform to create pure DNA hydrogels t...

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A rapidly formed supramolecular polypeptide-DNA hydrogel was prepared and used for in situ multilayer three-dimensional bioprinting for the first time. By alternative deposition of two complementary bio-inks, designed structures can be printed. Based on their healing properties and high mechanical strengths, the printed structures are geometrically uniform without boundaries and can keep their shapes up to the millimeter scale without collapse. 3D cell printing was demonstrated to fabricate live-cell-containing structures with normal cellular functions. Together with the unique properties of biocompatibility, permeability, and biodegradability, the hydrogel becomes an ideal biomaterial for 3D bioprinting to produce designable 3D constructs for applications in tissue engineering.

Biological membranes fulfill many important tasks within living organisms. In addition to separating cellular volumes, membranes confine the space available to membrane-associated proteins to two dimensions (2D), which greatly increases their probability to interact with each other and assemble into multiprotein complexes. We here employed two DNA origami structures functionalized with cholesterol moieties as membrane anchors—a three-layered rectangular block and a Y-shaped DNA structure—to mimic membrane-assisted assembly into hierarchical superstructures on supported lipid bilayers and small unilamellar vesicles. As designed, the DNA constructs adhered to the lipid bilayers mediated by the cholesterol anchors and diffused freely in 2D with diffusion coefficients depending on their size and number of cholesterol modifications. Different sets of multimerization oligonucleotides added to bilayer-bound origami block structures induced the growth of either linear polymers or two-dimensional lattices on the membrane. Y-shaped DNA origami structures associated into triskelion homotrimers and further assembled into weakly ordered arrays of hexagons and pentagons, which resembled the geometry of clathrin-coated pits. Our results demonstrate the potential to realize artificial self-assembling systems that mimic the hierarchical formation of polyhedral lattices on cytoplasmic membranes.

Nanopores are key in portable sequencing and research given their ability to transport elongated DNA or small bioactive molecules through narrow transmembrane channels. Transport of folded proteins could lead to similar scientific and technological benefits. Yet this has not been realised due to the shortage of wide and structurally defined natural pores. Here we report that a synthetic nanopore designed via DNA nanotechnology can accommodate folded proteins. Transport of fluorescent proteins through single pores is kinetically analysed using massively parallel optical readout with transparent silicon-on-insulator cavity chips vs. electrical recordings to reveal an at least 20-fold higher speed for the electrically driven movement. Pores nevertheless allow a high diffusive flux of more than 66 molecules per second that can also be directed beyond equillibria. The pores may be exploited to sense diagnostically relevant proteins with portable analysis technology, to create molecular gates for drug delivery, or to build synthetic cells.