Cell-sized liposomes and droplets coated with lipid layers have been used as platforms for understanding live cells, constructing artificial cells, and implementing functional biomedical tools such as biosensing platforms and drug delivery systems. However, these systems are very fragile, which results from the absence of cytoskeletons in these systems. Here, we construct an artificial cytoskeleton using DNA nanostructures. The designed DNA oligomers form a Y-shaped nanostructure and connect to each other with their complementary sticky ends to form networks. To undercoat lipid membranes with this DNA network, we used cationic lipids that attract negatively charged DNA. By encapsulating the DNA into the droplets, we successfully created a DNA shell underneath the membrane. The DNA shells increased interfacial tension, elastic modulus, and shear modulus of the droplet surface, consequently stabilizing the lipid droplets. Such drastic changes in stability were detected only when the DNA shell was in the gel phase. Furthermore, we demonstrate that liposomes with the DNA gel shell are substantially tolerant against outer osmotic shock. These results clearly show the DNA gel shell is a stabilizer of the lipid membrane akin to the cytoskeleton in live cells.iposomes have been used as artificial cell models to understand cell shape, membrane protein function, and lipid− protein interaction, among other biological functions (1-3). In addition, liposomes have been used as a platform for biosensing and as drug delivery systems (DDS) because of their excellent biocompatibility and biodegradability (4). However, liposomes collapse easily against environmental shifts and mechanical forces because of their low bending modulus. The fragility of liposomes causes uncontrolled leakage of the entrapped compounds and thus inhibits their use in biomedical applications and artificial cells experiments.In contrast, cell membranes are tolerant against environmental shifts and mechanical forces. The stability of cell membrane arises from the cytoskeleton underneath the membrane. The major component of cytoskeletons is actin (5). Actin gels show high elasticity (6), which ensures the stability of cell membranes against various forces. For liposomes, the use of actin filaments as a cytoskeleton is not an optimal strategy for the following three reasons: First, although actin bundles and actomyosin rings have been reconstituted in artificial cells (7,8), formation of an actin cortex underneath artificial membranes has been still challenging. Second, actin is hard to modify by chemical and genetic means because of its essentiality for cell growth. Third, the physicochemical properties of actin gels are still unclear (9, 10). Hence, the cytoskeleton of liposomes should be constructed with defined and designable materials. To accomplish this aim, DNA nanotechnology, which uses limited components with high designability in a nanometer scale (11), is a feasible candidate to construct cytoskeleton structures in artificial cells.DNA nanostructure...

An amoeba-like molecular robot changes its shape in response to sequence-designed DNA signal molecules.

In this study, a Langmuir-Blodgett (LB) system has been utilized for the regulation of polymerization of a DNA origami structure at the air-water interface as a two-dimensionally confined medium, which enables dynamic condensation of DNA origami units through variation of the film area at the macroscopic level (ca. 10-100 cm(2)). DNA origami sheets were conjugated with a cationic lipid (dioctadecyldimethylammonium bromide, 2C18N(+)) by electrostatic interaction and the corresponding LB-film was prepared. By applying dynamic pressure variation through compression-expansion processes, the lipid-modified DNA origami sheets underwent anisotropic polymerization forming a one-dimensionally assembled belt-shaped structure of a high aspect ratio although the thickness of the polymerized DNA origami was maintained at the unimolecular level. This approach opens up a new field of mechanical induction of the self-assembly of DNA origami structures.

Stimuli-responsive DNA gels that can undergo a sol-gel transition in response to photo-irradiation provide a way to engineer functional gel material with fully designed DNA base sequences. We propose an X-shaped DNA motif that turns into a gel by hybridization of self-complementary sticky ends. By embedding a photo-crosslinking artificial base in the sticky-end sequence, repetitive gel-sol transitions are achieved through UV irradiation at different wavelengths. The concentration of the DNA motif necessary for gelation is as low as 40 μm after modification of the geometrical properties of the motif. The physical properties, such as swelling degree and diffusion coefficient, were assessed experimentally.

Making use of the programmability and structural flexibility of the DNA molecule, a DNA‐origami nanoarm capable of undergoing large deformation is constructed. This DNA‐origami nanoarm comprised serially repeated tension‐adjustable modules, the cumulative actuation of which resulted in a large deformation of the arm structure, which transformed from a linear shape into an arched shape. Combining atomic force microscopy and theoretical analyses based on the mechanics of materials, we demonstrate that the degree of deformation can be systematically controlled by merely replacing a set of strands that is required for the actuation of the module. Moreover, by employing a G‐quadruplex‐forming sequence for the actuation, we could achieve reversible ion‐induced contraction and relaxation of the nanoarm. The adjustability and scalability of this design could enable the production of DNA nanodevices that exhibit large deformation in response to external stimuli.