Three-dimensional crystalline frameworks with nanoscale periodicity are valuable for many emerging technologies, from nanophotonics to nanomedicine. DNA nanotechnology has emerged as a prime route ...for constructing these materials, with most approaches taking advantage of the structural rigidity and bond directionality programmable for DNA building blocks. Recently, we have introduced an alternative strategy reliant on flexible, amphiphilic DNA junctions dubbed C-stars, whose ability to crystallize is modulated by design parameters, such as nanostructure topology, conformation, rigidity, and size. While C-stars have been shown to form ordered phases with controllable lattice parameter, response to stimuli, and embedded functionalities, much of their vast design space remains unexplored. Here, we investigate the effect of changing the chemical nature of the hydrophobic modifications and the structure of the DNA motifs in the vicinity of these moieties. While similar design variations should strongly alter key properties of the hydrophobic interactions between C-stars, such as strength and valency, only limited differences in self-assembly behavior are observed. This finding suggests that long-range order in C-star crystals is likely imposed by structural features of the building block itself rather than the specific characteristics of the hydrophobic tags. Nonetheless, we find that altering the hydrophobic regions influences the ability of C-star crystals to uptake hydrophobic molecular cargoes, which we exemplify by studying the encapsulation of antibiotic penicillin V. Besides advancing our understanding of the principles governing the self-assembly of amphiphilic DNA building blocks, our observations thus open up new routes to chemically program the materials without affecting their structure.
A number of colloidal systems, including polymers, proteins, micelles and hard spheres, have been studied in thermal gradients to observe and characterize their driven motion. Here we show ...experimentally the thermophoretic behaviour of unilamellar lipid vesicles, finding that mobility depends on the mean local temperature of the suspension and on the structure of the exposed polar lipid head groups. By tuning the temperature, vesicles can be directed towards hot or cold, forming a highly concentrated region. Binary mixtures of vesicles composed of different lipids can be segregated using thermophoresis, according to their head group. Our results demonstrate that thermophoresis enables robust and chemically specific directed motion of liposomes, which can be exploited in driven processes.
Malaria has had a major effect on the human genome, with many protective polymorphisms-such as the sickle-cell trait-having been selected to high frequencies in malaria-endemic regions
. The blood ...group variant Dantu provides 74% protection against all forms of severe malaria in homozygous individuals
, a similar degree of protection to that afforded by the sickle-cell trait and considerably greater than that offered by the best malaria vaccine. Until now, however, the protective mechanism has been unknown. Here we demonstrate the effect of Dantu on the ability of the merozoite form of the malaria parasite Plasmodium falciparum to invade red blood cells (RBCs). We find that Dantu is associated with extensive changes to the repertoire of proteins found on the RBC surface, but, unexpectedly, inhibition of invasion does not correlate with specific RBC-parasite receptor-ligand interactions. By following invasion using video microscopy, we find a strong link between RBC tension and merozoite invasion, and identify a tension threshold above which invasion rarely occurs, even in non-Dantu RBCs. Dantu RBCs have higher average tension than non-Dantu RBCs, meaning that a greater proportion resist invasion. These findings provide both an explanation for the protective effect of Dantu, and fresh insight into why the efficiency of P. falciparum invasion might vary across the heterogenous populations of RBCs found both within and between individuals.
Two colloidal spheres are maintained in oscillation by switching the position of an optical trap when a sphere reaches a limit position, leading to oscillations that are bounded in amplitude but free ...in phase and period. The interaction between the oscillators is only through the hydrodynamic flow induced by their motion. We prove that in the absence of stochastic noise the antiphase dynamical state is stable, and we show how the period depends on coupling strength. Both features are observed experimentally. As the natural frequencies of the oscillators are made progressively different, the coordination is quickly lost. These results help one to understand the origin of hydrodynamic synchronization and how the dynamics can be tuned. Cilia and flagella are biological systems coupled hydrodynamically, exhibiting dramatic collective motions. We propose that weakly correlated phase fluctuations, with one of the oscillators typically precessing the other, are characteristic of hydrodynamically coupled systems in the presence of thermal noise.
Short DNA linkers are increasingly being exploited for driving-specific self-assembly of Brownian objects. DNA-functionalized colloids can assemble into ordered or amorphous materials with tailored ...morphology. Recently, the same approach has been applied to compliant units, including emulsion droplets and lipid vesicles. The liquid structure of these substrates introduces new degrees of freedom: the tethers can diffuse and rearrange, radically changing the physics of the interactions. Unlike droplets, vesicles are extremely deformable and DNA-mediated adhesion causes significant shape adjustments. We investigate experimentally the thermal response of pairs and networks of DNA-tethered liposomes and observe two intriguing and possibly useful collective properties: negative thermal expansion and tuneable porosity of the liposome networks. A model providing a thorough understanding of this unexpected phenomenon is developed, explaining the emergent properties out of the interplay between the temperature-dependent deformability of the vesicles and the DNA-mediated adhesive forces.
Equilibrium self-assembly relies on the relaxation of disordered mixtures of building blocks towards an ordered ground state. The main drawback of this traditional approach lies in the kinetic traps ...that often interrupt the progression of the system towards equilibrium and lead to the formation of arrested phases. The latest techniques to control colloidal interactions open up the possibility of exploiting the tendency to dynamically arrest in order to construct amorphous materials with a specific morphology and local separation between multiple components. Here we propose strategies to direct the gelation of two-component colloidal mixtures by sequentially activating selective interactions. We investigate morphological changes in the structure of the arrested phases both by means of molecular dynamics simulations and experimentally by using DNA-coated colloids. Our approach can be exploited to assemble multicomponent mesoporous materials with possible applications in hybrid photovoltaics, photonics and drug delivery.
We demonstrate experimental control over tubule growth in giant unilamellar vesicles with liquid-liquid phase coexistence, using a thermal gradient to redistribute lipid phase domains on the ...membrane. As studied previously, the domains of the less abundant phase always partition towards hotter temperatures, depleting the cold side of the vesicle of domains. We couple this mechanism of domain migration with the inclusion of negative-curvature lipids within the membrane, resulting in control of tubule growth direction towards the high temperature. Control of composition determines the interior/exterior growth of tubules, whereas the thermal gradient regulates the length of the tubule relative to the vesicle radius. Maintaining lipid membranes under non-equilibrium conditions, such as thermal gradients, allows the creation of thermally-oriented protrusions, which could be a key step towards developing functional materials or artificial tissues. Interconnected vesicle compartments or ejected daughter vesicles as transport intermediaries towards hot/cold are just two possibilities.
Domain migration is observed on the surface of ternary giant unilamellar vesicles held in a temperature gradient in conditions where they exhibit coexistence of two liquid phases. The migration ...localizes domains to the hot side of the vesicle, regardless of whether the domain is composed of the more ordered or disordered phase and regardless of the proximity to chamber boundaries. The distribution of domains is explored for domains that coarsen and for those held apart due to long-range repulsions. After considering several potential mechanisms for the migration, including the temperature preferences for each lipid, the favored curvature for each phase, and the thermophoretic flow around the vesicle, we show that observations are consistent with the general process of minimizing the system’s line tension energy, because of the lowering of line interface energy closer to mixing. DNA strands, attached to the lipid bilayer with cholesterol anchors, act as an exemplar “cargo,” demonstrating that the directed motion of domains toward higher temperatures provides a route to relocate species that preferentially reside in the domains.
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