Smart nanosystems: Bio-inspired technologies that interact with the host environment

Nanoparticle technologies intended for human administration must be designed to interact with, and ideally leverage, a living host environment. Here, we describe smart nanosystems classified in two categories: (i) those that sense the host environment and respond and (ii) those that first prime the host environment to interact with engineered nanoparticles. Smart nanosystems have the potential to produce personalized diagnostic and therapeutic schema by using the local environment to drive material behavior and ultimately improve human health.     

Determining hydrodynamic forces in bursting bubbles using DNA nanotube mechanics

Quantifying the mechanical forces produced by fluid flows within the ocean is critical to understanding the ocean’s environmental phenomena. Such forces may have been instrumental in the origin of life by driving a primitive form of self-replication through fragmentation. Among the intense sources of hydrodynamic shear encountered in the ocean are breaking waves and the bursting bubbles produced by such waves. On a microscopic scale, one expects the surface-tension–driven flows produced during bubble rupture to exhibit particularly high velocity gradients due to the small size scales and masses involved. However, little work has examined the strength of shear flow rates in commonly encountered ocean conditions. By using DNA nanotubes as a novel fluid flow sensor, we investigate the elongational rates generated in bursting films within aqueous bubble foams using both laboratory buffer and ocean water. To characterize the elongational rate distribution associated with a bursting bubble, we introduce the concept of a fragmentation volume and measure its form as a function of elongational flow rate. We find that substantial volumes experience surprisingly large flow rates: during the bursting of a bubble having an air volume of 10 mm³, elongational rates at least as large as ϵ˙=1.0×108 s⁻¹ are generated in a fragmentation volume of  ～ 2 × 10^?6 μL. The determination of the elongational strain rate distribution is essential for assessing how effectively fluid motion within bursting bubbles at the ocean surface can shear microscopic particles and microorganisms, and could have driven the self-replication of a protobiont.Functioning like a giant heat engine between the high-temperature heat bath of the sun and the low-temperature heat bath of outer space, the earth’s atmosphere generates wind and rain with intense fluid flows. The mechanical stresses produced by these hydrodynamic flows are among the environmental stresses that biological organisms must cope with. Organisms often exploit these stresses and fluid flows, most notably to aid reproduction. A well-known example at the macroscopic scale is the wind dispersal of spores, seeds, and pollen. Less well-known, fragmentation resulting from fluid-flow-induced stress is used by a number of marine organisms as a means of vegetative reproduction, such as macrophyte algae (1) and sponge and coral colony (2, 3) propagation by storm-induced fragmentation. Can analogous mechanical forces facilitate vegetative reproduction at the microscale? Current evidence is at best indirect: Filamentous cyanobacteria are known to fragment under environmental stress (4, 5), suggesting that prokaryotes may use fluid-flow-induced fragmentation as a means of clonal reproduction and dispersal as well.Several origin-of-life hypotheses invoke processes in which environmentally produced microscale mechanical forces drive self-replication through fragmentation. Oparin proposed that fragmentation of coacervates may have constituted a primitive form of self-replication allowing for Darwinian evolution by natural selection (6). More concretely, Cairns-Smith proposed that life arose from mineral crystals that replicated by fragmentation into new seed crystals, thereby propagating genetic information consisting of the patterns of defects within the mother crystal (7–9). Szostak’s group also proposed that division of protocells (having a lipid bilayer) can be driven by fluid flow (10–12). Inspired by Cairns-Smith’s proposal, Schulman, Yurke, and Winfree used DNA tile self-assembly to construct a self-replicating system in which fragmentation was induced by intense elongational flow at a constriction in a flow channel (13). This synthetic system is analogous to an in vitro system in which exponential growth of prions is driven via fragmentation by mechanical shearing of amyloid fibrils (14). Similarities between regeneration (self-healing) and asexual reproduction in modern organisms have led some to postulate fragmentation-and-regeneration as a primordial form of reproduction (15).To effectively shear microscopic objects such as bacteria or protobionts, fluid flows must exhibit high-velocity gradients over the length scale of the object. Such small-scale high-velocity-gradient flows occur naturally in breaking ocean waves that produce whitecaps (16). Within these waves, the highest velocity gradients are expected to occur in the films of bursting bubbles due to the rapid acceleration produced by surface tension forces acting on the small fluid mass. Moreover, bursting bubbles can generate mechanical stresses of sufficient intensity to be biologically relevant to organisms living in the sea surface microlayer (neuston) (17). As a technological example, cell death at the air–liquid interface during the sparging of bioreactors to enhance oxygen diffusion has been attributed to bubble bursting (18).The fluid flows most effective at shearing small free-floating objects are those that exhibit strain deformation. In such flows, a rod-shaped object will tend to align itself along the direction of maximum fluid extension. In this orientation the rod experiences the greatest tensile stress and is most susceptible to fragmentation. In a given fluid element, the rate of fluid extension––i.e., the rate at which two points in the fluid separate, divided by the distance between them––has a maximum that is referred to as the elongational rate and is here denoted by ϵ˙. A useful way to conceptualize the meaning of ϵ˙ is to consider the case when it is constant. In this case, the time it takes for the fluid element to double its length is tb=ln(2)/ϵ˙.Fig. 1 shows a mechanism by which rod-shaped objects within bursting fluid films can be fragmented. As the hole produced in the bubble film expands, its circumference increases (Fig. 1B). Due to this, fluid elements near the hole’s edge will experience elongation in the direction perpendicular to the velocity of the hole edge. As shown in Fig. 1 C and D, rod-shaped structures within the bubble film will align along the circumference of the expanding hole. If the tension generated along the length of the structure exceeds its tensile strength, the structure will fragment (Fig. 1E).Open in a separate windowFig. 1.DNA nanotubes fragmentation by bursting bubbles. Side (A) and top (B) views of a bubble filled with air bursting on a water surface. Color gradient loosely corresponds to the expected magnitude of the hydrodynamic forces. (B–E) As the hole travels outward driven by surface tension, the liquid film is accumulated into a growing toroidal rim (gray rings). The enlargement of the hole produces elongational flow, with rate ϵ˙=v/r, which is tangential to the perimeter where r is the hole radius and v is the outward velocity of the hole perimeter. The two blue arcs are the two volume elements of the bursting film. (C and D). As the hole expands, the fluid flow orients DNA nanotubes (black, red). (D and E) The elongational flow breaks sufficiently long DNA nanotubes (black) of length l into fragments of length l₁ and l₂ due to tension applied to the nanotube by the elongational fluid flow. Short nanotubes (red) are not fragmented due to insufficient build-up of tension.The elongational rates generated by this mechanism can be estimated using a model of film hole dynamics, for a film of uniform thickness. Initially considered by Dupré (19), Rayleigh (20), and Ranz (21), then corrected by Culick (22) and Taylor (23), the model treats the rupture as a circular hole that propagates outward with the film fluid accumulating in a toroid at the hole perimeter. From momentum balance, the hole propagates outward with a constant speed v=2σ/ρδ, where σ is the surface tension of the film, ρ is the fluid density, and δ is the film thickness. The elongational rate of the circumference is given by ϵ˙=v/r, where r is the hole radius. The volume of fluid subjected to elongational rates greater than ϵ˙, in this simple model, is given by Vf(ϵ˙)=πδr2=2πσ/ρϵ˙2, which is, surprisingly, independent of film thickness. Such volumes provide a natural way to characterize the ability of a bursting bubble to fragment objects suspended within the bubble film that will shear under given elongational rate ϵ˙. Importantly, Vf(ϵ˙) can be defined in a model-independent way as the volume of fluid that experiences elongational rates greater than ϵ˙ during the course of bubble bursting. We will refer to such volumes as fragmentation volumes.Although easiest to explain, the Culick and Taylor model does not describe the only type of elongational flow that can be generated within a bursting bubble; therefore the estimate for Vf(ϵ˙) based on this model should be considered a loose lower bound for the true value. In fact, only half the surface-tension energy released is converted into the kinetic energy of the outward motion of the fluid (24). This suggests that the other half of the surface-tension energy must be dissipated within the film near the edge of the hole. For fluids with low viscosity, such as water, this implies that there are intense small-scale fluid flows near the edge of the hole (18) in addition to those illustrated in Fig. 1. Hydrodynamic instabilities, particularly with larger bubbles, can occur along the perimeter, resulting in fingering and the formation of droplets (25). Also, particularly for small bubbles, the expanding hole produces an inward propagating wave at the bottom surface of the bubble that forms a jet that may launch droplets (26, 27). High-flow gradients are expected in the region where these jets pinch to form droplets. A recent discussion of droplet production during bubble bursting in ocean-like (i.e., not soapy) water was given by Lhuissier and Villermaux (28).As discussed by Lhuissier and Villermaux, at the instant the bubble bursts it possesses a cap of uniform thickness that, at a well-defined edge, joins with the bulk fluid in a region where the thickness rapidly increases with distance from the center of the bubble (Fig. 1A). The critical thickness at which bubble films spontaneously burst depends on the bubble radius (28), increasing from 0.05 to 30 μm as the bubble radius increases from 1 to 20 mm. For an object such as a microorganism to be fully impacted by the mechanical stresses produced by bubble bursting, it would have to reside in the cap film or close to the cap boundary; that is, its thinnest dimension would have to be smaller than the film thickness. Nevertheless, mechanical stresses produced by bursting bubbles are among the stresses that microorganisms, particularly those that occupy the niche consisting of the neuston or sea surface microlayer (29–31), must cope with. We hypothesize that protobionts, small enough to be suspended within the bubble film, also occupied this niche and used these stresses to facilitate replication. However, little work seems to have been done to characterize the elongational rates produced during the bursting of a bubble that would facilitate assessing whether forces of sufficient magnitude are generated.In this study the fragmentation of DNA nanotubes is used to characterize both the magnitude of the elongational rates produced and the volume of fluid subjected to these elongational rates during bubble bursting. These nanotubes are constructed from short DNA oligomers referred to as single-stranded tiles, which each have four sequence domains by which a given oligomer binds with four neighboring oligomers via Watson–Crick base pairing. Thus, whereas each DNA oligomer is held together by covalent bonds, the entire tube assembly is held together by the supramolecular interactions that enable two complementary single-stranded oligomers to form duplex DNA. Base sequences of the oligomers are designed so that the axes of the duplex DNA are parallel to the long axis of the tube. The supramolecular Watson–Crick bonds between neighboring single-stranded tiles are much weaker than the covalent bonds of the phosphate backbone of a single-stranded tile (32). Under sudden tension along the axis of the duplex DNA (33), the tensile force at which the supramolecular bonding fails is referred to as the overstretching force f_c, which has a value of about 65 pN (34, 35). For a tube in which there are n duplex strands in cross-section, the tensile force will be T_c = nf_c. For the tubes used in the experiments reported here, n = 7 (SI Appendix, Fig. S1) and consequently the tubes fragment when subjected to tensile forces in excess of 455 pN. The tubes have a radius of 4 nm, a persistence length of 5 μm (36), and a length distribution that peaks at 5 μm at the start of the experiment (SI Appendix, Fig. S2; see Fig. 3 B and G).Open in a separate windowFig. 3.Nanotube length distributions for bubble bursting experiments in assay buffer or in ocean water. Fluorescence microscopy images and fragment length distributions of DNA nanotubes withdrawn from a sample with an initial volume of 100 μL after 0 mL (A and B), 60 mL (C and D), and 360 mL (E and F) of air had passed through the sample at a flow rate of 18 mL/min. The mean tube length ?l? for each distribution is given at the top of each histogram. Nanotube length distribution in bubble bursting experiment with ocean water after 0 mL (G), 60 mL (H), and 360 mL (I) of air.Some of these tubes will be trapped in the bubble film and will be subjected to elongational forces in the manner illustrated in Fig. 1. Although nanotubes will necessarily also be subject to compressive fluid flows, they are not fragile under compression. The junctions at which a given single-stranded tile connects with two neighboring tiles are flexible, allowing the tube to crumple and then straighten when the compressive forces are relieved. This collapse into a coil configuration followed by stretching has been studied for other stiff linear biopolymers and synthetic fibers in hydrodynamic flows near stagnation points (33, 37, 38). Generally, the tubes will crumple under the compressive flow and reorient and stretch along the axis of the elongational flow (Movie S1 and SI Appendix, section 10). A further complication is that Brownian motion will tend to counteract the alignment produced by the elongational flow. However, as will be shown, under the conditions in which our DNA nanotubes break, the Péclet number––which is the ratio of the active transport rate to the diffusive transport rate––is in excess of 1.4 × 10⁴, indicating that diffusive misalignment of the nanotubes plays a negligible role in our experiments. Due to the viscous stresses exerted on the DNA nanotube as it reorients along the direction of maximum extension flow, the tension experienced by the tube will be greatest at the center of the tube and will be greater for longer tubes, scaling as T∝ϵ˙l2/ln(l/2R), where l is the tube length and R the tube radius (34). If the tensile force is exceeded, the tube will break into two fragments of nearly equal length. If the elongational flow continues to intensify so that the two fragments experience a tension at their centers that exceeds the tensile force, each of these in turn will fragment into two shorter pieces of equal length. This cascading process will continue until the elongational rate reaches its maximum value.DNA nanotubes are well-suited to serve as probes of hydrodynamic flows within bubble films for three reasons. First, their fragmentation in elongational flows has already been extensively characterized (34). Second, they are highly soluble in water and do not exhibit a surfactant-like tendency to stick to the air–water interface, unlike many proteins. Third, it is straightforward to measure histograms of nanotube lengths using fluorescence microscopy. Here, from the evolution of the DNA nanotube fragment length during the course of bubbling, we were able to determine the fragmentation volumes for elongational rates over five orders of magnitude, although our experimental techniques were not able to distinguish where the DNA nanotubes were broken within the bubble. Our findings suggest that, via bubbles, ocean waves provide a source of strong mechanical forces at the micron-scale mechanical stresses that ocean surface-dwelling microbes must cope with, that may be involved in the natural breakdown of pollutants, and that would have been available for protobionts to use as a means of driving self-replication.     

顺磁性纳米微粒的磁靶向微血管栓塞研究

目的测试纳米微粒在磁场导向下对微血管的栓塞效果。方法利用壳聚糖和Fe3O4磁流体合成顺磁性纳米微粒,利用体外模拟微血管观察磁粒在磁场下的凝聚,然后将纳米微粒静脉注射入大鼠并在脑区放置磁场．取脑组织后通过普鲁士蓝染色观察脑微血管栓塞情况。结果制得的顺磁性纳米微粒混悬液呈黑色,无絮状物或沉淀。电镜下测量微粒的平均有效粒径为15．3nm。其在外加磁场下能在体内外微血管内发生凝聚,栓塞微小血管。结论利用顺磁性纳米微粒进行磁靶向微血管栓塞是可行的,这可能成为一种治疗浅表肿瘤和脑血管疾病的新方法。     

克服肿瘤多药耐药的药物共递送纳米载体的设计及研究新方向

多药耐药（multidrug resistance，MDR）是肿瘤治疗成功的主要障碍，药物共递送纳米载体因其肿瘤靶向、控制释放、一致的药动学曲线而被认为是克服MDR的有效策略。本综述总结了当前克服MDR的药物共递送纳米载体的设计思路，并分析了具有前景的研究方向，包括精确药物负载纳米载体、呈时序释放的纳米载体和对肿瘤微环境设计纳米载体，这些新兴策略为临床肿瘤治疗提供了新颖且更好的定制组合方案。     

Pharmaceutical applications of framework nucleic acids

DNA is a biological polymer that encodes and stores genetic information in all living organism. Particularly, the precise nucleobase pairing inside DNA is exploited for the self-assembling of nanostructures with defined size, shape and functionality. These DNA nanostructures are known as framework nucleic acids (FNAs) for their skeleton-like features. Recently, FNAs have been explored in various fields ranging from physics, chemistry to biology. In this review, we mainly focus on the recent progress of FNAs in a pharmaceutical perspective. We summarize the advantages and applications of FNAs for drug discovery, drug delivery and drug analysis. We further discuss the drawbacks of FNAs and provide an outlook on the pharmaceutical research direction of FNAs in the future.     

Real-time SERS monitoring anticancer drug release along with SERS/MR imaging for pH-sensitive chemo-phototherapy

In situ and real-time monitoring of responsive drug release is critical for the assessment of pharmacodynamics in chemotherapy. In this study, a novel pH-responsive nanosystem is proposed for real-time monitoring of drug release and chemo-phototherapy by surface-enhanced Raman spectroscopy (SERS). The Fe₃O₄@Au@Ag nanoparticles (NPs) deposited graphene oxide (GO) nanocomposites with a high SERS activity and stability are synthesized and labeled with a Raman reporter 4-mercaptophenylboronic acid (4-MPBA) to form SERS probes (GO-Fe₃O₄@Au@Ag-MPBA). Furthermore, doxorubicin (DOX) is attached to SERS probes through a pH-responsive linker boronic ester (GO-Fe₃O₄@Au@Ag-MPBA-DOX), accompanying the 4-MPBA signal change in SERS. After the entry into tumor, the breakage of boronic ester in the acidic environment gives rise to the release of DOX and the recovery of 4-MPBA SERS signal. Thus, the DOX dynamic release can be monitored by the real-time changes of 4-MPBA SERS spectra. Additionally, the strong T₂ magnetic resonance (MR) signal and NIR photothermal transduction efficiency of the nanocomposites make it available for MR imaging and photothermal therapy (PTT). Altogether, this GO-Fe₃O₄@Au@Ag-MPBA-DOX can simultaneously fulfill the synergistic combination of cancer cell targeting, pH-sensitive drug release, SERS-traceable detection and MR imaging, endowing it great potential for SERS/MR imaging-guided efficient chemo-phototherapy on cancer treatment.     

Interactions between modified fullerenes and proteins in cancer nanotechnology

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Targeted delivery of RNAi to cancer cells using RNA-ligand displaying exosome

Exosome is an excellent vesicle for in vivo delivery of therapeutics, including RNAi and chemical drugs. The extremely high efficiency in cancer regression can partly be attributed to its fusion mechanism in delivering therapeutics to cytosol without endosome trapping. However, being composed of a lipid-bilayer membrane without specific recognition capacity for aimed-cells, the entry into nonspecific cells can lead to potential side-effects and toxicity. Applying engineering approaches for targeting-capacity to deliver therapeutics to specific cells is desirable. Techniques with chemical modification in vitro and genetic engineering in cells have been reported to decorate exosomes with targeting ligands. RNA nanoparticles have been used to harbor tumor-specific ligands displayed on exosome surface. The negative charge reduces nonspecific binding to vital cells with negatively charged lipid-membrane due to the electrostatic repulsion, thus lowering the side-effect and toxicity. In this review, we focus on the uniqueness of RNA nanoparticles for exosome surface display of chemical ligands, small peptides or RNA aptamers, for specific cancer targeting to deliver anticancer therapeutics, highlighting recent advances in targeted delivery of siRNA and miRNA that overcomes the previous RNAi delivery roadblocks. Proper understanding of exosome engineering with RNA nanotechnology promises efficient therapies for a wide range of cancer subtypes.