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Repeatability of the responsiveness with time is one important concern for effective durable functions of stimuli-responsive materials. Although the increase in the yield and tensile strength of the hybrid composite materials by nanoparticle (NP) incorporation has been reported, exact NP effect on stimuli-responsiveness is rarely reported. In this study, a set of nanoscale actuating system is demonstrated by a thermo-sensitive process operated by polyethylene glycol (PEG) linked by gold nanoparticle (AuNP). This designed nanocomposite exclusively provides an artificial on/off gate function for selective passages of permeate molecules. The results demonstrate high repetition efficiency with sharp responding in a timely manner. In terms of the morphology changes induced by repeated swelling-deswelling mechanics, the nanocomposite exhibits phase separation between AuNP clusters and PEG domains. This leads to a delay in responsiveness in a cumulative way with time. Acting as stable junction points in the nanocomposite network structures, the incorporated AuNPs contribute to maintain repeatability in responsiveness. This study contributes to new-concept smart material design and fundamental understanding on the hybrid nanomaterials for various applications in terms of a dynamic mechanical behavior. [ABSTRACT FROM AUTHOR]

Cellular uptake pathway of nanoparticle (NP) is different from that of free drugs. Therefore, NP-mediated nanotherapeutics can be designed to overcome the adverse effects of free drugs. However, synthetic NPs are typically trapped in the endosome and have difficulty to reach the cytosol because of the characteristic endocytosis, where the endosomal membranes wrap-up the introduced NPs. In this study, the Spacer molecules linking the apoptotic anticancer drug and the gold NP (AuNP) are designed and cellular uptake procedure and drug deployment in the cancer cells are controlled. X-ray nanoscopy and two-photon microscopy are employed to observe the AuNPs in a cell in-situ without additional dye molecule or imaging agent introduction on an AuNP. We confirm that the effective design of the Spacer molecules importantly control the cellular interaction of the AuNPs. This technology can be generalized to broad biomedical applications utilizing nanotherapeutics-mediated diagnosis and new-concepted disease treatment technologies. [ABSTRACT FROM AUTHOR]

Recently, there has been significant progress in the field of soft- and hard-X-ray imaging for a wide range of applications, both technically and scientifically, via developments in sources, optics and imaging methodologies. While one community is pursuing extensive applications of available X-ray tools, others are investigating improvements in techniques, including new optics, higher spatial resolutions and brighter compact sources. For increased image quality and more exquisite investigation on characteristic biological phenomena, contrast agents have been employed extensively in imaging technologies. Heavy metal nanoparticles are excellent absorbers of X-rays and can offer excellent improvements in medical diagnosis and X-ray imaging. In this context, the role of gold (Au) is important for advanced X-ray imaging applications. Au has a long-history in a wide range of medical applications and exhibits characteristic interactions with X-rays. Therefore, Au can offer a particular advantage as a tracer and a contrast enhancer in X-ray imaging technologies by sensing the variation in X-ray attenuation in a given sample volume. This review summarizes basic understanding on X-ray imaging from device set-up to technologies. Then this review covers recent studies in the development of X-ray imaging techniques utilizing gold nanoparticles (AuNPs) and their relevant applications, including two- and three-dimensional biological imaging, dynamical processes in a living system, single cellbased imaging and quantitative analysis of circulatory systems and so on. In addition to conventional medical applications, various novel research areas have been developed and are expected to be further developed through AuNP-based X-ray imaging technologies. [ABSTRACT FROM AUTHOR]

We have recently reported on poly(vinyl alcohol) microparticles containing X-ray contrast agent, iopamidol, designed as a flow tracer working in synchrotron X-ray imaging (Biosens. Bioelectron.2010, 25, 1571). Although iopamidol is physically encapsulated in the microparticles, it displays a great contrast enhancement and stable feasibility in in vitro human blood pool. Nonetheless, a direct relation between the absolute amount of incorporated iopamidol and the enhancement in imaging efficiency was not observed. In this study, physical properties of the designed microparticle are systematically investigated experimentally with theoretical interpretation to correlate an enhancement in X-ray imaging efficiency. The compositional ratio of X-ray contrast agent in polymeric microparticle is controlled as 1/1 and 10/1 [contrast agent/polymer microparticle (w/w)] with changed degree of cross-linkings. Flory−Huggins interaction parameter (χ), retractive force (τ) and degree of swelling of the designed polymeric microparticles are investigated. In addition, the hydrodynamic size (DH) and ζ-potential are evaluated in terms of environment responsiveness. The physical properties of the designed flow tracer microparticles under a given condition are observed to be strongly related with the X-ray absorption efficiency, which are also supported by the Beer−Lambert−Bouguer law. The designed microparticles are almost nontoxic with a reasonable concentration and time period, enough to be utilized as a flow tracer in various biomedical applications. This study would contribute to the basic understanding on the physical property connected with the imaging efficiency of contrast agents. [ABSTRACT FROM AUTHOR]

Ion and pH effects on the phase transition behaviors are studied with a series of thermosensitive neutral and acidic poly(organophosphazene) counterparts. Poly(organophosphazenes) are substituted by hydrophobic l-isoleucine ethyl ester (IleOEt) and hydrophilic α-amino-ω-methoxy-poly(ethylene glycol) 550 Da (PEG550) together with a relatively small amount of glycylglycine ally ester (GlyGlyOALL). After deprotection, GlyGlyOALL changes into glycylglycine (GlyGlyOH), and neutral GlyGlyOALL and acidic GlyGlyOH polymers with same substituent ratios are compared as counterparts. All the synthesized poly(organophosphazenes) in this work exhibit lower critical solution temperature (LCST) for which sequential phase transitions are suggested: (i) homogeneous solution, (ii) homogeneous gel, (iii) heterogeneous gel, to (iv) heterogeneous solution as hydrophobicity increases either driven by temperature or substituent composition. Ions act on the hydrophobicity modification of the polymers where the polymers with lower hydrophobic/hydrophilic ratios are more sensitively salted-out by NaCl, while those with higher ratios are more effectively salted-in by NaI. At higher concentration of the added ions, the acid group effect on the cloud point becomes deactivated. Meanwhile, because of the conflicting role of amine and carboxylic acid in pH-responsiveness, neutral and acidic polymer counterparts exhibit opposite tendencies in the cloud points. Systematically controlled responsiveness to temperature, ion, and pH changes are created in random amphiphilic graft copolymers, poly(organophosphazenes). The results highlight the importance of the cooperative function of the dominant components in the poly(organophosphazenes) and also expand the general understanding in designing stimuli-responsive smart materials especially useful for various biomedical applications. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis and characterization of poly(butadiene)m−poly(l-lysine)n(m−n107−200, 107−100, and 60−50) block copolymers. The polymers are prepared in a two-step process whereby amine-terminated polybutadiene is used to initiate the ring-opening polymerization of the -benzyloxycarbonyl l-lysine N-carboxyanhydride. After deprotection, the self-assembly of the block copolymers in aqueous media were studied using dynamic light scattering, transmission electron microscopy, and circular dichroism spectroscopy. These block copolymers were found to form either spherical micelles or rod-like micelles at high pH depending on the composition of the block copolymer. As the pH is decreased, the micelles swell due to charge−charge repulsions between corona chains and from the helix-coil transition of the polypeptide block. The two systems that form rod-like micelles at high pH also exhibit a pH-induced rod-sphere transition at low pH. This transition was verified from Kratky analysis of the static light scattering data and via CONTIN analysis of the dynamic light scattering data, which shows a bimodal distribution in particle sizes. [ABSTRACT FROM AUTHOR]

In vascular plants, the xylem network constitutes a complex microfluidic system. The relationship between vascular network architecture and functional hydraulic regulation during actual water flow remains unexplored. Here, we developed a method to visualize individual xylem vessels of the 3D xylem network of Arabidopsis thaliana, and to analyze the functional activities of these vessels using synchrotron X-ray computed tomography with hydrophilic gold nanoparticles as flow tracers. We show how the organization of the xylem network changes dynamically throughout the plant, and reveal how the elementary units of this transport system are organized to ensure both long-distance axial water transport and local lateral water transport. Xylem vessels form distinct clusters that operate as functional units, and the activity of these units, which determines water flow pathways, is modulated not only by varying the number and size of xylem vessels, but also by altering their interconnectivity and spatial arrangement. Based on these findings, we propose a regulatory model of water transport that ensures hydraulic efficiency and safety. [ABSTRACT FROM AUTHOR]