Surface-initiated SET living radical polymerisation for the synthesis of silica–polymer core–shell nanoparticles

We report the use of surface-initiated single-electron transfer living radical polymerisation (SI SET-LRP) to prepare inorganic–organic core–shell nanoparticles with functional grafted chains of high molecular weight. The potential of SI SET-LRP is demonstrated by the preparation of a series of silica–polymer core–shell materials from a silica nanoparticle template bearing a bromo ester initiating group in the presence of a free initiator, with detailed kinetic investigations using methyl acrylate and tert-butyl acrylate. Under optimised polymerisation conditions, concentrated polymer brushes with grafting densities as high as 0.8 chains per nm2 and relatively high molecular weight polymer grafts (degree of polymerisation, DPn, up to 1000) were achieved whilst employing a heterogeneous copper(0) wire catalyst at low polymerisation temperatures. Under optimal conditions, the polymer shell grows similarly to the free polymer with increasing monomer conversion to produce well-defined monodisperse particles with a narrow size distribution. The particle uniformity results in the formation of particle assemblies that display long-range 2D and 3D order, as characterised by electron microscopy

Selective patterning of gold surfaces by core/shell, semisoft hybrid nanoparticles

The generation of patterned surfaces with well-defined nano- and microdomains is demonstrated by attaching core/shell, semisoft nanoparticles with narrow size distribution to microdomains of a gold-coated silicon wafer. Near monodisperse nanoparticles are prepared using reversible addition-fragmentation chain transfer (RAFT) polymerization, initiated from a silica surface, to prepare a polystyrene shell around a silica core. The particles are then used as-prepared, or after aminolysis of the terminal thiocarbonyl group of the polystyrene shell, to give thiol-terminated nanoparticles. When gold-coated silicon wafers are immersed into very dilute suspensions of these particles (as low as 0.004 wt%), both types of particles are shown to adhere to the gold domains. The thiolated particles adhere selectively to the gold microdomains, allowing for microdomain patterning, while particles that contain the trithiocarbonate functionality lead to a much more even coverage of the gold surface with fewer particle aggregations

Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers

The dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe3O4) NPs are grafted with PMMA brushes with molecular weights from M = 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P = 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multi-component Flory–Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation

Colloidal Crystallization of C60/Polymer-Grafted Silica Particles in Organic Solvent

Synthesis of fullerene (C60)-tethered polymer-grafted silica and colloidal crystallization of the particles was investigated. The particles were prepared by the reaction of C60 with 4-azidobenzoyl groups introduced in poly(methyl methacrylate-co-2-hydroxyethyl methacrylate), followed by esterification of 2-hydroxyethyl metharylate moieties with 4-azidobenzoyl chloride and grafting onto colloidal silica. The reaction afforded bindings of C60 in the range from 0.44 × 104 to 1.71 × 104 molecules/particle. The C60 amounts did not monotonously increase with 4-azidobenzoyl group on the particles, but decreased with mole fraction of methyl methacrylate in the copolymer. Colloidal crystallizations of the C60-tethered silica particles were observed in acetonitrile with critical volume fractions in the range from 0.018 to 0.024. Inter-sphere distances in the colloidal crystals were consistent with calculated values on assumption of face-centered cubic-closed packing, and then it was suggested that the crystallization took place due to electrostatic repulsion between the particles

Neutron Irradiation Effects in Al-Li and Al-Mg-Li Alloys

Al-2.3wt%Li and Al-4.1wt%Mg-1.1wt%Li alloys were neutron-irradiated in JOYO, JMTR and RTNS-II with different types of energy spectra. The changes of He production by different neutron sources and of precipitates due to the isothermal annealing at 400℃ were investigated by transmission electron microscopy (TEM). It was confirmed from TEM observations that He production by transmutation and the coagulation of He atoms after the annealing depend on neutron energy spectra used for the irradiation. It was also found that the addition of Mg to Al-Li alloy strongly suppresses the growth of He bubbles. Interrelations among precipitates, vacancies, He atoms and Li atoms were investigated, obtaining a reasonable coincidence between mutual amounts

Extracts of Cistanche deserticola

The senescence accelerated mouse prone 8 substrain (SAM-P8), widely accepted as an animal model for studying aging and antiaging drugs, was used to examine the effects of dietary supplementation with extracts of Cistanche deserticola (ECD) which has been used extensively in traditional Chinese medicine because of its perceived ability to promote immune function in the elderly. Eight-month-old male SAM-P8 mice were treated with ECD by daily oral administrations for 4 weeks. The results showed that dietary supplementation of 150 mg/kg and 450 mg/kg of ECD could extend the life span measured by Kaplan-Meier survival analysis in dose-dependent manner. Dietary supplementation of SAM-P8 mice for 4 weeks with 100, 500, and 2500 mg/kg of ECD was shown to result in significant increases in both naive T and natural killer cells in blood and spleen cell populations. In contrast, peripheral memory T cells and proinflammatory cytokine, IL-6 in serum, were substantially decreased in the mice that ingested 100 and 500 mg/kg of ECD daily. Additionally, Sca-1 positive cells, the recognized progenitors of peripheral naive T cells, were restored in parallel. Our results provide clear experimental support for long standing clinical observational studies showing that Cistanche deserticola possesses significant effects in extending life span and suggest this is achieved by antagonizing immunosenescence

Grafted polymer chains suppress nanoparticle diffusion in athermal polymer melts

We measure the center-of-mass diffusion of poly(methyl methacrylate) (PMMA)-grafted nanoparticles (NPs) in unentangled to slightly entangled PMMA melts using Rutherford backscattering spectrometry. These grafted NPs diffuse ∼100 times slower than predicted by the Stokes-Einstein relation assuming a viscosity equal to bulk PMMA and a hydrodynamic NP size equal to the NP core diameter, 2Rcore = 4.3 nm. This slow NP diffusion is consistent with an increased effective NP size, 2Reff ≈ 20 nm, nominally independent of the range of grafting density and matrix molecular weights explored in this study. Comparing these experimental results to a modified Daoud-Cotton scaling estimate for the brush thickness as well as dynamic mean field simulations of polymer-grafted NPs in athermal polymer melts, we find that 2Reff is in quantitative agreement with the size of the NP core plus the extended grafted chains. Our results suggest that grafted polymer chains of moderate molecular weight and grafting density may alter the NP diffusion mechanism in polymer melts, primarily by increasing the NP effective size

Therapeutic Potential of Intracerebroventricular Replacement of Modified Human β-Hexosaminidase B for GM2 Gangliosidosis

To develop a novel enzyme replacement therapy for neurodegenerative Tay-Sachs disease (TSD) and Sandhoff disease (SD), which are caused by deficiency of β-hexosaminidase (Hex) A, we designed a genetically engineered HEXB encoding the chimeric human β-subunit containing partial amino acid sequence of the α-subunit by structure-based homology modeling. We succeeded in producing the modified HexB by a Chinese hamster ovary (CHO) cell line stably expressing the chimeric HEXB, which can degrade artificial anionic substrates and GM2 ganglioside in vitro, and also retain the wild-type (WT) HexB-like thermostability in the presence of plasma. The modified HexB was efficiently incorporated via cation-independent mannose 6-phosphate receptor into fibroblasts derived from Tay-Sachs patients, and reduced the GM2 ganglioside accumulated in the cultured cells. Furthermore, intracerebroventricular administration of the modified HexB to Sandhoff mode mice restored the Hex activity in the brains, and reduced the GM2 ganglioside storage in the parenchyma. These results suggest that the intracerebroventricular enzyme replacement therapy involving the modified HexB should be more effective for Tay-Sachs and Sandhoff than that utilizing the HexA, especially as a low-antigenic enzyme replacement therapy for Tay-Sachs patients who have endogenous WT HexB