Abstract. Generations 5 and 6 (G5 and G6) poly(amidoamine) (PAMAM) dendrimers have been shown to be highly efficient nonviral carriers in in vitro gene delivery. However, their high toxicity and unsatisfied in vivo efficacy limit their applications. In this study, to improve their characteristics as gene delivery carriers, polyethylene glycol (PEG, molecular weight 5,000) was conjugated to G5 and G6 PAMAM dendrimers (PEG-PAMAM) at three different molar ratios of 4%, 8%, and 15% (PEG to surface amine per PAMAM dendrimer molecular). Compared with unconjugated PAMAM dendrimers, PEG conjugation significantly decreased the in vitro and in vivo cytotoxicities and hemolysis of G5 and G6 dendrimers, especially at higher PEG molar ratios. Among all of the PEG-PAMAM dendrimers, 8% PEG-conjugated G5 and G6 dendrimers (G5-8% PEG, G6-8% PEG) resulted in the most efficient muscular gene expression when polyplexes were injected intramuscularly to the quadriceps of neonatal mice. Consistent with the in vivo results, these two 8% PEG-conjugated PAMAM dendrimers could also mediate the highest in vitro transfection in 293A cells. Therefore, G5-8% PEG and G6-8% PEG possess a great potential for gene delivery both in vivo and in vitro.

In recent years, it has been an attractive challenge to fabricate multiple stimuli-responsive hybrid microgels composed of polymer microgel and gold nanoparticle (AuNP). Herein, we report on the detailed synthesis of poly(N-isopropylacrylamide-co-methacrylic acid)--Au hybrid microgels by in situ reduction of gold precursor in the presence of thiol-functionalized poly(N-isopropylacrylamide-co-methacrylic acid) microgels. The as-synthesized hybrid microgels showed well-defined swelling/deswelling transition in response to the surrounding temperature, pH, and light irradiation. The hybrid microgels had a unique microstructure where a large number of AuNP's distribute mainly in the interior of microgel with a fluff-like surface. The plasmonic property of the hybrid microgels can be modulated through the volume phase transition induced by the external triggers such as temperature and pH. In the reduction of 4-nitrophenol catalyzed by the hybrid microgels, it was found that the reaction rate did not increase monotonously with temperature but greatly decreased in a certain temperature range, showing a tunable catalytic activity.

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Organic-inorganic hybrid materials, such as polyhedral oligomeric silsesquioxanes (POSS), have the potential to improve the mechanical properties of the methacrylate-based composites and resins used in dentistry. In this article, nanocomposites of methacryl isobutyl POSS (MI-POSS [bears only one methacrylate functional group]) and methacryl POSS (MA-POSS [bears eight methacrylate functional groups]) were investigated to determine the effect of structures on the properties of dental resin. The structures of the POSS-containing networks were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Monofunctional POSS showed a strong tendency toward aggregation and crystallization, while multifunctional POSS showed higher miscibility with the dimethacrylate monomer. The mechanical properties and wear resistance decreased with increasing amounts of MI-POSS, indicating that the MI-POSS agglomerates act as the mechanical weak point in the dental resins. The addition of small amounts of MA-POSS improved the mechanical and shrinkage properties. However, samples with a higher MA-POSS concentration showed lower flexural strength and flexural modulus, indicating that there is a limited range in which the reinforcement properties of MA-POSS can operate. This concentration dependence is attributed to phase separation at higher concentrations of POSS, which affects the structural integrity, and thus, the mechanical and shrinkage properties of the dental resin. Our results show that resin with 3% MA-POSS is a potential candidate for resin-based dental materials.

A large number of gold nanoparticles (ca. 3.8 nm in diameter) were homogeneously and effectively incorporated into thiol-functionalized poly(N-isopropylacrylamide) (PNIPAM) microgels through the well-known Au-thiol chemistry. Here, the thiol-functionalized PNI-PAM microgels were obtained by carbodiimide-mediated amide bond formation between the carboxyl-functionalized PNIPAM microgels and 2-aminoethanethiol. The prepared PNIPAM-Au hybrid microgels exhibited well-defined thermally modulated optical and catalytic properties.