Electromagnetic Interference Shielding Properties of Highly Flexible Poly(styrene-co-butyl acrylate)/PEDOT:PSS Films Fabricated by Latex Technology.

As the use of stretchable electronic devices increases, the importance of flexible electromagnetic interference (EMI) shielding films is emerging. In this study, a highly flexible shielding film was fabricated using poly(styrene-co-butyl acrylate) (p(St-co-BA)) latex as a matrix and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a conductive filler, and then the mechanical properties and EMI shielding performance of the film were examined. Styrene and butyl acrylate were copolymerized to lower the high glass transition temperature and increase the ductility of brittle polystyrene. The latex blending technique was used to produce a shielding film in which the aqueous filler dispersion was uniformly dispersed in the emulsion polymerized resin. To determine the phase change in the copolymer matrix with temperature, the storage modulus was measured, and a time-temperature superposition master curve was constructed. The drying temperature of water-based copolymer resin suitable for film fabrication was set based on this curve. The glass transition temperature and flexibility of the blends were determined by evaluating the thermomechanical analysis and tensile tests. The EMI shielding effectiveness (SE) of the films was analyzed at frequencies from 50 MHz to 1.5 GHz, covering the VHF and UHF ranges. As the filler content increased, the SE of the blend film increased, but the elongation increased until a certain content and then decreased. The optimal content of PEDOT:PSS that satisfied both the ductility and shielding performance of the film was found to be 10 wt%. In this case, the elongation at break reached 300%, and the SE of a 1.6 mm thick film was about 35 dB. The film developed in this study can be used as an EMI shielding material that requires high flexibility.

Galactosylation of chitosan-graft-spermine as a gene carrier for hepatocyte targeting in vitro and in vivo.

Polyethyleneimine (PEI) has been described as a highly efficient gene carrier due to its efficient proton sponge effect within endosomes. However, many studies have demonstrated that PEI is toxic and associated with a lack of cell specificity despite high transfection efficiency. In order to minimize the toxicity of PEI, we prepared chitosan-graft-spermine (CHI-g-SPE) in a previous study. CHI-g-SPE showed low toxicity and high transfection efficiency. However, this compound also had limited target cell specificity. In the present study, we synthesized galactosylated CHI-g-SPE (GCS) because this modified GCS could be delivered specifically into the liver due to hepatocyte-specific galactose receptors. The DNA-binding properties of GCS at various copolymer/DNA weight ratios were evaluated by a gel retardation assay. The GCS copolymer exhibited significant DNA-binding ability and efficiently protected DNA from nuclease attack. Using energy-filtered transmission electron microscopy (EF-TEM), we observed dense spherical, nano-sized GCS/DNA complexes with a homogenous distribution. Most importantly, GCS was associated with remarkably low cytotoxicity compared to PEI in HepG2, HeLa, and A549 cells. Moreover, GCS carriers specifically delivered the gene-of-interest into hepatocytes in vitro as well as in vivo. Our results suggest that the novel GCS described here is a safe and highly efficient carrier for hepatocyte-targeted gene delivery.

Suppression of tumor growth in H-ras12V liver cancer mice by delivery of programmed cell death protein 4 using galactosylated poly(ethylene glycol)-chitosan-graft-spermine.

Non-viral gene delivery systems based on polyethyleneimine (PEI) are efficient due to their proton-sponge effect within endosomes, but they have poor physical characteristics such as slow dissociation, cytotoxicity, and non targeted gene delivery. To overcome many of the problems associated with PEI, we synthesized a galactosylated poly(ethylene glycol)-chitosan-graft-spermine (GPCS) copolymer with low cytotoxicity and optimal gene delivery to hepatocytes using an amide bond between galactosylated poly(ethylene glycol) and chitosan-graft-spermine. The GPCS copolymer formed complexes with plasmid DNA, and the GPCS/DNA complexes had well-formed spherical shapes. The GPCS/DNA complexes were nanoscale size with homogenous size distribution and a positive zeta potential by dynamic light scattering (DLS). The GPCS copolymer had lower cytotoxicity than that of PEI 25K in HepG2, HeLa, and A549 cell lines at various concentrations and showed good hepatocyte-targeting ability. Furthermore, GPCS/DNA complexes showed higher levels of GFP expression in the liver in model mice after intravenous injection than naked DNA and metoxy-poly(ethylene glycol)-chitosan-graft-spermine as controls without remarkable fibrosis, inflammation, lipidosis, or necrosis. In a tumor suppression study, an intravenous injection of the GPCS/Pdcd4 complexes significantly suppressed tumor growth, activated apoptosis, and suppressed proliferation and angiogenesis in liver tumor-bearing H-ras12V mice. Our results indicate that the GPCS copolymer has potential as a hepatocyte-targeting gene carrier.