Novel biocompatible polymeric gene carriers have been examined for their potential in treating various genetic and acquired diseases. The use of polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. However, effective polymer-based gene therapy requires the control of cellular access and uptake, intracellular trafficking, and nuclear retention of plasmid DNA. Inefficient endosomal release, cytoplasmic transport, and nuclear entry of plasmids are currently limiting factors in the use of polymers for effective plasmid-based gene therapy. Therefore, several different polymeric gene carriers have been designed recently in an attempt to overcome these problems. This review explores the conceptual and experimental aspects of polymer-based gene delivery and presents an overview on the recent use of polymers to enhance the effectiveness of plasmid-based systems. Despite their current limitations, polymeric carriers have significant potential as commercially viable gene medicines.

The use of biocompatible polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. Nontoxic water-soluble lipopolymer (WSLP), poly(ethylenimine)-co-[N-(2-aminoethyl) ethyleneimin]-co-N-(N-cholesteryloxycarbonyl-(2-aminoethyl)ethylenimine) was synthesized using branched poly(ethylenimine) (PEI, mw 1800) and cholesteryl chloroformate. Following synthesis and purification, the structure and molecular weight of WSLP were confirmed by (1)H NMR and MADI-TOF mass spectrometry, respectively. The percentage of cholesterol conjugated to PEI was about 47%, and the average molecular weight of WSLP was approximately 2000 Da. WSLP/pDNA complexes were prepared at different N/P (nitrogen atoms of WSLP/phosphate of plasmid DNA) ratios and characterized in terms of particle size, zeta potential, osmolarity, surface morphology, and cytotoxicity. WSLP condensed plasmid DNA when N/P ratio reached 2.5/1 and no free DNA was detected at N/P ratio of 5/1 and above, as determined by agarose gel electrophoresis. The mean particle size was in the range of 25.9 to 148.5 nm and was dependent on N/P ratios. Atomic force microscopy (AFM) showed complete condensation of plasmid DNA with spherical particles of approximately 50 nm in diameter. WSLP/pDNA complexes or WSLP itself were nontoxic to CT-26 colon adenocarcinoma and 293 T human embryonic kidney transformed cells when formulated at the N/P ratio of 10/1 and below as determined by MTT assay. In contrast, PEI25000/pDNA complexes were toxic to these cells. Erythrocytes aggregated when incubated with PEI25000/pCMV-Luc complexes at high DNA concentrations, but there was little aggregation with WSLP/pCMV-Luc complexes. WSLP/pCMV-Luc complexes demonstrated higher transfection efficiency in both CT-26 and 293 T cells compared to PEI25000- or PEI1800-based formulations. WSLP/pCMV-Luc complexes are nontoxic and showed enhanced in vitro transfection. Thus, WSLP will be a suitable carrier for in vivo gene delivery.

Magnetorheological (MR) fluids are a type of smart material with rheological properties that may be controlled through mesostructural transformations. MR fluids form solid-like fibril structures along the magnetic field direction upon application of a magnetic field due to magnetopolarization of soft-magnetic particles when suspended in an inert medium. A reverse structural transition occurs upon removal of the applied field. The structural changes are very fast on the order of milliseconds. The rheological properties of MR fluids vary with the application of a magnetic field, resulting in non-Newtonian viscoplastic flow behaviors. Recent applications have increased the demand for MR materials with better performance and good long-term stability. A variety of industrial MR materials have been developed and tested in numerous experimental and theoretical studies. Because modeling and analysis are essential to optimize material design, a new macroscale structural model has been developed to distinguish between static yield stress and dynamic yield stress and describe the flow behavior over a wide range of shear rates. Herein, this recent progress in the search for advanced MR fluid materials with good stability is described, along with new approaches to MR flow behavior analysis. Several ways to improve the stability and efficiency of the MR fluids are also summarized.

Hollow polydivinylbenzene@Fe3O4 (h-PDVB@Fe3O4) nanoparticles with a relatively narrow size distribution were prepared by depositing Fe3O4 nanoparticles on h-PDVB. Because of the cavity in the hollow structure, the density of h-PDVB@Fe3O4 (ρ = 1.83 g/cm3) was significantly reduced from that of Fe3O4 (4.52 g/cm3). Deposition of Fe3O4 particles of 10–20 nm size (average particle size ≃14.3 ± 2.5 nm) on the h-PDVB made the h-PDVB@Fe3O4 particle surface quite rough while preserving the spherical shape. The MR suspensions were prepared by dispersing h-PDVB@Fe3O4 in silicone oil medium, and their magnetorheological properties were investigated. The dynamic modulus and the yield stress under magnetic field decreased compared to those of pure Fe3O4 suspension, but the MR behavior of h-PDVB @ Fe3O4 suspension was well preserved. Interestingly, contrasting MR performance of two suspensions (h-PDVB@Fe3O4 (Fe3O4 nanoparticle size ≃14.3 ± 2.5 nm) and foamed PS/Fe3O4 (Fe3O4 nanoparticle size ≃50–100 nm)) with similar densities was observed at high and low magnetic field strength regions due to the particle size difference. The long-term sedimentation stability of the suspensions was investigated with a Turbiscan apparatus. Because of reduced density mismatch between particles and silicon oil medium, the h-PDVB@Fe3O4 suspension exhibited a significantly improved stability compared to that of the pure Fe3O4 suspension, with only 13% of light transmission after 24 h. The MR performance and enhanced long-term sedimentation stability represent a viable application of h-PDVB@Fe3O4 suspensions to microfluidic devices.

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Targeting is one of the primary considerations in designing a specific and efficient gene delivery system. Here, an angiogenic endothelial cell-targeted polymeric gene delivery carrier was developed by conjugating an alpha(v)beta3/alpha(v)beta5 integrin-binding RGD peptide, ACDCRGDCFC, into the cationic polymer polyethyleneimine (PEI) via a hydrophilic poly(ethylene glycol) (PEG) spacer. The incorporation of PEG into PEI improved the poor physicochemical properties of PEI-DNA complexes. At a neutral charge ratio, DNA complexes with PEI were polydisperse and substantially aggregated, whereas DNA complexes with PEI-g-1PEG-RGD were homogeneous with 100-200 nm effective diameter. Their surface charge was also significantly reduced due to the charge shielding effect of PEG. However, the extensive grafting of PEI with PEG was shown to inhibit the DNA condensation process, significantly decreasing transfection efficiency. In in vitro transfection experiments with angiogenic endothelial cells, PEI-g-1PEG-RGD showed an approximately fivefold increase in transfection efficiency over PEI, due to an integrin-mediated internalization pathway. PEI-g-1PEG-RGD also exhibited high specificity to angiogenic endothelial cells compared with normal endothelial cells, which was confirmed by in vitro transfection experiments with non-targeting PEI-g-1PEG-RAE in angiostatic endothelial cells.

Our objective was to design a water-soluble lipopolymer (WSLP) and an interleukin-12 (IL-12) expression plasmid for enhanced delivery of the IL-12 gene. We synthesized WSLP using branched polyethylenimine (PEI) of 1800 Da and cholesteryl chloroformate, and constructed p2CMVmIL-12, encoding the IL-12 subunits p35 and p40, each under the transcriptional control of a separate cytomegalovirus (CMV) promoter. The percentage of cholesterol conjugated to PEI was about 47% and the average molecular weight of WSLP was approximately 2000 Da. The mean particle size of WSLP/p2CMVmIL-12 complexes formulated in 5% glucose was 26 to 62 nm and xi potential was 8 to 60 mV. The WSLP/p2CMVmIL-12 complexes were nontoxic to CT-26 colon carcinoma cells at the N/P ratio (nitrogen atoms of WSLP/phosphate of plasmid DNA) of 20 and below; PEI25000/pDNA complexes were highly toxic. WSLP/p2CMVmIL-12 complexes demonstrated higher transfection in CT-26 cells compared with the DNA formulations prepared using PEI of molecular weights 1800, 10,000 and 25,000 Da. Transfection efficiency increased with an increase in N/P ratios from 5 to 15, then there was no significant increase in transfection up to the N/P ratio of 30/1. There was an increase in the level of IL-12 when free or complexed p2CMVmIL-12 was compared with free or complexed pIRESmIL-12 in which the p35 and p40 subunits were linked to the internal ribosome entry sites (IRES). At 48 hours post-injection of WSLP/p2CMVmIL-12 complexes into BALB/c mice bearing CT-26 subcutaneous tumors, the levels of IL-12, IFN-gamma, and nitric oxide (NO) in the supernatant of the cultured tumors were higher for the WSLP/p2CMVmIL-12 complexes than for the naked p2CMVmIL-12, WSLP, and 5% glucose injected groups. There was a significant improvement in the survival rate and the inhibition of tumor growth after a single injection of WSLP/p2CMVmIL-12 complexes. We have designed an effective, nontoxic WSLP and an IL-12 expression plasmid with two CMV promoters.

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