Liandong Feng

Synthesis and characterization of a novel semi-IPN hydrogel based on Salecan and poly(N,N-dimethylacrylamide-co-2-hydroxyethyl methacrylate).

Salecan is a novel water-soluble, high molecular mass extracellular β-glucan produced by Agrobacterium sp. ZX09. Salecan has excellent physicochemical and biological properties, making it very suitable for hydrogel preparation. In this study, a series of novel semi-interpenetrating polymer network (semi-IPN) hydrogels containing Salecan and poly(N,N-dimethylacrylamide-co-2-hydroxyethylmethacrylate) (poly(DMAA-co-HEMA)) were synthesized by radical polymerization and semi-IPN technology. Structure and morphology of the hydrogels were characterized by FTIR, XRD, TGA and SEM. The semi-IPNs had a well-interconnected porous structure with tunable pore size ranging from 6 to 41μm. Swelling capability of the hydrogels was improved by introducing the hydrophilic Salecan. Rheological results indicated that the incorporation of poly(DMAA-co-HEMA) into hydrogels enhanced the storage modulus. Compression tests revealed that these semi-IPNs were robust materials with compressive modulus between 13.3 and 90.5kPa, the addition of Salecan increased the fracture strain from 71.1% to 88.8%. Degradation and cytotoxicity tests demonstrated that semi-IPNs were degradable and non-toxic.

Synthesis and characterization of a novel hydrogel: salecan/polyacrylamide semi-IPN hydrogel with a desirable pore structure

Salecan is a novel water-soluble β-glucan produced by a salt-tolerant strain Agrobacterium sp. ZX09 which was isolated from a soil sample in our laboratory and the 16S rDNA sequence of this novel strain was deposited in the GenBank database under the accession number GU810841. Salecan has excellent physicochemical properties and can be used in industries such as food and medicine. In this paper, novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on salecan and polyacrylamide (PAAm) were synthesized by radical polymerization/cryopolymerization and semi-IPN techniques. The resulting hydrogels with different salecan/PAAm composition ratios and preparation temperatures were characterized using FTIR, XRD, TGA and SEM measurements. The semi-IPNs exhibited a homogeneous porous architecture with a tunable pore size in a very broad range of 5-150 μm. Furthermore, swelling behaviors of the hydrogels were also studied to investigate the response properties of the hydrogels. The hydrogels obtained at subzero temperature can attain the equilibrium state in water within 260 seconds. Mechanical measurements showed that all semi-IPNs possessed good mechanical properties. In vitro degradation was also studied in PBS solution. Cytotoxicity results suggested that semi-IPN hydrogels were non-toxic to COS-7 cells. A cell culture experiment performed using COS-7 cells revealed their appropriateness for cell adhesion. Together, these results make salecan/PAAm semi-IPNs promising materials for biomedical applications.

A releasable disulfide carbonate linker for polyethyleneimine (PEI)-based gene vectors

In this study, a releasable disulfide carbonate linker is used to prepare disulfide-containing crosslinked polyethyleneimines (PEI-SS-CLs) for gene delivery. ESI-MS analysis shows that after being incubated with 1,4-dithio-DL-threitol (DTT), the degradable linkages in the polyethyleneimine (PEI) derivatives undergo disulfide bond cleavage followed by intramolecular cyclization and cleavage of the neighboring carbamate bond. Moreover, it is observed that thiol/polyanions trigger the release of DNA from polyplexes via the reductive degradability of PEI-SS-CLs and ion-exchange. In vitro transfection results indicate that PEI-SS-CL-1.5 (at a crosslinker/PEI feed molar ratio of 1.5) exhibits higher transfection efficacy than the commercially available reagents such as the high molecular weight PEI with a molecular weight of 25 kDa (PEI 25k) and the versatile liposomes Lipofectamine 2000. PEI-SS-CL-1.5 also demonstrates significantly lower cytotoxicity, compared with PEI 25k and Lipofectamine 2000. Our study indicates that incorporating the thiol-specific cleavable disulfide bond into crosslinked PEIs and implementing regulated release of DNA are effective strategies for designing safe and effective gene vectors.

Construction of efficacious hepatoma-targeted nanomicelles non-covalently functionalized with galactose for drug delivery

Polymeric micelles with surface immobilized galactose (Gal) are promising candidates for hepatoma-targeted drug delivery. Herein, a novel hepatoma-targeted micellar system was prepared through the non-covalent attachment of Gal to the micellar surface. A series of pH-responsive methoxyl poly(ethylene glycol)-b-poly(β-amino ester) (MPEG-PBAE) consisting of a hydrophobic alkyl chain were easily synthesized through Michael addition between amine monomer and diarcrylate. The micelles of the pH-responsive polymers exhibited stability at physiological pH and accelerated doxorubicin (DOX) release without burst release in response to an acidic pH environment. Furthermore, N-(1-deoxylactitol-1-yl) dodecylamine (Gal-C12) as a targeting ligand was successfully bound to the micellar surface by hydrophobic interaction. The results of cellular uptake, in vitro cytotoxicity and cell cycle analysis indicated that the Gal functionalized micelles effectively transferred DOX to hepatoma cells (e.g. HepG2 cells) via asialoglycoprotein receptor (ASGPR) mediated endocytosis, released DOX from the micelles and resulted in enhanced proliferation inhibition efficacy. The ease of surface functionalization and enhanced drug efficacy make the present platform promising for hepatoma-targeted drug delivery in cancer therapy.

Cationic Charged Polymer Vesicles from Amphiphilic PEI-g-PSSA-g-PEI as Potential Gene Delivery Vehicles

Polymer vesicles have attracted extensive interest for a variety of biomedical applications. Herein, novel polymer vesicles are prepared by the self-assembly of amphiphilic polyethyleneimine-g-poly(disulfide amine)-g-polyethyleneimine (PEI-g-PSSA-g-PEI) for gene delivery. To investigate the effect of hydrophobicity on transfection efficiency, a small series of PEI-g-PSSA-g-PEI were prepared under uniform conditions containing PEI fragments of the same molecular weight. The hydrophobicity of PEI-g-PSSA-g-PEI was adjusted by varying the hydrophobic content in the poly(disulfide amine) backbone and by choosing hydrophobic monomers ranging in length from C12 to C16. The hydrophobicity of polymers was also related to DNA binding affinity. Polymer vesicles obtained from the water-insoluble polymers condensed with DNA into polyplexes with sizes below 200 nm and surface charge ranging from +10 to +35 mV that were suitable for cell endocytosis. DNA polyplexes exhibited an inverted hexagonal structure, observed by transmission electron microscopy. The results of in vitro transfection demonstrate that the hydrophobic–hydrophilic balance of copolymers greatly affects their transfection properties. The top-performing polymer, II-70 %, showed improved transfection efficiency and significantly lower cytotoxicity on COS-7 cells when compared with commercial reagents polyethyleneimine (PEI 25K) and Lipofectamine 2000. These results indicate that cationic polymer vesicles with tunable hydrophobicity are promising materials for gene delivery.

The synthesis of 5-substituted 1 H -tetrazoles in molten tetrabutylammonium bromide

An economical and environmentally benign method for the synthesis of 5-substituted 1H-tetrazoles has been established. In this protocol, molten tetrabutylammonium bromide (TBAB) is used as both the solvent and catalyst. A mechanism involving the intermediacy of tetrabutylammonium azide (TBAN3) is proposed.

Diglycidyl Esters Cross-Linked with Low Molecular Weight Polyethyleneimine for Magnetofection

Magnetic polyethyleneimine (PEI) complexes have demonstrated to be simple and efficient vectors for enhancing gene transfection. However, the high cytotoxicity of PEI restricts its further application in vivo. In this study, we synthesized several low cytotoxicity biodegradable cationic polymers derived from PEI (Mw 600) linked with diglycidyl tartrate (DT-PEI) or its analogues (diglycidyl succinate (DS-PEI) and diglycidyl malate (DM-PEI); D-PEIs for all 3 polymers). Moreover, a type of biocompatible magnetic nanoparticles (MNPs) with negative charges was prepared to assemble with D-PEIs/DNA complexes via electrostatic interactions. The magnetic ternary complexes have appropriate sizes of 120–150 nm and zeta potential values of ~20–25 mV. The transfection ability and cell viability of D-PEIs increased as the amount of hydroxyl groups increased in the repeat unit, which indicated that increasing the hydroxyl number in the backbone of D-PEIs can enhance gene expression and decrease cytotoxicity in A549 cells. Magnetofection of DT-PEI showed similar transfection efficiency with 30 min incubation; in contrast, the standard incubation time was 4 h. All three magnetic complexes displayed lower cytotoxicity when compared with those of PEI complexes in COS-7 and A549. These results indicated that these series of magnetic PEI derivatives complexes could be potential nanocarriers for gene delivery.

Novel Disulfide-Containing Poly(β-amino ester)-Functionalised Magnetic Nanoparticles for Efficient Gene Delivery

Poly(β-amino ester)s (PBAEs) have been proved to effectively transfer DNA to various cell types. However, PBAEs with high molecular weights also show considerable toxicities, partly resulting from inadequate degradation of their polyester backbone. In this study, we created novel poly(β-amino ester)s (SF-1, 2, 3, and 4; notation SFs refers to all the four polymers) which were characterised by the cleavable disulfide bonds. Moreover, a new technique, termed magnetofection that uses magnetic nanoparticles to enhance gene expression, has recently been well developed. The negatively charged magnetic nanoparticles (MNPs) with good biocompatibility in vitro were prepared here to subsequently combine with SFs and DNA via electrostatic interaction, leading to the formation of the magnetic gene complexes MNP/SFs/DNA. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays and transfection experiments were performed in A549 cells to investigate all the resulting complexes. Studies indicated that the synthesised PBAEs exhibited good biodegradation and regulated release of DNA as a result of the reductive cleavage of the disulfide bonds, giving higher transfection efficiency along with much lower cytotoxicity compared with commercially available transfection agent polyethylenimine (Mw 25 kDa). Furthermore, when MNP was involved at a MNP/DNA weight ratio of 0.5, the magnetic gene complexes MNP/SFs/DNA showed enhanced levels of gene expression while maintaining low cytotoxicity.