Cationic lipid-DNA (CL-DNA) complexes are abundantly used in nonviral gene therapy clinical applications. Surface functionality is the next step in developing these complexes as competent, target-specific gene carriers. Poly(ethylene glycol) (PEG) is the natural choice to serve as a protective coat or act as a tether for a specific ligand on the surface of these complexes due to its biocompatibility and ability to convey stealth-like properties. Understanding the effect of PEG on the internal structure and surface properties of CL-DNA complexes is essential in developing vectors with more complex derivatives of PEG, such as Arg-Gly-Asp (RGD)-based peptide-PEG-lipids. We report on x-ray diffraction studies to probe the internal structure of CL-DNA complexes consisting of a ternary mixture of cationic lipids, neutral lipids, and PEG-lipids. The PEG-coated complexes are found to exhibit a structure consistent with the lamellar phase. In addition, three distinct DNA interchain interaction regimes were found to exist, due to a), repulsive long-range electrostatic forces; b), short-range repulsive hydration forces; and c), novel polymer-induced depletion attraction forces in two dimensions. Optical microscopy and reporter gene assays further demonstrate the incorporation of the PEG-lipids into the lamellar CL-DNA complexes under biologically relevant conditions, revealing surface modification. Both techniques show that PEG-lipids with a polymer chain of molecular weight 400 do not provide adequate shielding of the PEGylated CL-DNA complexes, whereas PEG-lipids with a polymer chain of molecular weight 2000 confer stealth-like properties. This surface functionalization is a crucial initial step in the development of competent vectors for in vivo systemic gene delivery and suggests that a second type of surface functionality can be added specifically for targeting by the incorporation of peptide-PEG-lipids.

In this paper, the synthesis of novel divalent cationic lipids with poly(ethylene glycol) segments is described. The lipids consist of an unsaturated double-chain hydrophobic moiety based on 3, 4-dihydroxy benzoic acid, attached to a hydrophilic poly(ethylene glycol) spacer which contains a divalent cationic end group. As poly(ethylene glycol) spacers monodisperse triethylene glycol and telechelic poly(ethylene glycol)s with an average degree of polymerization of 9, 23, and 45 were used. The divalent cationic end group was attached by coupling a protected dibasic amino acid to the PEG spacer and following cleavage of the protecting groups. These novel class of cationic lipids is of particular interest for nonviral gene delivery applications.

We report the first evidence of the potential of new amphiphilic ABA-triblock copolymers as gelling agents for lamellar liquid crystalline L R phases. Recently, we described a new type of lamellar hydrogels which are not based on a polymer network swollen in water but are obtained by the addition of small amounts of a nonionic polymer surfactant to the fluid lamellar LR phase of the dimyristoylphosphatidyl-choline(DMPC)/pentanol/water system. In contrast with these previously reported gelling agents which were all AB-diblock copolymers, the novel ABA-triblock copolymers consist of double chain hydrophobic moieties (A) attached to each end of a poly(ethylene glycol) chain (B). The synthesis of these new macromolecules and their gelation properties are described. The comparison of these novel lamellar hydrogels with those based on the AB-diblock copolymers provides direct evidence for the existence of cross-bridging conformations of the ABA-triblock copolymers between adjacent membranes.

This article reports on the modification of unsaturated polyesters by poly (ethylene glycol) end groups in order to influence the solution behavior in styrene and to modify mechanical properties of the cured resin. The synthesis was done by the reaction of a carboxyl-terminated unsaturated polyester with various poly(ethylene glycol) mono-methyl ethers of molecular weights from 350 to 2000 g/mol. The characterization and curing properties of the synthesized block copolymers are presented. The glass transition temperatures decrease with increasing length of the poly(ethylene glycol) end groups. The introduction of long poly(ethylene glycol) end groups (2000 g/ mol) leads to a phase separated and partly crystalline block copolymer with a melting point of 48ЊC. The block copolymers can be easily diluted in styrene to create the curable resins. The mixtures containing the block copolymers with the short poly(ethylene glycol) end groups (350 and 550 g/mol) could be cured in a reasonably short time. Compared to commercial unsaturated polyesters the mechanical testing revealed that the tensile strength is decreasing while the elongation is increasing.

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