Nonviral gene delivery with the help of polycations has raised considerable interest in the scientific community over the past decades. Herein, we present a systematic study on the influence of the molecular weight and architecture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) on the transfection efficiency and the cytotoxicity in CHO-K1 cells. A library of well-defined homopolymers with a linear and star-shaped topology (3- and 5-arm stars) was synthesized via atom transfer radical polymerization (ATRP). The molecular weights of the polycations ranged from 16 to 158 kDa. We found that the cytotoxicity at a given molecular weight decreased with increasing number of arms. For a successful transfection a minimum molecular weight was necessary, since the polymers with a number-average molecular weight, M(n), below 20 kDa showed negligible transfection efficiency at any of the tested polyelectrolyte complex compositions. From the combined analysis of cytotoxicity and transfection data, we propose that polymers with a branched architecture and an intermediate molecular weight are the most promising candidates for efficient gene delivery, since they combine low cytotoxicity with acceptable transfection results.

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2850 wileyonlinelibrary.com large amounts of liquids and are excellent fi lters. Sponges with a volume of 1000 cm 3 can process up to 3000 L water h −1 . Furthermore, they can conduct light as discovered recently by Brümmer et al. [ 2 ] In addition, Natalio et al. reported on the formation of sponge skeletons shown to feature great bending strength and on the role of silicatein-α in the biomineralization of silicates in sponges, which accounts for the high reversible compressibility of sponges in spite of low densities. [ 3 ] Aizenberg et al. pointed out on the example of the so-called glass sponges ( Euplectella ) the important role of the hierarchical design from the nanometer to macroscopic length scale for structural materials. [ 4 ] The structural base of sponges are multiarmed spicules of silicate or calcium carbonate, which form highly porous structures of several hierarchical layers as shown in Figure 1 A,B. This leads to highly porous ultralight 3D materials (ultralight is defi ned when the density of material is <10 mg cm −3 ).[ 5 ] In recent literature, a variety of highly porous ultralight 3D materials were reported based on carbon, ceramics, and cellulose, which were characterized by porosities >99% and relatively high compressive strength. [6][7][8][9][10] Carbon and cellulose based sponges show ultralow densities and excellent mechanical properties but soft sponges with similar mechanical integrity are missing.Since spicules of natural sponges conspicuously resemble polymer fi bers, formation of such fi brous structures by electrospinning [ 11 ] could be a promising concept for the preparation of polymer-based biomimetic analogous of natural sponges and would open the huge potential of electrospun materials for 3D sponge-type structures. Indeed, 3D porous structures were prepared by electrospinning which was nicely summarized in comprehensive review in recent literature. [ 7 ] However, previous efforts of making 3D highly porous electrospun materials, for example, via ultrasonic treatment, resulted in higher densities and correspondingly lower porosities of <99%, [ 12 ] as well as relatively poor mechanical performance. Remarkably, Eichhorn et al. claimed that theoretically ultrahigh porosities of electrospun nonwovens >99% could not be achieved. [ 13 ] In contrast to these reports, we present here the formation of ultralight weight highly porous 3D electrospun polymer fi ber-based spongy structures with densities as low as 2.7 mg cm −3 corresponding to a porosity of 99.6%. They were prepared by electrospinning of a photo cross-linkable polymer followed by UV cross-linking, mechanical cutting, suspending cut fi bers in liquid dispersion, and freezedrying. These polymer sponges showed in analogy to natural Ultralight, Soft Polymer Sponges by Self-Assembly of Short Electrospun Fibers in Colloidal DispersionsGaigai Duan , Shaohua Jiang , Valérie Jérôme , Joachim H. Wendorff , Amir Fathi , Jaqueline Uhm , Volker Altstädt , Markus Herling , Josef Breu , Ruth Freitag , Seema Agarwal , and Andreas Gre...

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IntroductionThere exist two main approaches for the functionalization of nanoparticles (NPs) with polymer chains fixed on the NPs' surface. The "grafting-to" method is performed by utilizing polymers bearing suitable functional end groups (anchor groups), which are able to bind to the surface of the particle. Alternatively, the "grafting-from" approach can be used to obtain core-shell nanoparticles. In this case, the initiating moiety is immobilized on the nanoparticle surface and the polymerization takes place directly from the surface. 1,2 We present the synthesis of core-shell NPs via the grafting-from approach utilizing a dopamine based ATRP initiator. Dopamine is considered to be a robust anchor for iron oxide surfaces in aqueous media. Grafting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) via surface-initiated ATRP yielded dual responsive core-shell NPs being responsive to temperature and pH. Due to the great potential of cationic polymers for non-viral gene delivery the hybrid material was further investigated related to biotechnical applications. The cytotoxicity and the efficiency as transfection reagent were studied under standard conditions and compared to the "gold standard" poly(ethylene imine), PEI.

Delivery of polynucleotides such as plasmid DNA (pDNA) and siRNA to nondividing and primary cells by nonviral vectors presents a considerable challenge. In this contribution, we introduce a novel type of PDMAEMA-based star-shaped nanoparticles that (i) are efficient transfection agents in clinically relevant and difficult-to-transfect human cells (Jurkat T cells, primary T lymphocytes) and (ii) can efficiently deliver siRNA to human primary T lymphocytes resulting to more than 40% silencing of the targeted gene. Transfection efficiencies achieved by the new vectors in serum-free medium are generally high and only slightly reduced in the presence of serum, while cytotoxicity and cell membrane disruptive potential at physiological pH are low. Therefore, these novel agents are expected to be promising carriers for nonviral gene transfer. Moreover, we propose a general design principle for the construction of polycationic nanoparticles capable of delivering nucleic acids to the above-mentioned cells.

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Monodisperse, magnetic nanoparticles as vectors for gene delivery were successfully synthesized via the grafting-from approach. First, oleic acid stabilized maghemite nanoparticles (γ-Fe2O3) were encapsulated with silica utilizing a reverse microemulsion process with simultaneous functionalization with initiating sites for atom transfer radical polymerization (ATRP). Polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) from the core-shell nanoparticles led to core-shell-corona hybrid nanoparticles (γ-Fe2O3@silica@PDMAEMA) with an average grafting density of 91 polymer chains of DP(n) = 540 (PDMAEMA540) per particle. The permanent attachment of the arms was verified by field-flow fractionation. The dual-responsive behavior (pH and temperature) was confirmed by dynamic light scattering (DLS) and turbidity measurements. The interaction of the hybrid nanoparticles with plasmid DNA at various N/P ratios (polymer nitrogen/DNA phosphorus) was investigated by DLS and zeta-potential measurements, indicating that for N/P ≥ 7.5 the complexes bear a positive net charge and do not undergo secondary aggregation. The hybrids were tested as transfection agents under standard conditions in CHO-K1 and L929 cells, revealing transfection efficiencies >50% and low cytotoxicity at N/P ratios of 10 and 15, respectively. Due to the magnetic properties of the hybrid gene vector, it is possible to collect most of the cells that have incorporated a sufficient amount of magnetic material by using a magnetic activated cell sorting system (MACS). Afterward, cells were further cultivated and displayed a transfection efficiency of ca. 60% together with a high viability.