Establishing clear structure−property−transfection relationships is a critical step in the development of clinically relevant polymers for nonviral gene therapy. In this study, we determined the ...influence of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) molecular weight on cytotoxicity, DNA binding, and in vitro plasmid DNA delivery efficiency in human brain microvascular endothelial cells (HBMEC). Conventional free radical polymerization was used to synthesize PDMAEMA with weight-average molecular weights ranging from 43 000 to 915 000 g/mol. MTT and LDH assays revealed that lower molecular weight PDMAEMA (M w = 43 000 g/mol) was slightly less toxic than higher molecular weights (M w > 112 000 g/mol) and that the primary mode of toxicity was cellular membrane destabilization. An electrophoretic gel shift assay revealed that all PDMAEMA molecular weights completely bound with plasmid DNA. However, heparin competitive binding experiments revealed that higher molecular weight PDMAEMA (M w = 915 000 g/mol) had a greater binding affinity toward plasmid DNA than lower molecular weight PDMAEMA (M w = 43 000 g/mol). The molecular weight of PDMAEMA was found to have a dramatic influence on transfection efficiency, and luciferase reporter gene expression increased as a function of increasing molecular weight. However, cellular uptake of polyplexes was determined to be insensitive to PDMAEMA molecular weight. In addition, our data did not correlate polyplex size with transfection efficiency. Collectively, our data suggested that the intracellular fate of the polyplexes, which involves endosomal release and DNase resistance, is more important to overall transfection efficiency than barriers to entry, such as polyplex size.
Phospholipid Nonwoven Electrospun Membranes McKee, Matthew G; Layman, John M; Cashion, Matthew P ...
Science (American Association for the Advancement of Science),
01/2006, Letnik:
311, Številka:
5759
Journal Article
Recenzirano
Nonwoven fibrous membranes were formed from electrospinning lecithin solutions in a single processing step. As the concentration of lecithin increased, the micellar morphology evolved from spherical ...to cylindrical, and at higher concentrations the cylindrical micelles overlapped and entangled in a fashion similar to polymers in semi-dilute or concentrated solutions. At concentrations above the onset of entanglements of the wormlike micelles, electrospun fibers were fabricated with diameters on the order of 1 to 5 micrometers. The electrospun phospholipid fibers offer the potential for direct fabrication of biologically based, high-surface-area membranes without the use of multiple synthetic steps, complicated electrospinning designs, or postprocessing surface treatments.
Structure‐property relationships for polymerized ionic liquids (PILs) relate chemical structure to ionic conductivity and reveal the importance of glass transition temperature (Tg) and the energy ...associated with an ion‐hopping mechanism for ion conduction for a series of alkyl‐substituted vinylimidazolium PILs. The alkyl‐substituted vinylimidazolium‐based PILs with varying lengths of n‐alkyl substituents provide diverse precursors with exchangeable anions to further enhance thermal stability and ionic conductivity. As the anion size increases, regardless of alkyl substituent length, Tg decreases and the onset of weight loss, TD, increases. As the length of the alkyl substituent increases, Tg decreases for PILs with Br− and BF4− counteranions. Ionic conductivity increases over an order of magnitude upon exchange of the counteranion from TfO− < Tf2N−.
A series of vinylimidazolium‐based ionic liquids with varying hydrophobic counteranions and alkyl substituent lengths indicate that larger, bulkier counteranions reduce Tg, increase thermal stability, and increase ionic conductivity. VFT‐analysis of the ionic conductivity shows similar infinite temperature conductivities, T0 values well below Tg, and increased VFT activation energy with increased alkyl substituent length.
The influence of polyelectrolyte rheological behavior on the electrospinning process was determined for a series of poly(2-(dimethylamino)ethyl methacrylate hydrochloride) (PDMAEMA·HCl) aqueous ...solutions in the presence of added NaCl. Solution rheological studies revealed that PDMAEMA·HCl in an 80/20 w/w water/methanol cosolvent displayed polyelectrolyte behavior based on the scaling relationship between specific viscosity (ηsp) and concentration in the semidilute unentangled and semidilute entangled regimes. The entanglement concentration (C e) increased with NaCl concentration due to screening of the electrostatic repulsive forces along the PDMAEMA·HCl backbone, which enabled the PDMAEMA·HCl chains to adopt a flexible, coillike conformation. Moreover, the scaling behavior in the semidilute entangled regime shifted from polyelectrolyte (ηsp ∼ C 1.5) to neutral polymer behavior (ηsp ∼ C 3.75) in the high salt limit. The electrospinning performance of PDMAEMA·HCl solutions was also dependent on NaCl concentration, and NaCl-free PDMAEMA·HCl solutions did not form fibers at concentrations less than 8C e. The minimum concentration for fiber formation decreased as the level of NaCl was increased due to screening of the repulsive, electrostatic interactions between charged repeating units that served to stabilize the electrospinning jet. Moreover, because of the high electrical conductivity of the polyelectrolyte solutions, the electrospun polyelectrolyte fibers were 2−3 orders of magnitude smaller in diameter compared to fibers that were electrospun from solutions of neutral polymers of equal zero shear viscosity (η0) and normalized concentration (C/C e).
Solutions of poly(ethylene-co-vinyl alcohol) or EVOH, ranging in composition from 56 to 71
wt% vinyl alcohol, can be readily electrospun at room temperature from solutions in 70% 2-propanol/water ...(rubbing alcohol). The solutions are prepared at 80°C and allowed to cool to room temperature. Interestingly, the solutions are not stable at room temperature and eventually the polymer precipitates after several hours. However, prior to precipitation, electrospinning is extensive and rapid, allowing coverage of fibers on various substrates, including a grounded metal plate, dielectrics interposed between the charged jet and the metal ground, and on the human body. Fiber diameters of ca. 0.2–8.0
μm were obtained depending upon the solution concentration, an attractive range for tissue engineering, wound healing, and related applications. Electrospun EVOH mats have been shown to support the culturing of smooth muscle cells and fibroblasts.
Electrospun fiber mats are explored as drug delivery vehicles using tetracycline hydrochloride as a model drug. The mats were made either from poly(lactic acid) (PLA), poly(ethylene-co-vinyl acetate) ...(PEVA), or from a 50:50 blend of the two. The fibers were electrospun from chloroform solutions containing a small amount of methanol to solubilize the drug. The release of the tetracycline hydrochloride from these new drug delivery systems was followed by UV–VIS spectroscopy. Release profiles from the electrospun mats were compared to a commercially available drug delivery system, Actisite
® (Alza Corporation, Palo Alto, CA), as well as to cast films of the various formulations.
Cationic aliphatic ammonium polyionenes, specifically 12,12- and 6,12-ionenes, were synthesized using step-growth polymerization and aqueous-based size exclusion chromatography (SEC) coupled with ...multiangle laser light scattering (MALLS) revealed absolute molecular weight information. The chromatographic separation of cationic polyelectrolytes presents many additional challenges compared to SEC of nonassociating, neutral polymers. Therefore, an aqueous-based SEC-MALLS mobile phase composition was identified to separate these notoriously challenging polyelectrolytes in an effort to achieve absolute molecular weight analysis. Various solvent compositions were evaluated for their ability to solvate and reproducibly separate both 6,12- and 12,-12-ionenes. Dynamic light scattering (DLS) verified the absence of aggregation of polyionenes in preferred mobile phase compositions. The optimum solvent composition comprised a ternary mixture of 54/23/23 water/methanol/glacial acetic acid, 0.54 M NaOAc, at a pH of 4.0. Weight-average molecular weights for the synthesized ammonium 12,12-ionenes ranged from 11 000 to 40 000 g/mol, and ammonium 6,12-ionenes had weight-average molecular weights ranging from 19 000 to 49 900 g/mol. Mark−Houwink parameters were also determined for both the 12,12- and 6,12-ionenes in the optimum mobile phase using an online capillary viscometer.
Water-soluble 12,12-ammonium ionenes were prepared via the Menschutkin reaction from 1,12-dibromododecane and 1,12-bis(N,N-dimethylamino)dodecane. A stoichiometric imbalance of monomers controlled ...the final molecular weights of the polymers. The absolute molecular weights were determined for the first time using an online multiangle laser light scattering (MALLS) detector in aqueous size exclusion chromatography (SEC). Weight-average molecular weights ranged from 4300 to 20 900 g/mol. Relationships between weight-average molecular weight and mechanical properties were established for a series of 12,12-ammonium ionenes using both tensile testing and dynamic mechanical analysis (DMA). Tensile analysis of the higher molecular weight ionenes revealed an average tensile strength of 20 MPa and elongations ranging from 230 to 440%. Dissociation of ionic aggregates was observed at 85−88 °C in DMA experiments, and the glass transition temperatures increased with increasing molecular weight (61−88 °C). X-ray scattering revealed an amorphous polyethylene peak at ≈14 nm−1 and a sharp ionic group correlation peak at 4.38 nm−1. These correlations agreed well with the proposed macromolecular structure.
A vinylpyridine block copolymer was prepared by stepwise controlled/living radical polymerization with a novel bifunctional initiator, ...4‐(2‐bromopropanoyloxy)‐N‐(p‐methylbenzyloxy)‐2,2,6,6‐tetramethylpiperidine. The initiator was synthesized in a facile manner using commercially available p‐xylene and 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (4‐hydroxy TEMPO). Through stepwise atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and nitroxide‐mediated radical polymerization (NMRP) of 4‐vinylpyridine (4VP), the PMMA‐b‐P4VP copolymer was prepared with a wide range of the copolymer compositions. Microphase‐separation was demonstrated in cross sectional TEM images of self‐standing block copolymer membranes.
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