Hyperbranched Polylysine Research Articles

Long-term active antimicrobial coatings for surgical sutures based on silver nanoparticles and hyperbranched polylysine

The goal of this study was to develop a long-term active antimicrobial coating for surgical sutures. To this end, two water-insoluble polymeric nanocontainers based on hyperbranched polylysine (HPL), hydrophobically modified by either using glycidyl hexadecyl ether, or a mixture of stearoyl/palmitoyl chloride, were synthesized. Highly stabilized silver nanoparticles (AgNPs, 2–5 nm in size) were generated by dissolving silver nitrate in the modified HPL solutions in toluene followed by reduction with L-ascorbic acid. Poly(glycolic acid)-based surgical sutures were dip-coated with the two different polymeric silver nanocomposites. The coated sutures showed high efficacies of more than 99.5% reduction of adhesion of living Staphylococcus aureus cells onto the surface compared to the uncoated specimen. Silver release experiments were performed on the HPL-AgNP modified sutures by washing them in phosphate buffered saline for a period of 30 days. These coatings showed a constant release of silver ions over more than 30 days. After this period of washing, the sutures retained their high efficacies against bacterial adhesion. Cytotoxicity tests using L929 mouse fibroblast cells showed that the materials are basically non-cytotoxic.

DNA delivery with hyperbranched polylysine: A comparative study with linear and dendritic polylysine

PEI and polylysine are among the most investigated synthetic polymeric carriers for DNA delivery. Apart from their practical use, these 2 classes of polymers are also of interest from a fundamental point of view as they both can be prepared in different architectures (linear and branched/dendritic) and in a wide range of molecular weights, which is attractive to establish basic structure–activity relationships. This manuscript reports the results of an extensive study on the influence of molecular weight and architecture of a library of polylysine variants that includes linear, dendritic and hyperbranched polylysine. Hyperbranched polylysine is a new polylysine-based carrier that is structurally related to dendritic polylysine but possesses a randomly branched structure. Hyperbranched polylysine is attractive as it can be prepared in a one-step process on a large scale. The performance of these 3 classes of polylysine analogs was evaluated by assessing eGFP and IgG production in transient gene expression experiments with CHO DG44 cells, which revealed that protein production generally increased with increasing molecular weight and that at comparable molecular weight, the hyperbranched analogs were superior as compared to the dendritic and linear polylysines. To understand the differences between the gene delivery properties of the hyperbranched polylysine analogs on the one hand and the dendritic and linear polylysines on the other hand, the uptake and trafficking of the corresponding polyplexes were investigated. These experiments allowed us to identify (i) polyplex–external cell membrane binding, (ii) free, unbound polylysine coexisting with polyplexes as well as (iii) polymer buffer capacity as three possible factors that may contribute to the superior transfection properties of the hyperbranched polylysines as compared to their linear and dendritic analogs. Altogether, the results of this study indicate that hyperbranched polylysine is an interesting, alternative synthetic gene carrier. Hyperbranched polylysine can be produced at low costs and in large quantities, is partially biodegradable, which may help to prevent cumulative cytotoxicity, and possesses transfection properties that can approach those of PEI.

Comparative Study on the In Vitro Cytotoxicity of Linear, Dendritic, and Hyperbranched Polylysine Analogues

Lysine-based polycations are widely used as nonviral carriers for gene delivery. This manuscript reports the results of a comparative study on the in vitro cytotoxicity of a library of three structural polylysine variants, namely, linear polylysine (LPL), dendritic polylysine (DPL), and hyperbranched polylysine (HBPL). The aim of this study was to identify possible effects of polymer molecular weight and architecture on both immediate and delayed cytotoxicity and also to provide a mechanistic understanding for possible differences. Acute cytotoxicities were evaluated using cell viability assays with CHO DG44 cells. At comparable molecular weights, the EC(50) values for the LPL analogues were ∼5-250 times higher as compared to the DPL and HBPL samples. For low molecular weight polycations, osmotic shock was found to be an important contributor to immediate cell death, whereas for the higher molecular weight analogues, direct cell membrane disruption was identified to play a role. Delayed cytotoxicity (≥3 h) was assessed by identifying several of the hallmark events that characterize apoptosis, including phosphatidyl serine translocation, mitochondrial membrane depolarization, cytoplasmic cytochrome C release, and caspase 3 activation. At comparable molecular weights, apoptosis was found to be more pronounced for DPL and HBPL as compared to LPL. This difference was ascribed to the fact that LPL is completely enzymatically degradable, in contrast to DPL and HBPL, which also contain ε-peptidic bonds and are only partially degradable. Because their toxicity profiles are similar, HBPL is an interesting (i.e., synthetically easily accessible and inexpensive) alternative to DPL for the nonviral delivery of DNA.

Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core–shell nanocontainers for metal nanoparticles

Hyperbranched amphiphilic polymeric systems with core–shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30–0.32. The molecular weight Mn could be controlled in a range of 5000–12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core–shell systems.

Nuclear entry of hyperbranched polylysine nanoparticles into cochlear cells

Background:Gene therapy is a potentially effective therapeutic modality for treating sensorineural hearing loss. Nonviral gene delivery vectors are expected to become extremely safe and convenient, and nanoparticles are the most promising types of vectors. However, infrequent nuclear localization in the cochlear cells limits their application for gene therapy. This study aimed to investigate the potential nuclear entry of hyperbranched polylysine nanoparticles (HPNPs) for gene delivery to cochlear targets.Methods:Rat primary cochlear cells and cochlear explants generated from newborn rats were treated with different concentrations of HPNPs. For the in vivo study, HPNPs were administered to the rats’ round window membranes. Subcellular distribution of HPNPs in different cell populations was observed with confocal microscope 24 hours after administration.Results:Nuclear entry was observed in various cochlear cell types in vitro and in vivo. In the primary cochlear cell culture, concentration-dependent internalization was observed. In the cochlear organotypic culture, abundant HPNPs were found in the modiolus, including the spiral ganglion, organ of Corti, and lateral wall tissues. In the in vivo study, a gradient distribution of HPNPs through different layers of the round window membrane was observed. HPNPs were also distributed in the cells of the middle ear tissue. Additionally, efficient internalization of HPNPs was observed in the organ of Corti and spiral ganglion cells. In primary cochlear cells, HPNPs induced higher transfection efficiency than did Lipofectamine™.Conclusion:These results suggest that HPNPs are potentially an ideal carrier for gene delivery into the cochlea.

Potential Novel Drug Carriers for Inner Ear Treatment: Hyperbranched Polylysine and Lipid Nanocapsules

Treatment of sensorineural hearing loss could be advanced using novel drug carriers such as hyperbranched polylysine (HBPL) or lipid nanocapsules (LNCs). This study examined HBPL and LNCs for their cellular uptake and possible toxicity in vitro and in vivo as the first step in developing novel nanosized multifunctional carriers. Having incubated HBPL and LNCs with fibroblasts, nanoparticle uptake and cell viability were determined by confocal laser scanning microscopy, fluorescence measurements and neutral red staining. In vivo, electrophysiology, confocal laser scanning microscopy and cytocochleograms were performed for nanoparticle detection and also toxicity studies after intracochlear application. Both nanoparticles were detectable in the fibroblasts' cytoplasm without causing cytotoxic effects. After in vivo application they were visualized in cochlear cells, which did not lead to a change in hearing threshold or loss of hair cells. Biocompatibility and traceability were demonstrated for HBPL and LNCs. Thus, they comply with the basic requirements for drug carriers for potential application in the inner ear.

Hyperbranched polylysines: Mechanism of formation

To gain insight into the mechanism treating formation of hyperbranched polylysines through the polymerization of N ɛ-carbobenzoxylysine N-carboxyanhydride under conditions of the reductive removal of a N ɛ-carbobenzoxy group, hyperbranched polylysine has been synthesized with the use of trifluoroacetic acid as a terminator in the polymerization of N-carboxyanhydride. The structure of the polymers is studied by capillary electrophoresis, low-pressure gel-permeation chromatography, circular dichroism, and enzymatic hydrolysis with trypsin. At the first stage of synthesis, a low-molecular-mass strongly branched core of the polymer is formed. At the second stage, polylysine chains are grafted via one point onto amino groups of N-terminal lysine moieties of the low-molecular-mass core through their carboxyl ends.

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

This work describes the dilute solution and solid-state structure of polyelectrolyte complexes generated from hyperbranched polylysine (HBPL) and various anionic, sodium alkyl sulfate surfactants. In dilute solution, the radius of gyration (Rg) of the HBPL and HBPL-surfactant complexes was determined in the Guinier regime in good solvent conditions by means of small-angle X-ray scattering (SAXS). With increasing molecular weight of the HBPL, an increase in Rg up to a maximum of 3.7 and 4.2 nm was observed for the HBPLs and HBPL-surfactant complexes, respectively. In the solid state, HBPL-surfactant complexes were found to form liquid crystalline (LC) phases, whose thermal stability and structure depended both on the molecular weight of the HBPL as well as on the nature of the anionic surfactant. Depending on the surfactant alkyl chain length, liquid crystalline phases with short range liquid-like order, columnar hexagonal packing or lamellar ordering were observed. By combination of small-angle X-ray scattering, differential scanning calorimetry (DSC), and cross-polarized light optical microscopy (CPOM), the exact structure of the LC phases, as well as their region of thermal stability, could be identified. HBPL-sodium dodecyl sulfate LC phases showed thermotropic behavior and underwent two transitions with increasing temperature. First, at lower temperatures, an order-nematic transition was observed. Upon further temperature increase, a second transition from a nematic to an isotropic phase was observed. Structural models for these different LC phases are proposed. © 2007 American Chemical Society.