Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

Biodegradable amphiphilic diblock copolymers based on an aliphatic ester block and various hydrophilic methacrylic monomers were synthesized using a novel hydroxyl-functionalized trithiocarbonate-based chain transfer agent. One protocol involved the one-pot simultaneous ring-opening polymerization (ROP) of the biodegradable monomer (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione (L-lactide, LA) and reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) or oligo(ethylene glycol) methacrylate (OEGMA) monomer, with 4-dimethylaminopyridine being used as the ROP catalyst and 2,2′-azobis(isobutyronitrile) as the initiator for the RAFT polymerization. Alternatively, a two-step protocol involving the initial polymerization of LA followed by the polymerization of DMA, glycerol monomethacrylate or 2-(methacryloyloxy)ethyl phosphorylcholine using 4,4′-azobis(4-cyanovaleric acid) as a RAFT initiator was also explored. Using a solvent switch processing step, these amphiphilic diblock copolymers self-assemble in dilute aqueous solution. Their self-assembly provides various copolymer morphologies depending on the block compositions, as judged by transmission electron microscopy and dynamic light scattering. Two novel disulfide-functionalized PLA-branched block copolymers were also synthesized using simultaneous ROP of LA and RAFT copolymerization of OEGMA or DMA with a disulfide-based dimethacrylate. The disulfide bonds were reductively cleaved using tributyl phosphine to generate reactive thiol groups. Thiol–ene chemistry was utilized for further derivatization with thiol-based biologically important molecules and heavy metals for tissue engineering or bioimaging applications, respectively.

Enhancement of the properties of EPDM/NBR elastomers using nanoclay for seal applications

In this research, we have investigated the effects of addition of different percentages of nanoclay to the ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR) on the characteristics of these rubbers as seal material. Properties such as tensile strength, modulus at different extensions, elongation at break, compressive set, hardness, and permeability and abrasion resistance are tested to assess the effect of addition of the nanoclay. Results indicate that addition of nanoclay at certain compositions could slightly reduce the strength of the rubber. However more stable modulus at different strains are provided, the hardness of the rubber is preserved and slightly enhanced, the permeability is reduced in both rubbers especially considerable decrease in EPDM is observed which is desirable in diminishing the effect of explosive decompression. At the same time the compression test shows that the nanoclay improves the performance of the rubbers under compression which is essential in seal application. The X-ray diffraction tests clarify that the dispersion of the nanoclay in the NBR samples is of high quality. In the EPDM samples, the dispersion is in need of improvement. POLYM. COMPOS., 30:1657-1667, 2009. © 2008 Society of Plastics Engineers.

Efficient Drug Delivery and Induction of Apoptosis in Colorectal Tumors Using a Death Receptor 5-Targeted Nanomedicine

Death Receptor 5 (DR5) is a pro-apoptotic cell-surface receptor that is a potential therapeutic target in cancer. Despite the potency of DR5-targeting agents in preclinical models, the translation of these effects into the clinic remains disappointing. Herein, we report an alternative approach to exploiting DR5 tumor expression using antibody-targeted, chemotherapy-loaded nanoparticles. We describe the development of an optimized polymer-based nanotherapeutic incorporating both a functionalized polyethylene glycol (PEG) layer and targeting antibodies to limit premature phagocytic clearance whilst enabling targeting of DR5-expressing tumor cells. Using the HCT116 colorectal cancer model, we show that following binding to DR5, the nanoparticles activate caspase 8, enhancing the anti-tumor activity of the camptothecin payload both in vitro and in vivo. Importantly, the combination of nanoparticle-induced DR5 clustering with camptothecin delivery overcomes resistance to DR5-induced apoptosis caused by loss of BAX or overexpression of anti-apoptotic FLIP. This novel approach may improve the clinical activity of DR5-targeted therapeutics while increasing tumor-specific delivery of systemically toxic chemotherapeutics.Molecular Therapy (2014); doi:10.1038/mt.2014.137.

Synergistic effects on gene delivery - co-formulation of small disulfide-linked dendritic polycations with Lipofectamine 2000 (TM)

This paper describes the application of gene delivery vectors based on connecting together two well-defined low-generation poly(L-lysine) (PLL) dendrons using a disulfide-containing linker unit. We report that the transfection ability of these vectors in their own right is relatively low, because the low-generation number limits the endosomal buffering capacity. Importantly, however, we demonstrate that when applied in combination with Lipofectamine 2000 (TM), a vector from the cationic lipid family, these small cationic additives significantly enhance the levels of gene delivery (up to four-fold). Notably, the cationic additives have no effect on the levels of transfection observed with a cationic polymer, such as DEAE dextran. We therefore argue that the synergistic effects observed with Lipofectamine 2000 (TM) arise as a result of combining the delivery advantages of two different classes of vector within a single formulation, with our dendritic additives providing a degree of pH buffering within the endosome. As such, the data we present indicate that small dendritic structures, although previously largely overlooked for gene delivery owing to their inability to transfect in their own right, may actually be useful well-defined additives to well-established vector systems in order to enhance the gene delivery payload.

Dendrons with spermine surface groups as potential building blocks for nonviral vectors in gene therapy

This paper investigates a series of dendrons based on the Newkome dendritic scaffold that displays a naturally occurring polyamine (spermine) on their surface. These dendrons have previously been shown to interact with DNA in a generation dependent manner with the more highly branched dendrons exhibiting a strong multivalency effect for the spermine surface groups. In this paper, we investigate the ability of these dendrons to transfect DNA into cells (human breast carcinoma cells, MDA-MB-231, and murine myoblast cells, C2C12) as determined by the luciferase assay. Although the dendrons are unable to transfect DNA in their own right, they are capable of delivering DNA in vitro when administered with chloroquine, which assists with escape from endocytic vesicles. The cytotoxicity of the dendrons was determined using the XTT assay, and it was shown that the dendrons were nontoxic either alone or in the presence of DNA. However, when administered with DNA and chloroquine, the most highly branched dendron did exhibit some cytotoxicity. This paper elucidates the relationship between in vitro transfection efficiency and toxicity. While transfection efficiencies are modest, the low toxicity of the dendrons, both in their own right, and in the presence of DNA, provides encouragement that this type of building block, which has a relatively high affinity for DNA, will provide a useful starting point for the further synthetic development of more effective gene transfection agents.

Self-assembly using dendritic building blocks - towards controllable nanomaterials

Dendritic molecules have well defined, three-dimensional branched architectures, and constitute a unique nanoscale toolkit. This review focuses on examples in which individual dendritic molecules are assembled into more complex arrays via non-covalent interactions. In particular, it illustrates how the structural information programmed into the dendritic architecture controls the assembly process, and as a consequence, the properties of the supramolecular structures which are generated. Furthermore, the review emphasises how the use of non-covalent (supramolecular) interactions, provides the assembly process with reversibility, and hence a high degree of control. The review also illustrates how self-assembly offers an ideal approach for amplifying the branching of small, synthetically accessible, relatively inexpensive dendritic systems (e.g. dendrons), into highly branched complex nanoscale assemblies.

The review begins by considering the assembly of dendritic molecules to generate discrete, well-defined supramolecular assemblies. The variety of possible assembled structures is illustrated, and the ability of an assembled structure to encapsulate a templating unit is described. The ability of both organic and inorganic building blocks to direct the assembly process is discussed. The review then describes larger discrete assemblies of dendritic molecules, which do not exist as a single well-defined species, but instead exist as statistical distributions. For example, assembly around nanoparticles, the assembly of amphiphilic dendrons and the assembly of dendritic systems in the presence of DNA will all be discussed. Finally, the review examines dendritic molecules, which assemble or order themselves into extended arrays. Such systems extend beyond the nanoscale into the microscale or even the macroscale domain, exhibiting a wide range of different architectures. The ability of these assemblies to act as gel-phase or liquid crystalline materials will be considered.

Taken as a whole, this review emphasises the control and tunability that underpins the assembly of nanomaterials using dendritic building blocks, and furthermore highlights the potential future applications of these assemblies at the interfaces between chemistry, biology and materials science. 

Investigation of influence of process variables on mechanical strength, size and homogeneity of pharmaceutical granules produced by fluidised hot melt granulation

The overall aim of the project was to study the influence of process variables on the distribution of a model active pharmaceutical ingredient (API) during fluidised melt granulation of pharmaceutical granules with a view of optimising product characteristics. Granules were produced using common pharmaceutical excipients; lactose monohydrate using poly ethylene glycol (PEG1500) as a meltable binder. Methylene blue was used as a model API. Empirical models relating the process variables to the granules properties such as granule mean size, product homogeneity and granule strength were developed using the design of experiment approach. Fluidising air velocity and fluidising air temperature were shown to strongly influence the product properties. Optimisation studies showed that strong granules with homogeneous distribution of the active ingredient can be produced at high fluidising air velocity and at high fluidising air temperatures.

Physicochemical Investigation of Adiponitrile-Based Electrolytes for Electrical Double Layer Capacitor

Low pressure methane solubility in lithium-ion batteries based solvents and electrolytes as a function of temperature. Measurement and prediction

The methane solubility in five pure electrolyte solvents and one binary solvent mixture for lithium ion batteries – such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and the (50:50 wt%) mixture of EC:DMC was studied experimentally at pressures close to atmospheric and as a function of temperature between (280 and 343) K by using an isochoric saturation technique. The effect of the selected anions of a lithium salt LiX (X = hexafluorophosphate,

Water and Temperature Relations of Growth of the Entomogenous Fungi Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces farinosus

The effects of temperature (5-50°C), water availability (0.998-0.88 water activity, aw), and aw × temperature interactions (15-45°C) on growth of three entomogenous fungi, Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces farinosus, were evaluated on a Sabouraud dextrose-based medium modified with the ionic solute KCl, the non-ionic solute glycerol, and an inert solute, polyethylene glycol (PEG) 600. The temperature ranges for growth of B. bassiana, M. anisopliae, and P. farinosus were 5-30, 5-40, and 5-30°C, and optimum growth temperatures were 25, 30, and 20°C, respectively. All three species grew over a similar aw range (0.90-0.998) at optimum temperatures for growth. However, there were significant interspecies variations in growth rates on media modified with each of the three aw-modifying solutes. Growth aw optima ranged between 0.99 and 0.97 on KCl-, glycerol-, and PEG 600-modified media for M. anisopliae and P. farinosus. B. bassiana grew optimally at 0.998 aw, regardless of aw. Comprehensive two-dimensional profiles of aw × temperature relations for growth of these three species were constructed for the first time. The results are discussed in relation to the environmental limits that determine efficacy of entomogenous fungi as biocontrol agents in nature. © 1999 Academic Press.

Ethanol-induced water stress and fungal growth

Fungal growth inhibition by ethanol was compared with that caused by five other agents of water stress (at 25, 40 and 42.5°C), using Aspergillus oryzae. Ethanol, KCl, glycerol, glucose, sorbitol, and polyethylene glycol 400 were incorporated into media at concentrations corresponding to water activity (a(w)) values in the range 1 to 0.75. Generally, as temperature increased there was a decrease in the a(w) value at which optimum growth occurred. The a(w) limit for growth on KCl, glycerol, glucose, sorbitol, or polyethylene glycol 400 media was about 0.85, regardless of temperature. However, the a(w) limit for growth on ethanol media varied between 0.97 and 0.99 a(w) and was temperature-dependent. Water stress accounted for up to 31, 18 and 6% of growth inhibition by ethanol at 25, 40, and 42.5°C, respectively. For media containing ethanol, the decrease in growth rate per unit of a(w) reduction was greater as temperature increased. However, ethanol-induced water stress remained constant regardless of temperature, suggesting that other inhibitory effects of ethanol are closely temperature- dependent. Water stress may account for considerably more than 30% of growth inhibition by ethanol in cells that remain metabolically active at higher ethanol concentrations.

Self-Assembled Supramolecular Gels of Reverse Poloxamers and Cyclodextrins

A series of supramolecular aggregates were prepared using a poly(propylene oxide) poly(ethylene oxide) poly(propylene oxide) (PPO-PEO-PPO) block copolymer and beta- or alpha-cyclodextrins (CD). The combination of beta-CD and the copolymer yields inclusion complexes (IC) with polypseudorotaxane structures. These are formed by complexation of the PPO blocks with beta-CD molecules producing a powder precipitate with a certain crystallinity degree that can be evaluated by X-ray diffraction (XRD). In contrast, when combining alpha-CD with the block copolymer, the observed effect is an increase in the viscosity of the mixtures, yielding fluid gels. Two cooperative effects come into play: the complexation of PEO blocks with alpha-CD and the hydrophobic interactions between PPO blocks in aqueous media. These two combined interactions lead to the formation of a macromoleculaf network. The resulting fluid gels were characterized using different techniques such as differential scanning calorimetry (DSC), viscometry, and XRD measurements.

Phase Behavior of Reverse Poloxamers and Poloxamines in Water

The phase behavior of two types of poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) copolymers in aqueous solutions was studied by light scattering, viscometry, and infrared spectroscopy. Both the reverse poloxamer (Pluronic 10R5) and the star type poloxamine (Tetronic 90R4) have practically the same PEO/PPO ratio with their hydrophobic blocks (PPO) located in the outer part. The temperature-composition phase diagrams show that both 10R5 and 90R4 tend to form aggregates in water. Up to four different phases can be detected in the case of Tetronic 90R4 for each temperature: unimers, random networks, micellar networks, and macrophase separation. Viscometric and infrared measurements complemented the results obtained by light scattering and visual inspection.

Non-covalent hydrogels of cyclodextrins and poloxamines for the controlled release of proteins

Different types of gels were prepared by combining poloxamines (Tetronic), i.e. poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) octablock star copolymers, and cyclodextrins (CD). Two different poloxamines with the same molecular weight (ca. 7000) but different molecular architectures were used. For each of their four diblock arms, direct Tetronic 904 presents PEO outer blocks while in reverse Tetronic 90R4 the hydrophilic PEO blocks are the inner ones. These gels were prepared by combining alpha-CD and poloxamine aqueous solutions. The physicochemical properties of these systems depend on several factors such as the structure of the block copolymers and the Tetronic/alpha-CD ratio. These gels were characterized using differential scanning calorimetry (DSC), viscometry and X-ray diffraction measurements. The 90R4 gels present a consistency that makes them suitable for sustained drug delivery. The resulting gels were easily eroded: these complexes were dismantled when placed in a large amount of water, so controlled release of entrapped large molecules such as proteins (Bovine Serum Albumin, BSA) is feasible and can be tuned by varying the copolymer/CD ratio. 

Microwave-Assisted Preparation of Hydrogel-Forming Microneedle Arrays for Transdermal Drug Delivery Applications

A microwave (MW)-assisted crosslinking process to prepare hydrogel-forming microneedle (MN) arrays was evaluated. Conventionally, such MN arrays are prepared using processes that includes a thermal crosslinking step. Polymeric MN arrays were prepared using poly(methyl vinyl ether-alt-maleic acid) crosslinked by reaction with poly(ethylene glycol) over 24 h at 80 °C. Polymeric MN arrays were prepared to compare conventional process with the novel MW-assisted crosslinking method. Infrared spectroscopy was used to evaluate the crosslinking degree, evaluating the area of the carbonyl peaks (2000–1500 cm−1). It was shown that, by using the MW-assisted process, MN with a similar crosslinking degree to those prepared conventionally can be obtained in only 45 min. The effects of the crosslinking process on the properties of these materials were also evaluated. For this purpose swelling kinetics, mechanical characterisation, and insertion studies were performed. The results suggest that MN arrays prepared using the MW assisted process had equivalent properties to those prepared conventionally but can be produced 30 times faster. Finally, an in vitro caffeine permeation across excised porcine skin was performed using conventional and MW-prepared MN arrays. The release profiles obtained can be considered equivalent, delivering in both cases 3000–3500 μg of caffeine after 24 h.