Heidi Johnsen

Preparation of polyurethane nanocapsules by miniemulsion polyaddition

The encapsulation of organic liquids in polyurethane nanocapsules by interfacial miniemulsion polycondensation of isophorone diisocyanate and propanetriol has been performed. The influence of type and amount of encapsulated organic liquid has been studied and it was found that the encapsulation efficiency is dependent on the water solubility of the organic liquids, their interfacial tension against water and their compatibility with polyurethane. It was also shown how different types of surfactants and variations in pH and ionic strength of the continuous phase affected the stability during polymerization and the diameter of the miniemulsion droplets and the resulting nanocapsules. The long-chained anionic surfactant Disponil FES77 can be utilized over a larger pH range than SDS due to the contribution of steric stabilization. Relatively narrow size distributions were obtained.

Nanoparticle-stabilized microbubbles for multimodal imaging and drug delivery

Microbubbles (MBs) are routinely used as contrast agents for ultrasound imaging. The use of ultrasound in combination with MBs has also attracted attention as a method to enhance drug delivery. We have developed a technology platform incorporating multiple functionalities, including imaging and therapy in a single system consisting of MBs stabilized by polyethylene glycol (PEG)-coated polymeric nanoparticles (NPs). The NPs, containing lipophilic drugs and/or contrast agents, are composed of the widely used poly(butyl cyanoacrylate) (PBCA) polymer and prepared in a single step. MBs stabilized by these NPs are subsequently prepared by self-assembly of NPs at the MB air-liquid interface. Here we show that these MBs can act as contrast agents for conventional ultrasound imaging. Successful encapsulation of iron oxide NPs inside the PBCA NPs is demonstrated, potentially enabling the NP-MBs to be used as magnetic resonance imaging (MRI) and/or molecular ultrasound imaging contrast agents. By precise tuning of the applied ultrasound pulse, the MBs burst and the NPs constituting the shell are released. This could result in increased local deposit of NPs into target tissue, providing improved therapy and imaging contrast compared with freely distributed NPs.

Uptake and toxicity of methylmethacrylate‐based nanoplastic particles in aquatic organisms

The uptake and toxicity of 2 poly(methylmethacrylate)-based plastic nanoparticles (PNPs) with different surface chemistries (medium and hydrophobic) were assessed using aquatic organisms selected for their relevance based on the environmental behavior of the PNPs. Pure poly(methylmethacrylate) (medium; PMMA PNPs) and poly(methylmethacrylate-co-stearylmethacrylate) copolymer (hydrophobic; PMMA-PSMA PNPs) of 86 nm to 125 nm were synthesized using a miniemulsion polymerization method. Fluorescent analogs of each PNP were also synthesized using monomer 7-[4-(trifluoromethyl)coumarin]acrylamide and studied. Daphnia magna, Corophium volutator, and Vibrio fischeri were employed in a series of standard acute ecotoxicity tests, being exposed to the PNPs at 3 different environmentally realistic concentrations (0.01 mg/L, 0.1 mg/L, and 1.0 mg/L) and a high concentration 500 mg/L to 1000 mg/L. In addition, sublethal effects of PNPs in C. volutator were determined using a sediment reburial test, and the uptake and depuration of fluorescent PNPs was studied in D. magna. The PNPs and fluorescent PNPs did not exhibit any observable toxicity at concentrations up to 500 mg/L to 1000 mg/L in any of the tests except for PMMA-PSMA PNPs and fluorescent PNPs following 48-h exposure to D. magna (median lethal concentration values of 879 mg/L and 887 mg/L, respectively). No significant differences were observed between labeled and nonlabeled PNPs, indicating the suitability of using fluorescent labeling. Significant uptake and rapid excretion of the fluorescent PNPs was observed in D. magna. Environ Toxicol Chem 2016;35:1641-1649.

Influence of salinity, dissolved organic carbon and particle chemistry on the aggregation behaviour of methacrylate-based polymeric nanoparticles in aqueous environments

This study investigates the influence of salinity, dissolved organic matter (DOM) concentration, particle chemistry and particle concentration on the aggregation behaviour of methacrylate-based polymeric nanoparticles (PNPs) in aquatic systems. Three PNPs with different chemical compositions were synthesised by mini-emulsion polymerisation using an ionic (sodium dodecyl sulphate; SDS) and a non-ionic stabiliser (Lutensol AT50). The most hydrophobic PNPs formed stable dispersions in deionised water, with the most hydrophilic aggregating immediately. All PNPs synthesised using SDS rapidly aggregated under mildly saline conditions whilst those synthesised using Lutensol AT50 were unaffected effected by salinity. The rate of PNP aggregation under saline conditions increased with increasing PNP concentration. Natural DOM in lake water did not influence the aggregation behaviour of the PNPs except at high PNP concentrations (500 mg/L). The results show that salinity, PNP particle chemistry, PNP concentration and the type of stabilising agent used in synthesis can strongly influence their behaviour in aquatic environments, whilst DOM concentration is less significant.

Needleless electrospun nanofibers containing microcapsules: a methodology for self-supported microcontainers

The present paper investigates the facile production of electrospun polyvinyl alcohol (PVA) nanofibers containing either micro-sized polymer or hybrid capsules, using a needleless electrospinning system. Oilcontaining microcapsules with diameters of around 3 or 10 μm, respectively, were produced via an oil-in-water miniemulsion and mixed with a PVA solution. Appropriate adjustment of electrospinning parameters enabled a controlled assembly of PVA nanofibers into a network containing microcapsules, without damaging their integrity. The PVA nanofibers have diameters in a range of 200-300 nm and showed good homogeneity. The introduction of microcapsules caused an increase in the PVA nanofiber diameters probably due to an increase in the solution viscosity. The production of such self-supported and loaded microcontainers could be of high interest for various applications.