Modification of microcapsules for controlled release

Fouling of marine organisms such as algae and barnacles on the boat hull is an enormous problem for the shipping industry. The negative consequences for the society are both economical and environmental. To prevent fouling in general, biocides are typically incorporated directly into the paint. Premature leakage of the biocides is a drawback which reduces the lifetime of the coating and pollutes the surrounding ecosystems. Microencapsulation is an efficient way of encapsulating active substances for controlling the release and thereby prolonging the antifouling properties of the coating. The microcapsules used in this work consist of an oil core and a hydrophobic polymer shell. The rate of release into the marine environment may be further tailored by modifying the microcapsules. Triggered release is achieved by rendering the microcapsule shell water sensitive. This may be accomplished by incorporating salt into the shell using imidazole coordination chemistry. On the other hand, extended release is achieved by improving the barrier properties of the microcapsule. This may be realized by providing the microcapsule with an additional shell, such as a highly charged polyelectrolyte multilayer or a lipid bilayer. The objective of this thesis is subsequently twofold: 1) To synthesize and characterize imidazole containing shell materials with a view to obtain triggered release. 2) To surface modify microcapsules with polyelectrolyte multilayers and lipid bilayers toward extended release. Imidazole containing polymers were synthesized using vinyl and maleimide radical polymerization, as well as grafting techniques comprising maleimide bond formation and epoxide ring opening. The imidazole-containing polymeric materials, with and without the salts CuCl2 or ZnCl2, were characterized using differential scanning calorimetry, electron paramagnetic resonance (EPR) and vibrational spectroscopy. The coordination chemistry of the imidazole-metal ion complex was investigated using vibrational spectroscopy, EPR and ab initio calculations. The imidazole coordination to the transition metal ions Cu2+ and Zn2+ in polymeric materials generates cross-links. The interaction between the imidazole moiety and the transition metal ions is very strong and specific. As a consequence, the coordinating polymer is rendered insoluble in conventional solvents, excluding only strongly coordinating solvents. The specificity and strength of the imidazole-transition metal ion interaction may be used for a variety of applications. However, with respect to the microencapsulation route used in this project, the limited solubility of the coordinating polymer material is unfortunate. The use of strongly coordinating solvents during the microencapsulation results in aggregation and phase separation instead of microcapsule formation. Routes for synthesising highly charged microcapsules for further surface modification were investigated using three types of ionic dispersants; a weak polyacid, a small set of amphiphilic block copolymers and a hydrophobic anionic surfactant in combination with a polycation. The charged microcapsules were subsequently modified with polyelectrolyte multilayers using the Layer-by-Layer technique and with lipid bilayers using lipid vesicle spreading. The microcapsules and model systems thereof were characterized mainly using micro-electrophoresis, light microscopy, optical tensiometry and quartz crystal microbalance with dissipation (QCM-D). The release behaviour in aqueous suspension of a hydrophobic model compound was investigated using UV-Vis spectroscopy. The use of the ionic dispersants facilitated the formation of highly charged microcapsules and the subsequent polyelectrolyte multilayer assembly and lipid bilayer formation were also successful. In particular, the block copolymer based microcapsules displayed excellent properties with respect to high and stable surface charge, as well as long term colloidal stability through electrostatic and steric stabilization. The release of the hydrophobic model compound was considerably reduced after modification with polyelectrolyte multilayers. In addition, the type of dispersant had a significant impact on the release. The block copolymer based microcapsules with a higher charge density had a much lower release compared to the weak polyelectrolyte based microcapsules. The polyelectrolyte multilayer is an efficient barrier against hydrophobic molecules and the low permeability is clearly a result of the high charge density. As of yet, the effect of the lipid bilayers on the release has not been investigated but has a large potential since the permeability may be altered by the lipid composition. A microcapsule consisting of an oil core, a hydrophobic polymer shell, a polyelectrolyte multilayer and a lipid bilayer is a complex release system with large degrees of freedom for tailoring the release behaviour

Directed self-assembly of silica nanoparticles in ionic liquid-spun cellulose fibers

The application range of man-made cellulosic fibers is limited by the absence of cost- and manufacturing-efficient strategies for anisotropic hierarchical functionalization. Overcoming these bottlenecks is therefore pivotal in the pursuit of a future bio-based economy. Here, we demonstrate that colloidal silica nanoparticles (NPs), which are cheap, biocompatible and easy to chemically modify, enable the control of the cross-sectional morphology and surface topography of ionic liquid-spun cellulose fibers. These properties are tailored by the silica NPs’ surface chemistry and their entry point during the wet-spinning process (dope solution DSiO2 or coagulation bath CSiO2). For CSiO2-modified fibers, the coagulation mitigator dimethylsulphoxide allows for controlling the surface topography and the amalgamation of the silica NPs into the fiber matrix. For dope-modified fibers, we hypothesize that cellulose chains act as seeds for directed silica NP self-assembly. This results for DSiO2 in discrete micron-sized rods, homogeneously distributed throughout the fiber and for glycidoxy-surface modified DSiO2@GLYEO in nano-sized surface aggregates and a cross-sectional core-shell fiber morphology. Furthermore, the dope-modified fibers display outstanding strength and toughness, which are both characteristic features of biological biocomposites

Formulation of polyphthalaldehyde microcapsules for immediate UV-light triggered release

Triggered release from responsive drug reservoirs activated by remote stimuli is desired in a range of fields. Critical bottlenecks are cost-efficient formulation avenues applicable for industrial scale-up, viable triggers and immediate release rather than continuous release upon activation. UV-sensitive microcapsules based on self-immolating polymers in combination with thin shells and morphological weak spots should allow for immediate triggered release. Polyphthalaldehyde-based microcapsules were prepared using several variations of the internal phase separation route. In addition, a fluorescence microscopy method was developed to study both the microcapsule morphology and the triggered release in-situ. The microcapsule formation was driven by the surface activity of the stabilizer, effectively lowering the high polymer-water interfacial tension, which is in sharp contrast to conventional encapsulation systems. Contrary to previous findings, a core–shell morphology was obtained via slow emulsion-to-suspension transformation. Rapid transformation captured intermediate inverted core–shell structures. The capsules were highly sensitive to both acid- and UV-mediated triggers, leading to an unzipping and rupturing of the shell that released the core content. Poly(methacrylic acid)-stabilized microcapsules displayed immediate UV-triggered release provided by their stimuli-sensitive blueberry morphology. Both capsules in aqueous and dry environment started to lose their core content after less than one minute of UV light exposure

Microcapsule functionalization enables rate-determining release from cellulose nonwovens for long-term performance

Functional textiles is a rapidly growing product segment in which sustained release of actives often plays a key role. Failure to sustain the release results in costs due to premature loss of functionality and resource inefficiency. Conventional application methods such as impregnation lead to an excessive and uncontrolled release, which - for biocidal actives - results in environmental pollution. In this study, microcapsules are presented as a means of extending the release from textile materials. The hydrophobic model substance pyrene is encapsulated in poly(d,l-lactide-co-glycolide) microcapsules which subsequently are loaded into cellulose nonwovens using a solution blowing technique. The release of encapsulated pyrene is compared to that of two conventional functionalization methods: surface and bulk impregnation. The apparent diffusion coefficient is 100 times lower for encapsulated pyrene compared to impregnated pyrene. This clearly demonstrates the rate-limiting barrier properties added by the microcapsules, extending the potential functionality from hours to weeks

Solution-Spinning of a Collection of Micro- and Nanocarrier-Functionalized Polysaccharide Fibers

Continuous polysaccharide fibers and nonwovens—based on cellulose, hydroxypropyl cellulose, chitosan, or alginate—containing biopolymeric microcapsules (MC) or mesoporous silica nanoparticles (MSN) are prepared using a wet-spinning or solution blowing technique. The MCs are homogeneously distributed in the fiber matrices whereas the MSNs form discrete micron-sized aggregates as demonstrated using scanning electron-, fluorescence-, and confocal microscopy. By encapsulating the model compound pyrene, it is shown that 95% of the substance remains in the fiber during the formation process as compared to only 7% for the nonencapsulated substance. The material comprising the MC has a strong impact on the release behavior of the encapsulated pyrene as investigated using methanol extraction. MCs based on poly(l-lactic acid) prove to be practically impermeable with no pyrene released in contrast to MCs based on poly(lactic-co-glycolic acid) which allow for diffusion of pyrene through the MC and fiber as visualized using fluorescence microscopy

The effect of surfactant chain length on the morphology of poly(methyl methacrylate) microcapsules for fragrance oil encapsulation

The solvent evaporation method for producing microcapsules relies upon the correct wetting conditions between the three phases involved in the synthesis to allow core-shell morphologies to form. By measuring the interfacial tensions between the oil, polymer and aqueous phases, spreading coefficients can be calculated, allowing the capsule morphology to be predicted. In this work we explore the effect of surfactant chain length on capsule morphology using poly(methyl methacrylate) as the polymer and hexadecane as the core. We compared the predicted morphologies obtained using the polymer as a solid, and the polymer dissolved in dichloromethane to represent the point at which capsule formation begins. We found that using the polymer in its final, solid form gave predictions which were more consistent with our observations. The method was applied to successfully predict the capsule morphologies obtained when commercial fragrance oils were encapsulated

HP1a Targets the Drosophila KDM4A Demethylase to a Subset of Heterochromatic Genes to Regulate H3K36me3 Levels

The KDM4 subfamily of JmjC domain-containing demethylases mediates demethylation of histone H3K36me3/me2 and H3K9me3/me2. Several studies have shown that human and yeast KDM4 proteins bind to specific gene promoters and regulate gene expression. However, the genome-wide distribution of KDM4 proteins and the mechanism of genomic-targeting remain elusive. We have previously identified Drosophila KDM4A (dKDM4A) as a histone H3K36me3 demethylase that directly interacts with HP1a. Here, we performed H3K36me3 ChIP-chip analysis in wild type and dkdm4a mutant embryos to identify genes regulated by dKDM4A demethylase activity in vivo. A subset of heterochromatic genes that show increased H3K36me3 levels in dkdm4a mutant embryos overlap with HP1a target genes. More importantly, binding to HP1a is required for dKDM4A-mediated H3K36me3 demethylation at a subset of heterochromatic genes. Collectively, these results show that HP1a functions to target the H3K36 demethylase dKDM4A to heterochromatic genes in Drosophila

Hydration of water- and alkali-activated white Portland cement pastes and blends with low-calcium pulverized fuel ash

Pastes of white Portland cement (wPc) and wPc-pulverized fuel ash (pfa) blends were studied up to 13 years. The reaction of wPc with water was initially retarded in the presence of pfa particles but accelerated at intermediate ages. Reaction with KOH solution was rapid with or without pfa. A universal compositional relationship exists for the C-A-S-H in blends of Pc with aluminosilicate-rich SCMs. The average length of aluminosilicate anions increased with age and increasing Al/Ca and Si/Ca; greater lengthening in the blends was due to additional Al3+ at bridging sites. The morphology of outer product C-A-S-H was always foil-like with KOH solution, regardless of chemical composition, but with water it had fibrillar morphology at high Ca/(Si+Al) ratios and foil-like morphology started to appear at Ca/(Si+Al) ≈1.2-1.3, which from the literature appears to coincide with changes in the pore solution. Foil-like morphology cannot be associated with entirely T-based structure

Modification of microcapsules for controlled release

Fouling of marine organisms such as algae and barnacles on the boat hull is an enormous problem for the shipping industry. The negative consequences for the society are both economical and environmental. To prevent fouling in general, biocides are typically incorporated directly into the paint. Premature leakage of the biocides is a drawback which reduces the lifetime of the coating and pollutes the surrounding ecosystems. Microencapsulation is an efficient way of encapsulating active substances for controlling the release and thereby prolonging the antifouling properties of the coating. The microcapsules used in this work consist of an oil core and a hydrophobic polymer shell. The rate of release into the marine environment may be further tailored by modifying the microcapsules. Triggered release is achieved by rendering the microcapsule shell water sensitive. This may be accomplished by incorporating salt into the shell using imidazole coordination chemistry. On the other hand, extended release is achieved by improving the barrier properties of the microcapsule. This may be realized by providing the microcapsule with an additional shell, such as a highly charged polyelectrolyte multilayer or a lipid bilayer. The objective of this thesis is subsequently twofold: 1) To synthesize and characterize imidazole containing shell materials with a view to obtain triggered release. 2) To surface modify microcapsules with polyelectrolyte multilayers and lipid bilayers toward extended release.Imidazole containing polymers were synthesized using vinyl and maleimide radical polymerization, as well as grafting techniques comprising maleimide bond formation and epoxide ring opening. The imidazole-containing polymeric materials, with and without the salts CuCl2 or ZnCl2, were characterized using differential scanning calorimetry, electron paramagnetic resonance (EPR) and vibrational spectroscopy. The coordination chemistry of the imidazole-metal ion complex was investigated using vibrational spectroscopy, EPR and ab initio calculations.The imidazole coordination to the transition metal ions Cu2+ and Zn2+ in polymeric materials generates cross-links. The interaction between the imidazole moiety and the transition metal ions is very strong and specific. As a consequence, the coordinating polymer is rendered insoluble in conventional solvents, excluding only strongly coordinating solvents.The specificity and strength of the imidazole-transition metal ion interaction may be used for a variety of applications. However, with respect to the microencapsulation route used in this project, the limited solubility of the coordinating polymer material is unfortunate. The use of strongly coordinating solvents during the microencapsulation results in aggregation and phase separation instead of microcapsule formation.Routes for synthesising highly charged microcapsules for further surface modification were investigated using three types of ionic dispersants; a weak polyacid, a small set of amphiphilic block copolymers and a hydrophobic anionic surfactant in combination with a polycation. The charged microcapsules were subsequently modified with polyelectrolyte multilayers using the Layer-by-Layer technique and with lipid bilayers using lipid vesicle spreading. The microcapsules and model systems thereof were characterized mainly using micro-electrophoresis, light microscopy, optical tensiometry and quartz crystal microbalance with dissipation (QCM-D). The release behaviour in aqueous suspension of a hydrophobic model compound was investigated using UV-Vis spectroscopy.The use of the ionic dispersants facilitated the formation of highly charged microcapsules and the subsequent polyelectrolyte multilayer assembly and lipid bilayer formation were also successful. In particular, the block copolymer based microcapsules displayed excellent properties with respect to high and stable surface charge, as well as long term colloidal stability through electrostatic and steric stabilization. The release of the hydrophobic model compound was considerably reduced after modification with polyelectrolyte multilayers. In addition, the type of dispersant had a significant impact on the release. The block copolymer based microcapsules with a higher charge density had a much lower release compared to the weak polyelectrolyte based microcapsules.The polyelectrolyte multilayer is an efficient barrier against hydrophobic molecules and the low permeability is clearly a result of the high charge density. As of yet, the effect of the lipid bilayers on the release has not been investigated but has a large potential since the permeability may be altered by the lipid composition. A microcapsule consisting of an oil core, a hydrophobic polymer shell, a polyelectrolyte multilayer and a lipid bilayer is a complex release system with large degrees of freedom for tailoring the release behaviour

Self-assembly of lipid domains in the extracellular leaflet of the plasma membrane and models thereof

Lipid domain formation and phase coexistence in biological membranes is a subject which has received considerable attention during the last two decades, especially the topic concerning so-called lipid rafts, a theory which has become as popular to confirm as to disproof. Regardless of the existence or precise composition and function of the classical rafts, the occurrence of lateral lipid segregation in biological membranes is indisputable. This review starts by focusing on state of the art findings concerning lipid domains and lateral heterogeneity in a biological context. Then, the physicochemical properties of lipid mixtures, phase properties and domain dynamics are considered. Canonical lipid models of the exofacial leaflet of the plasma membrane are treated in detail and the proper choices of model lipids are discussed. A special attention is given to polar lateral interactions (including carbohydrate-carbohydrate head group interactions), whose importance for spatial segregation and crystallization is commencing to be appreciated by the scientific community