Macromolecule encapsulation in diazoresin-based hollow polyelectrolyte microcapsules

A stable enzyme encapsulation technique based on the conversion of weak interactions between diazo resin/poly(styrene sulfonate) to covalent bonds was explored. Photosensitive diazoresin-based polyelectrolyte microcapsules were prepared via layer-by-layer electrostatic self-assembly of poly(styrene sulfonate) and diazoresin on MnCO(3) templates. UV-vis and zeta-potential measurements confirmed the alternate deposition of {PSS/DAR} multilayers on the micrometer-sized dissolvable templates. The DAR-based microcapsules were demonstrated to be permeable to enzymes prior to UV irradiation, while the permeability of the multilayer wall was changed substantially after photo-cross-linking. Encapsulated molecules were stably entrapped after UV irradiation, as shown by confocal microscopy and atomic force microscopy images. Activity assays revealed that encapsulated glucose oxidase possessed 52.8% of the catalytic activity exhibited by the same amount of free enzyme, proving the preservation of native conformation and accessibility of substrate. This encapsulation technique is promising for many biomedical and biotechnological applications, particularly enzyme biosensors, which require stable immobilization of functional components while allowing sufficient transport rates for substrate molecules.     

High-capacity functional protein encapsulation in nanoengineered polypeptide microcapsules

Addition of polyethylene glycol to aqueous assembly solutions of oppositely charged polypeptides enables high-capacity "loading" of functional protein in biocompatible microcapsules by template-supported layer-by-layer nanoassembly.     

Structural alteration of hybrid supramolecular capsule induced by guest encapsulation

Heterofunctionalized C(2v) symmetrical cavitand 1 with 4-pyridylethynyl and 3-carbamoylphenyl groups in alternating arrangement was designed and synthesized. A 1:1 mixture of the cavitand 1 and a cis-coordinated palladium(II) or platinum(II) complex self-assembled into a hybrid supramolecular capsule via both metal-ligand coordination bonds and hydrogen bonds. Formation of the capsular assembly was confirmed by NMR spectroscopy and mass spectrometry. The hybrid capsule encapsulated the appropriate guest, the molecular sizes of which fit the size of the capsular cavity. Structural alteration of the hybrid capsule was induced by the guest encapsulation. A C(2h) structure for the encapsulation complex was assigned by 2D NMR spectra analysis. Thermodynamic and kinetic properties of the guest encapsulation were investigated. The kinetics of in/out guest exchange was strongly influenced by hydrogen bonding in the hybrid capsule.     

Composite block copolymer stabilized nanoparticles: simultaneous encapsulation of organic actives and inorganic nanostructures

We describe the preparation and characterization of hybrid block copolymer nanoparticles (NPs) for use as multimodal carriers for drugs and imaging agents. Stable, water-soluble, biocompatible poly(ethylene glycol)-block-poly(epsilon-caprolactone) NPs simultaneously co-encapsulating hydrophobic organic actives (beta-carotene) and inorganic imaging nanostructures (Au) are prepared using the flash nanoprecipitation process in a multi-inlet vortex mixer. These composite nanoparticles (CNPs) are produced with tunable sizes between 75 nm and 275 nm, narrow particle size distributions, high encapsulation efficiencies, specified component compositions, and long-term stability. The process is tunable and flexible because it relies on the control of mixing and aggregation timescales. It is anticipated that the technique can be applied to a variety of hydrophobic active compounds, fluorescent dyes, and inorganic nanostructures, yielding CNPs for combined therapy and multimodal imaging applications.     

Hollow microcapsules built by layer by layer assembly for the encapsulation and sustained release of curcumin

Hollow microcapsules fabricated by layer-by-layer assembly (LbL) using oppositely charged polyelectrolytes have figured in studies towards the design of novel drug delivery systems. The possibility of loading a fair amount of active component of poor aqueous solubility is one of the encouraging factors on the wide spread interest of this emerging technology. Curcumin has potent anti-cancer properties. Clinical application of this efficacious agent in cancer and other diseases has been limited due to poor aqueous solubility and consequently minimal systemic bioavailability. LbL constructed polyelectrolyte microcapsules based drug delivery systems have the potential for dispersing hydrophobic agent like curcumin in aqueous media. Here we report the preparation of LbL assembled microcapsules composed of poly(sodium 4-styrene sulfonic acid) and poly(ethylene imine) one after another. The microcapsules were characterized using various analytical techniques. Curcumin was encapsulated in these microcapsules and the efficacy of the released curcumin was studied using L929 cells.     

Deposition of continuous platinum shells on gold nanoparticles by chemical precipitation

Continuous platinum shells consisting of ~5 atomic layers were deposited onto preformed gold seeds in aqueous medium by reducing hexachloroplatinic acid with ascorbic acid. By controlling the reduction kinetics of Pt(IV) species and the properties of the substrate, it was possible to ensure a slow and controlled deposition of platinum atoms onto the gold cores. Electrochemical evaluations revealed the presence of a compact platinum shell. The mass specific oxygen reduction activity of platinum in the AuPt core-shell nanoparticles was found to be four times higher than that of platinum black and comparable to that of polycrystalline bulk metal.     

Guest encapsulation and self-assembly of a cavitand-based coordination capsule

The synthesis and spectroscopic characterization of a cavitand-based coordination capsule 14 BF4 of nanometer dimensions is described. Encapsulation studies of large aromatic guests as well as aliphatic guests were performed by using 1H NMR spectroscopy in [D1]chloroform. In addition to the computational analysis of the shape and geometry of the capsule, an experimental approach to estimate the interior size of the cavity is discussed. The cavity provides a highly rigid binding space in which molecules with lengths of approximately 14 A can be selectively accommodated. The rigid cavity distinguished slight structural differences in the flexible alkyl-chain guests as well as the rigid aromatic guests. The detailed thermodynamic studies revealed that not only CH-pi interactions between the methyl groups on the guest termini and the aromatic cavity walls, but also desolvation of the inner cavity play a key role in the guest encapsulation. The cavity preferentially selected the hydrogen-bonded heterodimers of a mixture of two or three carboxylic acids 18-20. The chiral capsule encapsulated a chiral guest to show diastereoselection.     

Guest encapsulation in a water-soluble molecular capsule based on ionic interactions

We report on the synthesis and characterization of a water-soluble molecular capsule based on multiple ionic interactions. The assembly has been studied by means of 1H NMR, ESI-MS spectroscopy, and isothermal titration calorimetry (ITC), showing an association constant in water, Ka, of 3.3 x 104 M-1. The achieved water solubility of the system opens the possibility of using this supramolecular assembly for molecular recognition in pure water. Encapsulation studies have been performed and are reported in this Communication.     

Cytocompatible encapsulation of individual Chlorella cells within titanium dioxide shells by a designed catalytic peptide

The individual encapsulation of living cells has a great impact on the areas of single cell-based sensors and devices as well as fundamental studies in single cell-based biology. In this work, living Chlorella cells were encapsulated individually with abiological, functionalizable TiO(2), by a designed catalytic peptide that was inspired by biosilicification of diatoms in nature. The bioinspired cytocompatible reaction conditions allowed the encapsulated Chlorella cells to maintain their viability and original shapes. After formation of the TiO(2) shells, the shells were postfunctionalized by using catechol chemistry. Our work suggests a bioinspired approach to the interfacing of individual living cells with abiological materials in a controlled manner.     

Nanoassembly of biocompatible microcapsules for urease encapsulation and their use as biomimetic reactors

Biocompatible polypeptide capsules with high enzyme loading and activity prepared by templating mesoporous silica spheres were used as biomimetic reactors for performing CaCO3 synthesis exclusively inside the capsule interior via urease-catalyzed urea hydrolysis.     

Sulfate encapsulation in a metal-assisted capsule based on a mono-pyridylurea ligand

A sulfate-encapsulating complex, [Cu(1)L(6)]·3[Cu(2)L(2)(DMF)(4)](SO(4))(4) (1, L = N-(1-naphthyl)-N'-(3-pyridyl)urea) is synthesized in which two C(3)-clefts of the octahedral complexes interdigitate to form a cavity to encapsulate the sulfate ion by six urea groups.     

Enhanced loading of water-soluble actives into bicontinuous cubic phase liquid crystals using cationic surfactants

Over the past few years, bicontinuous cubic phase liquid crystals have been investigated for their applicability to controlled delivery of active ingredients. These liquid crystals have a unique structure of interpenetrating channels of water and lipid that provides compatibility with water-soluble, lipid-soluble, and amphiphilic active ingredients. Actives tend to be stable in the matrix and the structure provides control over their release. However, loading of water-soluble actives is difficult. It is especially problematic for cubic phase liquid crystal dispersions (cubosomes) given the large fraction of bulk water present. The inherent problem reflects the preference of the water-soluble actives to associate with water rather than with the liquid crystals. Ideally, the properties of the liquid crystal can be tailored to enhance the association of the liquid crystal with the active, thereby increasing loading. It is found that the inclusion of surfactant into the liquid crystal can provide this function. This work illustrates the enhanced loading of negatively charged, water-soluble active ketoprofen by the inclusion of positively charged surfactants into the liquid crystal. Loading differences resulting from the inclusion of dioctadecyl dimethyl ammonium chloride (DODMAC) and dioctadecyl ammonium chloride (DOAC) into the liquid crystal demonstrate that the magnitude of the enhancement is dependent on the surfactant concentration and the steric nature of its head group. The upper limit of the enhancement is explored by the inclusion of di(canola ethyl ester) dimethyl ammonium chloride (DEEDAC) formulated to greater than 20 wt% and demonstrates an order-of-magnitude enhancement over previous reports. This work provides a practical demonstration of functionalizing cubic phase liquid crystals and lays the framework for future work.     

Oil core-polymer shell microcapsules prepared by internal phase separation from emulsion droplets. I. Characterization and release rates for microcapsules with polystyrene shells

Microcapsules with an oil core surrounded by a polymeric shell have been prepared by the controlled phase separation of polymer dissolved within the oil droplets of an oil-in-water emulsion. The dispersed oil phase consists of the shell polymer (polystyrene), a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (typically hexadecane). Removal of the good solvent results in phase separation of the polymer within the oil droplets. If the three interfacial tensions between the core oil, the shell-forming polymer, and the continuous phase are of the required relative magnitudes, a polymer shell forms surrounding the poor solvent. A UV-responsive organic molecule was added to the oil phase, prior to emulsification, to investigate the release of a model active ingredient from the microcapsules. This molecule should be soluble in the organic core but also have some water solubility to provide a driving force for release into the continuous aqueous phase. As the release rate of the active ingredient is a function of the thickness of the polymeric shell, for controlled release applications, it is necessary to control this parameter. For the preparative method described here, the thickness of the shell formed is directly related to the mass of polymer dissolved in the oil phase. The rate of volatile solvent removal influences the porosity of the polymer shell. Rapid evaporation leads to cracks in the shell and a relatively fast release rate of the active ingredient. If a more gentle evaporation method is employed, the porosity of the polymer shell is decreased, resulting in a reduction in release rate. Cross-linking the polymer shell after capsule formation was also found to decrease both the release rate and the yield of the active ingredient. The nature of the oil core also affected the release yield.     

Using a liquid emulsion membrane system for the encapsulation of organic and inorganic substrates within inorganic microcapsules

We report the development of a novel technique for the encapsulation of molecular and condensed organic and inorganic substrates within hollow calcium carbonate microspheres; the process utilises precipitation at the oil-water interface of a pseudovesicular water-in-oil-in-water emulsion liquid membrane (ELM) system in order to create an inorganic shell around the pre-dispersed media.     

Synthesis of spherical microcapsules by photopolymerization in aerosols

 The preparation of polymer microcapsules of well defined size in the range of 10–50 μm with different shell thickness to core diameter ratios is described. An aerosol of monodisperse droplets of a homogeneous ternary liquid system which contained a hydrophobic component and a hydrophilic component dissolved in a high-volatile mutual solvent, was produced by dispersing with a vibrating-orifice aerosol generator. After the evaporation of the solvent in a nitrogen atmosphere the particles demix and form a two-phase droplet of core-shell type. These droplets were illuminated with UV light and polymerized to highly monodisperse microcapsules with a solid polymer shell and a liquid core. The properties of the resulting particles (size, size distribution, shell thickness, shape and surface characteristics) were investigated by scanning electron microscopy, Raman spectroscopy on single optically levitated particles, and confocal Raman micro spectroscopy. The microcapsules were highly monodisperse and have spherical shape. Received: 24 July 1996 Accepted: 29 August 1996     

The effect of pulsed laser radiation on polyelectrolyte capsule shells modified with fluorescent dyes

Polyelectrolyte capsules containing rhodamine 6G and fluorescein isothiocyanate in their shells are obtained by successive adsorption on spherical microscopic CaCO₃ particles followed by the dissolution of the latter. Suspensions of the capsules are irradiated with a laser operating at a wavelength corresponding to the absorption bands of the dyes, and it is shown that shell modification with the selected dyes promotes photosensitized disruption of these structures. The mechanism proposed for this disruption is realized via energy transfer from photoexcited dye molecules to the polymer matrix. Therewith, the dye-modified capsules are disrupted due to their nonuniform local heating.     

Fabrication,characterization and evaluation of bacterial cellulose-based capsule shells for oral drug delivery

Bacterial cellulose (BC) was investigated for the first time for the preparation of capsule shells for immediate and sustained release of drugs. The prepared capsule shells were characterized using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The BC capsule shells were studied for drug release using an USP type-I dissolution apparatus. Irrespective of the drying method and the thickness of the BC sheet, the capsule shells displayed an immediate drug release profile. Moreover, the addition of release-retardant cellulosic polymers sustained the drug release having first-order kinetics for hydroxypropylmethylcellulose and carboxymethyl cellulose sodium with R ² values of 0.9995 and 0.9954, respectively. Furthermore, these capsules shells remained buoyant in 0.1 N HCl (pH 1.2) solution up to 12 h. This study showed that BC is a promising alternative to gelatin capsules with both immediate and sustained drug release properties depending upon the compositions of the encapsulated materials.     

Fragrance encapsulation in polymeric matrices by emulsion electrospinning

We present the successful application of emulsion electrospinning for the encapsulation of a model for highly volatile fragrances, namely (R)-(+)-limonene in a poly(vinyl alcohol) (PVA) fibrous matrix. The influence of the emulsion formulation and of its colloidal properties on the fiber morphology, as well as on the limonene encapsulation efficiency, is described. The release profile of the fragrance from the electrospun nanofibers over a fifteen days range shows that this type of nanofibrous matrices with a high fragrance loading capacity is of great potential for applications in various fields, such as cosmetics or food packaging.     

ITC and NMR analysis of the encapsulation of fatty acids within a water-soluble cavitand and its dimeric capsule

We report here NMR and Isothermal Titration Calorimetry studies of the binding of ionisable guests (carboxylate acids) to a deep-cavity cavitand. These studies reveal that the shortest guests favoured 1:1 complex formation, but the longer the alkyl chain the more the 2:1 host-guest capsule is favoured. For intermediate-sized guests, the equilibrium between these two states is controlled by pH; at low values the capsule containing the carboxylic acid guest is favoured, whereas as the pH is raised deprotonation of the guest favours the 1:1 complex. Interestingly, for one host–guest pair the energy required to decap the 2:1 capsular complex and form the 1:1 complex is sufficient to shift the pK_a of the guest by ~3–4 orders of magnitude (4.1–5.4 kcal mol^?1). The two largest guests examined form stable 2:1 capsules, with in both cases the guest adopting a relatively high energy J-shaped motif. Furthermore, these 2:1 complexes are sufficiently stable that at high pH guest deprotonation occurs without decapping of the capsule.     

Isotopomer encapsulation in a cylindrical molecular capsule: a probe for understanding noncovalent isotope effects on a molecular level

Isotope effects for the encapsulation of deuterated versus nondeuterated guests are determined. This system involves the use of social isomers, and the origin of the isotope effect is localized to methyl groups interacting with aromatic rings.