Photolysis Triggered Sealing of Multilayer Capsules to Entrap Small Molecules

Novel microcapsule systems containing UV-responsive diazonium groups were fabricated as microcontainers for cargo substance encapsulation by using a layer-by-layer (LbL) assembly technique. Upon direct exposure to UV light with a wavelength of approximately 380 nm, the diazonium groups of diazoresion (DAR) rapidly reacted with sulfonate or diazo-sulfonate groups of counterpart polyelectrolytes, which converted electrostatic interactions to covalent bonds, demonstrating an effective in situ cross-linking within multilayers via photolysis. Such chemical transition eliminated the paired ionic groups, therefore generating more hydrophobic multilayer shells, offering a unique approach to seal the porous polyelectrolyte capsule shells. Fluorescent molecule rhodamine B (RhB) was consequently studied as a typical example for small molecule encapsulation. Results indicated that the dye was remarkably retained within the microcapsules after UV-triggered capsule shell sealing

UV-Cross-Linkable Multilayer Microcapsules Made of Weak Polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm². The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers

Local and Sustained Activity of Doxycycline Delivered with Layer-by-Layer Microcapsules

Achieving localized delivery of small molecule drugs has the potential to increase efficacy and reduce off target and side effects associated with systemic distribution. Herein, we explore the potential use of layer-by-layer (LbL) assembled microcapsules for the delivery of doxycycline. Absorbance of doxycycline onto core dextran sulfate of preassembled microcapsules provides an efficient method to load both synthetic and biodegradable microcapsules with the drug. Application of an outer layer lipid coat enhances the sustained in vitro release of doxycycline from both microcapsule types. To monitor doxycycline delivery in a biological system, C2C12 mouse myoblasts are engineered to express EGFP under the control of the optimized components of the tetracycline regulated gene expression system. Microcapsules are not toxic to these cells, and upon delivery to the cells, EGFP is more efficiently induced in those cells that contain engulfed microcapsules and monitored EGFP expression clearly demonstrates that synthetic microcapsules with a DPPC coat are the most efficient for sustain intracellular delivery. Doxycycline released from microcapsules also displayed sustained activity in an antimicrobial growth inhibition assay compared with doxycycline solution. This study reveals the potential for LbL microcapsules in small molecule drug delivery and their feasible use for achieving prolonged doxycycline activity

Toward Self-Assembly of Nanoparticles on Polymeric Microshells: Near-IR Release and Permeability

We present a novel approach to construct hollow polymeric microcontainers that can be remotely addressed using a low-power near-infrared laser to release encapsulated materials. Microshells possessing walls with aggregates of gold nanoparticles are found to release encapsulated materials upon near-IR irradiation, while shells containing the same amount of nonaggregated gold nanoparticles did not release their contents. The permeability of thermally shrunk microcapsules to dextran molecules is the lowest for shells containing nonaggregated nanoparticles and the highest for microcapsules with no nanoparticles. The wall thickness, roughness, influence of concentration of encapsulated materials, and general shrinking behavior of the microcapsules are studied. Aggregation of nanoparticles increases the absorption coefficient in the near-infrared part of electromagnetic spectrum. The temperature increase upon near-infrared laser illumination for different gold nanoparticle distributions is simulated. Important implications of this approach are expected in development of drug delivery systems as well as in temperature- and light-sensitive materials and membranes

Overgrowth of Gold Nanorods by Using a Binary Surfactant Mixture

Seed-mediated surfactant-assisted growth is widely used as the most effective method for gold nanorod (NR) synthesis. Using prepared nanorods as seeds for further overgrowth can increase the dimensional tunability of the final particles. However, overgrowth in usual cetyltrimethylammonium bromide (CTAB) surfactant solutions leads to poor control of the final particle shape and size. In this work, we report an improved strategy to demonstrate the controllable overgrowth of gold NRs in the binary surfactant mixture sodium oleate (NaOL) + CTAB. This approach overcomes the difficulty of growing NR suspensions with small amounts of impurities. By controlling the total amount of added NR seeds, it is possible to tune the average length, diameter, and plasmon resonances of overgrown particles in a wide range. Together with the original NaOL + CTAB method developed by Murray and co-workers (Nano Lett. 2013, 13, 555), this overgrowth approach expands the dimensional and plasmonic tunability of the fabrication technology without any decrease in the monodispersity and purity of samples

Drug-Eluting Sandwich Hydrogel Lenses Based on Microchamber Film Drug Encapsulation

Corticosteroids are widely used as an anti-inflammatory treatment for eye inflammation, but the current methods used in clinical practice for delivery are in the form of eye drops which is usually complicated for patients or ineffective. This results in an increase in the risk of detrimental side effects. In this study, we demonstrated proof-of-concept research for the development of a contact lens-based delivery system. The sandwich hydrogel contact lens consists of a polymer microchamber film made via soft lithography with an encapsulated corticosteroid, in this case, dexamethasone, located inside the contact lens. The developed delivery system showed sustained and controlled release of the drug. The central visual part of the lenses was cleared from the polylactic acid microchamber in order to maintain a clean central aperture similar to the cosmetic-colored hydrogel contact lenses

Peculiarities of Polyelectrolyte Multilayer Assembly on Patterned Surfaces

The layer-by-layer assembly of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) is studied on templates with imprinted arrays of microwells ranging from 2 to 25 μm and different aspect ratios. The thickness and microstructure of polyelectrolyte multilayers (PEMs) are measured using scanning electron microscopy. At 0.2 M ionic strength, the PEM film evenly coats the template both inside and outside the microwells. If the film is thinner than the critical value of about 400 nm, PEM microstructures collapse upon dissolving the template. Euler’s model of critical stress is used to describe the collapse. At 2 M ionic strength, a substantially thinner PEM film is assembled inside the 25 μm wells than outside. If the well diameter is reduced to 7 and 2 μm, a much thicker PEM film is formed inside the microwells. These observations have been attributed to the changing of polyelectrolyte conformation in the solutions

Adhesion of Polyelectrolyte Multilayers: Sealing and Transfer of Microchamber Arrays

Polyelectrolyte multilayer (PEM) films with array of responsive microchambers are promising candidates for site-specific release of chemicals in small and precisely defined quantities on demand. It requires effective sealing of the microchambers toward a support to prevent leakage of a cargo. In this paper, we study the pressure-induced adhesion of poly­(allylammonium)-poly­(4-styrenesulfonate) (PAH-PSS) multilayers assembled on different templates toward the poly­(4-styrenesulfonate)-poly­(diallyldimethylammonium) multilayer. The tensile bond strength increases from 0.4 to 3.5 MPa upon the increase of PAH-PSS bilayers from 10 to 40, if assembled on a silicon template. Weaker tensile bond strength of 0.35 MPa between the PAH-PSS multilayer and a poly­(methylmethacrylate) (PMMA) template results in adhesive break at this interface and allows mechanical removal of the template. The successful PEM transfer is demonstrated for templates of various geometrical patterns, while the tensile break of a multilayer film happens for the others

Layer-by-Layer Assembled Multilayer Shells for Encapsulation and Release of Fragrance

Layer-by-layer assembled shells are prospective candidates for encapsulation, stabilization, storage, and release of fragrances. A shell comprising four alternative layers of a protein and a polyphenol is employed to encapsulate the dispersed phase of a fragrance-containing oil-in-water emulsion. The model fragrance used in this work consists of 10 ingredients, covering a range of typically employed aroma molecules, all premixed in equal mass and with sunflower oil acting as the base. The encapsulated emulsion is stable after 2 months of storage at 4 °C as revealed by static light scattering and confocal laser scanning microscopy. Gas chromatography/mass spectrometry data show that the encapsulation efficiency of 8 out of 10 fragrance ingredients depends on the water solubility: the less water-soluble an ingredient, the more of it is encapsulated. The amount of these fragrance ingredients remaining encapsulated decreases linearly upon emulsion incubation at 40 °C and the multilayer shell does not hinder their release. The other two fragrance ingredients having the lowest saturation vapor pressure demonstrate sustained release over 5 days of incubation at 40 °C. The composition of released fragrance remains almost constant over 3 days of incubation, upon further incubation it becomes enriched with these two ingredients when others start to be depleted