Maxim V. Kiryukhin

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.

Multilayer Capsules of Bovine Serum Albumin and Tannic Acid for Controlled Release by Enzymatic Degradation

With the purpose to replace expensive and significantly cytotoxic positively charged polypeptides in biodegradable capsules formed via Layer-by-Layer (LbL) assembly, multilayers of bovine serum albumin (BSA) and tannic acid (TA) are obtained and employed for encapsulation and release of model drugs with different solubility in water: hydrophilic-tetramethylrhodamine-isothiocyanate-labeled BSA (TRITC-BSA) and hydrophobic 3,4,9,10-tetra-(hectoxy-carbonyl)-perylene (THCP). Hydrogen bonding is proposed to be predominant within thus formed BSA/TA films. The TRITC-BSA-loaded capsules comprising 6 bilayers of the protein and polyphenol are benchmarked against the shells composed of dextran sulfate (DS) and poly-l-arginine (PARG) on degradability by two proteolytic enzymes with different cleavage site specificity (i.e., α-chymotrypsin and trypsin) and toxicity for murine RAW264.7 macrophage cells. Capsules of both types possess low cytotoxicity taken at concentrations equal or below 50 capsules per cell, and evident susceptibility to α-chymotrypsin resulted in release of TRITC-BSA. While the BSA/TA-based capsules clearly display resistance to treatment with trypsin, the assemblies of DS/PARG extensively degrade. Successful encapsulation of THCP in the TRITC-BSA/TA/BSA multilayer is confirmed, and the release of the model drug is observed in response to treatment with α-chymotrypsin. The thickness, surface morphology, and enzyme-catalyzed degradation process of the BSA/TA-based films are investigated on a planar multilayer comprising 40 bilayers of the protein and polyphenol deposited on a silicon wafer. The developed BSA/TA-based capsules with a protease-specific degradation mechanism are proposed to find applications in personal care, pharmacology, and the development of drug delivery systems including those intravenous injectable and having site-specific release capability.

Individually Addressable Patterned Multilayer Microchambers for Site-Specific Release-On-Demand

Patterned arrays of light-responsive microchambers are suggested as candidates for site-specific release of chemicals in small and precisely defined quantities on demand. A composite film is made of poly(allylammonium)-poly(styrene sulfonate) multilayers and gold nanoparticles incorporated between subsequent stacks of polyelectrolytes. The film shaped as microchambers is loaded with colloid particles or oil-soluble molecules. The microchambers are sealed onto a glass slide precoated with an adhesive poly(diallyldimethylammonium)-poly(styrene sulfonate) multilayer film. A focused laser beam is used for remote addressing the individual microchambers and site-specific release of the loaded cargo.

Fabrication and mechanical properties of microchambers made of polyelectrolyte multilayers

A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using the layer-by-layer assembly of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on sacrificial templates with imprinted patterns of wells. Polyelectrolyte multilayer (PEM) chambers collapse if made of shells that are thinner than a critical value. This critical thickness of the shells is measured experimentally and is found to depend on the chambers geometry. Eulers model of critical stress is used to describe the collapse of the chambers. Adhesive contact of the chamber’s roof with the support is suggested as a major mechanism responsible for the collapse. Deformation of individual PEM chambers made of thicker shells is studied using a sharp indenter and varying the loading speed. At loading speeds of less than 0.33 mN s−1, the elastic theory describes the experimental data well for small deformations, yielding a Youngs modulus of 4 ± 1 GPa for the PEM shell, while further deformation causes severe plastic buckling of the chamber. If the loading speed exceeds 0.33 mN s−1, the sharp indenter starts to pierce the chambers roof and the size of the resulted hole can be precisely controlled by changing the penetration depth of the indenter. Filling the PEM chambers with oil micro-droplets by solvent-exchange method is also demonstrated.

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.

Micropackaging via layer-by-layer assembly: microcapsules and microchamber arrays

Abstract The micropackaging of chemical compounds in a small and precisely defined quantity, which can be encased, stored, is essential for response to a specific chemical, biological or physical trigger in a controllable manner is one of the premier challenges in the development of delivery systems. In this review, the authors discuss the application of layer-by-layer (LbL) assemblies of macromolecules for micropackaging and controlled release of various types of cargo. The LbL assembly method provides unique opportunities by incorporation of different functional and responsive layer constituents tailored into one entity. Micron and submicron sized capsules made on colloidal templates are used for biomolecule encapsulation and enable time- and site-specific release when triggered by pH, temperature, specific enzymes, mechanic load, light, ultrasound, or magnetic field. In comparison to individual capsules, the authors discuss the recently introduced micropackaging approach involving cargo loading into arrays of microchambers, made by a combination of imprinting technology and LbL assembly. In conclusion, the authors summarise advantages and fabrication obstacles for micropackaging in capsules and microchambers and discuss already existing as well as potential future applications.

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. Eulers 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.

Patterned microcontainers as novel functional elements for µTAS and LOC

Using nanoimprint lithography, arrays of highly ordered patterns of polyelectrolyte multilayer microcapsules consisting of alternating layers of poly(allylamine hydrochloride) and poly(sodium 4-styrene sulfonate) have been achieved. Anchoring the capsules on a pre-patterned substrate facilitates the utilization of their various capabilities in lab-on-a chip devices. In this paper we have demonstrated a very effective method to entrap soft capsules into surface cavities. Supported microcapsules were applied as the depots for loading and storage of macromolecular cargo (glucose oxidase and peroxidase) and as preserved microvessels for the cascade of enzymatic reactions. The loading of capsules was achieved under a pre-determined pH environment. This development is potentially useful for the realization of novel multianalytical systems for catalytic, bio-affinity and pH detection with protected sensing molecules.

Patterned Microstructure Fabrication: Polyelectrolyte Complexes vs Polyelectrolyte Multilayers

Polyelectrolyte complexes (PEC) are formed by mixing the solutions of oppositely charged polyelectrolytes, which were hitherto deemed “impossible” to process, since they are infusible and brittle when dry. Here, we describe the process of fabricating free-standing micro-patterned PEC films containing array of hollow or filled microchambers by one-step casting with small applied pressure and a PDMS mould. These structures are compared with polyelectrolyte multilayers (PEM) thin films having array of hollow microchambers produced from a layer-by-layer self-assembly of the same polyelectrolytes on the same PDMS moulds. PEM microchambers “cap” and “wall” thickness depend on the number of PEM bilayers, while the “cap” and “wall” of the PEC microchambers can be tuned by varying the applied pressure and the type of patterned mould. The proposed PEC production process omits layering approaches currently employed for PEMs, reducing the production time from ~2 days down to 2 hours. The error-free structured PEC area was found to be significantly larger compared to the currently-employed microcontact printing for PEMs. The sensitivity of PEC chambers towards aqueous environments was found to be higher compared to those composed of PEM.

Active drug release systems: current status, applications and perspectives.

Active drug release systems offer an important privilege to manage the dosage, time and sometimes site of drug release after the implantation procedure has been performed. Once developed, they could cover such applications as hormone therapy, implantation surgery, and delivery of immunization boosters. A number of existing approaches towards such systems include arrays of microreservoirs equipped with stimuli-responsive actuators or valves. The very first developed system has reached the stage of in-human trials recently. A breakthrough could happen if microreservoirs themselves are made of responsive material susceptible towards remote triggers. A promising candidate is a material made of Layer-by-Layer assembled films which currently are widely exploited only as passive implantable drug release systems.