Gleb B. Sukhorukov

Novel Hollow Polymer Shells by Colloid-Templated Assembly of Polyelectrolytes

Exact control of the film thickness of polyelectrolyte shells (a transmission electron microscopy image is shown) is achieved by colloid-templated consecutive adsorption of polyanions and polycations followed by decomposition of the templating core. Possible areas of application for these shells range from the pharmaceutical, food, cosmetic, and paint industries to catalysis and microcrystallization.

Layer-by-layer self assembly of polyelectrolytes on colloidal particles.

Abstract Polyelectrolytes have been consecutively adsorbed onto charged polystyrene latex particles, forming stable ultrathin multilayer films. Film growth has been followed by electrophoresis, dynamic light scattering, single particle light scattering and fluorescence intensity measurements. Desorption of bound polyelectrolytes has been followed by HPLC. A low percentage of particle aggregates were found if a centrifugation-based technique was applied, whereas a larger number of particle aggregates were observed if polyelectrolytes were consecutively added at saturating concentrations and if centrifugation was avoided. Single particle light scattering allowed for adsorption layer thickness determination. If a layer refractive index of 1.47 was assumed the thickness of a poly(allylamine hydrochloride)/poly(styrene sulfonate) layer pair formed in 0.5 M NaCl was found to be 2–3 nm.

Stepwise polyelectrolyte assembly on particle surfaces: a novel approach to colloid design

Polyelectrolyte multilayers were deposited onto polystyrene and melamine formaldehyde latex particles by means of consecutive adsorption. Two different methods of multilayer growth were employed. First, adsorption of polyelectrolytes at a concentration exceeding saturation amounts was combined with the removal of the nonbound polyelectrolyte by means of centrifugation. Second, adsorption of polyelectrolyte was performed at a concentration just sufficient for saturation coverage. Both methods yielded continuous layer growth. The process of film formation was followed by electrophoresis, dynamic light scattering, single particle light scattering and fluorescence intensity measurements. Layer deposition onto partially crosslinked melamine resin latex particles, which were soluble at pH values of less than 1.6, resulted in the production of three-dimensional thin polyelectrolyte shells upon dissolving the core. The ultrathin shells were observed by means of scanning and transmission electron microscopy.

Release mechanisms for polyelectrolyte capsules

Polyelectrolyte capsules have recently been introduced as new microscopic vehicles which could have high potential in the biomedical field. In this critical review we give an introduction to the layer-by-layer (LbL) technique which is used to fabricate these polyelectrolyte capsules as well as to the different triggers that have been exploited to obtain drug release from these capsules. Furthermore, other types of triggered delivery systems are compared and critically discussed with regard to their clinical relevance. (171 references.).

pH‐Controlled Macromolecule Encapsulation in and Release from Polyelectrolyte Multilayer Nanocapsules

pH-Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8.

Porous calcium carbonate microparticles as templates for encapsulation of bioactive compounds

The paper describes the preparation and characterisation of porous calcium carbonate microparticles with an average size of 5 µm and their use for encapsulation of biomacromolecules. The average pore size of about 30–50 nm enables size selective and time-dependent permeation of different macromolecules. Layer-by-layer adsorption of polyelectrolytes into these particles followed by core dissolution leads to formation of interconnecting networks (matrix-like structure) made of polyelectrolyte complexes. The structure can be used for accumulation of bio-macromolecules, mainly proteins. Besides the inter-polyelectrolyte structure templated on porous CaCO3 microparticles the microgel particles (“ghost”) can also be made inside by complexing alginate and calcium. The adsorption of biomacromolecules inside the porous calcium carbonate particles is presumably regulated by electrostatic interactions on the microparticle surface within pores and protein–protein interactions. Protein adsorption into CaCO3 microparticle voids together with layer-by-layer assembly of biopolymers provide a way for fabrication of completely biocompatible microcapsules envisaging their use as biomaterials.

Protein-calcium carbonate coprecipitation: A tool for protein encapsulation

A new approach of encapsulation of proteins in polyelectrolyte microcapsules has been developed using porous calcium carbonate microparticles as microsupports for layer‐by‐layer (LbL) polyelectrolyte assembling. Two different ways were used to prepare protein‐loaded CaCO3 microparticles: (i) physical adsorption – adsorption of proteins from the solutions onto preformed CaCO3 microparticles, and (ii) coprecipitation – protein capture by CaCO3 microparticles in the process of growth from the mixture of aqueous solutions of CaCl2 and Na2CO3. The latter was found to be about five times more effective than the former (∼100 vs ∼20 μg of captured protein per 1 mg of CaCO3). The procedure is rather mild; the revealed enzymatic activity of α‐chymotrypsin captured initially by CaCO3 particles during their growth and then recovered after particle dissolution in EDTA was found to be about 85% compared to the native enzyme. Core decomposition and removal after assembly of the required number of polyelectrolyte layers resulted in release of protein into the interior of polyelectrolyte microcapsules (PAH/PSS)5 thus excluding the encapsulated material from direct contact with the surrounding. The advantage of the suggested approach is the possibility to control easily the concentration of protein inside the microcapsules and to minimize the protein immobilization within the capsule walls. Moreover, it is rather universal and may be used for encapsulation of a wide range of macromolecular compounds and bioactive species.

Polyelectrolyte multilayer capsule permeability control

Abstract The permeability properties of hollow polyelectrolyte multilayer capsules for different substances were investigated as a function of pH and salt concentration. Capsules were prepared by layer-by-layer (LBL) adsorption of oppositely charged polyelectrolytes onto the surface of melamine formaldehyde and CdCO3 particles followed by core removal. It was shown that the capsules are closed at a pH value of 8 and higher, but at a pH lower than 6 the macromolecules permeate into the capsule interior. For low molecular weight molecules capsules, templated on CdCO3 cores were found to be less permeable than MF-derived capsules. The open and closed states of the capsule wall are reversible. It provides thus an opportunity to encapsulate different materials into polyelectrolyte capsules.

Polyelectrolyte microcapsules for biomedical applications

In this paper we review the recent contributions of polyelectrolyte microcapsules in the biomedical field, comprising in vitro and in vivodrug delivery as well as their applications as biosensors.

Polymer microcapsules as mobile local pH-sensors

Polyelectrolyte microcapsules have been loaded with a pH-sensitive, high molecular weight SNARF-1-dextran conjugate. SNARF-1 exhibits a significant pH-dependent emission shift from green to red fluorescence under acidic and basic conditions, respectively. The unique spectral properties of the dye were maintained after the encapsulation. By investigating both human breast cancer cells and fibroblasts, we were able to follow the pH change of the local environment of SNARF-1-filled capsules during the transition from the alkaline cell medium to the acidic endosomal/lysosomal compartments. The incorporation of magnetite nanoparticles and an additional pH-insensitive fluorophore within the capsule shell resulted in a novel type of sensor system based on multifunctional polymer capsules.