Matthieu F. Bédard

Polymeric microcapsules with light responsive properties for encapsulation and release.

This review is dedicated to recent developments on the topic of light sensitive polymer-based microcapsules. The microcapsules discussed are constructed using the layer-by-layer self-assembly method, which consists in absorbing oppositely charged polyelectrolytes onto charged sacrificial particles. Microcapsules display a broad spectrum of qualities over other existing microdelivery systems such as high stability, longevity, versatile construction and a variety of methods to encapsulate and release substances. Release and encapsulation of materials by light is a particularly interesting topic. Microcapsules can be made sensitive to light by incorporation of light sensitive polymers, functional dyes and metal nanoparticles. Optically active substances can be inserted into the shell during their assembly as a polymer complex or following the shell preparation. Ultraviolet-addressable microcapsules were shown to allow for remote encapsulation and release of materials. Visible- and infrared- addressable microcapsules offer a large array of release strategies for capsules, from destructive to highly sensitive reversible approaches. Besides the Introduction and Conclusions, this review contains in four sections reviewing the effects of light 1) on polymer-based microcapsules, 2) microcapsules containing metal nanoparticles and 3) functional dyes, as well as a fourth section that revisits the implications of light addressable polymeric microcapsules as a microdelivery system for biological applications.

Reversibly permeable nanomembranes of polymeric microcapsules.

Polymeric nanometer-thick membranes or nanomembranes possessing photocontrollable permeability are presented. Microcapsules are used as membrane model systems, while gold nanoparticle aggregates are used as active absorption centers. Upon laser light illumination the membranes change permeability reversibly because nanoparticles transiently affect the nearby polymeric network. Nanomembranes reseal to their impermeable state when the laser is switched off. This presents a novel and simple way of reversible permeability control of interest to intracellular signaling and membranes.

Photoactivated release of cargo from the cavity of polyelectrolyte capsules to the cytosol of cells.

Polyelectrolyte capsules with metal nanoparticles in their walls and fluorescently labeled polymers as cargo inside their cavity were prepared. Capsules were ingested by living cells with no uncontrolled release of the cargo upon the incorporation process. Photoinduced heating of the metal nanoparticles in the capsule walls lead to rupture of the capsule walls, and the polymeric cargo was released to the whole cytosol. Viability tests demonstrate that opening of capsules at moderate light intensities does not impair the cellular metabolism, whereas capsule opening at high light intensities ultimately leads to cell death.

Controlled intracellular release of peptides from microcapsules enhances antigen presentation on MHC class I molecules.

To understand the time course of action of any small molecule inside a single cell, one would deposit a defined amount inside the cell and initiate its activity at a defined moment. An elegant way to achieve this is to encapsulate the molecule in a micrometer-sized reservoir, introduce it into a cell, remotely open its wall by a laser pulse, and then follow the biological response by microscopy. The validity of this approach is validated here using microcapsules with defined walls that are doped with metallic nanoparticles so as to enable them to be opened with an infrared laser. The capsules are loaded with a fluorescent antigenic peptide and introduced into mammalian cultured cells where, upon laser-induced release, the peptide binds to major histocompatibility complex (MHC) class I proteins and elicits their cell surface transport. The concept of releasing a drug inside a cell and following its action is applicable to many problems in cell biology and medicine.

On the mechanical stability of polymeric microcontainers functionalized with nanoparticles

We present key factors that influence the mechanical stability of polyelectrolyte/nanoparticle composite microcontainers and their encapsulation behavior by thermal shrinkage. Poly(diallyldimethylammonium chloride) (PDADMAC), poly(styrenesulfonate) (PSS) microshells and citrate-stabilized gold nanoparticles are used. The presence of nanoparticles in the microshell renders the encapsulation process by heat-shrinking more difficult. The encapsulation efficiency is found to decrease as the concentration of material to be encapsulated increases. Increasing nanoparticle content in the microshell or the concentration of dextran increases the likelihood of getting fused and damaged capsules during encapsulation. On the other hand, mechanical studies show that doping microshells with gold nanoparticles significantly increases their stiffness and resistance to deformation. Internalization of capsules by cells supports that the incorporation of metal nanoparticles makes the shells more resistant to deformation. This work provides information of significant interest for the potential biomedical applications of polymeric microshells such as intracellular storage and delivery.

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.

Assembling polyelectrolytes and porphyrins into hollow capsules with laser-responsive oxidative properties

Photoactive microcapsules consisting of the polyelectrolytes poly(allylamine hydrochloride) and poly(styrene sulfonate) and the tetrapyrrolic dye meso-tetrakis(4-sulfonatophenyl)porphine (TPPS) are fabricated using the technique of layer-by-layer self-assembly. Microscopy images and spectroscopy measurements showed the formation of stable capsules with the porphyrin embedded mainly in the shell wall. Interaction of TPPS with polyelectrolytes in solution and on a quartz slide revealed that in the multilayer system TPPS exists as tetranion along with the formation of some H aggregates. Irradiating the fluorescent capsules using a standard xenon lamp with high ultraviolet emission had no effect on the morphology of the capsules. However, illumination with laser light in the presence of an oxidizing agent led to disruption of the capsule wall. The ability of the porphyrin to induce the formation of active oxygen species on irradiation with suitable light leads to the disruption of the capsules. Such porphyrin-incorporated capsules could have the potential to be developed into a remote releasing system, which can be opened with lower laser intensity than existing systems.

Impact of magnetite nanoparticle incorporation on optical and electrical properties of nanocomposite LbL assemblies

Optical and electrical properties of polyelectrolyte/iron oxide nanocomposite planar films on silicon substrates were investigated for different amount of iron oxide nanoparticles incorporated in the films. The nanocomposite assemblies prepared by the layer-by-layer assembly technique were characterized by ellipsometry, atomic force microscopy, and secondary ion mass-spectrometry. Absorption spectra of the films reveal a shift of the optical absorption edge to higher energy when the number of deposited layers decreases. Capacitance-voltage and current-voltage measurements were applied to study the electrical properties of metal-oxide-semiconductor structures prepared by thermal evaporation of gold electrodes on nanocomposite films. The capacitance-voltage measurements show that the dielectric constant of the film increases with the number of deposited layers and the fixed charge and the trapped charge densities have a negative sign.

Retrieval of a Metabolite from Cells with Polyelectrolyte Microcapsules

To monitor cellular processes in individual cells, it is important to measure the concentrations of intracellular metabolites and to retrieve them for analysis. The use of functionalized polyelectrolyte microcapsules as intracellular sensors for in vivo reporting is persented. Capsules loaded with streptavidin-rhodamine, which was introduced into fibroblasts by electroporation, autonomously escaped from an endocytic compartment and efficiently recruited biotin-fluorescein from the cytosol. This work demonstrates the utility of polyelectrolyte microcapsules for intracellular capture of metabolites and eventually for drug delivery on an organismic level.

Relaxation times of colloidal iron platinum in polymer matrixes

Colloidal magnetic iron platinum nanoparticles were embedded at different densities into the walls of polyelectrolyte multilayer capsules. Changes in their magnetic properties such as relaxivities as a function of average distances between the magnetic nanoparticles were investigated and their properties for magnetic resonance imaging discussed.