A New Living Emulsion Polymerization Mechanism: Episulfide Anionic Polymerization

Emulsion macromonomer cross-linking. A preparative method for oxidation-responsive nanoparticles with a controlled network structure

We here report on a preparative, template-based method for oxidation-responsive, poly(propylene sulfide) cross-linked nanoparticles. In this study we demonstrate that preformed, narrow polydispersity, and end-functional polysulfides can be dispersed to yield stable emulsions, which can then be converted into stable nanoparticles through photochemically initiated cross-linking. The nanoparticle size is substantially templated on that of the precursor emulsions; the nanoparticles bulk is an elastomeric material with a homogeneous cross-linking density. The nanoparticles show a peculiar, two-stage behavior upon exposure to oxidants, which is likely composed of a first agglomeration phase followed by swelling.

In vivo targeting of dendritic cells in lymph nodes with poly(propylene sulfide) nanoparticles

Delivery of biodegradable nanoparticles to antigen-presenting cells (APCs), specifically dendritic cells (DCs), has potential for immunotherapy. This study investigates the delivery of 20, 45, and 100nm diameter poly(ethylene glycol)-stabilized poly(propylene sulfide) (PPS) nanoparticles to DCs in the lymph nodes. These nanoparticles consist of a cross-linked rubbery core of PPS surrounded by a hydrophilic corona of poly(ethylene glycol). The PPS domain is capable of carrying hydrophobic drugs and degrades within oxidative environments. 20 nm particles were most readily taken up into lymphatics following interstitial injection, while both 20 and 45nm nanoparticles showed significant retention in lymph nodes, displaying a consistent and strong presence at 24, 72, 96 and 120h post-injection. Nanoparticles were internalized by up to 40-50% of lymph node DCs (and APCs) without the use of a targeting ligand, and the site of internalization was in the lymph nodes rather than at the injection site. Finally, an increase in nanoparticle-containing DCs (and other APCs) was seen at 96h vs. 24h, suggesting an infiltration of these cells to lymph nodes. Thus, PPS nanoparticles of 20-45nm have the potential for immunotherapeutic applications that specifically target DCs in lymph nodes.

Oxidation-sensitive polymeric nanoparticles

We have recently demonstrated the possible use of organic polysulfides for the design of oxidation-sensitive colloidal carriers in the form of polymeric vesicles, which are particularly suitable for the encapsulation of hydrosoluble drugs. In the present research we extend our efforts to carriers specifically suitable for hydrophobic molecules. Exploiting the living emulsion polymerization of episulfides, we have produced new cross-linked polysulfide nanoparticles. Here we demonstrate how this process allows the production of stable nanoparticles with a good control over their size and functionality. The nanoparticles showed negligible cytotoxicity on a fibroblast model; furthermore, they exhibited sensitivity to oxidative conditions, which first produce swelling and then solubilize the material.

Diffusion NMR Spectroscopy for the Characterization of the Size and Interactions of Colloidal Matter: The Case of Vesicles and Nanoparticles

We report the application of the pulse gradient spin-echo (PGSE) NMR technique (PGSE NMR) to the analysis of large colloidal materials, specifically vesicles formed from macromolecular amphiphiles and nanoparticles. Measurements of size and size distribution were demonstrated to be comparable to those obtained through dynamic light scattering or hydrodynamic chromatography. In comparison to these more common analytical methods, the use of PGSE NMR is particularly advantageous in that, as a spectroscopic technique, it adds chemical selectivity to the study of physical dimensions. In this way, chemically different species contemporarily present in a sample may be individually studied. In addition, we demonstrate the use of PGSE NMR to probe the existence of equilibria between macroamphiphiles present in solution and those present in vesicles or on the surface of nanoparticles. This feature in particular opens exciting possibilities for the characterization of the phase behavior and of the surface adsorption phenomena of colloids.

Michael-type addition as a tool for surface functionalization

Michael-type addition (conjugate addition reaction between electron-poor olefins and nucleophiles, such as thiols) has been successfully used as a convenient tool for surface functionalization. Due to its mild character, this method is potentially useful for the introduction of sensitive groups, which can provide bioactivity and targeting possibilities to surfaces of, for example, colloidal carriers. As reaction partners, in our study we have used thiols, possibly present in peptidic structures, and acrylates, at the end of protein-repellant PEG chains. Satisfactory results were obtained with thiols in solution and acrylic groups bound to the surface. Alternatively, the use of thiols on the particles, even if generated in situ, did not provide useful results.