Evaluation of the surface properties of dextran-coated poly(isobutylcyanoacrylate) nanoparticles by spin-labelling coupled with electron resonance spectroscopy

Poly(alkylcyanoacrylate) nanoparticles are developed as carrier for the in vivo delivery of drugs. In this area of research, one of the major challenges is to design nanoparticles able to carry a drug to a specific site in the body. This appears to be mainly governed by the surface properties of the carrier. Results from previous independent studies suggest that the way dextran chains are arranged at the nanoparticle surface can affect the in vivo fate of the carrier. Thus, the purpose of the present study was to investigate for the first time whether electronic paramagnetic resonance (EPR) could highlight a difference between the physico-chemical surface properties of dextran-coated nanoparticles obtained by two different emulsion polymerisation mechanisms of isobutylcyanoacrylate. Poly(isobutylcyanoacrylate) nanoparticles were prepared either by anionic or by radical polymerisation, initiated in both cases by dextran. The respective copolymers self-organised as nanoparticles. Dextran chains located at the nanoparticle surface could be labelled with a free nitroxide radical containing a probe and EPR analysis could be performed on freeze-dried nanoparticles, rehydrated nanoparticles and dispersed nanoparticles in water. The mobility of dextran chains appeared to differ according to the degree of hydration of the systems. More interestingly, EPR spectra clearly highlighted differences in dextran chain mobility comparing the nanoparticles obtained by radical and anionic polymerisation. Therefore, this technique opens an interesting prospect of investigating surface properties of polysaccharide-coated nanoparticles by a new physico-chemical approach to further correlate the mobility of the polysaccharide chains with the fate of the nanoparticles in biological systems.     

A new approach for the characterization of insoluble amphiphilic copolymers based on their emulsifying properties

The purpose of the present study was to propose a new approach for the characterization of insoluble amphiphilic copolymers using their emulsifying properties. The capacity of four newly-synthesized block copolymers to stabilize a model emulsion formed by mixing equal volumes of water and ethyl acetate was investigated. The copolymers were composed of dextran or heparin and poly(isobutylcyanoacrylate) and were obtained either by anionic or by radical polymerization of isobutylcyanoacrylate in emulsion, initiated on dextran or heparin. A quantitative analysis of the stability of the emulsion obtained with the different copolymers was evaluated using a Turbiscan MA 2000. The results suggested that this approach provides a new methodology for investigating emulsifying properties of polymers that are insoluble in pure solvents, allowing quantitative comparisons to be made between them.     

Plug-in Spectrometry with Optical Fibers as a Novel Analytical Tool for Nanoparticles Technology: Application to the Investigation of the Emulsion Polymerization of the Alkylcyanoacrylate

This paper advances a simple technique to follow, in situ, the emulsion polymerization of isobutylcyanoacrylate (IBCA) performed in different conditions. The method is based on the monitoring of the optical density of the polymerization medium using a plug-in spectrometer equipped with optical fibers since during polymerization the optical density of the medium increases. The technique is demonstrated using poly(alkylcyanoacrylate) nanoparticles developed as carrier for the delivery of drugs in vivo. These nanoparticles are produced by emulsion polymerization of alkylcyanoacrylates (ACA) which are among the highest reactive monomers. The results showed that the spontaneous anionic polymerization of IBCA induced by water could be controlled at pH 1. It was initiated after a delay whereas an immediate and extremely rapid polymerization could be monitored when it was initiated using a combination of cerium IV and dextran allowing the radical polymerization to occur. At higher pH, the spontaneous anionic polymerization could not be controlled. The method developed in this study appeared suitable to monitor emulsion polymerization of ACA and to highlight different mechanisms of polymerization.