Stimuli-responsive magnetic particles for biomedical applications.

In recent years, magnetic nanoparticles have been studied due to their potential applications as magnetic carriers in biomedical area. These materials have been increasingly exploited as efficient delivery vectors, leading to opportunities of use as magnetic resonance imaging (MRI) agents, mediators of hyperthermia cancer treatment and in targeted therapies. Much attention has been also focused on "smart" polymers, which are able to respond to environmental changes, such as changes in the temperature and pH. In this context, this article reviews the state-of-the art in stimuli-responsive magnetic systems for biomedical applications. The paper describes different types of stimuli-sensitive systems, mainly temperature- and pH sensitive polymers, the combination of this characteristic with magnetic properties and, finally, it gives an account of their preparation methods. The article also discusses the main in vivo biomedical applications of such materials. A survey of the recent literature on various stimuli-responsive magnetic gels in biomedical applications is also included.

Pseudolatex preparation using a novel emulsion-diffusion process involving direct displacement of partially water-miscible solvents by distillation.

Pseudolatexes were obtained by a new process based on an emulsification-diffusion technique involving partially water-miscible solvents. The preparation method consisted of emulsifying an organic solution of polymer (saturated with water) in an aqueous solution of a stabilizing agent (saturated with solvent) using conventional stirrers, followed by direct solvent distillation. The technique relies on the rapid displacement of the solvent from the internal into the external phase which thereby provokes polymer aggregation. Nanoparticle formation is believed to occur because rapid solvent diffusion produces regions of local supersaturation near the interface, and nanoparticles are formed due to the ensuing interfacial phase transformations and polymer aggregation that occur in these interfacial domains. Using this method, it was possible to prepare pseudolatexes of biodegradable and non-biodegradable polymers such as poly(D,L-lactic acid) and poly(epsilon-caprolactone), Eudragit E, cellulose acetate phthalate, cellulose acetate trimellitate using ethyl acetate or 2-butanone as partially water-miscible solvents and poly(vinyl alcohol) or poloxamer 407 as stabilizing agent. A transition from nano- to microparticles was observed at high polymer concentrations. At concentrations above 30% w/v of Eudragit E in ethyl acetate or cellulose acetate phthalate in 2-butanone only microparticles were obtained. This behaviour was attributed to decreased transport of polymer molecules into the aqueous phase.

An in vitro release kinetic examination and comparative evaluation between submicron emulsion and polylactic acid nanocapsules of clofibride.

Polylactic acid nanocapsules of clofibride containing soybean oil (SO) or medium-chain triglycerides (MCT) as the oil core were prepared. The in-vitro drug release kinetic profiles were determined and compared to those of a clofibride submicron emulsion using two different kinetic techniques: the bulk equilibrium reverse dialysis sac technique, and the centrifugal ultrafiltration technique. The former technique was shown to be inadequate for in-vitro kinetic comparison purposes as a result of drug diffusion limitations through the dialysis membrane. The latter technique yielded rapid in-vitro release profiles of clofibride from both emulsion and nanocapsule delivery systems under perfect sink conditions although a consistent lower maximum drug amount was released from the MCT nanocapsules as compared to the corresponding emulsion. This was attributed to the relatively higher aqueous solubility of MCT as compared to SO. This comparative study, carried out, to the best of our knowledge, for the first time, clearly showed that both colloidal carriers behave similarly with respect to drug release despite their different morphological characteristics. The kinetic results clearly exclude either the use of submicron emulsion or of nanocapsules as colloidal controlled release delivery systems for any administration route where perfect sink conditions should prevail.