Structural Designing of Drug Carrier Particles

Abstract

Low molecular weight drugs are loaded into polymeric particles to enable the targeting and concentration of drugs at the aimed spaces, controlled and sustained release of drugs, maintaining of drug activity, etc. The particles should not be toxic and residuary in the body. To prepare the particles which satisfy these conditions, materials employed are restricted and, in most cases, natural and/or biodegradable polymers are preferred. The preparative methods are classified into two categories, fabrication of existing polymers into particulate forms and particle-forming polymerizations. The former includes precipitation of polymers from saturated solution, coacervation of polymer solution, self-assembling of amphiphilic polymers, emulsification followed by solidification via crosslinking, solvent evaporation, solvent extraction, spray drying, etc. The latter, particle-forming polymerization, includes emulsion polymerization, modified emulsion polymerization, dispersion polymerization, sedimentation polymerization, etc. In most cases, attention is paid on the conditions of particle surfaces not only during the particle formation but also in the time when they are applied. Polyethyleneglycol (PEG) is one of the most popular polymers which lowers the interfacial energy between polymer and aqueous phase and, therefore, they or their graft/block polymers have been used widely in drug carrying systems. PEG-block-lyophilic polymers construct polymer micelles and well-designed dendrimers are developed. They are expected to be the leading materials in fine chemistry.