Responsive Nanoparticles

Responsive nanoparticles are hollow particles wherein the permeability of the particle changes in response to a change in one or more environmental conditions, such as pH, temperature, light, ionic strength, electric field, magnetic field, solvent composition, etc. The particles could be used for drug delivery, wherein the drug is released from the particle when it reaches the pH of the small intestine, for example.

The particles are made by one of a number of methods from a stimulus-responsive polymer. For example, polyacrylic acid can be made into hollow particles that are contracted at pH less than 5. At a higher pH, the acrylic groups become charged, leading to repulsion of the charged acrylate groups and expansion of the particles. This creates pores through which certain "active agents" can pass. Active agents refers to drugs as well as perfumes, dyes, proteins, genes, etc.

An appropriate polymer is chosen depending upon the type of stimulus that can be applied, i.e. pH, temperature, etc. The intensity of the stimulus required can be varied by selection of the polymer, crosslinking density of the polymer, and inclusion of comonomers.

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