Thermally Responsive Interpenetrating Polymer Network Nanoparticles

Stimuli-responsive polymer hydrogels which are capable of responding to changes in their environment such as pH (1), osmotic strength (2), or temperature (3) have received growing attention in recent years for applications in a wide variety of areas including controlled drug delivery (4). Also, due to the size limitations imposed by the body’s natural defense mechanisms, such as the reticuloendothelial system, polymer systems 0.3 μm in diameter and smaller will be required in order to create effective in vivo drug delivery systems (5-7). Under normal conditions these stimuli-responsive particles exist in a collapsed state where diffusion or release of an encapsulated agent is limited or prevented by the small size of openings in the polymer mesh that comprises the nanoparticle. However, upon activation or change in a specific environmental factor, these particles swell, thereby increasing their mesh size and allowing for the release of any encapsulated agents. Due to the highly buffered nature of blood serum, thermally responsive nanoparticles appear to be the most likely candidates for use in injectable systems because this environmental factor is much easier to change and control.