Micro and Nanoscale Smart Polymer Technologies in Biomedicine

Abstract

Polymers that exhibit a sharp hydrophilic to hydrophobic phase transition on the application of an environmental stimulus such as pH or temperature are called smart polymers. These smart polymers, or stimuli responsive polymers, have been used to develop several drug delivery technologies. The emergence of the fields of nanotechnology and microfluidics has created new opportunities for smart polymers. We have recently developed two nano- and microscale technologies for diagnostic applications. The first is a reversible particle system using stimuli-responsive polymer-protein conjugates. We have found that conjugates of streptavidin and the temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm), rapidly form stable and uniformly sized mesoscale particles above the lower critical solution temperature (LCST) of the polymer. The size of these particles is dependent on concentration, molecular weight of the polymer used and formulation parameters such as the heating rate. The second is a stimuli-responsive bioanalytical bead system. Latex beads were dualconjugated with PNIPAAm and an affinity ligand to confer temperature-responsiveness to the beads. Above the LCST of the PNIPAAm, the bead surface becomes hydrophobic and the modified beads aggregate and adhere to the walls of microfluidic channels. They have been used to develop a reversible microfluidic affinity chromatography matrix for the upstream processing of complex fluids and for immunoassays. Both technologies can be used in a wide variety of formats, including microfluidic-based micro-total analytical systems (μTAS) devices and simple, rapid field tests.