Micro and Nanoscale Smart Polymer Technologies in Biomedicine

Abstract

A review. Polymers that exhibit a sharp hydrophilic to hydrophobic phase transition on the application of an environmental stimulus such as pH or temp. 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 nanotechnol. 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 temp.-responsive poly(N-isopropylacrylamide) (PNIPAAm), rapidly form stable and uniformly sized mesoscale particles above the lower crit. soln. temp. (LCST) of the polymer. The size of these particles is dependent on concn., mol. wt. of the polymer used and formulation parameters such as the heating rate. The second is a stimuli-responsive bioanal. bead system. Latex beads were dual-conjugated with PNIPAAm and an affinity ligand to confer temp.-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 chromatog. 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 anal. systems (micro TAS) devices and simple, rapid field tests. [on SciFinder (R)]