Remotely controllable microcapsules for site - specific delivery of a chemical payload

The problem of targeted delivery and controlled release of a chemical payload in difficult-toaccess microstructured environments such as living tissues or porous soil is considered. Composite microcapsules consisting of the thermo-responsive hydrogel poly-Nisopropylacrylamide (PNIPAM) with dispersed iron oxide nanoparticles have been prepared by w/o emulsion polymerization. The microcapsules are able to reversibly change their size and shape, adhesion to substrates under laminar flow conditions, and permeability to diffusing molecules as a result of local temperature change induced by radiofrequency heating of incorporated super-paramagnetic iron oxide nanoparticles. The structural analysis of the composite capsule by x-ray micro-tomography revealed the existence of several internal compartments as well as uniform distribution of iron oxide nanoparticles within the polymer. The thermo-responsive shrinking/swelling behavior of the composite particles around the lower critical solution temperature (LCST) of PNIPAM was verified and the ability to reach the LCST by means of remote induction heating using a 400 kHz alternating magnetic field was demonstrated. The release rate of a model active substance (vitamin B12) from the capsules at two different temperatures was measured, confirming the possibility to influence the release characteristics remotely by the application of a radiofrequency magnetic field. The temperaturedependent adhesion characteristics of the microcapsules towards various substrates were measured in a purpose-build mircofluidic flow cell.