Synthesis of membranes with permeability controlled by an external magnetic field

In recent years the research on novel “intelligent” materials has attracted much attention. Intelligent materials include those with self-healing properties, novel sensors, and materials for medical usages such as drug delivery. Drug delivery materials are very promising for increasing the potency of drugs and are therefore the subject of intense investigation. One of the most interesting classes of drug delivery materials are 2-dimensional membranes with drug-specific permeability. The pore size of membranes determines the membrane permeability. We intend to create membranes with defined pores by crosslinking a regular array of iron oxide nanoparticles; the pore size will then be controllably through the heat induced collapse of the polymer shell surrounding the nanoparticles. The heating possibility associated with superparamagnetic iron oxide nanoparticles in a magnetic field will be combined with the thermo-responsive polymer PNIPAM in order to produce a membrane with permeability that can be controlled by an external magnetic field. The application of a magnetic field will cause the heating of the nanoparticles, which will lead to the contraction of the PNIPAM-chains (coil/globule transition) changing the membrane pore size and thus the membrane permeability. In order to obtain useful membranes we have to have highly stable particles and controlled pore sizes. Highly stable particles can be achieved by the usage of specific and particularly stable binding groups, such as the nitrodopamine-derivatives developed by the group of Prof. Reimhult. Iron oxide nanoparticles functionalized with initiators bound to the core through nitrodopamine anchors can then be further modified by ongoing living or controlled “grafting-from” polymerization of PNIPAM. This methodology (Controlled Nitroxide-Mediated-Polymerization (NMP)1) allows the optimal control over the density and length of the polymer chains and allows a specific modification of the chain ends for the binding of the desired crosslinking groups to create defined core-shell nanoparticles. This will be a significant advance in the synthesis of well-defined iron oxide nanoparticles as building blocks for thermoresponsive smart materials. Self-assembly of these core-shell particles at interfaces (liquid-liquid, liquid-air) will directly lead to ordered and well defined structures. The order (architecture) of these assemblies can be varied by changing the chemical properties of the polymer shell. After assembly, the particles will be cross-linked using UV-light to create a stable membrane. These membranes will be analyzed to determine permeability, mechanical properties and morphology. One of the most important aspects of this project is to study the change of passive diffusion with respect to magnetic stimuli. The possibility to use the heating effects that can be induced by application of an external magnetic field onto super-paramagnetic nanoparticles assemblies will be tested.