Electroactive Layer-by-Layer (LBL) Films for Controlled Release and Mechanomutability

Layer-by-layer assembly is a versatile technique for constructing conformal polymer thin films with ultimate control over film thickness, morphology, and functionality. My project focuses on films containing a redox-active nanoparticle called Prussian Blue. This is a multifaceted material that has been used since the 18th century as a dye both by artists and in the textile industry. More recently, it has been researched for its electrochromic, electrocatalytic, magnetic, and ion exchange properties. Interestingly, Prussian Blue was approved by the FDA in 2003 for treatment of heavy metal and radiation poisoning. Work utilizes the ability of Prussian Blue to change its surface charge in response to an electrochemical potential. Two projects are currently underway.

Electroactive controlled release -- The goal of this project is to fabricate an implantable drug delivery device that can be remotely triggered to release precise quantities of drugs on demand. Implantable devices allow localized delivery of drugs that can reduce the required dosage and reduce side effects from systemic delivery. Further, a platform that is responsive to an external stimulus, in this case an electric potential, can allow for active control over drug release. This active control then allows for complex release profiles that can be adjusted for a desired therapeutic response.

A variety of therapeutics can be incorporated in a layer-by-layer film along with Prussian Blue nanoparticles. Upon an applied electric potential of 1.25 V (vs. SCE), the Prussian Blue (negatively charged) switches to its Prussian Brown (neutral) redox state. When the particles lose their surface charge, the cohesive electrostatic attractions holding the film together are lost. Adjacent like-charged groups then repel each other leading to dissolution of the film and release of drug. We have demonstrated the controlled release of the model agent dextran sulfate. Current work includes delivery of small, hydrophobic drugs and fabrication of a multidrug microarray.

Mechanomutable materials -- Mechanomutable materials are those that alter their mechanical properties in response to an environmental stimulus. There are a number of examples of such behavior in nature (e.g. sea cucumbers, starfish, etc.). Practical applications of mechanomutable materials could include control over cellular migration and adhesion, control of protein adsorption, mechanical motors to perform work, and dynamic coatings for nanoscale devices in general. Since Prussian Blue nanoparticles can reversibly change their surface charge in response to an electrochemical potential, we suspect that film swelling can be controlled by an applied potential. This project focuses on the fabrication and mechanical characterization of crosslinkable, Prussian Blue-containing layer-by-layer films.