Nicole S. Zacharia

Spraying asymmetry into functional membranes layer-by-layer

As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities. By simply varying the flow rate of charged species passing through an electrospun material during spray-assisted layer-by-layer deposition, individual fibres within the matrix can be conformally functionalized for ultrahigh-surface-area catalysis, or bridged to form a networked sublayer with complimentary properties. Exemplified here by the creation of selectively reactive gas purification membranes, the myriad applications of this technology also include self-cleaning fabrics, water purification and protein functionalization of scaffolds for tissue engineering.

Electroactive controlled release thin films

We present the fabrication of nanoscale electroactive thin films that can be engineered to undergo remotely controlled dissolution in the presence of a small applied voltage (+1.25 V) to release precise quantities of chemical agents. These films, which are assembled by using a nontoxic, FDA-approved, electroactive material known as Prussian Blue, are stable enough to release a fraction of their contents after the application of a voltage and then to restabilize upon its removal. As a result, it is possible to externally trigger agent release, exert control over the relative quantity of agents released from a film, and release multiple doses from one or more films in a single solution. These electroactive systems may be rapidly and conformally coated onto a wide range of substrates without regard to size, shape, or chemical composition, and as such they may find use in a host of new applications in drug delivery as well as the related fields of tissue engineering, medical diagnostics, and chemical detection.

Controlling Surface Mobility in Interdiffusing Polyelectrolyte Multilayers

The phenomenon of interdiffusion of polyelectrolytes during electrostatic layer-by-layer assembly has been extensively investigated in the past few years owing to the intriguing scientific questions that it poses and the technological impact of interdiffusion on the promising area of electrostatic assembly processes. In particular, interdiffusion can greatly affect the final morphology and structure of the desired thin films, including the efficacy and function of thin film devices created using these techniques. Although there have been several studies on the mechanism of film growth, little is known about the origin and controlling factors of interdiffusion phenomena. Here, we demonstrate a simple but robust method of observing the process of polyelectrolyte interdiffusion by adsorbing charged viruses onto the surface of polyelectrolyte multilayers. The surface mobility of the underlying polycation enables the close-packing of viruses adsorbed electrostatically to the film so as to achieve a highly packed structure. The ordering of viruses can be controlled by the manipulation of the deposition pH of the underlying polyelectrolyte multilayers, which ultimately controls the thickness of each layer, effective ionic cross-link density of the film, and the surface charge density of the top surface. Characterization of the films assembled at different pH values were carried out to confirm that increased quantities of the mobile polycation LPEI incorporated at higher pH adsorption conditions are responsible for the ordered assembly of viruses. The surface mobility of viruses atop the underlying polyelectrolyte multilayers was determined using fluorescence recovery after photobleaching technique, which leads to estimate of the diffusion coefficient on the order of 0.1 microm(2)/sec for FITC-labeled viruses assembled on polyelectrolyte multilayers.