Bacteria Attachment Control and Antibacterial Properties - Jenny Lichter
We are investigating the use of polymer coatings formed using layer by layer assembly to create coatings capable of preventing the growth of a biofilm. We are researching the effects of key surface properties, such as mechanical stiffness and surface charge, on bacteria attachment and cytotoxicity. Using the layer by layer approach and tuning synthesis and post-assembly conditions, chemically identical films can be created with different elastic moduli and chemical functional group densities. These films are then used to isolate the effects of various properties.
Left Figure: Few bacterial colonies grow on a bacteria-resistant polyelectrolyte multilayer. Right Figure: Many bacterial colonies grow on glass control. Both images are taken at 4x magnification.
Highlighted Publication: Lichter, J.A., et al., Substrata Mechanical Stiffness Can Regulate Adhesion of Viable Bacteria, Biomacromolecules, 2008, 9 (10), p 2967
Mechanomutable Nanotubes via Layer-by-Layer Assembly - Gary ChiaThe ultimate goal of my thesis is to design and synthesize mechanomutable nanotubes that exhibit reversible and tunable mechanical responses to different types of external stimuli via layer-by-layer assembly. The design of such highly refined heteronanomaterials, by the incorporation of constituents from a wide range of materials as the fundamental units, provides versatility and variability in mechanical properties. Mechanomutable heteronanomaterials can be useful for the development of multi-responsive tunable sensor arrays, synthetic extracellular matrix, and dynamic armor coatings.
The layer-by layer assembly technique provides a versatile and inexpensive approach to the design and synthesis of mechanomutable heteronanomaterials. The sequential adsorption of oppositely-charged species enables the precise design and control over the molecular architectures of the film, which can be manipulated for different functionalities. The synthesis of hollow, cylindrical nanotubes using a porous-templated layer-by-layer approach is of particular interest arising from their interesting dimensions. In contrast to previously reported systems, the synthesis of mechanomutable nanotubes via layer-by-layer assembly can be designed in many different ways that result in materials that exhibit reversible and tunable mechanical responses to different types of external stimuli.
Omni-directional structural color by layer-by-layer nanoparticle assembly- Dr. Pinar Kurt
Some colors in nature do not come from material's inherent properties, but are as a result of light interference. This kind of color, called 'structural color,' can be seen in some species such as butterflies and beetles. We are investigating the methods and conditions for creating structural color using layer-by-layer assembly of various nanoparticles. By building alternating layers of nanoparticles with low and high refractive indices, it is possible to obtain high reflectance with any color. With optical simulation programs, we are able to design nanoparticle assembly and obtain any color with more than 90% reflectance. The ultimate goal is to control the angle-dependence of the reflectance and to create omni-directional structural color by a layer-by-layer assembly process.
This project is in collaboration with Toyota Research Institute North America (TRI-NA)
Polymer Filtration Membranes: Part 1- Ayse Asatekin
Membrane fouling, which can simplistically be described as the clogging of a membrane due to the adsorption of feed components, is one of the major obstacles faced by the membrane industry. It drives up energy consumption as well as cleaning and membrane replacement, and is especially severe in processes where the feed has high concentrations of biomolecules, such as in wastewater treatment, and in food and pharmaceutical industries. The most common way to prevent fouling is to graft a hydrophilic polymer from the membrane surface, but this is often an expensive and poorly controlled process. My project aims to develop improved membranes that resist fouling making use of the self-organization of copolymers, specifically comb copolymers with a hydrophobic backbone and hydrophilic side-chains.
Polyacrylonitrile-graft-poly(ethylene oxide) (PAN-g-PEO) is such a polymer: It has a backbone of PAN, a glassy polymer used in membrane industry, and side-chains of PEO, a hydrophilic polymer well known for its resistance to adsorption. When this copolymer is added to the casting solution during the manufacture of porous ultrafiltration (UF) membranes, the side-chains are driven to the polymer/water interface due to their hydrophilic nature. The polymer is pinned down by the PAN backbone, creating a brush of PEO chains on the membrane surface as well as lining all the pores. Membranes prepared using this method were found to resist irreversible fouling completely to a range of foulants, including protein, humic acid and alginate solutions, and oil-well produced water: The membrane can be cleaned simply by water, potentially decreasing cleaning costs and increasing membrane life. These membranes are very promising for waste-water treatment and membrane bioreactors.
Another application, this time used to prepare membranes with selectivity in the small molecule scale, relies on the microphase separation of PAN-g-PEO. In this process, a porous support membrane is coated with a thin (0.2-2 micron) film of PAN-g-PEO. The copolymer microphase separates into a bicontinuous network of each phase. The PEO phase, which is hydrophilic, allows the passage of water and molecules smaller than its diameter, acting as PEO-lined "nanochannels". The membranes produced have size-based selectivity in the nanofiltration scale, and can be used to fractionate small-molecule dyes by size. They also have a high pure water permeability, and complete resistance to irreversible fouling. Furthermore, the size cut-off of these membranes is responsive to a range of factors that affect the conformation of PEO chains, such as temperature, pressure, and ionic strength.
Polymer Filtration Membranes: Part 2 - Nathan Lovell
Amphiphilic comb copolymers impart fouling resistance to polymer membranes, an increasingly important part of the world's water supply sustainability. Research is underway to expand the application of the morphology and properties of these combs to create membranes with regenerative fouling-resistant surfaces, nanosieving membranes, and improved desalination membranes.
