Top-down Particle Fabraction by Layer-by-Layer Assembly and Microcontact Printing

Microparticles are widely used for biomedical applications. Top-down techniques are able to generate particles with non-spherical shapes, precisely defined geometries, and complex structures and compositions. These properties allow well-defined interactions between microparticles and biomolecules, cells, and tissues, and are therefore desirable for drug delivery and biomedical imaging applications. However, biomedical application of microparticles is currently limited by lack of robust, versatile and inexpensive production methods. We intend to solve this problem by developing a novel top-down approach for fabricating microparticles. In this approach, a thin film composed of multiple layers of polyelectrolytes is deposited on a stamp carrying micrometer-sized topological surface structures via layer-by-layer assembly. The multilayer film is then partially transferred onto a substrate by microContact Printing to form isolated pieces of films. When the substrate is coated with a water soluble sacrificial film, dissolving the film with water releases the films as free microparticles. We have used this method to produce microparticles with various shapes, sizes, numbers of layers, and compositions. We have also found that particles consisting of only a few layers (''10 layer) fold significantly in water, but the folding can be inhibited either by increasing the number of layers or by covalently crosslinking the component materials. Meanwhile, spin-assisted layer-by-layer assembly has been utilized for the first time to fabricate multilayer particles in this work. In addition, we have developed a series of methods for producing microparticles with complex structures. Moreover, we have developed a method capable of producing a particle array that consisted of multiple types of particles arranged in a well-defined pattern. Taken together, this approach is simple, inexpensive, and highly versatile. It thus possesses great potential to be useful for biomedical applications especially drug delivery and biomedical imaging.