(346b) Surface Patterning of Microspheres Using Photodefinable Ultra-Thin Polymer Coatings
Conventional modifications on two-dimensional surfaces will no longer be enough for the increasing needs on biological assays and biomedical devices. Modifications that are applicable to 3-D objects such as microparticles, and more importantly, selective modifications on three-dimensional geometries will be essential and will be the challenge to the next generation of surface modification. Chemical vapor deposition (CVD) polymerization of functionalized [2.2]paracyclophanes establishes a simple, but general protocol for preparation of ultrathin polymer coatings (20-100 nm). The resulting reactive coatings provide an appealing alternative to the currently employed arsenal of surface modification methods consisting mainly of wet-chemical approaches. Recently, we have shown the usefulness of the CVD polymerization process to prepare a novel photodefinable polymer  which can be used to prevent non-specific protein adsorption within PDMS-based microfluidics devices. Herein, we demonstrate the usefulness of this photodefinable CVD coating for surface modification to create biofunctional surfaces on three-dimensional geometries (e.g. stents, PDMS microchannels, microspheres). With the help of a digital micromirror device (DMD) system, UV light is directed to the desire areas, reactive sites can be initiated selectively and well defined surface patterns can be created by photopattering reaction on the polymer coated devices. In order to demonstrate the chemical and biological activity (bio-actvie) of the corresponding binding patterns, PEO-amine-derived biotin was immobilized onto the particle surfaces through photopattering reaction, and we allowed rhodamine (TRITC) conjugated streptavidin to bind to the biotin-modified areas. On the other hand, we used 4-arm star PEO instead of biotin for the immobilization to study protein adsorption. Alex-fluoro 546 conjugated fibrinogen was used as model protein for incubation; in this case, we were able to establish a well-defined non-fouling (bio-inert) environment on the microsphere surfaces. Results were visualized using fluorescence and confocal microscopy. This generic surface engineering protocol is widely applicable to a wide range of materials and even hybrid structures, and we will be able to (1) prepare well defined biofunctional patterns in micron scale range; (2) selectively initiate the binding sides; (3) precisely modify the surface properties on almost any kind of substrates (2-D, 3-D) without rendering the spatial resolution. With the precise control and the programmable flexibility of this protocol, we foresee the technology to be useful for cell-based screening and diagnostic bioassays.
References:  Suh, K. Y.; Langer, R.; Lahann, J. Advanced Materials 2004, 16, 1401-1405.  Chen, H.-Y.; Lahann, J. Analytical Chemistry 2005, 77, 6909-6914.