Nanohydrogels and Biospecific Surfaces

This aspect of our research concentrates on creating surfaces whose bioactivity is controlled by surface-patterned nanohydrogels - individual gels with characteristic dimensions of order 100 nm patterned on surfaces with intergel spacings on the order of microns or less (figure 1). We are exploring these in the context of high-sensitivity protein-array applications. We are also developing multiscale-structuring technologies using nanohydrogels in order to control the differential interactions between surfaces, bacteria, and eukaryotic cells.

We use focused electron beams to create nanohydrogels from thin-film macromolecular precursors and bind them to silicon or glass substrates (figure 2). This process is very much like the electron-beam lithography practiced by the device industry. Instead of using a photoresist to pattern the underlying substrate, we instead use precursors such as poly(ethylene glycol) [PEG].

We have shown (Krsko et al., Langmuir 2003) that the swelling properties of the nanohydrogels can be controlled by the electron dose and the precursor molecular weight. We have also shown that high-swelling PEG nanohydrogels resist nonspecific adsorption. By incorporating functional groups (Hong et al, Langmuir 2004), such as amines, into the precursor we can create high-swelling nanohydrogels to which biomolecules such as proteins, antibodies, and oligonucleotides can be covalently grafted (figure 3). Importantly, the flexible patterning capabilities of modern electron-optical systems not only enable us to make nanosclae feature sizes but also do so in user-defined patterns (fig. 3). Hence we can create surfaces with nanoscale biospecific features patterned at micro length scales. Such surfaces can be used in ultra-high-sensitivity detection applications as well as in controlling cell-surface interactions at cellular and sub-cellular length scales. We are particularly interested in using surface-patterned nanohydrogels to control the interactions between synthetic surfaces, such as orthopaedic implant material, and bacteria (figure 4).