Mussels and other marine organisms (e.g. barnacles, kelps, coral reefs) secrete remarkable protein-based adhesive materials for adherence to the substrates upon which they reside. The protein adhesives are secreted as fluids that undergo an in-situ crosslinking or hardening reaction leading to the formation of a solid adhesive plaque, which mediates the attachment of the organism to a variety of substrates (e.g. minerals, metal surfaces, and wood). One of the unique structural features of mussel adhesive proteins (MAPs) is the presence of L-3,4-dihydroxyphenylalanine (DOPA), an amino acid that is responsible for both adhesion and crosslinking characteristics of MAPs.

Taking into account these remarkable adhesive and hardening properties we have designed a novel functional polymer and utilized it for preparation of high-strength thin film organic/inorganic hybrid nanocomposite using layer-by-layer (LBL) assembly technique. For this purpose, we have prepared a novel, four armed poly(ethylene glycol) with DOPA and positively charged lysine molecules randomly grafted at the four ends (~5 molecules of DOPA and ~5 of L-lysine at each end) and assembled it with negatively charged nanosheets of Na+-montmorillonite clay.

Previously, we have shown that LBL assembled thin films from the same clay nanosheets and highly charged poly(diallylmethyl ammonium chloride) (Nature Materials, 2003, 2, 413) possess unique mechanical properties (tensile strength = 100 MPa and Y = 11 GPa), mimicking those of natural nacre. While our PEG-DOPA polymer has an overall DOPA content of only ~22%, the resulting composites possess tensile strength approaching that of our previously reported values, tensile strength ~78 MPa and Y ~ 4 GPa. Further crosslinking with Fe3+, implicated to be the natural crosslinking agent, results in dramatic increase in the tensile strength to 220 MPa and Y = 6 GPa. In this talk we will discuss preparation and characterization of this novel material.