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    Layer-by-Layer Polyelectrolyte Deposition: A Mechanism for Forming Biocomposite Materials

    Year: 2013

    Journal: Biomacromolecules, 2013, 14 (6), pp 1715-1726, 20130926

    Authors: YerPeng Ta, Umit Hakan Yildiz, Wei Wei, J. Herbert Waite, Ali Miserez

    Organizations: Biomolecular Science and Engineering Program, University of California, Santa Barbara, Santa Barbara, California 93106, United States; Marine Science Institute, University of California, Santa Barbara, Santa Barbara, California 93106, United States; School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore; Center for Biomimetic Sensor Science, Block X Frontier, Research Technological Plaza, Nanyang Technological University, 50 Nanyang Avenue, Singapore; Materials Research Laboratory, University of California, Santa Barbara, Santa Barbara, California 93106, United States; School of Biological Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore

    Complex coacervates prepared from poly(aspartic acid) (polyAsp) and poly-l-histidine (polyHis) were investigated as models of the metastable protein phases used in the formation of biological structures such as squid beak. When mixed, polyHis and polyAsp form coacervates whereas poly-l-glutamic acid (polyGlu) forms precipitates with polyHis. Layer-by-layer (LbL) structures of polyHis–polyAsp on gold substrates were compared with those of precipitate-forming polyHis–polyGlu by monitoring with iSPR and QCM-D. PolyHis–polyAsp LbL was found to be stiffer than polyHis–polyGlu LbL with most water evicted from the structure but with sufficient interfacial water remaining for molecular rearrangement to occur. This thin layer is believed to be fluid and like preformed coacervate films, capable of spreading over both hydrophilic ethylene glycol as well as hydrophobic monolayers. These results suggest that coacervate-forming polyelectrolytes deserve consideration for potential LbL applications and point to LbL as an important process by which biological materials form.