Several studies have demonstrated the use of biomimetic approaches in the synthesis of a variety of inorganic materials. Poly-L-lysine (PLL) promotes the precipitation of silica from a silicic acid solution within minutes. The molecular weight of PLL was found to affect the morphology of the resulting silica precipitate. Larger-molecular weight PLL produced hexagonal silica platelets, whereas spherical silica particles were obtained using low-molecular weight PLL. Here we report on the polypeptide secondary-structure transition that occurs during the silicification reaction. The formation of the hexagonal silica platelets is attributed to the PLL helical chains that are formed in the presence of monosilicic acid and phosphate ions. Hexagonal PLL crystals can also serve as templates in directing the growth of the silica in a manner that generates a largely mesoporous silica phase that is oriented with respect to the protein crystal template.

Herein, we report on the ability to create complex 2-D and 3-D silica networks in vitro via polycationic peptide-mediated biosilicification under experimentally altered chemical and physical influences. These structures differ from the sphere-like silica network of particles obtained in vitro under static conditions. Under chemical influences, overall morphologies were observed to shift from a characteristic network of sphere-like silica particles to a sheetlike structure in the presence of -OH groups from additives and to sharp-edged, platelike structures in the presence of larger polycationic peptide matrixes. Under physical influences, using externally applied force fields, overall silica morphologies were observed to transition from sphere-like to fiberlike and dendrite-like structures. These findings could lead to the future development of bio-inspired complex 2-D and 3-D silica micro- and nano-devices.