3.2. Bioinspired silicification catalyzed by silk protein and chimeras in
solution
Silicification reactions were performed in solution in order to
observe the morphology of the silk–silica composite structures
formed. The colloidal instability of silk protein and chimeras in
solution, controlled by pH, accelerates the condensation of silica
and promotes the formation of spherical particles [1]. The silicification
reaction was performed at pH 7.0 in the present study as the
6mer and the chimeras showed the greatest colloidal instability at
near neutral pH (Fig. 2A). In addition, population diameter measurements
of the silk protein and the chimeras by DLS showed
increasing particle sizes with increasing pH from 3 to 5.5, with
the 6mer aggregating into the largest particles with a diameter of
600 nm (Fig. 2B). At pH 7 only the 6mer-A1 chimera produced
a stable particle population. The other chimeras and the 6mer
showed aggregation and precipitation with apparent high diameters
and high polydispersity at this pH and above.
The morphology of the silk–silica composite structures formed
is depicted in Fig. 3. Spherical particles were observed for the
6mer and each of chimeras and these particles formed interconnected
dense networks. However, the spherical particles formed
in the presence of either the 6mer or each of the chimeras were
heterogenous in size (Fig. 3a–e). The 6mer produced particles