These observations suggest that morphology of condensed silica
structures and the rate of silica condensation on the surface of solid
silk–SiBP materials can be tuned by fusing SiBPs with different
capacities of self-assembly as well as by controlling the post-fabrication
processing of the materials.
5. Conclusions
Bioinspired silicification was performed with genetically engineered
silk protein and silk–SiBP fusion proteins using both solution–
solution and solution–solid interfaces. Nanoparticles were
produced in the solution studies and particles formed by fusion
proteins were smaller than when the molecular weight of the silk
domain was smaller, suggesting that molecular weight plays a role
in controlling the size of silk–silica particles. This feature impacts
silica degradation and may influence cell growth and differentiation
in bone regeneration [29,30]. In solution–solid interface systems,
silica particles were formed on the films and 6mer-A1/-R5
films supported a higher silica precipitation activity. This feature
was at least in part related to the b-sheet content of the films, further
offering control of silica condensation rate and precipitation
activity. Different morphologies of condensed silica structures
were observed on the 6mer-A1 films because the silica particles
appeared to be incorporated into the films, suggesting that there
was a crosstalk between silk domain and SiBPs that led to control
of the morphology of the condensed silica structures which may
influence interfacial bonding between materials and cells or tissues
in bone regeneration. Thus, tuning bioinspired silicification with
artificial macromolecular-SiBP chimeras by controlling the molecular
weight of the silk domain and the nature of the SiBP
sequences, along with post treatment processes to impact secondary
structure of the proteins, can play roles in generating tuned
biopolymer–silica composites for use in biomedical engineering.
Acknowledgements
We thank the NIH (R01 DE017207) and Natural Science Foundation
of China (NSFC, project no. 51273138) for support of this
research.
C O Si
6mer
6mer-A1
6mer-A3
6mer-R5
Fig. 8. Elemental analysis of structures on the films treated by water vapor annealing at 70 C. Elemental maps are shown for carbon (C), oxygen (O) and silicon (Si). Insets are
EDX spectra for samples. White arrows indicate the position of particles identified by the elemental mapping for 6mer and 6mer-A3