Genetically engineered spider silk block copolymers are promising candidates to study the effect of block composition, sequence, and length on fiber formation. Spider silk block copolymers were prepared based on the assembly of two individual blocks, a hydrophobic poly-alanine rich block (A) and a hydrophilic glycine-rich block (B) using recombinant DNA technology. The constructs were cloned, expressed and purified and their secondary structures and morphologies were assessed by FTIR, SEM, and AFM. In terms of morphology, as the number of AB repeats increase, the transformation from disordered structures to nanofibrils occurred.   H(AB)12 block copolymer with Mw of 43.7 kDa self-assembled into fibrils with an average diameter of 25 nm in aqueous media; whereas, H(AB)2 with an Mw of 11.6 kDa did not form specific morphologies. Moreover, fiber formation of H(AB)12 was induced by applying shear force in protein solution using an AFM tip. Monodisperse nanoparticles with an average diameter of 100 nm were observed, when 2-propanol was used as a solvent for H(AB)3. Using mesoscopic dissipative particle dynamics simulations with a coarse-grained description of the two block copolymers and solvents, we validated the experimentally observed trend in aggregate sizes of H(AB)2 and H(AB)12. In addition, the simulation also predicted fiber formations with H(AB)12 under applied shear forces. Applying network analysis on copolymer aggregates under shear forces, we found that the longer sequence promotes fiber formation by forming more bridges (via the B blocks) between aggregate centers (composed of the A blocks). This experimental approach demonstrates successful implementation of our strategy to regulate material features by manipulating the block length and composition in spider silk block copolymers. The combined experimental-computational approach provides the platform for the rational design of new sequences, solution environment, and other physicochemical conditions for future biomimetic fiber production.

Effect of AB sequence length on fiber formation in spider silk block copolymers: Integrated experimental, computational approach

247th National Meeting (2014)

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