We report on the biosynthesis of 65 kDa A-B-A triblock copolymers consisting of pH-responsive (acidic) silklike blocks and nonresponsive collagenlike blocks, and we show that at pH values where the silklike blocks become uncharged, these polymers form transparent high-modulus gels, that is, 7-15 kPa at 8 g • L -1 , that consist of supramolecular nanotapes with a height of 2.8 nm, a width of ∼14 nm, and an average length of >10 µm. At the concentrations employed, both of these protein triblocks essentially form the same structure, irrespective of block order. The amount of product isolated from the extracellular medium is in the gram per liter range. This high yield makes various applications of this promising class of biocompatible materials possible.

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Triblock peptide copolymers (made by biological expression of a designed DNA template), organic bisligands with two terdentate groups, and Zn 2+ ions associate spontaneously into well-defined nanoribbons (width: 20-25 nm; thickness: 2-3 nm; lengths in the mm range) when dissolved at proper ratios in water at moderate pH values. These nanoribbons are stabilized by an extraordinary concerted effect of distinct noncovalent interactions: metal-ligand complexation (yielding supramolecular coordination polymers), hydrogen bonding, hydrophobic interactions (supporting secondary and ternary structure of the peptide copolymer), and polyelectrolyte complexation between coordination polymers and the charged blocks of the peptide copolymers. Combining complementary experimental results and established knowledge on related peptide polymers, we have arrived at a model for the molecular structure of the nanoribbons.

Rheological data on monodisperse block copolymer hydrogels are rare because the amounts produced with various methods usually are not sufficient for materials testing. By biotechnological means, expression of a block copolymer encoding gene in the yeast Pichia pastoris, we produced enough protein block copolymer for a study of the macroscopic properties of several gels. To study the effect of block order on the mechanical properties of self-assembling block copolymer hydrogels, we tested gels of two molecules with complementary triblock organization: CS E S E C and S E CCS E , in which the S E block self assembles at low pH while the C block remains a random coil. Dynamic mechanical spectroscopy revealed differences in gelling kinetics and mechanical properties. The gels displayed non-linear elasticity comparable to that of actin gels and other networks of cross-linked semiflexible polymers. Moreover, exceptionally high storage moduli, exceeding 40 kPa, were reached already at concentrations as low as 1.5 wt%, without any additional crosslinking agent. Increasing the temperature of a CS E S E C gel led to stiffening until 50 C, above which it melted.