Triblock Protein Copolymers Forming Supramolecular Nanotapes and pH-Responsive Gels

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.