A permanent change in protein mechanical responses can be produced by thermally-induced microdomain mixing.

Electrospinning was employed to fabricate 3-D fiber networks from a recombinant amphiphilic elastin-mimetic tri-block protein polymer and the effects of moderate thermal conditioning (60 degrees C, 4 h) on network mechanical responses investigated. Significantly, while cryo-high resolution scanning electron microscopy (cryo-HRSEM) revealed that the macroscopic and microscopic morphology of the network structure was unchanged, solid-state (1)H-NMR spectroscopy demonstrated enhanced interphase mixing of hydrophobic and hydrophilic blocks. Significantly, thermal annealing triggered permanent changes in network swelling behavior (28.75 +/- 2.80 non-annealed vs. 13.55 +/- 1.39 annealed; P < 0.05) and uniaxial mechanical responses, including Young's modulus (0.170 +/- 0.010 MPa non-annealed vs. 0.366 +/- 0.05 MPa annealed; P < 0.05) and ultimate tensile strength (0.079 +/- 0.008 MPa vs. 0.119 +/- 0.015 MPa; P < 0.05). To our knowledge, these investigations are the first to note that mechanical responses of protein polymers can be permanently altered through a temperature-induced change in microphase mixing. (c) Koninklijke Brill NV, Leiden, 2009