The effect of processing on large, self-assembled amyloid fibers

It has been shown that micrometer-sized amyloid fibers can spontaneously self-assemble from peptide mixtures. Varying the molar ratio and type of peptides in the mixture affected fiber morphology and properties. Here, the same peptide mixtures at constant molar ratio are studied at different processing conditions to note influences on fiber formation. This study illustrates that changes in solution pH, temperature, and ionic strength can also influence the extent of fiber formation. In addition, processing variables greatly affect the size, morphology, and modulus of large amyloid fibers. Fibers segregate into two classes: flat ribbons or tapes of low modulus and cylindrical fibers of high modulus. Cylindrical cross-sections appear to result from twisted tapes and processing conditions can affect the transition from flat to cylindrical. Solution conditions could prevent or enhance the twisting transition, depending on the amino acid composition of the peptides in the mixture. The most robust fiber properties result from cylindrical fibers with diameters of 10–20 μm. The transition from flat to cylindrical appears to be highly influenced by the glutamine (Q) or lysine (K) content of the peptides. Thus it is possible to design useful, macroscopic fibers with predictable shape and properties.