Two samples of full-length amylin fibril samples were also prepared using a modified procedure from Gallardo et al. For sample 1 (Figure , S1e), 1.2 mg of peptide was disaggregated in HFIP for a final concentration of 0.31 mM and incubated at room temperature for 15 min with gentle agitation. After incubation, HFIP was evaporated off using nitrogen gas. PBS (pH 7.4) was chilled and then added to the disaggregated peptide to create a 0.31 mM solution with 0.01 % (v/v) NaN 3 in PBS (0.01 M phosphate). The sample was incubated at 37 • C for 4 days. For amylin sample 2 (Figure , S1f), the same procedure was followed as sample 1, but a higher starting amount of peptide 1.4 mg was used. Sample 2 was incubated at 22 • C for 47 days.