Particle size and zeta potential measurements. A Zetasizer Nano-ZS90 (Malvern) was employed to measure the particle size and zeta potential of the fibril and fibril cluster suspensions. The measurements were taken immediately after diluting the samples to 0.02% (w/v, counted by fibrils) with NaCl solution (0.9%). All measurements were performed in triplicate at 25 °C.