Abstract
Neurofilaments are intermediate filaments assembled from the subunits
neurofilament-low, neurofilament-medium and neurofilament-high. In
axons, parallel neurofilaments form a nematic liquid-crystal hydrogel
with network structure arising from interactions between the
neurofilaments' C-terminal sidearms. Here we report, using small-angle
X-ray-scattering, polarized-microscopy and rheometry, that with
decreasing ionic strength, neurofilament-low-high,
neurofilament-low-medium and neurofilament-low-medium-high hydrogels
transition from the nematic hydrogel to an isotropic hydrogel (with
random, crossed-filament orientation) and to an unexpected new
re-entrant liquid-crystal hydrogel with parallel filaments-the
bluish-opaque hydrogel-with notable mechanical and water retention
properties reminiscent of crosslinked hydrogels. Significantly, the
isotropic gel phase stability is sidearm-dependent:
neurofilament-low-high hydrogels exhibit a wide ionic strength range,
neurofilament-low-medium hydrogels a narrow ionic strength range,
whereas neurofilament-low hydrogels lack the isotropic gel phase. This
suggests a dominant regulatory role for neurofilament-high sidearms in
filament reorientation plasticity, facilitating organelle transport in
axons. Neurofilament-inspired biomimetic hydrogels should therefore
exhibit remarkable structure-dependent moduli and slow and fast
water-release properties.
