title: Neurofilament sidearms modulate parallel and crossed-filament orientations inducing nematic to isotropic and re-entrant birefringent hydrogels.
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.
authors.affiliation: Chemistry and Biochemistry Department, University of California, Santa Barbara, California 93106, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: Deek
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chung
authors.forename: Jona
authors.initials: J
authors.lastname: Kayser
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Bausch
authors.forename: Cyrus R
authors.initials: CR
authors.lastname: Safinya
mesh_terms: D000818:Animals; D001369:Axons / Q000737:chemistry*; D001718:Birefringence; D002417:Cattle; D003599:Cytoskeleton / Q000737:chemistry* / Q000378:metabolism; D020100:Hydrogels / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry*; D009994:Osmolar Concentration; D053838:Scattering, Small Angle; D013116:Spinal Cord / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D020100:Hydrogels; D014867:Water