SCIENCE sciencemag.orgGRAPHIC: C. BICKEL/
SCIENCE
; (PHOTOS) M. H. GODINHO
predicted to be destabilized if polydisperse,
smooth curved particles were used to pro-
duce the colloidal suspensions. However, in
the work of Fernández-Rico et al., there was
no evidence for the twist-bend nematic phase
(see the figure, bottom right). This phase is
characterized by the simultaneous assembly
of curved particles into right and left helices
to form an achiral system, as has been seen in
thermotropic molecular liquid crystals ( 12 ).
Through precise control of the curvature
of the particles, Fernández-Rico et al. could
tune the sequence of phases that includes not
only the splay-bend phase but also the biaxial
nematic and smectic phases. For small cur-
vature, the microparticles self-assemble into
nematic and smectic phases as the concentra-
tion of the solvent decreases. As the value of
the curvature increases, the splay-bend nem-
atic phase disappears. At the highest curva-
ture (almost circular arcs), only the isotropic
phase develops.
The study of Fernández-Rico et al. makes
possible the production of a range of nematic
colloidal liquid crystals. Theoretical predic-
tions suggest that tuning the curvature and
the interactions with the boundaries could
lead to phases not yet observed for colloidalliquid crystals, including the twist-bend nem-
atic. Chiral particles could further enhance
this class of smooth curved colloidal particles
and generate new phases. The optical proper-
ties and response to external fields of these
phases may form the basis for future studies
that cannot be carried out for molecular liq-
uid crystalline phases. j
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ACKNOWLEDGMENTS
M.H.G. is supported by the Portuguese Foundation
for Science and Technology under project nos. UID/
CTM/50025/2019 and M-ERA-NET2/0007/2016 (CellColor)
and by the European Topology Interdisciplinary Action
(EUTOPIA CA17139).
10.1126/science.abd3548
Scanning electron microscopy images
Curved solid lines are equidistant twisted layers and arcs
(red, left), and the “peaks” (right) can be attributed to the
fracture of the twisted layers.Left-handed
twistCurved structures
Long flaments can exhibit left- and
right-handed helices or spirals.Long-curved flaments
Similar structures are formed in certain liquid crystal phases.Helicoidal structure
The twisted plywood model, proposed
by Bouligand ( 6 ), accounts for the
helicoidal nature of the layers and arcs.1 mm 400 nm400 nmRight-
handed twistNTB
Right
twistLeft
twistNSBCellulose-nanorod chiral nematics
Solutions of cellulose nanorods form a nematic liquid crystalline phase that has a chiral twist.Curved phases
Slightly curved rods
organize in a nematic
splay-bend (NSB) phase
(right). No microrod
studied ( 1 ) led to the
nematic twist bend (NTB)
phase that can switch
from right- to left-
handed helices (left).PlaneMEDICINERemodeling
vasculature to
avoid blindness
Pathological vasculature
marks itself for repair
by deploying neutrophil
extracellular traps
By Eugene A. Podrez and Tatiana V. ByzovaV
ascular remodeling is essential for
building hierarchically structured
vascular networks, which in turn
support proper organ function ( 1 ).
The retina is particularly depen-
dent on optimal blood supply, and
insufficient or excessive vasculature often
leads to blindness. The process of vascular
regression reduces blood vessel density, fa-
cilitating normalization of vasculature and
subsequent tissue repair ( 2 ). Regression is
either caused by the withdrawal of essential
vascular growth factors or by triggering en-
dothelial apoptosis and subsequent pruning
of vasculature ( 3 ). However, it is unknown
how dysfunctional and excessive retinal
blood vessels are selected and marked for
pruning. On page 934 of this issue, Binet et
al. ( 4 ) reveal that pathological vasculature
in the retina of mice and humans orches-
trates its own remodeling by promoting the
extrusion of neutrophil extracellular traps
(NETs). This mechanism might be applied
to other pathologies that require vascular
remodeling, such as cancer, pulmonary hy-
pertension, and heart disease ( 3 ).
Retinal ischemic diseases, such as reti-
nopathy of prematurity and diabetic reti-
nopathy, are triggered by insufficient vascu-
lature, leading to ischemia (lack of oxygen),
which is compensated for by excessive
production of vascular growth factors, pri-
marily vascular endothelial growth factor
(VEGF). This leads to overgrowth of misdi-
rected and leaky vasculature, with signs of
vascular deterioration and senescence (in
which cells stop dividing and become dys-
functional) stimulated by aging or stress,
similar to processes observed in tumors ( 3 ).
Regression of this excessive and pathologi-
cal vasculature is a necessary step to avoidLerner Research Institute, Cleveland Clinic, Cleveland, OH,
USA. Email: [email protected]Liquid crystals from smooth curved colloidal systems
Fernández-Rico et al. found that different liquid crystals form from microrods with different degrees
of curvature. Natural systems such as cellulose nanorods form liquid crystals but have a chiral nature.21 AUGUST 2020 • VOL 369 ISSUE 6506 919
Published by AAAS