comparable with that of silicon. The same
strategy that allows a bumper to adsorb
impact when hitting an obstacle allows the
fibers embedded in a soft matrix (composed
of an elastomer) to inhibit crack propaga-
tion when the device is stretched. Remark-
ably, after optimization of the process, this
complex geometry can be obtained via a
surprisingly low-cost procedure. Upon mix-
ing, the components spontaneously assem-
ble in their final shape and remain stable
for a time scale much longer than those of
These results are not the first case in
which unusual material properties, or
extraordinary applications, are associ-
ated with confinement effects. Wang et al.
discovered that an adequately processed
20-nm-thin layer of poly(ethylene oxide)
(PEO) has the same gas permeability of a
4-mm-thick film of the same polymer ( 10).
Careful analysis of the morphology of these
nanofilms revealed that the unexpected
two-orders-of-magnitude increase in bar-
rier properties arose from improved crystal
ordering upon confinement. Permeation in
bulk PEO is possible via the many defects
in the crystalline structure. The nanostruc-
ture films instead resemble a jigsaw puzzle
of impermeable large crystals that allows
diffusion of gas molecules only through the
rare interfaces among pieces.
The path that brought about the devel-
opment of 100% stretchable electronics is
quite different from this membrane work.
Xu et al. actively used the insights gained
from fundamental research on confine-
ment effects of polymers to solve a long-
standing problem of applied electronics.
Similar strategies for other applications
should be able to exploit the broad set of
known nanoconfinement effects. For exam-
ple, the intrinsic manifestation of nonequi-
librium effects in nanoconfined polymers
could be used to fabricate systems that re-
produce active membrane motion ( 11) and
other cell activities. j
REFERENCES AND NOTES
1. J. Xu etal .,Science 355, 59 (2017).
2. Y. Sun et al ., Nat. Nanotechnol. 1, 201 (2006).
3. T. C. Shyu etal. , Nat.Mater. 14, 785 (2015).
4. A. D. Printz, D. J. Lipomi, Appl. Phys. Lett. 3, 021302 (2016).
5. M.Alcoutlabi, G.B.McKenna, J. Phys.: Condes. Matter 17,
Confined Soft Matter (Springer, 2015).
7. Z.Fakhraai, J.A.Forrest, Science 319,600(2008).
8. Z.H.Yang et al., Science 328,1676(2010).
9. C. W. Frank et al., Science 273, 912 (1996).
10. H. P. Wang et al. , Science 323, 757 (2009).
11. H. Turlier etal., Nat.Phys. 12,513(2016).
This work was supported by the Fonds de la Recherche
Scientifique under grant T.0037.15 INCODYNCO.
Perception drives the
evolution of observable traits
By Hamilton Farris
The phrase “perception is reality” is used in many contexts but is often not rue. For example, human inability to perceive ultraviolet light does not ne- gate its reality. Nevertheless, percep- tion can cause reality to evolve. This
is the insight of the study by Nachev et al.
on page 75 of this issue (1). The authors integrated field and laboratory experiments
with computer simulations to explain how
perceptual mechanisms in a pollinator—a
bat—can cause the evolution of counterintuitive traits in flowers.
The appearance, sound, taste, and smell
of an organism are determined by the per-
ceptual abilities of the observer. This means
that the perceptual abilities of observers are
likely to have played a role in the evolution of
countless traits across species. For example,
Are there general perceptual rules that
could be used to explain and predict selec-
tion on such traits? It has been known since
the 1800s that for a constant or linear change
in the physical magnitude of a stimulus, hu-
mans do not experience an equivalent change
in perception ( 3). For example, if the number
of bulbs lighting a room is increased from
one to two, an observer is likely to notice the
difference in brightness. If, however, the in-
crease is from 50 to 51 bulbs, many observ-
ers will struggle to notice the change, even
though the absolute change is the same in
both cases. In fact, to be noticeable, the dif-
ference between two stimuli must be not con-
stant but rather proportional to its physical
Neuroscience Center, Department of Cell Biology and
Anatomy, Department of Otorhinolaryngology, Louisiana
State University School of Medicine, 2020 Gravier Street,
New Orleans, LA 70112, USA. Email: firstname.lastname@example.org
Bats choose flowers on the basis of nectar volume and
concentration, affecting how the flowers evolve
Proportional perception by the nectar-feeding bat Glossophaga commissarisi can explain why the flowers they
feed on evolve to have intermediate sugar concentrations.