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ARTICLE
Basal complex: a smart wing component for
automatic shape morphing
Sepehr H. Eraghi1, Arman Toofani 1, Ramin J. A. Guilani1,2, Shayan Ramezanpour1, Nienke N. Bijma 3,
Alireza Sedaghat4, Armin Yasamandaryaei4, Stanislav Gorb 3& Hamed Rajabi 1,5✉
Insect wings are adaptive structures that automatically respond to flight forces, surpassing
even cutting-edge engineering shape-morphing systems. A widely accepted but not yet
explicitly tested hypothesis is that a 3D component in the wing’s proximal region, known as
basal complex, determines the quality of wing shape changes in flight. Through our study, we
validate this hypothesis, demonstrating that the basal complex plays a crucial role in both the
quality and quantity of wing deformations. Systematic variations of geometric parameters of
the basal complex in a set of numerical models suggest that the wings have undergone
adaptations to reach maximum camber under loading. Inspired by the design of the basal
complex, we develop a shape-morphing mechanism that can facilitate the shape change of
morphing blades for wind turbines. This research enhances our understanding of insect
wing biomechanics and provides insights for the development of simplified engineering
shape-morphing systems.
https://doi.org/10.1038/s42003-023-05206-1 OPEN
1Mechanical Intelligence (MI) Research Group, South Bank Applied BioEngineering Research (SABER), School of Engineering, London South Bank University,
London, UK. 2Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran. 3Functional Morphology and Biomechanics, Institute of Zoology, Kiel
University, Kiel, Germany. 4Department of Mechanical Engineering, Lahijan Branch, Islamic Azad University, Lahijan, Iran. 5Division of Mechanical
Engineering and Design, School of Engineering, London South Bank University, London, UK. ✉email: rajabijh@lsbu.ac.uk
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Birds and bats possess flight muscles that actively control
their wing movements and deformations, thereby enhan-
cing their flight performance. On the contrary, insect wings
lack muscles, except those that are situated in the thorax and
control wing movements in the basal region of the wings. Instead,
insect wings consist of structural components that enable them to
automatically respond to flight forces1–6. The controlled
responses include bending, twisting and camber formation for
efficient lift and thrust generation2,7,8. Although the direct flight
muscles in the thorax can change and control the wing base
profile to a limited extent, the lack of muscles within insect wings
necessitates automatic shape control of the wings beyond the
wing base, encoded in the wing structural design and material
composition9. This distinguishing feature of insect wings, i.e.,
automatic shape control, makes them unique among all natural
and engineering systems and, more importantly, a potential
candidate for engineering applications that seek to achieve
automatic shape control10,11.
Dragonflies and damselflies from the insect order Odonata
outperform almost any other insect in terms of flight perfor-
mance. They exhibit intriguingly sophisticated flight thanks to
their highly specialised wings1–9. Many of the wing features,
including gradients of material properties12,13 and thickness14,15,
venation pattern2,16,17, corrugation18,19, nodus16,20,
pterostigma21, vein joints and joint-associated spikes22,23, resilin
patches24–26, vein ultrastructure23,27,flexion lines28, and the basal
complex4,29,30 contribute to the automatic deformability of odo-
natan wings, and in particular, wing camber formation. A widely
accepted but not yet explicitly tested hypothesis is that the basal
complex—a 3D structure at the wing base with a special
arrangement of veins—is key to determining the quality of wing
deformations in odonatan species2,16,29. Although the shape,
dimension, and position of the basal complex within the wing,
comprising a large part of the wing’s proximal region, suggest that
this may be a reasonable hypothesis, the literature data are mostly
descriptive, and quantitative and/or systematic investigations of
the role of the basal complex in wing deformations are still
rare4,31,32. A comprehensive study that establishes a link between
the structure, material and mechanical performance of the basal
complex can help us fill this literature gap. This is the overarching
aim of this study.
Here we selectively collected three species of Odonata,
including Ischnura elegans (Coenagrionidae), Calopteryx splen-
dens (Calopterygidae), and Sympetrum vulgatum (Libellulidae)
with morphologically different basal complexes and flight styles.
We used a combination of experimental methods and imaging
techniques, including scanning electron microscopy (SEM),
micro-computed tomography (micro-CT), confocal laser scan-
ning microscopy (CLSM), wide-field fluorescence microscopy
(WFM), mechanical testing, finite element analysis (FEA), para-
metric modelling, conceptual design, and 3D printing to (1)
examine both the structure and material of the basal complex, (2)
characterise how they influence the mechanical behaviour of the
basal complex, (3) determine the role of the basal complex in
wing deformations, and (4) use wing-inspired design concepts in
a real-world application. Our results are significant as they not
only enhance our understanding of the biomechanics of insect
wings but also inform the design of shape-morphing structures
that do not require complicated active controls.
Results and discussion
Structural, material, and mechanical characterisation. The
basal complex is a 3D corrugated structure at the wing base
of Odonata wings, which can comprise multiple structural
elements, including arculus, discoidal cell, triangle, subtriangle,
mediocubital bar, composite vein, and a network of inter-
connected veins (Fig. 1A–D). Although the structural design of
the basal complexes from different wings shares some com-
monalities, they are morphologically diverse, and their design
varies from one species to another. We used SEM, CLSM, WFM,
and micro-CT to investigate the structure and material properties
of the basal complex of the forewings in the two damselflies,
I. elegans and C. splendens, and the fore- and hindwings of the
dragonflyS. vulgatum, as three representatives of the order
Odonata (Fig. 1, Supplementary Fig. S1, Supplementary
Videos S1–S4). It is important to note that the fore- and
hindwings of damselflies (Zygoptera) are almost identical,
whereas they show rather strong differences in dragonflies
(Anisoptera).
The basal complexes of the investigated species are corrugated
structures with a multitude of vein joints, resilin patches, and a
network of veins and the membranes between them, comprising a
large portion of the wing base (Fig. 1, Supplementary Fig. S1).
They can be distinguished among the species based on their
structure and material composition. The basal complex of the
small damselflyI. elegans is the simplest in terms of design; it
consists of an arculus and a discoidal cell along with the smallest
network of veins (Fig. 1B). Its dorsal-ventral corrugation patterns,
as well as dorsal-ventral distribution of resilin patches, are
asymmetric (Supplementary Fig. S3). The basal complex of the
large damselflyC. splendens has also a relatively simple design but
possesses more structural elements than that of I. elegans.It
includes a mediocubital bar, a composite vein, and a dense
network of veins (Fig. 1C). In contrast to that observed in the
wings of I. elegans, both the dorsal-ventral corrugation patterns
and the dorsal-ventral distribution of resilin patches are
almost symmetric (Supplementary Fig. S5A, Q). The dragonfly
S. vulgatum possesses the most structurally complex basal
complex among the examined species (Fig. 1A, B). It has an
arculus and a discoidal cell, which is divided into two sub-
elements called triangle and subtriangle, both radically different
in fore- and hindwings. The corrugation patterns and distribution
of the resilin joints show dorsoventral asymmetry. Further, the
wings of S. vulgatum have a higher abundance of double-flexible
joints in comparison to both damselfly species (Fig. 2Ai–Aviii,
2Bi–Bviii, Supplementary Figs. S2 and S4).
The differences observed in the structural and material
properties of the basal complex between the studied species raise
an interesting question: How do these differences influence the
mechanical behaviour of the basal complex and the whole wing?
To address this question, we reproduced the deformations of the
wings in flight by subjecting them to a point force applied to the
radial vein posterior (RP) from below (Supplementary Fig. S21),
as this loading can result in deformations similar to those
exhibited by the wings in flight29. We performed the mechanical
testing on the forewings of damselflies I. elegans and C. splendens
and the fore- and hindwing of the dragonfly species S. vulgatum.
All experiments were conducted on live specimens, as insect
wings are living systems, which contain haemolymph inside their
veins, and their properties would change upon removal from the
body33,34. The wings were fixed at their base using bee wax to
avoid the influence of the deformations at the wing hinge on the
results. We subdivided the wings into two groups of intact and
cut wings. The cut wings had about one-third of the wing from
the base, and the rest of the wing was removed. Testing the two
groups of wings enabled us to investigate the mechanical
behaviour of the basal complex both within the wing and in
isolation.
The first interesting observation was that the force required to
deflect the wings for 10% of the lever arm (i.e., the distance between
the applied force and the fixation site) raised almost linearly with
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the displacement (Fig. 2Ci, Supplementary Figs. S3–S5). This
indicates the linear response of the wing to forces/displacements
applied within this range. Second, applying a force to the dorsal
side of the forewing of S. vulgatum, as an example, caused only a
small deformation in the basal complex (Fig. 2Ciii, Cv). In contrast,
a force applied to the ventral side resulted in a noticeable
deformation in the basal complex, which also formed a cambered
section (Fig. 2Cvii, Cix). Comparison of the results from the intact
and shortened wings showed that regardless of the direction of the
applied force, the deformation patterns of the intact wings and cut
wings were similar (Fig. 2Ciii–Cx, Supplementary Figs. S3–S5). In
both dorsal and ventral loadings, the deformations observed in the
whole wings were influenced by those of the basal complex—
applying a force on the ventral side of the wings resulted in a
camber formation (Fig. 2Cvi, Cx). The only difference was that the
camber formation in cut wings was slightly shifted towards the base
of the wing, an effect that can be due to the absence of the
pterostigma in the cut wings as a counterweight at the wing tip19.
These results suggest that the two-thirds of the wing domain distal
to the basal complex may have a comparatively small influence on
the wing deformation pattern, a finding which supports the
hypothesis mentioned earlier.
The mechanism of deformation is relatively simple yet very
effective (Fig. 2Di–Diii). When the force is applied to the radial
vein posterior (RP) from the ventral side, RP raises and elevates
the radial vein anterior (RA). The elevation of the radial vein
anterior (RA) causes the leading-edge spar to move downwards
slightly. The rotation of the wing about the axis of the median
vein anterior (MA) lowers the trailing edge. This deformation is
accompanied by the rotation of the triangle and subtriangle,
promoting the camber. The mechanism of deformation is almost
the same between the investigated wings and similar to that
described previously for comparatively simple Diptera wings31
(see Supplementary Note 1 for more information).
An interesting finding is that the wings of both the damselfly
I. elegans and the dragonflyS. vulgatum (Fig. 2C, Supplementary
Figs. S3 and S4) showed asymmetric deformation patterns when
bent upwards and downwards, whereas those of the damselfly
C. splendens exhibited an almost symmetric deformation
(Supplementary Figs. S5 and S10). Specifically, for the wings of
S. vulgatum, although no significant difference was found in the
bending moments required to deflect the wings between the two
opposite directions, a pressure applied to the wings resulted in
camber formation only when they were loaded on the ventral side
Fig. 1 Basal complex and its key components in odonate wings. A–DBasal complex of the dragonflyS. vulgatum forewing (A) and hindwing (B), the
damselflyI. elegans forewing (C) and the damselflyC. splendens forewing (D) (according to the nomenclature of Rehn, 2003). Wings are shown from the
dorsal side with “+”and “−”indicating if veins are raised (hill) or lowered (valley) in reference to the midline of the wing. Red areas show the discoidal
cells. AA anal vein anterior, C costal vein, CuA cubital vein anterior, CuP cubital vein posterior, IR intercalated vein, MA median vein anterior, MP median
vein posterior, RA radial vein anterior, RP radial vein posterior, ScA subcostal vein anterior, ScP subcostal vein posterior. Scale bars: 0.5 cm (A,B,D),
0.2 cm (C).
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(Fig. 2Cii–Cx, Supplementary Fig. S3). This is the characteristic
asymmetric deformation pattern of dragonfly wings, which
generates lift in the downstrokes29. This dorsal-ventral asymme-
try is likely the result of the distribution of asymmetric joints and
pre-cambered cross-sections of the wings (Fig. 2B, Supplementary
Fig. S2), which are less obvious for wings of C. splendens
(Supplementary Fig. S5).
To better understand how the basal complex influences wing
deformations, we developed one of the most comprehensive finite
element models of insect wings to date. This is a model of the
forewing of the dragonflyS. vulgatum, which includes many
morphological details of the wings, including longitudinal veins,
cross veins, vein joints, layered structure of veins, resilin patches,
nodus, pterostigma, corrugation patterns, and membranes
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(Supplementary Fig. S11). We used this model to investigate the
influence of the basal complex on both the quality and quantity of
wing bending, twisting, and camber. After verifying the validity of
the model and its accuracy in simulating wing response to
loadings (see “Methods”and Supplementary Fig. S12), we
removed the basal complex by modelling it as a flat plate. We
found that the removal of the basal complex from the wing
noticeably altered its deformations; wing bending increased by 1.7
times, the wing twisted in the opposite direction, and wing
camber decreased by 1.7 times (Fig. 3A, 3Bi–Bii, Supplementary
Fig. S13). Considering the detrimental effect of the wing bending
and the importance of the wing twisting and camber for the
aerodynamic load generation, the results suggest the key role of
the basal complex in the automatic shape changes of the wings,
supporting our experiments on the real wings.
We used our comprehensive numerical model in a comparative
study to understand how changing the geometric parameters of
the basal complex, including those shown in Fig. 3Ci, Cii, can
influence wing camber formation. Except for the rotation angle δ
of the longitudinal veins, which shows a linear decreasing trend
by increasing the angle, the variation of other geometric
parameters resulted in non-linear changes in the wing camber.
Among the studied parameters, the parameter ‘longitudinal veins
rotation angle δ’had the strongest influence; changing the angle
by 16 degrees increased the camber by 1.4 times (Fig. 3C,
Supplementary Figs. S14–S19). Subtriangle rotation angle γ,on
the other hand, had the smallest influence on the wing camber.
Interestingly, the basal complex model with geometric parameters
as those of the basal complex of the forewing of S. vulgatum
showed one of the largest cambers among all model variations
(Fig. 3C). This is important as it suggests the adaptation of the
wing basal complex to develop cambered sections in flight, a
phenomenon that can increase the ability of the wings to produce
aerodynamic forces.
Bioinspired design and application. The design strategies of the
basal complex investigated here demonstrated that the basal
complex is an automatic mechanism for shape morphing, which
can change configuration upon loading to form a cambered
shape. The basal complex indeed represents a striking example
that can inform studies in mechanical intelligence (MI), a new
research area that exploits nature-inspired mechanisms for
automatic adaptability and applies them to the design of struc-
tural components35. In general, this mechanism can inspire the
design of shape-morphing structures that do not require com-
plicated actuations to achieve functionality. In particular, the
basal complex can enable us to develop bioinspired symmetric
and asymmetric shape-changing mechanisms for a variety of
high-tech applications, such as flapping-wing robots, shape-
adaptive turbine blades, shape-adaptive airplane wings, airplane
wing flaps, and shape-adaptive car spoilers.
Using the conceptual parametric design, here we developed a
simplified model inspired by the wing basal complex. The
bioinspired mechanism consists of links that are connected to
each other via shafts and pin joints (Fig. 4Ai, Supplementary
Fig. S21). To guide the link motions, we designed a frame which
included a few pin slot joints (Fig. 4Aii, Supplementary Fig. S21).
By applying an upward force on the link RP, the mid-part of the
mechanism moves upwards, whereas the trailing edge is pushed
down, thereby creating a cambered configuration similar to that
seen in the natural wings (Fig. 4Aiii, Aiv, Supplementary
Video S5). Using a 3D-printed prototype, we tested the
functionality of our bioinspired design in practice (Fig. 4Bi–Bii).
This was found to be a simple yet functional mechanism that can
be easily manufactured and simply assembled/disassembled.
Using the example of deformable blades of a wind turbine, we
showed in a conceptual design that the mechanism is potentially
capable of automatic shape control of the chord-wise camber of
the blades and their angle of attack under varying wind forces,
thus enhancing their efficiency (Fig. 4C, 4Di–Diii)36–40. Our
proposed shape-morphing mechanism can offer advantages over
the conventional wind turbine blades, which only work efficiently
at specific operating points or over the shape-morphing blades
that require complex motor control systems and/or smart
material design36–40.
Methods
Specimens. In this study, we used adult damselflies Ischnura elegans (Vander
Linden, 1820) (Coenagrionidae) and Calopteryx splendens (Harris, 1782) (Calop-
terygidae) and adult dragonflies Sympetrum vulgatum (Linnaeus, 1758) (Libellu-
lidae). These species were used as they have different wing morphologies: I. elegans
has small wings with relatively simple architecture, C. splendens is a large damselfly
with a dense network of reinforcing veins, and S. vulgatum is a mid-size dragonfly
with fore and hindwings that differ in venation and shape and in contrast to the
other two damselfly species has broad-based wings. The specimens used for this
study were collected in Kiel, Germany (I. elegans, C. splendens and S. vulgatum)in
2016 and in Crimea, Ukraine, in 1997 (C. splendens).
For mechanical testing, we used only fresh wings of male individuals of I.
elegans and S. vulgatum that were caught with the permission of the Landesamt für
Natur und Umwelt des Landes Schleswig-Holstein (LANU). We used fresh
specimens because the properties of wings can change upon desiccation. Prior to
the experiment, the insects were anaesthetised using CO
2
.
Morphology investigation
Scanning electron microscopy (SEM). The basal complex of the wings was examined
with SEM. Prior to the SEM, air-dried wings of the male specimen were sputter
coated with a 10 nm gold-palladium layer using a high vacuum sputter coater
(Leica SCD 500, Leica Microsystems GmbH, Wetzlar, Germany). For the SEM, a
Fig. 2 Structural, material, and mechanical characterisation of the basal complex of the forewing of the dragonflyS. vulgatum.AScanning electron
microscopy (SEM) images of the forewing. SEM images of the arculus (Avii,Aviii) and the basal-anterior corner (Av,Avi), the apical-anterior corner (Ai,
Aii), and the posterior corner (Aiii,Aiv) of the triangle. Venation pattern of the basal complex of the forewing (Aix). Dorsal and ventral sides are indicated
by downward-pointing and upward-pointing arrows, respectively. BConfocal laser scanning microscopy (CLSM) maximum intensity projection images,
showing the occurrence of resilin in the arculus (Bvii,Bviii) and the corners of the triangle: basal corner (Bv,Bvi), apical corner (Bi,Bii) and the posterior
corner (Biii,Biv). The blue colour indicates the presence of resilin. Red and green colours show highly sclerotised and less sclerotised cuticles, respectively.
Distribution map of resilin patches (Bix). The occurrence of resilin is illustrated by the blue colour according to its location in the wing (dorsal or/and
ventral). White circles indicate firmly connected joints that lack resilin. The grey area illustrates the anal loop (Aix,Bix). CResults of mechanical testing of
wing deformability. Intact and cut forewings were deflected from the dorsal and ventral sides. Representative force-displacement curve obtained from the
forewing (Ci). Bending moments required to deflect the wings (Cii). The top, middle, lower lines, and dots in box-and-whisker plots are the lower extreme,
median, upper extreme, and outlier data, respectively. Ciii–Cx Height profiles of the forewing. Intact and cut forewings were deflected from the dorsal and
ventral sides. Resulting height profiles before (Ciii,Civ,Cvii,Cviii) and after (Cv,Cvi,Cix,Cx)deflection. Downward and upward-pointing arrows indicate
the side from which forces were applied (dorsal side: Ciii–Cvi and ventral side: Cvii-Cx). DMechanism of deformation of the basal complex (Di) when
subjected to forces on the ventral (Dii) and the dorsal sides (Diii). Ac arculus, Cr cross vein, Cu cubital vein, CuA cubital vein anterior, M median vein, MA
median vein anterior, Mb mediocubital bar, MP median vein posterior, RA radial vein anterior, RP radial vein posterior. Scale bars: 0.5 mm (Aix,Bix),
100 µm(Ai,Aii,Av,Avi,Bi,Bii,Bv,Bvi), 250 µm(Aiii,Aiv,Biii,Biv), 500 µm(Avii,Aviii,Bvii,Bviii).
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Hitachi TM3000 Tabletop Microscope (Hitachi High-Tech. Corp., Tokyo, Japan) at
an accelerating voltage of 15 kV and a magnification of 100X–600X was used.
Micro-computed tomography (micro-CT). To investigate the morphology of the
basal complex of Odonata wings, we used micro-CT scanning. For this, air-dried
wings were scanned using a Skyscan 1172 desktop micro-CT scanner (Bruker
micro-CT, Kontich, Belgium). Due to the similarity of fore- and hindwings in
damselflies, only the forewings of I. elegans and C. splendens were examined. The
specimens were scanned at a source voltage of 35–40 kV and a source current of
216–250 μA (Supplementary Table S1). For 3D reconstruction of the basal com-
plex, we used NRecon (Bruker micro-CT, Kontich, Belgium) and generated images
with pixel sizes of 2.67–5.00 µm. Processing and visualisation were done with
Amira 6.0.1 (FEI Visualization Science Group, Berlin, Germany).
Material composition investigation
Confocal laser scanning microscopy (CLSM). Wings of male and female specimens
were examined with a CLSM, which enabled us to characterise the differences in the
material composition based on their different autofluorescence characteristics41.The
elastomeric protein resilin has a very narrow wavelength band of around 420nm, in
which it emits blue autofluorescence (Andersen and Weis-Fogh 1964), allowing the
identification of resilin-dominating areas (Supplementary Figs. S6–S9).
For CLSM, air-dried wings were rehydrated for 24 h in a 10:1 mix of distilled
water and phosphate-buffered saline (PBS). Following short immersion in 70%
ethanol, the wings were embedded in glycerine (≥99.5% free of water) on a glass
slide and covered by a cover slip. To prevent direct contact between the wings and
cover slips, five reinforcement rings (used for office work) were attached to the
glass slide. The wings were visualised with a CLSM Zeiss LSM 700 (Carl Zeiss
Fig. 3 Finite element analysis of parametric models of the basal complex developed based on the forewing of Sympetrum vulgatum.ABending, twisting,
and camber in wing models with and without basal complex. V
B
and V
A
refer to the volume under the wing before and after deformation. BDeformation of
the wing with and without basal complex from the top view. CEffect of variations of the geometric parameters of the basal complex on camber formation.
The panel shows the perspective view (Ci) and the top view (Cii) of the basal complex. Altered geometric parameters include triangle exterior angle (α),
triangle interior angle (β), longitudinal veins rotation angle (δ), triangle rotation angle (ψ), subtriangle rotation angle (γ), triangle incline depth (η). The
angles measured in the real wings are highlighted using a red outline.
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MicroImaging GmbH) equipped with an upright microscope (Zeiss Axio
Imager.M1m). Four lasers with 405, 488, 555, and 639 nm wavelengths were used
during scanning. A bandpass emission filter transmitting 420–480 nm and three
longpass emission filters with ≥490, ≥560 and ≥640 nm were used to collect emitted
light from the specimens. The gain and intensity for each laser were manually
adjusted to avoid oversaturation. Samples were excited sequentially with the four
lasers, and images were collected with a line average equal to two. The pinhole size
was set to 1 AU (Airy Unit).
Overlapping optical image stacks were created for the entire thickness of the
specimen. Maximum intensity projections were created based on the collected
image stacks using ZEN 2009 software, where colours represent certain detected
wavelengths (blue for 420–480 nm, green for ≥560 nm, and red for ≥560 and
≥640 nm).
Wide-field fluorescence microscopy (WFM). To test the distribution of resilin in vein
joints, as a complementary method to the CLSM, we used fluorescence microscopy
(FM). For this purpose, we examined specimens using a Zeiss Axioplan fluores-
cence microscope (Carl Zeiss Microscopy GmbH, Germany). The preparation
method is the same as that conducted for the CLSM. For visualisation of the
autofluorescence of resilin, the microscope was equipped with a DAPI filter set with
a bandpass excitation filter transmitting 321–378 nm and a bandpass emission filter
transmitting 420–470 nm. Light intensity was manually adjusted to obtain optimal
saturation. Images were taken using a Zeiss Axio Cam Mrc (Carl Zeiss Microscopy
GmbH, Germany) and the Zeiss Efficient Navigation software (Carl Zeiss Micro-
Imaging GmbH). Wings were examined from both the dorsal and ventral sides.
Investigation of the mechanical behaviour
Mechanical testing. Experiments were carried out to characterise the deformation
of the wings under loading. For each specimen, we recorded forces, displacements,
and 3D deformation patterns of the wings. Freshly killed five male individuals of
each of the species I. elegans,C. splendens and S. vulgatum were used in experi-
ments. In order to prevent desiccation, which can change the material properties,
and thereby the mechanical behaviour of the wings, the tests were performed on
live insects, and a droplet of bee wax was used to fix the wings at their joints to the
body (Supplementary Fig. S22).
For force measurements during wing deflection, we used a 10 g force sensor
(WPI Fort 10g, World Precision Instruments, Florida, US) connected to an MP 100
data acquisition system (Biopac System Inc, Goleta, CA) (Supplementary Fig. S22).
The data acquisition rate was set to 2000 Hz. The wings were deflected by applying
a point force to the radial vein posterior (RP) at ~30% of the wing length away
from the wing base (Supplementary Fig. S22). This is expected to reproduce the
deformation of the wings in flight29. The force was applied using the blunt side of
an insect pin attached to the force sensor. The displacements of the force sensor
were precisely controlled using a micromanipulator (Physik Instrumente (PI)
GmbH & Co. KG, Karlsruhe, Germany) via the software PIMikroMover 2.4.4.6.
The displacement speed was set as 0.05 mm/s. A displacement equal to 10% of the
wing’s length was applied to each specimen. The data from the data acquisition
system was recorded using the software AcqKnowledge 3.7 over the course of the
loading. The experiment was conducted under the 3D measurement microscope
Keyence VR300 (Keyence Microscope Europe, Mechelen, Belgium), which enabled
us to capture the 3D profile of the wings before and after loading. The experiments
were performed on both the dorsal and ventral sides of the wings.
The testing procedure was repeated for wings in which two-thirds of the wing
length was removed from the distal part (i.e., only the basal complex was left). This
enabled us to compare the deformations of the intact and cut wings and
characterise the role of the basal complex on wing deformations. The testing of
each specimen never exceeded 2 h.
Finite element analysis (FEA). We used finite element analysis to investigate the
influence of the basal complex and its geometric parameters on the mechanical
response of the wings to loading. For this purpose, we developed a detailed 3D
model of the forewing of the dragonflyS. vulgatum using the computer-aided
design software CATIA v5 (Dassault Systèmes, Sureness, France) based on the data
from micro-CT and SEM. In this model, the key structural features of wings,
including the corrugations, pre-camber, thickness gradient, longitudinal veins,
cross veins, the basal complex, resilin joints and resilin-rich layers within the veins,
were modelled. The thickness gradient included changes in both the thickness of
a edom
C conceptual design of wind turbine
A bio-inspired design of shape morphing mechanism
b edom
D shape morphing blade
B 3d-printing
iii
iii iv
i
ii
ii
i
iii
wind force
te
RP link
te RP link
te
RP link
Fig. 4 Bioinspired automatic shape morphing. A Bioinspired shape-morphing mechanism with the ability to change its configuration between mode
a(Ai,Aii) and mode b (Aiii,Aiv). B3D printing and testing. 3D-printed mechanism in mode a (Bi), in mode b (Bii). CConceptual turbine blade.
DApplication of the bioinspired mechanism in shape-morphing turbine blade in mode a (initial configuration) (Di) and in mode b (cambered configuration)
(Dii). Diii A perspective view of the mechanism. te trailing edge.
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the membranes and the costal vein. We developed this gradient using data reported
by Jongerius and Lentink14. Specifically, we set the thickness of the membrane to
change from 20 to 5 μm. In the thickest areas, we set the radius and thickness of the
costal vein to be 80 μm and 40 μm, respectively, and in the thinnest parts, we set
them to 50 μm and 20 μm, respectively. We also made a few simplifying
assumptions by considering the veins (except the costal vein) as circular tubes with
a constant radius and thickness of 20 μm and 7 μm, respectively, throughout the
model. Resilin patches were modelled through connections of different modelled
materials in the assembly, regardless of whether they were on the dorsal or the
ventral side.
To quantify the role of the basal complex on wing deformability, we developed
another model by removing the basal complex from the wing. In other words, the
second model is the same as our reference model, except that the basal part of the
model is flat.
Next, by changing the geometric parameters of the model of the S. vulgatum
forewing, we developed 27 models with distinct morphologies of the basal complex
for a comparative study. The models, in which the geometric parameters were
changed at set intervals, enabled us to quantify the effect of the geometric
parameters of the basal complex on its camber formation. The geometric
parameters included in our study were triangle exterior angle (α), triangle interior
angle (β), subtriangle rotation angle (γ), longitudinal veins rotation angle (δ),
triangle incline depth (η), and triangle rotation angle (ψ) (Fig. 3C). For complete
wing models, we utilised the volume below the wings to characterise camber. For
cut wing models (models of the basal complex only), we characterised the camber
by calculating the area below the free end of the models, as it was easily accessible
(Supplementary Fig. S20).
For simulations, the models were imported into the ABAQUS v.6.14 FE
software package (Simulia, Providence, RI). The Young’s modulus and the
Poisson’s ratio were set as 3 GPa and 0.49 for veins and 1.86 GPa and 0.49 for
membranes42,43, respectively. The Young’s modulus and the Poisson’s ratio of
resilin were 2 MPa and 0.4944, respectively (Supplementary Fig. S11). The two-
node beam elements B31 and the general-purpose shell elements S4R were used to
model veins and membranes, respectively. The models were subjected to the same
loading and boundary conditions as those used in mechanical testing described
earlier. Specifically, the wings were fixed at their base (both displacements and
rotations) and then subjected to a displacement at RP from the dorsal/ventral sides.
A mesh convergence analysis was conducted to find the suitable mesh size resulting
in reasonably accurate results in each simulation. We selected the mesh size at
which the results no longer changed significantly as the appropriate mesh size for
our models.
To validate the FEA model, we compared the force-displacement curves
obtained from the experiments conducted on intact wings with their respective
simulations (Supplementary Fig. S12). This comparison allowed us to assess the
accuracy of the model’s predictions. We measured the average stiffness of both the
wings and their corresponding FEA models from the two sets of curves. Our
validation results revealed a difference of ~12% between the measured stiffness
values.
Bioinspired application
Parametric modelling and conceptual design. Using the computer-aided design
software (Rhinoceros 7 3D, Seattle, WA) and Grasshopper plugin, we developed a
parametric model of a mechanism for camber formation inspired by the basal
complex. The mechanism consists of 16 linkages, 10 shafts, and 20 shaft pins,
which are assembled within a frame. The dimensions of the elements of the
mechanism are set as variable parameters and can be tuned to satisfy the
requirements of various design purposes. The mechanism was designed to undergo
considerable deformations and form a cambered shape when subject to upward/
downward forces on the RP linkage (Fig. 4, Supplementary Fig. S21). We further
developed a conceptual model of a deformable wind turbine blade to demonstrate
the application of our bioinspired mechanism in a real-world engineering system
(Fig. 4).
Fabrication. To show the functionality of the bioinspired camber formation
mechanism in practice, the individual elements of the mechanism were first fab-
ricated using 3D printing and then assembled. To this end, we used a Creality
Ender 3 FDM 3D Printer (Shenzhen Creality 3D Technology Co Ltd., Shenzhen,
China) and polylactic acid (PLA) filament (Basicfilfilament, filament diameter of
1.75 mm). Printing was done at a nozzle temperature of 220 °C, a bed temperature
of 60 °C, and a print speed of 40 mm/s. The layer height was set at 0.2mm. The
parts were printed at 100% infill density. No postprocessing was performed on the
3D-printed parts.
Statistics and reproducibility. Statistical analyses were performed to compare the
bending moments required to deform the wings at different states. Specifically,
we used t-test to compare the bending moments between the dorsal and ventral
side loadings. We also used analysis of variance (ANOVA) to compare the bending
moments between intact and cut wings.
Reporting summary. Further information on research design is available in the Nature
Portfolio Reporting Summary linked to this article.
Data availability
The authors declare that the data supporting the findings of this study are available
within the paper and its supplementary information files. Specifically, the data from
mechanical testing and numerical simulations can be found in Supplementary Table S2
and Supplementary Figs. S14–19, respectively.
Received: 12 February 2023; Accepted: 2 August 2023;
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Author contributions
Conceptualisation: S.G., H.R.; Supervision: S.G., H.R., A.S.; Formal analysis: S.R., N.N.B.,
H.R.; Investigation—modelling and simulation: S.R., R.J.A.G.; Investigation—micro-
scopy: N.N.B., H.R.; Investigation—product design: S.H.E., A.T.; Investigation—
mechanical testing: N.N.B., H.R.; Investigation—3D printing: A.Y.; Project administra-
tion: H.R.; Resources: S.G., H.R.; Methodology: S.G., H.R.; Validation: S.R., R.J.A.G.;
Visualisation: A.T., S.H.E., N.N.B.; Writing—original draft preparation: S.H.E., N.N.B.,
H.R.; Writing—review and editing: S.H.E., A.T., A.S., S.G., H.R.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information The online version contains supplementary material
available at https://doi.org/10.1038/s42003-023-05206-1.
Correspondence and requests for materials should be addressed to Hamed Rajabi.
Peer review information Communications Biology thanks Mary Salcedo and Ryan
Schwab for their contribution to the peer review of this work. Primary handling editors:
Luke Grinham and Christina Karlsson Rosenthal. A peer review file is available.
Reprints and permission information is available at http://www.nature.com/reprints
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