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Analysis on surface nanostructures present in hindwing of dragon fly (Sympetrum vulgatum) using atomic force microscopy
Micron 43 (2012) 1299–1303
Contents lists available at SciVerse ScienceDirect
Micron journal homepage: www.elsevier.com/locate/micron
Analysis on surface nanostructures present in hindwing of dragon fly (Sympetrum vulgatum) using atomic force microscopy Selvakumar Rajendran ∗ , Karthikeyan K Karuppanan, Radhakrishnan Pezhinkattil Nanobiotechnology Laboratory, Nanotech Research Facility, PSG Institute of Advanced Studies, Coimbatore 641 004, India
a r t i c l e
i n f o
Article history: Received 17 June 2011 Received in revised form 15 September 2011 Accepted 21 October 2011 Keywords: Dragon fly wing Sympetrum vulgatum Biological nanostructures Roughness AFM
a b s t r a c t The present study involves the analysis of surface nanostructures and its variation present in the hind wing of dragon fly (Sympetrum vulgatum) using atomic force microscopy (AFM). The hindwing was dissected into 4 parts (D1–D4) and each dissected section was analyzed using AFM in tapping mode at different locations. The AFM analysis revealed the presence of irregular shaped nanostructures on the surface of the wing membrane with size varying between 83.25 ± 1.79 nm to 195.08 ± 10.25 nm. The size and shape of the nanostructure varied from tip (pterostigma) to the costa part. The membrane surface of the wing showed stacked arrangement leading to increase in size of the nanostructure. Such arrangement of the nanostructures has lead to the formation of nanometer sized valleys of different depth and length on the membrane surface giving them ripple wave morphology. The average roughness of the surface nanostructures varied from 18.58 ± 3.12 nm to 24.25 ± 8.33 nm. Surfaces of the wings had positive skewness in D1, D2 and D4 regions and negative skewness in D3 region. These surface nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing. © 2011 Elsevier Ltd. All rights reserved.
1. Introduction Insect wings are of great interest to scientists for its flight mechanisms (Wootton, 1999; Grodnitsky, 1999). Insect wings comprises of multiple dense veins which holds the membrane intact. These wing structures offer stiffness, durability and ultra light aerofoil to the flapping of wings (Newman and Wootton, 1986). The wings of the insect have defined surface structures with unique physical, chemical, optical and mechanical properties (Wagner et al., 1996). For example, the wings surface structure of moths, Thaumantis diores and elytra determine their hydrophobicity, colors and mechanical properties respectively (Fang et al., 2007; Wang et al., 2009; Han et al., 2009; Yang et al., 2010). These studies clearly indicate that the surface morphologies and surface structures have close relationship with specific function. Among the various insect wings, the wings of dragon fly are well known for its stability and high load-bearing capacity during flapping flight, gliding and hover, despite the fact that their mass is
∗ Corresponding author at: Nanobiotechnology Laboratory, PSG Institute of Advanced Studies, P.B. No. 1609, Peelamedu, Coimbatore 641 004, India. Tel.: +91 9944920032. E-mail addresses: [email protected], [email protected] (R. Selvakumar). 0968-4328/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2011.10.017
less than 2% of a dragonfly’s total body mass. The flapping wings of dragonfly can perform various swift and highly maneuverable flights as a result of the highly functional and largely optimized mechanical constructions of its wings. The micro and macrostructures including the veination and functions of dragonfly wings have been systematically explored for many years (Wootton, 1991; Brackenbury, 1992). Numerous studies have been carried on the dragon fly wings to find out its structural properties and its role in flight mechanism. A dragonfly’s wing has different external components such as costa, nodus and pterostigma that assist in the wing function and structure (Song et al., 2007; Li et al., 2009). The wings of dragonflies are mainly composed of network of tubular veins and membranes made up of atypical two-dimensional (2D) composite structures in micro or nano-scale (Sun et al., 2010). The membrane is very uneven and is designed in such a way that it adsorbs stress and allows deformations to occur in the membrane (Wootton, 1991; Smith et al., 2000). The membrane is made up of structural proteins and polymers such as chitin and resilin protein which predominates in the stiff and flexible parts of the wings respectively (Marrocco et al., 2009, 2010). These membrane structures are reported to determine the wings response towards various aerodynamic forces including bending and twisting of wings (Combes and Daniel, 2003). Okamoto et al. (1996) characterized the effects of camber, thickness, sharpness of the leading edge and surface roughness on the aerodynamic characteristics of dragonfly wings
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R. Selvakumar et al. / Micron 43 (2012) 1299–1303
Fig. 1. Image of a dragonfly Sympetrum vulgatum hindwing showing 4 different sections considered for analysis.
in the flow field. Zeng et al. (1996) measured the thickness and shape of dragonfly wings. Sudo et al. (2000) investigated the surface roughness of dragonfly wings. Although lot of studies have been carried out on the micro and nanostructures structures present in the dragon fly wings, very few studies have significantly reported the variation in the structures within the wing membrane surface. The present study aims to explore the presence of distinct biological nanostructures present in the wings of the dragon fly and its variation in size and shape within the wing surface. The wing was divided into four different sections (D1–D4) starting from pterostigma to the costa part and was analyzed for the presence of surface nanostructure and its arrangements using atomic force microscopy (AFM). The average size of the nanostructures, peak height and trough depth formed due to the arrangement of nanostructure were analyzed. The average roughness and skewness was also analyzed and interpreted. Based on the results, a comparative analysis has been made on the nanostructures present at different locations of the wings and the results have been interpreted.
Fig. 2. AFM image of dragon fly wing with multilayer arrangements of membrane containing nanostructures (arrows indicating the different layers arranged one over the other; circle indicating the “ripple wave morphology”).
sample and mean of the values were taken. The roughness analyses, height between two nanostructures, size of the nanostructure, and grain analysis of the sample were measured using NTMDT image analysis software. 3. Results and discussion 3.1. Atomic force microscopy of dragon flies wings
2. Materials and methods 2.1. Wing collection Dragon fly (Sympetrum vulgatum) was caught from a nearby residential area of KK nagar, Tiruchirapalli, Tamilnadu, India and the wings were separated from the dragon fly without any damage to the membrane. The wing was brought to the laboratory in a dry plastic container and used for further analysis. 2.2. Processing of dragon fly wing The hind wing (4.9 cm in length) was dissected into four equal sections (D1–D4) (Fig. 1) carefully without causing any damage and was stored in a plastic container. The dissected wing was analyzed immediately. 2.3. Atomic force microscopic study The dissected wing sections of Sympetrum vulgatum were characterized using AFM. The wing section was mounted onto a safire platform using a double sided scotch tape and inserted into the sample platform. Images were then recorded by a multimode Scanning Probe Microscope (SPM) (Ntegra Aura, NTMDT Co, Russia) at ambient condition (25 ± 2 ◦ C) using single crystal silicon N type probes (NSG 03-A) having radius of curvature of 10 nm. The cantilever with long tips (aspect ratio 3:1) with force constants of 0.35–6.06 N/m and resonance frequencies of 47–150 kHz, was used to image the surface morphology. The wings were scanned using non-contact (tapping) mode AFM in different sizes starting from 50 × 50 m and then gradually reduced the scan area to lower area size. The images were recorded from 11 different areas of each
The wing membrane is a natural biological membrane made mainly from structural proteins, whose material and mechanical properties are closely associated with the flight capacity of the insects themselves (Wootton, 1990). The membrane is not simply a barrier to the passage of air through the wing but has a structural role as a stressed skin, stiffening the frame work of veins. There is all possibility for a local variation in the mechanical properties and, hence, in the structure of the membrane within the wing, with profound implications for it’s functioning in flight (Xiao et al., 2007). Despite of these possibilities, the basic material and mechanical properties of the membrane of the insect wings, as well as its micro and nano structure, have not been understood very well (Xiao et al., 2007; Combes and Daniel, 2003). In this present study, an attempt has been made to study the nano structural arrangement of proteins and polymers in the dragon fly wings membrane. The hind wing of Sympetrum vulgatum was dissected into four sections (D1–D4) and the lateral surface was characterized using atomic force microscope in non contact mode. The inter vein distance was less in D1 region and gradually increased with D2, D3 and D4 regions of the dragon fly wing. Imaging was carried out only between the veins. The AFM analysis of the wing with higher scan area (50 m × 50 m) revealed that the membranes were assembled in multiple layers like a stacked sheets (Fig. 2, indicated using arrow mark). The surface of the wing was rough and had serrated margins. The surface of the wings also showed many deformations. Xiao et al. (2010) studied the micro and nanostructures of the dragon fly wing veins. They found interesting pleat morphologies at their surfaces having “ripple wave morphologies” looking like ripple waves with alternative peak and a trough when imaged through scanning electron microscopy. However their observations did not reveal why such
R. Selvakumar et al. / Micron 43 (2012) 1299–1303
Fig. 3. AFM image of D1 (a), D2 (b), D3 (c) and D4 (d) sections of Sympetrum vulgatum hindwing with a varying scan area (i). (ii) The 3D image of scan area.
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Table 1 Analysis of height, trough depth and size of nanostructure in various regions of the dragon fly wing membrane. S. No
Region of wing
Average ten point height (nm)
1 2 3 4
D1 D2 D3 D4
188.31 133.09 79.63 170.2
± ± ± ±
10.82 8.34 6.39 126.25
Average trough depth (nm) 70.38 95.84 50.88 71.18
± ± ± ±
40.72 36.39 22.1 23.8
Size of the nanostructure in diameter (nm) 195.08 135.85 83.25 145.2
± ± ± ±
10.25 6.02 1.79 103.01
D1–D4: four different regions in the dragonfly wing; ±: standard deviation; Values of average of 11 random measurements. Table 2 Analysis of grains parameters in various regions of the dragon fly wing membrane. S. No
Region of wing
Surface skewness (Ssk )
1 2 3 4
D1 D2 D3 D4
0.05 0.137 −0.07 0.11
± ± ± ±
0.44 0.05 0.2 0.17
Aspect ratio (m/m) 0.049 0.019 0.018 0.033
± ± ± ±
0.03 0.02 0.01 0.01
Average roughness (nm) 22.47 24.25 18.58 23.21
± ± ± ±
3.36 8.33 3.12 11.26
D1–D4: four different regions in the dragonfly wing; ±: standard deviation; Values are average of 11 random measurements.
ripple waves morphologies occur at its surface. The present investigation gives the reason for such morphologies. Fig. 2 (encircled) clearly indicates the similarity of ripple wave as observed during the investigation by Xiao et al. (2010). The stacking of the membranes one over the other and the leading edges of the stacked membranes gives this unique ripple wave morphology. Moreover the stacking is not only contributed by the membrane but also by the size and distribution of the varying nanostructures present in each membrane layer. The initial AFM imaging of D1–D4 region clearly revealed the presence of near globular nanosized particle, tightly packed one above the other (Fig. 3). By decreasing the scan area, the arrangements of nanostructures one over the other as stacks were clearly visible. The size and shape of the nanostructures varied from one region to other (Fig. 3(i) and (ii) in a–d). The area below the pterostigma (D1) showed elongated nanostructures (Fig. 3a(i)) with an average size (in diameter) of 195.08 ± 10.25 nm (Table 1). The D2 area has irregular morphology with average size of 135.85 ± 6.02 (Fig. 3b(ii)). The area below the subcosta (D3 region) showed lowest size (83.25 ± 1.79) (Fig. 3c(ii)) when compared to other region and had irregular serrated margins. D4 region showed highly varied nanostructures where few areas were dominated by larger sized nanostructures and areas with smaller one were also predominant. Among these areas selected, D1 had maximum size when compared to others. The 3D images of the scan area depicted that the height of the nanostructures also varies with the regions leading to the ripple wave morphology at the surface of the dragon fly membrane (Fig. 3(iii) in a–d). The variation in ten point height of the nanostructure in D4 region of the wing was very high when compared to other regions. The average ten point height of the nanostructure was highest in D1 region (188.31 ± 10.82) followed by D4, D2 and D3 (Table 1). The maximum height of the nanostructures in D1, D2, D3 and D4 was 200 nm, 136.6 nm, 87.55 nm and 81.88 nm with a maximum count of 132, 113, 145 and 177 respectively. Recently, Marrocco et al. (2010) reported that a large part of the wing structure of dragonfly is made of chitin protein and the joints are made of less stiff resilin protein. The nanostructures observed during the AFM analysis of the wings may be due to the arrangement of chitin and resilin molecules giving a defined structural morphology. The grain analysis of the scanned membrane nanostructures revealed variation in roughness from one region to the other (Table 2). The average roughness (arithmetic mean of the absolute values of the surface departures from the mean plane) was high in D2 region when compared to D1, D3 and D4. Skewness is a measure of the distribution of heights. Positive value of skewness indicate the presence of height values considerably above the average while
negative values indicate the presence of height values considerably below the average. Thus a flat surface with protruding feature will have a positive skewness, while a surface with deep scratches/pits will exhibit negative skewness (Eaton and West, 2010). The skewness was positive for all the regions except D3 where the skewness went negative (Table 2).
4. Conclusion The atomic force microscopy clearly indicates the presence of varying size of nanostructures at various regions of Sympetrum vulgatum wing surface. The membranes are assembled in multiple layers like stacked sheets with nanostructures resembling ripple wave morphologies. The region near the costa part showed the presence of bigger nanostructures when compared to other region. The roughness and skewness of the wing nanostructure also varied from one area to other. These nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing. The spick like edges of these nanostructures may be the reason for high performance flight by causing increase in lift force. Hence this study clearly indicates that since the distribution and arrangement of nanostructure within the wing varies which leads to varying resistance, its influence in flight mechanism should not be neglected during designing/modeling of wings.
Acknowledgement The authors are thankful to Mr. V. Parthasarathy, Senior Research Fellow, PSG Institute of Advanced Studies, Coimbatore, for helping in getting the dragonfly wings.
References Brackenbury, J., 1992. Insects in Flight. Blandford Press, London. Combes, S.A., Daniel, T.L., 2003. Flexural stiffness in insect wings I. Scaling and the influence of wing venation. J. Exp. Biol. 206, 2979–2987. Eaton, P., West, P., 2010. Atomic Force Microscopy. Oxford University press, pp. 116–117. Fang, Y., Sun, G., Wang, T.Q., Cong, Q., Ren, L.Q., 2007. Hydrophobicity mechanism of non-smooth pattern on surface of butterfly wing. Chinese Sci. Bull. 52, 711–716. Grodnitsky, D.L., 1999. Form and Function of Insect Wings. The Johns Hopkins University Press, Maryland. Han, Z.W., Wu, L.Y., Qiu, Z.M., Ren, R.L., 2009. Microstructure and structural color in wing scales of butterfly Thaumantis diores. Chinese Sci. Bull. 54, 535–540. Li, Z.X., Wei, S., Tong, G.S., Tian, J.M., Loc, V.Q., 2009. On the vein-stiffening membrane structure of a dragonfly hindwing. J. Zhejiang Univ. Sci. A 10 (1), 72–81.
R. Selvakumar et al. / Micron 43 (2012) 1299–1303 Marrocco, J., Demasi, L., Venkataraman, S., 2010. Investigating the Structural Dynamics Implication of Flexible Resilin Joints on Dragonfly Wings. ACSESS Proceedings. San Diago State University, AP10-09. Marrocco, J., Venkataraman, S., Demasi, L., 2009. Biomimetic Design of a Flexible Wing. ACSESS Proceedings. San Diago State University, AP09-08. Newman, D.J.S., Wootton, R.J., 1986. An approach to the mechanics of pleating in dragonfly wings. J. Exp. Biol. 125, 361–372. Okamoto, M., Yasuda, K., Azuma, A., 1996. Aerodynamic characteristics of the wings and body of a dragonfly. J. Exp. Biol. 199 (2), 281–294. Smith, C.W., Herbert, R., Wootton, R.J., Evans, K.E., 2000. The hind wing of the desert locust (Schistocerca gregaria Forskål). II. Mechanical properties and functioning of the membrane. J. Exp. Biol. 203, 2933–2943. Song, F., Xiao, K.W., Bai, K., Bai, Y.L., 2007. Microstructure and nanomechanical properties of the wing membrane of dragonfly. Mater. Sci. Technol. A 457, 254–260. Sudo, S., Tsuyuki, K., Tani, J., 2000. Wing morphology of some insects. JSME Int. J. Series C: Mech. Syst. Mach. Elem. Manuf. 43 (4), 895–900. Sun, J.Y., Pan, C.X., Tong, J., Zhang, J., 2010. Coupled model analysis of the structure and nano-mechanical properties of dragon fly wings. IET Nanobiotechnol. 4 (1), 10–18.
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Wagner, T., Neinhuis, C., Barthlott, W., 1996. Wettability and contaminability of insect wings as a function of their surface sculptures. Acta Zool. 77, 213–225. Wang, X.J., Cong, Q., Zhang, J.J., Wan, W.L., 2009. Multivariate coupling mechanism of NOCTUIDAE moth wings’ surface superhydrophobicity. Chinese Sci. Bull. 54, 569–575. Wootton, R.J., 1999. How flies fly. Nature 400, 112–113. Wootton, R.J., 1990. The mechanical design of insect wings. Sci. Am. 11, 114–120. Wootton, R.J., 1991. Functional morphology of the wings of odonata. Adv. Odonatol. 5, 153–169. Xiao, K., Bai, K., Wang, W., Song, F., 2007. Experimental study on the microstructure and nanomechanical properties of the wing membrane of dragonfly. Acta Mech. Sin. 23, 281–285. Xiao, Z.H., YaJun, Y., Zheng, Z., 2010. Micro and nano structures and morphologies on the wing veins of dragonflies. Chinese Sci. Bull. 55 (19), 1993–1995. Yang, Z.X., Dai, Z.D., Guo, C., 2010. Morphology and mechanical properties of Cybister elytra. Chinese Sci. Bull. 55, 771–776. Zeng, L.J., Matsumoto, H., Kawachi, K., 1996. Simultaneous measurement of the shape and thickness of a dragonfly wing. Measure. Sci. Technol. 7 (12), 1728–1732.
Contents lists available at SciVerse ScienceDirect
Micron journal homepage: www.elsevier.com/locate/micron
Analysis on surface nanostructures present in hindwing of dragon fly (Sympetrum vulgatum) using atomic force microscopy Selvakumar Rajendran ∗ , Karthikeyan K Karuppanan, Radhakrishnan Pezhinkattil Nanobiotechnology Laboratory, Nanotech Research Facility, PSG Institute of Advanced Studies, Coimbatore 641 004, India
a r t i c l e
i n f o
Article history: Received 17 June 2011 Received in revised form 15 September 2011 Accepted 21 October 2011 Keywords: Dragon fly wing Sympetrum vulgatum Biological nanostructures Roughness AFM
a b s t r a c t The present study involves the analysis of surface nanostructures and its variation present in the hind wing of dragon fly (Sympetrum vulgatum) using atomic force microscopy (AFM). The hindwing was dissected into 4 parts (D1–D4) and each dissected section was analyzed using AFM in tapping mode at different locations. The AFM analysis revealed the presence of irregular shaped nanostructures on the surface of the wing membrane with size varying between 83.25 ± 1.79 nm to 195.08 ± 10.25 nm. The size and shape of the nanostructure varied from tip (pterostigma) to the costa part. The membrane surface of the wing showed stacked arrangement leading to increase in size of the nanostructure. Such arrangement of the nanostructures has lead to the formation of nanometer sized valleys of different depth and length on the membrane surface giving them ripple wave morphology. The average roughness of the surface nanostructures varied from 18.58 ± 3.12 nm to 24.25 ± 8.33 nm. Surfaces of the wings had positive skewness in D1, D2 and D4 regions and negative skewness in D3 region. These surface nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing. © 2011 Elsevier Ltd. All rights reserved.
1. Introduction Insect wings are of great interest to scientists for its flight mechanisms (Wootton, 1999; Grodnitsky, 1999). Insect wings comprises of multiple dense veins which holds the membrane intact. These wing structures offer stiffness, durability and ultra light aerofoil to the flapping of wings (Newman and Wootton, 1986). The wings of the insect have defined surface structures with unique physical, chemical, optical and mechanical properties (Wagner et al., 1996). For example, the wings surface structure of moths, Thaumantis diores and elytra determine their hydrophobicity, colors and mechanical properties respectively (Fang et al., 2007; Wang et al., 2009; Han et al., 2009; Yang et al., 2010). These studies clearly indicate that the surface morphologies and surface structures have close relationship with specific function. Among the various insect wings, the wings of dragon fly are well known for its stability and high load-bearing capacity during flapping flight, gliding and hover, despite the fact that their mass is
∗ Corresponding author at: Nanobiotechnology Laboratory, PSG Institute of Advanced Studies, P.B. No. 1609, Peelamedu, Coimbatore 641 004, India. Tel.: +91 9944920032. E-mail addresses: [email protected], [email protected] (R. Selvakumar). 0968-4328/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2011.10.017
less than 2% of a dragonfly’s total body mass. The flapping wings of dragonfly can perform various swift and highly maneuverable flights as a result of the highly functional and largely optimized mechanical constructions of its wings. The micro and macrostructures including the veination and functions of dragonfly wings have been systematically explored for many years (Wootton, 1991; Brackenbury, 1992). Numerous studies have been carried on the dragon fly wings to find out its structural properties and its role in flight mechanism. A dragonfly’s wing has different external components such as costa, nodus and pterostigma that assist in the wing function and structure (Song et al., 2007; Li et al., 2009). The wings of dragonflies are mainly composed of network of tubular veins and membranes made up of atypical two-dimensional (2D) composite structures in micro or nano-scale (Sun et al., 2010). The membrane is very uneven and is designed in such a way that it adsorbs stress and allows deformations to occur in the membrane (Wootton, 1991; Smith et al., 2000). The membrane is made up of structural proteins and polymers such as chitin and resilin protein which predominates in the stiff and flexible parts of the wings respectively (Marrocco et al., 2009, 2010). These membrane structures are reported to determine the wings response towards various aerodynamic forces including bending and twisting of wings (Combes and Daniel, 2003). Okamoto et al. (1996) characterized the effects of camber, thickness, sharpness of the leading edge and surface roughness on the aerodynamic characteristics of dragonfly wings
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R. Selvakumar et al. / Micron 43 (2012) 1299–1303
Fig. 1. Image of a dragonfly Sympetrum vulgatum hindwing showing 4 different sections considered for analysis.
in the flow field. Zeng et al. (1996) measured the thickness and shape of dragonfly wings. Sudo et al. (2000) investigated the surface roughness of dragonfly wings. Although lot of studies have been carried out on the micro and nanostructures structures present in the dragon fly wings, very few studies have significantly reported the variation in the structures within the wing membrane surface. The present study aims to explore the presence of distinct biological nanostructures present in the wings of the dragon fly and its variation in size and shape within the wing surface. The wing was divided into four different sections (D1–D4) starting from pterostigma to the costa part and was analyzed for the presence of surface nanostructure and its arrangements using atomic force microscopy (AFM). The average size of the nanostructures, peak height and trough depth formed due to the arrangement of nanostructure were analyzed. The average roughness and skewness was also analyzed and interpreted. Based on the results, a comparative analysis has been made on the nanostructures present at different locations of the wings and the results have been interpreted.
Fig. 2. AFM image of dragon fly wing with multilayer arrangements of membrane containing nanostructures (arrows indicating the different layers arranged one over the other; circle indicating the “ripple wave morphology”).
sample and mean of the values were taken. The roughness analyses, height between two nanostructures, size of the nanostructure, and grain analysis of the sample were measured using NTMDT image analysis software. 3. Results and discussion 3.1. Atomic force microscopy of dragon flies wings
2. Materials and methods 2.1. Wing collection Dragon fly (Sympetrum vulgatum) was caught from a nearby residential area of KK nagar, Tiruchirapalli, Tamilnadu, India and the wings were separated from the dragon fly without any damage to the membrane. The wing was brought to the laboratory in a dry plastic container and used for further analysis. 2.2. Processing of dragon fly wing The hind wing (4.9 cm in length) was dissected into four equal sections (D1–D4) (Fig. 1) carefully without causing any damage and was stored in a plastic container. The dissected wing was analyzed immediately. 2.3. Atomic force microscopic study The dissected wing sections of Sympetrum vulgatum were characterized using AFM. The wing section was mounted onto a safire platform using a double sided scotch tape and inserted into the sample platform. Images were then recorded by a multimode Scanning Probe Microscope (SPM) (Ntegra Aura, NTMDT Co, Russia) at ambient condition (25 ± 2 ◦ C) using single crystal silicon N type probes (NSG 03-A) having radius of curvature of 10 nm. The cantilever with long tips (aspect ratio 3:1) with force constants of 0.35–6.06 N/m and resonance frequencies of 47–150 kHz, was used to image the surface morphology. The wings were scanned using non-contact (tapping) mode AFM in different sizes starting from 50 × 50 m and then gradually reduced the scan area to lower area size. The images were recorded from 11 different areas of each
The wing membrane is a natural biological membrane made mainly from structural proteins, whose material and mechanical properties are closely associated with the flight capacity of the insects themselves (Wootton, 1990). The membrane is not simply a barrier to the passage of air through the wing but has a structural role as a stressed skin, stiffening the frame work of veins. There is all possibility for a local variation in the mechanical properties and, hence, in the structure of the membrane within the wing, with profound implications for it’s functioning in flight (Xiao et al., 2007). Despite of these possibilities, the basic material and mechanical properties of the membrane of the insect wings, as well as its micro and nano structure, have not been understood very well (Xiao et al., 2007; Combes and Daniel, 2003). In this present study, an attempt has been made to study the nano structural arrangement of proteins and polymers in the dragon fly wings membrane. The hind wing of Sympetrum vulgatum was dissected into four sections (D1–D4) and the lateral surface was characterized using atomic force microscope in non contact mode. The inter vein distance was less in D1 region and gradually increased with D2, D3 and D4 regions of the dragon fly wing. Imaging was carried out only between the veins. The AFM analysis of the wing with higher scan area (50 m × 50 m) revealed that the membranes were assembled in multiple layers like a stacked sheets (Fig. 2, indicated using arrow mark). The surface of the wing was rough and had serrated margins. The surface of the wings also showed many deformations. Xiao et al. (2010) studied the micro and nanostructures of the dragon fly wing veins. They found interesting pleat morphologies at their surfaces having “ripple wave morphologies” looking like ripple waves with alternative peak and a trough when imaged through scanning electron microscopy. However their observations did not reveal why such
R. Selvakumar et al. / Micron 43 (2012) 1299–1303
Fig. 3. AFM image of D1 (a), D2 (b), D3 (c) and D4 (d) sections of Sympetrum vulgatum hindwing with a varying scan area (i). (ii) The 3D image of scan area.
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Table 1 Analysis of height, trough depth and size of nanostructure in various regions of the dragon fly wing membrane. S. No
Region of wing
Average ten point height (nm)
1 2 3 4
D1 D2 D3 D4
188.31 133.09 79.63 170.2
± ± ± ±
10.82 8.34 6.39 126.25
Average trough depth (nm) 70.38 95.84 50.88 71.18
± ± ± ±
40.72 36.39 22.1 23.8
Size of the nanostructure in diameter (nm) 195.08 135.85 83.25 145.2
± ± ± ±
10.25 6.02 1.79 103.01
D1–D4: four different regions in the dragonfly wing; ±: standard deviation; Values of average of 11 random measurements. Table 2 Analysis of grains parameters in various regions of the dragon fly wing membrane. S. No
Region of wing
Surface skewness (Ssk )
1 2 3 4
D1 D2 D3 D4
0.05 0.137 −0.07 0.11
± ± ± ±
0.44 0.05 0.2 0.17
Aspect ratio (m/m) 0.049 0.019 0.018 0.033
± ± ± ±
0.03 0.02 0.01 0.01
Average roughness (nm) 22.47 24.25 18.58 23.21
± ± ± ±
3.36 8.33 3.12 11.26
D1–D4: four different regions in the dragonfly wing; ±: standard deviation; Values are average of 11 random measurements.
ripple waves morphologies occur at its surface. The present investigation gives the reason for such morphologies. Fig. 2 (encircled) clearly indicates the similarity of ripple wave as observed during the investigation by Xiao et al. (2010). The stacking of the membranes one over the other and the leading edges of the stacked membranes gives this unique ripple wave morphology. Moreover the stacking is not only contributed by the membrane but also by the size and distribution of the varying nanostructures present in each membrane layer. The initial AFM imaging of D1–D4 region clearly revealed the presence of near globular nanosized particle, tightly packed one above the other (Fig. 3). By decreasing the scan area, the arrangements of nanostructures one over the other as stacks were clearly visible. The size and shape of the nanostructures varied from one region to other (Fig. 3(i) and (ii) in a–d). The area below the pterostigma (D1) showed elongated nanostructures (Fig. 3a(i)) with an average size (in diameter) of 195.08 ± 10.25 nm (Table 1). The D2 area has irregular morphology with average size of 135.85 ± 6.02 (Fig. 3b(ii)). The area below the subcosta (D3 region) showed lowest size (83.25 ± 1.79) (Fig. 3c(ii)) when compared to other region and had irregular serrated margins. D4 region showed highly varied nanostructures where few areas were dominated by larger sized nanostructures and areas with smaller one were also predominant. Among these areas selected, D1 had maximum size when compared to others. The 3D images of the scan area depicted that the height of the nanostructures also varies with the regions leading to the ripple wave morphology at the surface of the dragon fly membrane (Fig. 3(iii) in a–d). The variation in ten point height of the nanostructure in D4 region of the wing was very high when compared to other regions. The average ten point height of the nanostructure was highest in D1 region (188.31 ± 10.82) followed by D4, D2 and D3 (Table 1). The maximum height of the nanostructures in D1, D2, D3 and D4 was 200 nm, 136.6 nm, 87.55 nm and 81.88 nm with a maximum count of 132, 113, 145 and 177 respectively. Recently, Marrocco et al. (2010) reported that a large part of the wing structure of dragonfly is made of chitin protein and the joints are made of less stiff resilin protein. The nanostructures observed during the AFM analysis of the wings may be due to the arrangement of chitin and resilin molecules giving a defined structural morphology. The grain analysis of the scanned membrane nanostructures revealed variation in roughness from one region to the other (Table 2). The average roughness (arithmetic mean of the absolute values of the surface departures from the mean plane) was high in D2 region when compared to D1, D3 and D4. Skewness is a measure of the distribution of heights. Positive value of skewness indicate the presence of height values considerably above the average while
negative values indicate the presence of height values considerably below the average. Thus a flat surface with protruding feature will have a positive skewness, while a surface with deep scratches/pits will exhibit negative skewness (Eaton and West, 2010). The skewness was positive for all the regions except D3 where the skewness went negative (Table 2).
4. Conclusion The atomic force microscopy clearly indicates the presence of varying size of nanostructures at various regions of Sympetrum vulgatum wing surface. The membranes are assembled in multiple layers like stacked sheets with nanostructures resembling ripple wave morphologies. The region near the costa part showed the presence of bigger nanostructures when compared to other region. The roughness and skewness of the wing nanostructure also varied from one area to other. These nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing. The spick like edges of these nanostructures may be the reason for high performance flight by causing increase in lift force. Hence this study clearly indicates that since the distribution and arrangement of nanostructure within the wing varies which leads to varying resistance, its influence in flight mechanism should not be neglected during designing/modeling of wings.
Acknowledgement The authors are thankful to Mr. V. Parthasarathy, Senior Research Fellow, PSG Institute of Advanced Studies, Coimbatore, for helping in getting the dragonfly wings.
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