Versatile actuators based on polypyrrole-coated metalized eggshell

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Versatile actuators based on polypyrrolecoated metalized eggshell membranes Mihaela Beregoi, Nicoleta Preda, Alexandru Evanghelidis, Andreea Costas, and Ionut Enculescu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01489 • Publication Date (Web): 23 Jun 2018 Downloaded from http://pubs.acs.org on June 23, 2018

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ACS Sustainable Chemistry & Engineering

Versatile actuators based on polypyrrole-coated metalized eggshell membranes Mihaela Beregoi, Nicoleta Preda*, Alexandru Evanghelidis, Andreea Costas, Ionut Enculescu** Multifunctional Materials and Structures Laboratory, National Institute of Materials Physics, Atomistilor Str. 405A, Magurele, Bucharest, 077125, Romania *Corresponding author: [email protected] (N. Preda) ** Corresponding author: [email protected] (I. Enculescu)

KEYWORDS: multi-responsive actuator, eggshell membrane, polypyrrole, microstructured actuator, humidity-triggered actuator, biomimetic micromanipulator

ABSTRACT: Eggshell membranes were employed as biological scaffolds for developing soft and versatile actuators. A particular architecture, consisting of eggshell membrane coated with polypyrrole, has been fabricated being found to be a green, inexpensive, lightweight and easy to handle class of actuators. The polypyrrole-coated eggshell membranes devices were tested in liquid, ambient atmosphere and controlled humidity environment, the recorded movements proving their versatility. In 1 M NaCl aqueous solution, by applying successive potential pulses, the actuator contracts/expands owing to the expulsion/insertion of the electrolyte ions out/into

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polypyrrole film, producing a displacement of ~0.1 cm. In air, by applying voltages from 2 to 5 V on a V-shaped geometry actuator, it bends due to water desorption from its structure induced by Joule heating, generating a displacement which reaches ~0.4 cm at 5 V. In a chamber with controlled humidity, the decrease of humidity stimulates a bending/curling motion of the actuator, achieving a displacement of ~2.1 cm at 50% relative humidity. By modifying the humidity, these actuators move, hold and release delicate and lightweight objects. Such polypyrrole-coated eggshell membrane actuators which operate in different environments and respond to multiple stimuli can have potential applications in biomimetic micromanipulators or artificial muscles field.

INTRODUCTION In the last two decades, devices that can mimic the motility of biological systems like actuators have become very attractive for next generation applications ranging from smart household devices to artificial organs, medical micro-active tools and human-like robots [1]. Recently, actuating systems that are capable of responding to multiple external stimuli (electricity, humidity and light irradiation [2, 3], moisture, heat and light [4], NIR light and humidity [5], IR light, humidity and temperature [6], UV light, humidity and heat [7], temperature and solvent concentration [8], humidity and organic solvent type [9]) have been developed. Lucrative practical perspectives represent a drive for an increasing demand to find new materials (as building components in the actuating structures) and straightforward architectures for designing such multi-responsive actuators. Conducting polymers (CP) have been widely used as key active component materials for soft actuators owing to their intrinsic characteristics, namely low power requirements, response


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to different stimuli, flexibility, etc. [10, 11]. Being featured by a high electrochemomechanical activity, high strain and stress for various applied stimuli [10, 11], polypyrrole (PPy) is the most used CP in the fabrication of the actuators [12-19]. Besides, due to its biocompatibility, this CP is an interesting choice for biomedical applications [20-24]. An enhancement of the actuation performances (displacement, bending angle and response time) of the fabricated devices can be achieved using actuating platforms which contain high active surface structures (membranes [12, 25], tubes [13] or fibers [14]) that can facilitate the ion diffusion in the PPy films. Also in air, PPy can undergo a rapid bending due to sorption of water vapors or a contraction because of desorption of these vapors caused by Joule heating, effect induced by applying a voltage [10, 15, 26]. Usually, the actuators working in air have a tri-layer configuration consisting in two PPy films separated by an electrolyte membrane [27-30] or a solid ion source [31, 32]. Additionally, PPy can be easily obtained under different morphologies and configurations by simple chemical and electrochemical methods using low-cost raw materials [33]. From a sustainability viewpoint, nowadays there is a tendency to develop actuators using materials from regenerable sources of biological origin, vegetal or animal, such as wood [34], onion foils [35] or silk fibroin, a polypeptide isolated directly from Bombyx mori silkworm cocoons [36, 37]. As examples, actuators in a bi-layer [37] or tri-layer [36] geometry were fabricated by coating silk fibroin with PPy film through chemical polymerization [37] or electropolymerization [36] demonstrating the potential of the biopolymer scaffold as component in an actuating system. Eggshell membrane (ESM) is another natural material which is also one of the ubiquitous wastes of our daily life. Thus, at industry level egg processing, eggshells (including ESM) residue results from the egg breakage. Hitherto, the eggshells were considered to have no economic value, but now in the frame of the “circular economy” concept, the


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attention of many research groups and industrial companies has been focused on finding and/or improving routes for their potential valorization [38, 39]. Hence, the ESM can be separately collected from the eggshells and transformed into a source for the synthesis of new value-added materials by bio-inspired pathways with benefits to the economy and environment [40, 41]. The unique 3D porous interwoven fibrous protein network of the ESM is responsible for its interesting and useful properties: high porosity, large surface area, high absorption capacity and flexibility. Being biocompatible, inexpensive, abundant and easily handled, the ESM was recently taken into consideration for biomedical applications regarding its use as an immobilization platform in biosensors [42] or as a biomaterial for tissue engineering [43], wound healing [44] and cell culture [45]. In the last years, few studies were reported on the coating of the ESM with CP (e.g. polyaniline [46, 47] and PPy [46, 48]) by aqueous solution polymerization reaction, the obtained hybrid materials being used in electrocatalysis [46] and supercapacitors [48]. A priori, CP-coated ESM can be an ideal candidate for inexpensive soft actuators. Moreover, combining characteristics of both its components, PPy as actuating material and ESM as a scaffold substrate, such actuators can have major advantages in terms of biocompatibility, lightweight, abundance and low price, finding potential applications in micromanipulation devices. Despite of this aspect, to our knowledge, the development of actuating systems based on CP-coated ESM has not been reported in any studies so far. In this context, the present paper is focused on the fabrication, characterization and actuation performance in different environments (liquid and ambient or controlled humidity atmosphere) of novel, low-cost soft actuators based on PPy-coated ESM. The 3D porous interwoven network of the ESM intrinsically possesses a large surface area which can lead to an increase of the actuating system performances. A thin gold layer sputtered on the surface of the


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ESM provides the conductive surface onto which the PPy layer is deposited by a simple and cost-effective

electropolymerization

technique.

The

structural,

morphological

and

electrochemical properties of pristine ESM, metalized ESM and PPy-coated ESM were studied. The actuators consisting in strips with predetermined sizes or having two contacts V-shaped geometry were tested in 1 M NaCl aqueous solution, in ambient air by applying different voltages in order to heat the actuating system and in a controlled environment by increasing/decreasing the relative humidity. The potential applications of these devices were illustrated by their ability to manipulate delicate and lightweight objects. Thus, a new insight is provided for designing inexpensive, lightweight and flexible multi-responsive actuators using ESM (a high occurrence bio-waste) and more environmental friendly preparation routes which do not require complex apparatus favoring their scaling-up for various applications in biomimetic micromanipulators or in the artificial muscles field.

EXPERIMENTAL SECTION ESM were obtained from commercial fresh hen eggs bought from local supermarkets. The reagents used in this work, namely pyrrole (98%, Aldrich), LiClO4 (battery grade, dry, 99.99% metals basis, Sigma Aldrich), acetonitrile (≥ 99.9%, Merck) and NaCl (≥ 99.5%, Sigma Aldrich) were used as received. A schematic representation of the preparation steps is depicted in Scheme 1. Thus, initially, the eggshells (resulted from the breakage of the raw eggs) were rinsed with distilled water to remove the yolk and albumen. ESM were carefully stripped from eggshells and washed several times with distilled water for two days, to ensure the complete removal of the residual albumen and of the eggshell traces. Then, the wet ESM were mechanically gripped between two


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overlapping stainless steel frames to prevent twisting during the drying process which was carried out for 2 days, in air at ambient conditions. Next, the dried ESM were taken off from the supports and covered (on one side only) with a thin gold layer by magnetron sputtering. Being conductive, the metalized ESM (labeled as Au/ESM) can be used as working electrode in the electrodeposition of PPy. Thus, the metal covered membrane was again mechanically gripped between the overlapped stainless steel frames for contact and immersed in the deposition solution containing 0.2 M pyrrole and 0.1 M LiClO4 in acetonitrile with 2% (v/v) water content [49]. The electrodeposition was performed using a three-electrode electrochemical cell configuration: the metalized ESM as the microstructured working electrode, a platinum plate (2 cm2) as counter electrode and a commercial saturated calomel electrode (SCE) as reference. PPy was electrodeposited in a potentiostatic mode by applying 0.872 V versus SCE for 70 s. After the deposition, the metalized ESM coated with PPy (labeled as PPy/Au/ESM) were carefully rinsed with demineralized water and dried in air.

Scheme 1. Schematic representation of the steps involved in the fabrication of PPy/Au/ESM.

The properties of the prepared samples (pristine ESM, Au/ESM and PPy/Au/ESM) were investigated from a structural, morphological and electrochemical point of view. The infrared


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absorption spectra were recorded at room temperature using a Perkin Elmer Spotlight Spectrum 100 spectrometer. The morphology was evaluated by a Zeiss Merlin Compact field emission scanning

electron

microscope

(FESEM).

The

electrodeposition

and

electrochemical

characterization (cyclic voltammetry (CV) and pulse chronoamperometry) were performed with a VoltaLab PGZ100 or Parstat 2273 Princeton Applied Research potentiostats. The performance of the actuators based on PPy/Au/ESM and Au/ESM (for comparison purpose) was evaluated by tests carried out in various environments (liquid, ambient atmosphere or with controlled relative humidity). To fabricate the actuator, PPy/Au/ESM and Au/ESM samples were cut either into a strip shape or in a V-shaped geometry with dimensions of 2 cm x 0.1 cm (length x width), a schematic representation of the V-shaped geometry being given in Scheme 2.

Scheme 2. Schematic representation of the PPy/Au/ESM actuator in a V-shaped geometry tested in air by applying different voltages.

Thus, using 1 M NaCl as electrolyte, the electrochemical actuation was performed by applying successive potential pulses (-0.6 V and +0.6 V versus SCE), each having a length of 5 s. A three electrode electrochemical cell was employed with a strip shaped actuator as working electrode. The behavior in ambient atmosphere was evidenced by applying different voltages (from 2 to 5 V) on the electrical contacts of an actuator in a V-shaped geometry. The temperature of the actuator was measured by applying the heating voltages on the actuator using an FLIR A305sc infrared camera with a resolution detector of 320 x 240 pixels and "ResearchIR" software. The investigations regarding the influence of the humidity were made on an actuator in


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strip shape in a chamber with controlled relative humidity atmosphere, modifying the humidity between 84 and 20%, without applying a voltage. In all tests, the digital photos and movies were recorded using a Canon DS126201 camera.

RESULTS AND DISCUSSION The synthesis of PPy was confirmed using infrared spectroscopy, the FTIR spectra of pristine ESM and PPy/Au/ESM being shown in Figure 1a and Figure 1b, respectively.

Figure 1. FTIR spectra of pristine ESM (a) and PPy/Au/ESM (b).

The typical infrared signature of the ESM can be identified in Figure 1a namely the absorption bands situated at: i) 3310 cm-1 due to the stretching vibrations of the O-H and N-H groups; ii) 3084, 2966 and 2878 cm-1 linked to the asymmetric stretching vibrations of the C-H bond from =C-H and =CH2 groups; iii) 1686, 1560 and 1240 cm-1 attributed to amide I, amide II and amide III groups from the protein structure of ESM and associated to the vibrations of the C=O bond and the deformation vibrations of the C-N and N-H bonds; iv) 1240 cm-1 related to the stretching vibrations of the C=C bond; v) 1082 cm-1 assigned to the C-O bond and vi) 662 cm-1 due to the vibration modes of C-S bond. The assignment of these absorption bands is in accordance with previous reports in literature [41].


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The specific infrared fingerprint of PPy can be observed in Figure 1b by the absorption bands located at: i) 1698 and 1590 cm-1 assigned to stretching vibrations of the C=C and C-C bonds from the pyrrole ring; ii) 1484 cm-1 linked to the stretching vibrations of the C-N bond; iii) 1724 cm-1 related to the vibrational modes of the C=O group and correlated with the formation of a slightly over-oxidized polymer; iv) 1374 cm-1 due to the stretching vibrations of the C-N bond; v) 1252 cm-1 attributed to in plane vibrational modes of the C-H bond; vi) 1220 cm-1 characteristic to C-N vibrations; vii) 1108 cm-1 associated with the in plane deformation of the N-H bond; viii) 1062 cm-1 assigned to the vibrations of the C-H bond and linked to the in plane deformation of the pyrrole rings and ix) 816 and 954 cm-1 related to out-of-plane stretching vibrations of the C-H group. The attribution of all these absorption bands is consisted with that given in literature [50]. It has to be noticed that the FTIR spectrum of PPy/Au/ESM was recorded considering as background the Au/ESM sample in order to evidence only the characteristic absorption bands of PPy. The next step was to investigate the morphology of Au/ESM and PPy/Au/ESM, their FESEM images being displayed in Figure 2(a, a’, a’’) and Figure 2(b, b’, b’’), respectively. For the metalized membranes, the FESEM images (Figure 2(a, a’)) reveal that the ESM is uniformly covered with a continuous Au thin layer, the membrane presenting a porous structure formed by interpenetrating fibers with diameters having sizes in the micrometer range. In the case of the metalized membrane coated with PPy, the FESEM images (Figure 2(b, b’)) confirm that the deposition time involved in the electropolymerization reaction was sufficient for avoiding the embedding of the ESM fibers in a PPy thick layer, the 3D porous network of the ESM being preserved during the synthesis of the PPy. Hence, a continuous PPy film featured by a grain structure was uniformly deposited only on the fibers, in this way being maintained the large


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active surface of the ESM. A similar morphology was also observed in the case of electroactive materials based on electrospun fiber scaffolds like poly(lactic-co-glycolic acid) or cross-linked nitrile

butadiene

ruber

and

conductive

polymers

such

as

PPy

or

poly(3,

4-

ethylenedioxythiophene) [22, 51]. From the cross-sectional FESEM images (Figure 2a’’ and Figure 2b’’), the thickness of Au and PPy layers was evaluated at ~35 nm and ~75 nm, respectively.

Figure 2. FESEM images of surface (at different magnification) and cross-section morphology of Au/ESM (a, a’, a’’) and PPy/Au/ESM (b, b’, b’’).


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The electrochemical behavior of the actuator based on PPy/Au/ESM can be analyzed from data presented in Figure 3. Thus, the CV recorded in 1 M NaCl aqueous solution by varying the potential between -0.7 and +0.2 V, at various scan rates are shown in Figure 3a, the CV registered at 50 mV/s revealing one pair of peaks current (at -0.2 V and -0.45 V) associated with oxidation/reduction of the PPy film [52]. The increase of the scan rate shifts the anodic peak towards more electropositive potential values (for oxidation reactions) and the cathodic peak towards more electronegative potential values (for reduction reactions).

Figure 3. CV of PPy/Au/ESM actuating system recorded in 1 M NaCl, at different scan rates (a) and the representation of the anodic and cathodic currents versus scan rate (b). R2 is the correlation coefficient.

From Figure 3b can be observed that the relation between anodic/cathodic peaks and scan rate is a linear one, with a slope of 0.89532 (for oxidation) and 0.59985 (for reduction), therefore the redox mechanisms are characterized by adsorption (dominant in oxidation) and diffusion processes (stronger in reduction). Further, the performance of the actuator based on PPy/Au/ESM in various environments (liquid, ambient atmosphere or with controlled relative humidity) was analyzed. The electrochemical actuation of the PPy/Au/ESM in liquid was tested using an electrochemical cell with 1 M NaCl aqueous solution as electrolyte, by applying consecutive


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pulses of -0.6 V and +0.6 V, the current and potential curves recorded versus time being presented in Figure 4a and Figure 4b, respectively. The snapshots taken during the actuation process are also shown in the Figure 4. By switching the potential between -0.6 and +0.6 V, the actuator moves due to the expulsion/insertion of the electrolyte ions out/in PPy film [52, 53], consequently generating the contraction/expansion of the entire PPy/Au/ESM system (see movie S1).

Figure 4. Current versus time (a) and potential versus time (b) of the PPy/Au/ESM actuator recorded in 1 M NaCl, by applying successive potential pulses of -0.6 V and + 0.6 V. Snapshots confirming the bending movements of the actuator based on PPy/Au/ESM in liquid electrolyte.

The actuating processes can be described as follows: the structure shrinks and generates a displacement of ~0.1 cm (at -0.6 V), after which it returns to its initial position and then relaxes by performing a movement of ~0.05 cm in the opposite direction (at +0.6 V). This behavior can be explained by the stiffness of the Au/ESM substrate in the PPy/Au/ESM structure which generates a rebound during the bending movement. As expected, when the voltage is applied, no displacement was observed in the case of the Au/ESM (see movie S2).


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The performance of the actuator based on PPy/Au/ESM in a V-shaped geometry was evaluated in air, at room temperature, by applying different voltages (2, 3, 4 and 5 V) for heating the material (labeled as “on” pulse) and 0.1 V (labeled as “off” pulse) to allow continuous recording of I-V data with minimal heating. In this configuration, when the voltage is applied, the actuating structure heats up due to the Joule effect, PPy film eliminates the absorbed water and contracts. By removing the heating source, PPy film absorbs water molecules from the environment, swells and generates a displacement. The actuating mechanism has been previously reported by H. Okuzaki and T. Kunugi, where a rotor operating on this principle was proposed [26]. For comparison reason, the Au/ESM was also tested in the same experimental conditions as PPy/Au/ESM. From the chronoamperograms obtained for each mentioned applied voltage and given in Figure 5 are observed that for both Au/ESM (Figure 5a) and PPy/Au/ESM (Figure 5b), the recorded current increases with the rise of the applied voltage. Still, for samples with similar sizes, the Au/ESM system presents slightly higher current values than those recorded for PPy/Au/ESM due to the better conductivity of Au compared with PPy.

Figure 5. Currents recorded during the actuation of the Au/ESM (a) and PPy/Au/ESM (b) at 2, 3, 4 and 5 V applied voltages.


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The snapshots taken during the actuation process for PPy/Au/ESM (for each applied voltage) and Au/ESM (at 5 V) are shown in Figure 6.

Figure 6. Snapshots confirming the bending movements of the actuator based on PPy/Au/ESM in air at: 2 V, 3 V, 4 V and 5 V applied voltage. Bending motion of the Au/ESM at 5 V applied voltage.


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Thus, by applying 2 V, PPy/Au/ESM generates a displacement of ~0.2 cm (see movie S3a) which reaches ~0.3 cm at 3 V (see movie S3b). In both cases, the applied voltage is not enough to heat strongly the structure (even for longer pulses (e.g. 30 s)) and to allow the return of the actuator to its initial position when the “off” pulse is applied. A 0.1 V pulse is applied instead of cutting off the current source in order to be able to continuously record I-V data. When the voltage increases at 4 V, the displacement achieves ~0.4 cm (see movie S3c). An explanation for this result resides in a more pronounced shrinkage of the PPy film due to a stronger dehydration of the PPy which in turn is a consequence of a higher generated temperature. With the application of the "off" pulse, similar with the situations described above, the actuator does not fully return to initial position. Finally, by applying 5 V (see movie S3d), the displacement of the actuator does not increase in comparison with that already obtained at 4 V. This means that the PPy film has reached a maximum degree of desorption and a further increase of the applied voltage will not generate any larger displacements. For Au/ESM, no significant movement was observed by applying 2, 3 or 4 V. Therefore, when these three voltages are applied, the bending of the PPy/Au/ESM is entirely linked to the presence of PPy film. By applying 5 V, the Au/ESM generates a displacement of ~0.1 cm when the structure cools down (see movie S3e), in opposite direction with that observed for PPy/Au/ESM. Accordingly, at 5 V applied voltage, PPy/Au/ESM returns to its initial position because Au/ESM became active at this voltage value. Ergo, these are the best operating conditions for the actuator based on PPy/Au/ESM due to its fast reversibility (5 s for heating and 5 s for cooling the system) with the maximum displacement (~0.4 cm). For the PPy/Au/ESM actuator, in Figure 7 are shown the following representations: the measured temperature as function of the applied voltages (Figure 7a), the recorded displacement


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versus the applied voltages (Figure 7b), the evaluated input electrical power as function of the applied voltages (Figure 7c) and the recorded displacement versus the input electrical power (Figure 7d).

Figure 7. Representation for PPy/Au/ESM actuator of the: measured temperature as function of the applied voltages (a), in the inset is given the infrared camera photograph obtained at 5 V applied voltage; recorded displacement versus the applied voltages (b); input electrical power as function of the applied voltages (c); recorded displacement versus the input electrical power (d). The data regarding the Au/ESM system are also presented.

From the data recorded during the bending of the actuator by applying different voltages, the input electrical power can be estimated using the following equation: PW=E·I, where E is the


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applied voltage (2, 3, 4 and 5 V), I is the recorded current (A) and PW is the input electrical power (W) calculated for each applied voltage. The IR camera measurements showed that the temperature of the actuator rises and stabilizes after 1 minute, reaching a maximum of ~80 0C at 5 V, the recorded temperature required for actuation being sufficiently low to prevent the damage of the ESM substrate. Also, the infrared camera photograph obtained when 5 V were applied on the PPy/Au/ESM actuator is given in the inset of Figure 7a. The input electrical power values are as well elevated for Au/ESM, but for the same value of this parameter, the displacement of PPy/Au/ESM is much larger than that of the metalized membranes. All these results emphasize the importance of the PPy layer in the PPy/Au/ESM actuating system when this works in air, at room temperature, by applying different voltages, the conducting polymer having the significant contribution in the performance of the actuator. The actuation properties of the PPy/Au/ESM were investigated in an environment with controlled relative humidity. Considering the high absorption capacity of the pristine ESM, for obtaining an accurate evaluation, the snapshots taken during the actuation process for Au/ESM and PPy/Au/ESM at various relative humidity values (84, 70, 60, 50 and 20%) are presented in a comparative manner in Figure 8. The actuating process involves the sorption/desorption of the water vapors by both components of the actuator. Thus, it can be seen that at 50% relative humidity, Au/ESM barely reaches ~0.2 cm in movement (see movie S4), while PPy/Au/ESM bends (due to the contraction of PPy film) and generates a displacement of ~2.1 cm, a further decrease in the relative humidity leading to a curling movement of this actuating system (see movie S5). Once more, it is confirmed that the PPy is the active material, ESM having only a


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small contribution in the actuating process. It is worth to mention that the strip samples return to their initial position as the relative humidity increases.

Figure 8. Snapshots confirming the bending motions of the actuating system based on Au/ESM and the curling movements of the actuator based on PPy/Au/ESM during the decrease of the relative humidity from 84 down to 20%.

In order to highlight the performance of the actuator in the environment with controlled relative humidity, a representation of the displacement versus relative humidity for PPy/Au/ESM and also for Au/ESM is given in Figure 9.

Figure 9. Displacement of the Au/ESM and PPy/Au/ESM recorded during the actuation process as function of the relative humidity.


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For these humidity-triggered actuators, the most important advantage is given by the fact that the movements of the actuating systems do not imply any energy consumption (no voltage was applied in these measurements), the bending/curling of the structure being caused only by the humidity changes. Considering that no actuating systems based on conducting polymers-coated ESM have been reported until now and the data reported for the PPy based actuators triggered by similar stimuli (humidity or voltage) [15, 27, 30-32], the performances of the PPy/Au/ESM actuator in terms of generated displacement promote its application in micromanipulation devices. Consequently, the ability of the actuator based on PPy/Au/ESM to manipulate delicate and lightweight objects is illustrated in Figure 10 by two simple tests: i) a fowl feather placed on a support is pushed off by the actuator when the relative humidity is decreased from 84 down to 20% (see movie S6) and ii) a ball from a braided yellow-gold ribbon is held (at 20% relative humidity) and released (at 84% relative humidity) by the actuator (see movie S7).

Figure 10. Snapshots taken during the manipulation of lightweight objects by the actuator based on PPy/Au/ESM when the relative humidity is modified: moving a fowl feather and releasing a ball from a braided yellow-gold ribbon.


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The motion of the actuator takes place in the first case, by losing the water vapors and resulting in the shrinking of the actuating structure and in the second case, by absorbing water vapors from the surrounding environment and leading to the swelling of the actuating structure. These two designed tests emphasize the reversibility of the actuator movement. As well, they are an irrefutable proof of the potential applications of such actuators as micromanipulators, their displacements being triggered by the increase/decrease of the humidity, without consuming any additional energy. Responding to multiple stimuli, the designed PPy-coated ESM actuators can operate in liquid, ambient atmosphere and controlled humidity environment, the tests carried out in this study proving their versatility.

CONCLUSIONS Novel multi-response actuators based on PPy/Au/ESM were obtained using ESM (an inexpensive, abundant and easy to handle bio-waste) and a simple electrochemical polymerization technique. The actuating systems, in different configurations, were tested in liquid, ambient or humidity controlled atmosphere. It was shown that the actuators are able to respond to different stimuli, while the amplitude of their displacement is highly influenced by the type of environment: ~0.1 cm in 1 M NaCl aqueous solution (due to the expulsion/insertion of the electrolyte ions out/in the PPy film), ~0.4 cm in air at 5 V applied voltage (linked to the sorption/desorption of water vapors into the actuator structure caused by the Joule heating) and ~2.1 cm in a chamber with controlled humidity (resulted from the loses of the accumulated water from both material components, PPy and ESM when the humidity is decreased). Further, by modifying the relative humidity, the fabricated actuators can manipulate delicate and lightweight


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objects such as moving a fowl feather or releasing a ball from a braided yellow-gold ribbon. The major advantage of such humidity triggered-actuators consists in the fact that they can operate in air without the need of an electrolyte or other electrical energy sources. These low-cost soft actuators based on polypyrrole-coated eggshell membranes can respond to multiple external stimuli (the best performance of the actuator being achieved when humidity is used as stimulus) and consequently they can work in various environments, the versatility feature expanding their potential range of applications. ASSOCIATED CONTENT Supporting Information PPy/Au/ESM actuation in liquid electrolyte - S1 (AVI) Au/ESM in liquid electrolyte - S2 (AVI) PPy/Au/ESM actuation in ambient atmosphere at 2 V applied voltage - S3a (AVI) PPy/Au/ESM actuation in ambient atmosphere at 3 V applied voltage - S3b (AVI) PPy/Au/ESM actuation in ambient atmosphere at 4 V applied voltage - S3c (AVI) PPy/Au/ESM actuation in ambient atmosphere at 5 V applied voltage - S3d (AVI) Au/ESM actuation in ambient atmosphere at 5 V applied voltage - S3e (AVI) Au/ESM actuation in controlled humidity environment (decreasing the humidity) - S4 (AVI) PPy/Au/ESM actuation in controlled humidity environment (decreasing the humidity) - S5 (AVI) PPy/Au/ESM actuator pushing off a fowl feather placed on a support by decreasing the humidity - S6 (AVI) PPy/Au/ESM actuator releasing a ball from a braided yellow-gold ribbon by increasing the humidity - S7 (AVI)


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AUTHOR INFORMATION Corresponding Author * Nicoleta Preda, e-mail: [email protected] ** Ionut Enculescu, e-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT Authors thank to Paul Ganea for infrared measurements and to Bogdan Popescu for IR camera investigations. This work was supported by the Core Program PN18-11. Financial support from the Romanian Ministry of Research and Innovation through Operational Programme Competitiveness 2014-2020, Project: NANOBIOSURF-SMIS 103528 is also acknowledged. REFERENCES (1) Bar-Cohen, Y. Biomimetics: Nature-based innovation, CRC Press, 2011. (2) Weng, M.; Zhou, P.; Chen, L.; Zhang, L.; Zhang, W.; Huang, Z.; Liu, C.; Fan, S. Multiresponsive bidirectional bending actuators fabricated by a pencil-on-paper method. Adv. Funct. Mater. 2016, 26 (40), 7244-7253, DOI 10.1002/adfm.201602772. (3) Amjadi, M.; Sitti, M. High-performance multiresponsive paper actuators. ACS Nano 2016, 10 (11), 10202–10210, DOI 10.1021/acsnano.6b05545.


22

Page 23 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4) Mu, J.; Hou, C.; Zhu, B.; Wang, H.; Li, Y.; Zhang, Q. A multi-responsive water-driven actuator with instant and powerful performance for versatile applications. Sci. Rep. 2015, 5 (9503), DOI 10.1038/srep09503. (5) Chen, L.; Weng, M.; Zhou, P.; Zhang, L.; Huang, Z.; Zhang, W. Multi-responsive actuators based on a grapheme oxide composite: intelligent robot and bioinspired applications. Nanoscale 2017, 9 (28), 9825-9833, DOI 10.1039/C7NR01913K. (6) Gao, L.; Guo, G.; Liu, M.; Tang, Z.; Xie, L.; Huo, Y. Multi-responsive, bidirectional, and large deformation bending actuators based on borax cross-linked polyvinyl alcohol derivative hydrogel. RSC Adv. 2017, 7, 40005-40014, DOI 10.1039/C7RA06617A. (7) Qin, C.; Feng, Y.; An, H.; Han, J.; Cao, C.; Feng, W. Tetra-carboxylated azobenzene/polymer supramolecular assemblies as high-Performance multiresponsive actuators. ACS Appl. Mater. Interfaces 2017, 9 (4), 4066–4073, DOI 10.1021/acsami.6b15075. (8) Morales, D.; Podolsky, I.; Mailen, R. W.; Shay, T.; Dickey, M. D.; Velev, O. D. Ionoprinted multi-responsive hydrogel actuators. Micromachines 2016, 7 (6), 98, DOI 10.3390/mi7060098. (9) Zhao, Q.; Dunlop, J. W. C.; Qiu, X.; Huang, F.; Zhang, Z.; Heyda, J.; Dzubiella, J.; Antonietti, M.; Yuan, J. An instant multi-responsive porous polymer actuator driven by solvent molecule sorption. Nat. Commun. 2014, 5 (4293), DOI 10.1038/ncomms5293. (10) Kaneto, K. Conducting Polymers. In Soft Actuators: Materials, Modeling, Applications, and Future Perspectives, Asaka, K. Ed.; Springer, Japan, 2014. (11) Okuzaki, H. Humidity-Sensitive Conducting Polymer Actuators, In Soft Actuators: Materials, Modeling, Applications, and Future Perspectives, Asaka, K. Ed.; Springer, Japan, 2014.


23


Page 24 of 29

(12) Ismail, Y. A.; Martinez, J. G.; Otero, T. F. Polyurethane microfibrous mat templated polypyrrole: Preparation and biomimetic reactive sensing capabilities. J. Electroanal. Chem. 2014, 719, 47-53, DOI 10.1016/j.jelechem.2014.01.025. (13) Kaneto, K.; Fujisue, H.; Yamato, K.; Takashima, W. Load dependence of soft actuators based

on

polypyrrole

tubes.

Thin

Solid Films

2008, 516

(9),

2808-2812,

DOI

10.1016/j.tsf.2007.04.056. (14) Beregoi, M.; Evanghelidis, A.; Diculescu, V.; Iovu, H.; Enculescu, I. Polypyrrole actuator based on electrospun microribbons. ACS Appl. Mater. Interfaces 2017, 9 (43), 38068-38075, DOI 10.1021/acsami.7b13196. (15) Okuzaki, H.; Kuwabara, T.; Funasaka, K.; Saido, T. Humidity-sensitive polypyrrole films for electro-active polymer actuators. Adv. Funct. Mater. 2013, 23 (36), 4400-4407, DOI 10.1002/adfm.201203883. (16) Smela, E.; Inganas, O.; Pei, Q.; Lundstriim, I. Electrochemical muscles: Micromachining fingers and corkscrews. Adv. Mater. 1993, 5 (9), 630-632, DOI 10.1002/adma.19930050905. (17) Zheng, W.; Alici, G.; Clingan, P. R.; Munro, B. J.; Spinks, G. M.; Steele, J. R.; Wallace, G. G. Polypyrrole stretchable actuators. J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (1), 57-63, DOI 10.1002/polb.23177. (18) Jager, E. W. H.; Smela, E.; Inganas, O. Microfabricating conjugated polymer actuators. Science 2000, 290 (5496), 1540-5, DOI 10.1126/science.290.5496.1540. (19) Ma, M.; Guo, L.; Anderson, D. G.; Langer, R. Bio-inspired polymer composite actuator and generator

driven

by

water

gradients.

Science

2013,

309

(6116),

186-189,

DOI

10.1126/science.1230262.


24

Page 25 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Smela, E. Conjugated polymer actuators for biomedical applications. Adv. Mater. 2003, 15 (6), 481-494, DOI 10.1002/adma.200390113. (21) Wang, X.; Gu, X.; Yuan, C.; Chen, S.; Zhang, P.; Zhang, T.; Yao, J.; Chen, F.; Chen, G. Evaluation of biocompatibility of polypyrrole in vitro and in vivo. J. Biomed. Mater. Res. A 2004, 68 (3), 411-22, DOI 10.1002/jbm.a.20065. (22) Gelmi, A.; Cieslar-Pobuda, A.; de Muinck, E.; Los, M.; Rafat, M.; Jager, E. W. H. Direct mechanical stimulation of stem cells: A beating electromechanically active scaffold for cardiac tissue

engineering.

Adv.

Healthcare

Mater.

2016,

5

(12),

1471-80,

DOI

10.1002/adhm.201600307. (23) Liu, A.; Zhao, L.; Bai, H.; Zhao, H.; Xing, X. Shi, G. Polypyrrole actuator with a bioadhesive surface for accumulating bacteria from physiological media. ACS Appl. Mater. Interfaces 2009, 1 (4), 951-5, DOI 10.1021/am9000387. (24) Immerstrand, C.; Holmgren-Peterson, K.; Magnusson, K. –E.; Jager, E. W. H.; Krogh, M.; Skoglund, M.; Selbing, A.; Inganäs, O. Conjugated-polymer micro- and milliactuators for biological applications. Mater. Res. Bull. 2002, 27 (6), 461-464. DOI 10.1557/mrs2002.146. (25) Wang, J.; Botelho, S. J.; Naguib, H. E.; Bazylak, A. Development of a novel active polypyrrole trilayer membrane. ACS Sustainable Chem. Eng. 2013, 1 (2), 226–231, DOI 10.1021/sc300078v. (26) Okuzaki H.; Kunugi, T. Adsorption-induced bending of polypyrrole films and its application to a chemomechanical rotor. J. Polym. Sci. Polym. Phys. 1996, 34 (10), 1747-1749, DOI 10.1002/(SICI)1099-0488(19960730)34:103.0.CO;2-N.


25


Page 26 of 29

(27) Jager, E. W. H.; Masurkar, N.; Nworah, N. F.; Gaihre, B.; Alici, G.; Spinks, G. M. Patterning and electrical interfacing of individually controllable conducting polymer microactuators. Sens. Actuators, B 2013, 183, 283-289, DOI 10.1016/j.snb.2013.02.075. (28) Temmer, R.; Maziz, A.; Plesse, C.; Aabloo, A.; Vidal, F.; Tamm, T. In search of better electroactive polymer actuator materials: PPy versus PEDOT versus PEDOT–PPy composites. Smart Mater. Struct. 2013, 22 (10), 104006, DOI 10.1088/0964-1726/22/10/104006. (29) Gaihre, B.; Alici, G.; Spinks, G. M.; Cairney, J. M. Synthesis and performance evaluation of thin film PPy-PVDF multilayer electroactive polymer actuators. Sens. Actuators, A 2011, 165 (2), 21-328, DOI 10.1016/j.sna.2010.10.009. (30) Song, D. S.; Cho, H. –Y.; Yoon, B. –R.; Jho, J. Y.; Park, J. H. Air-operating polypyrrole actuators based on poly(vinylidene fluoride) membranes filled with poly(ethylene oxide) electrolytes. Macromol. Res. 2017, 25 (2), 135–140, DOI 10.1007/s13233-017-5022-z. (31) Khaldi, A.; Maziz, A. K. A.; Alici, G.; Spinks, G. M.; Jager, E. W. H. Bottom-up microfabrication process for individually controlled conjugated polymer actuators. Sens. Actuators, B 2016, 230, 818–824, DOI 10.1016/j.snb.2016.02.140. (32) Choi, H. –J.; Song, Y. –M.; Chung, I.; Ryu, K. –S.; Jo, N. –J. Conducting polymer actuator based on chemically deposited polypyrrole and polyurethane-based solid polymer electrolyte working in air. Smart Mater. Struct. 2009, 18 (2), 024006, DOI 10.1088/09641726/18/2/024006. (33) Vernitskaya, T. V.; Efimov, O. N. Polypyrrole: a conducting polymer; its synthesis, properties

and

applications.

Russ.

Chem.

Rev.

1997,

66

(5),

443-457,

DOI

10.1070/RC1997v066n05ABEH000261.


26

Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Rüggeberg, M.; Burgert, I. Bio-inspired wooden actuators for large scale applications. PLoS ONE 2015, 10 (4), e0120718, DOI 10.1371/journal.pone.0120718. (35) Chen, C. –C.; Shih, W. –P.; Chang, P. –Z.; Lai, H. –M.; Chang, S. –Y.; Huang, P. –C.; Jeng, H. –A. Onion artificial muscles. Appl. Phys. Lett. 2015, 106 (18), 183702, DOI 10.1063/1.4917498. (36) Fengel, C. V; Bradshaw, N. P.; Severt, S. Y.; Murphy, A. R.; Leger, J. M. Biocompatible silk-conducting polymer composite trilayer actuators. Smart Mater. Struct. 2017, 26 (5), 055004, DOI 10.1088/1361-665X/aa65c4. (37) Romero, I. S.; Bradshaw, N. P.; Larson, J. D.; Severt, S. Y.; Roberts, S. J.; Schiller, M. L.; Leger, J. M.; Murphy, A. R. Biocompatible electromechanical actuators composed of silkconducting polymer composites. Adv. Funct. Mater. 2014, 24 (25), 3866-3873, DOI 10.1002/adfm.201303292. (38) Cordeiro, C. M. M.; Hincke, M. T. Recent patents on eggshell: shell and membrane applications.

Recent

Pat.

Food

Nutr.

Agric.

2011,

3

(1),

1-8,

DOI

10.2174/2212798411103010001. (39) Vlad, V. Eggshell membrane separation method. U.S. Patent 0306354A1, December 10, 2009. (40) Park, S.; Choi, K. S.; Lee, D.; Kim, D.; Lim, K. T.; Lee, K. H.; Seonwoo, H.; Kim, J. Eggshell membrane: review and impact on engineering. Biosyst. Eng. 2016, 151, 446-463, DOI 10.1016/j.biosystemseng.2016.10.014. (41) Balaz, M. Eggshell membrane biomaterial as a platform for applications in materials science. Acta Biomater. 2014, 10 (9), 3827-3843, DOI 10.1016/j.actbio.2014.03.020.


27


Page 28 of 29

(42) Ray, P. G.; Roy, S. Eggshell membrane: A natural substrate for immobilization and detection of DNA. Mater. Sci. Eng. C – Mater. Biol. Appl. 2016, 59, 404-410, DOI 10.1016/j.msec.2015.10.034. (43) Golafshan, N.; Gharibi, H.; Kharaziha, M.; Fathi, M. A facile one-step strategy for development of a double network fibrous scaffold for nerve tissue engineering. Biofabrication 2017, 9 (2), 025008, DOI 10.1088/1758-5090/aa68ed. (44) Guarderas, F.; Leavell, Y.; Sengupta, T.; Zhukova, M.; Megraw, T. L. Assessment of chicken-egg membrane as a dressing for wound healing. Adv. Skin Wound Care 2016, 29 (3), 314, DOI 10.1097/01.ASW.0000480359.58866.e9. (45) Jia, H.; Aw, W.; Saito, K.; Hanate, M.; Hasebe, Y.; Kato, H. Eggshell membrane ameliorates hepatic fibrogenesis in human C3A cells and rats through changes in PPARcEndothelin 1 signaling. Sci. Rep. 2014, 4 (7473), DOI 10.1038/srep07473. (46) Tang, Q.; Wu, J.; Tang, Z.; Li, Y.; Lin, J.; Huang, M. Flexible and macroporous networkstructured catalysts composed of conducting polymers and Pt/Ag with high electrocatalytic activity for methanol oxidation. J. Mater. Chem. 2011, 21 (35), 13354-13364, DOI 10.1039/C1JM11857A. (47) Gao, Y.; Li, X.; Gong, J.; Fan, B.; Su, Z.; Qu, L. Polyaniline nanotubes prepared using fiber mats membrane as the template and their gas-response behavior. J. Phys. Chem. C 2008, 112 (22), 8215–8222, DOI 10.1021/jp711601f. (48) Alcaraz-Espinoza, J. J.; Pinto de Melo, C.; de Oliveira, H. P. Fabrication of highly flexible hierarchical polypyrrole/carbon nanotube on eggshell membranes for supercapacitors. ACS Omega 2017, 2 (6), 2866–2877, DOI 10.1021/acsomega.7b00329.


28

Page 29 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49) Otero, T. F.; Cortés, M. T. A Sensing Muscle. Sens. Actuators, B 2003, 96 (1-2), 152-156, DOI 10.1016/S0925-4005(03)00518-5. (50) Mollahosseini, A.; Noroozian, E. Electrodeposition of a highly adherent and thermally stable polypyrrole coating on steel from aqueous polyphosphate solution. Synth. Met. 2009, 159 (13), 1247-1254, DOI 10.1016/j.synthmet.2009.02.015. (51) Kerr-Phillips, T. E.; Woehling, V.; Agniel, R.; Nguyen, G. T. M.; Vidal, F.; Kilmartin, P.; Plesse, C.; Travas-Sejdic, J. Electrospun rubber fibre mats with electrochemically controllable pore sizes. J. Mater. Chem. B 2015, 3 (20), 249-4258, DOI 10.1039/C5TB00239G. (52) Careem, M. A.; Velmurugu, Y.; Skaarup, S.; West, K. A voltammetry study on the diffusion of counter ions in polypyrrole films. J. Power Sources 2006, 159 (1), 210-214, DOI 10.1016/j.jpowsour.2006.04.026. (53) Smela, E.; Gadegaard, N. Volume change in polypyrrole studied by atomic force microscopy. J. Phys. Chem. B 2001, 105 (39), 9395–9405, DOI 10.1021/jp004126u.

SYNOPSIS: Eggshell membrane, an abundant bio-waste, has been successfully used as platform for development of low-cost multi-responsive polypyrrole based actuators. GRAPHIC FOR MANUSCRIPT


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Versatile actuators based on polypyrrole-coated metalized eggshell

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