Article Cite This: ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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Shrink Films Get a Grip Amber M. Hubbard,† Elton Luong,† Ana Ratanaphruks,† Russell W. Mailen,†,‡ Jan Genzer,*,† and Michael D. Dickey*,† †
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905, United States ‡ Department of Aerospace Engineering, Auburn University, Auburn, Alabama 36849, United States
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ABSTRACT: Robotics and active materials have forged the path for grasping and manipulating delicate objects of various geometries and sizes. To date, the majority of soft robotic grippers have used hydrogels or elastomers, which can repeatably grasp and manipulate small objects. Many of these grippers achieve their grip (due to shape change) only in the presence of either solvent exposure or external pneumatic pressure. Here, we demonstrate thermoplastic polystyrene sheets that actuate from flat sheets into grippers in response to light exposure and maintain their shape upon removal of the light. Black ink patterned on the sheet converts global light illumination to localized heating that causes the planar sheet to deform into the shape of a gripper. These grippers have significantly improved endurance and strength compared to their hydrogel or elastomeric counterparts as they can support >24 000 times their own mass. These grippers release objects upon additional uniform heating, and each gripper serves as a single use device. We report the significance of sample geometry and ink patterning for controlled, localized heating upon the resulting three-dimensional shape and its impact on precision and strength. Various designs for untethered, stimuli-responsive thermoplastic grippers are presented based on targeted applications such as encapsulation. KEYWORDS: stimuli-responsive, grippers, load bearing, active materials, polymer sheets, thermoplastics, self-folding
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INTRODUCTION The ability of a material to grip or encapsulate an object without direct human intervention is important for robotics, packaging, mechanical linkages, and materials handling. Although many mechanical mechanisms exist for gripping (e.g., electrically driven hinges in robotic arms), a variety of applications motivate new, material-based approaches. Examples include soft robotics that mimic the gentleness of human touch, encapsulating materials for packaging, or materials that respond to unconventional external stimuli (e.g., pH, temperature, or magnetic fields). In recent years, hydrogels and elastomers have gained interest as candidate materials for these applications due to their pliant and flexible nature along with their responsiveness to a variety of stimuli, including pH,1−3 temperature,3−12 magnetics,5,13,14 and others.15−24 A plethora of grippers has been generated using these soft materials as they are able to grasp and lift a wide variety of objects in a reversible manner without causing any damage to the maneuvered objects.25−31 However, these materials possess inherently low stiffness and require continuous exposure to the external stimulus (i.e., solvent, pneumatic air source, etc.) to retain their shape. In contrast, stimuli-responsive thermoplastics are excellent candidates for grippers due to their cost effectiveness, relative strength, and ability to maintain shape in the absence of a stimuli. Thermoplastics (i.e., glassy polymers such as polystyrene), however, are stiffer than hydrogels and © XXXX American Chemical Society
elastomers and therefore cannot readily adapt their shape to curve around an object. Recently, we demonstrated the ability to generate controllable curvature from stimuli-responsive thermoplastic sheets via local heat delivery.32 This raises the possibility to create stimuli-responsive thermoplastic grippers. Thermoplastics represent ideal candidates for gripping devices because they are much stiffer than hydrogels or elastomers and can maintain their deformed shape after the external stimulus has been removed. In this work, we use planar, prestrained polystyrene (PS) sheets, commercially known as Shrinky-Dinks. The PS in these sheets is glassy, high molecular weight, and entangled (but not cross-linked). These sheets are shape memory polymers (SMPs) that are prestrained such that they shrink by ∼55% when heated above the glass transition temperature of PS (∼103 °C).33 Thus, upon exposure to a uniform heat source (e.g. an oven), these SMP sheets become smaller (and thicker), yet remain flat. 34 Instead, here, we shrink only portions of the surface of the sheet to achieve folding. To accomplish the localized shrinkage, we inkjet print black ink onto the surface of the PS sheets in specified patterns and remove the two-dimensional design from the sheet using either Received: February 4, 2019 Accepted: April 1, 2019
A
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Polymer Materials
Figure 1. (a) Time lapse photographs demonstrating the gripping process; the folding process, ∼10−15 s, depends on the number of panels. (b) Photographs that demonstrate the ability of the grippers to hold large blocks of wood. The mass of each painted, red block is listed in the figure. The grippers mechanically fail after days or months, as stated in the figure. The gripper is ∼0.2 g. The scale bars represent 5 mm for part a and 5 cm for part b. Logo used with permission from North Carolina State University, 2019.
Figure 2. Photographs demonstrating the four modes of gripper failure. (a) When a gripper is unable to grasp an object, it is classified as a “bad grip”. (b) If the gripper is able to grasp an object but eventually slips when sufficient force is applied, the failure is classified as “slippage”. (c) In some cases, the gripper can mechanically break. (d) If the gripper has an excellent grasp on an object, then the wire can shear through the top, unshrunk portion of the plastic. The scale bars represent 10 mm.
scissors or a laser cutter. Irradiation with an infrared (IR) light causes the inked regions of the sample to warm faster than the noninked regions. This generates a temperature-induced strain gradient across the thickness of the sheet, resulting in out-ofplane movement. Because the samples are heated above their glass transition temperature (Tg) to initiate the grasping motion, the material is compliant as it grasps the object. Removing the IR light allows the gripper to cool below Tg, locking the new shape in place. Due to the stiffness of these thermoplastic materials, these grippers can withstand significant amounts of weight without failure. In addition, the
external stimulus (i.e., the IR light) can be removed without impacting the grasp on the object. Commercial SMPs have been utilized to form snug fits around objects via shrink wrap and shrink-tubing.35 The approach here is unique because it starts with a flat, strained thermoplastic sheet (easily inkjet printable) that responds to light, locally shrinks, and curls out-of-plane to wrap itself around the object of interest. In contrast, conventional shrink wrap deforms uniformly. This paper discusses and demonstrates this new gripping mechanism. B
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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ACS Applied Polymer Materials
Figure 3. (a) A load map shows the maximum load values for samples implementing the indirect mechanism of curvature with varying panel geometry and number of panels. Regions of high and low load bearing capabilities are shown by the red and white squares, respectively. The ink patterns for samples are superimposed onto the load map. Yield graphs are also plotted, showing gripper behavior yields for triangular (b), trapezoidal (c), and rectangular (d) panel geometries. The color of the bars indicates the mechanism of failure at maximum loading.
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as a “bad grip” and can be seen in Figure 2a. “Slippage”, the second mode of failure, occurs when the gripper initially grasps the object but later the object slips, upon application of sufficient force (cf., Figure 2b). In some cases, grippers are able to grasp various objects but eventually fail due to panels breaking at the tips or tearing from the panel base (cf., Figure 2c). This third mechanism, which we call “panel breakage”, is considered as a positive outcome since it reflects the mechanical limits of the material. The ideal form of failure is “wire shearing”, which occurs when the gripper fails due to the wire shearing through the top, unshrunk portion of the gripper. In these cases, the grasp on the targeted object is so strong that the only way the gripper fails is for the wire to physically shear through the PS sheet, in which case the gripper remains securely locked around the targeted object (cf. Figure 2d). To optimize the final shape and gripping strength, we varied the ink pattern, number of panels, and panel geometry. On the basis of our previous work, we investigated two separate methods for generating curvature in these sheets known as the “indirect” and “direct” methods for generating curvature.32 For the indirect method of generating curvature, ink is placed only on 50% of the sheets surface and in specified regions; in the case of grippers, ink is placed around the outer border of each panel as seen in the inset of Figure 3a. A 50% surface area ink coverage is chosen to ensure comparable amounts of shrinkage for all ink patterns studied. Noninked regions of the polymer also absorb some IR light, resulting in a softening of the noninked material. The localized heating of the inked regions induces curvature throughout the entirety of the gripper panel based on this softening of the uninked regions coupled with the compressive force exerted by the shrinking polymer material. In contrast, in the direct mechanism of generating
RESULTS AND DISCUSSION Figure 1a demonstrates, via a series of time-lapse images, how the grippers work. The gripper lies ink-side down on the head of a hex bolt, and an IR light irradiates the sample from above. As the inked regions on the underside of the material preferentially absorb IR light and heat above the polymer’s Tg, the panels of the gripper fold downward while each panel simultaneously curves. The entire folding process takes ∼10− 20 s (cf. Video S1) depending on the number of panels implemented; samples with more panels take slightly longer. Ideally, each panel in every sample folds to the same degree and possesses similar curvature, allowing for a uniform grasp on the object.32 The relevant experimental parameters for achieving this will be discussed in a later section. As an initial demonstration of the effectiveness of the grippers, we show in Figure 1b that these grippers can support the weight of wooden blocks. The weight of an individual gripper is ∼0.2 g, and the blocks of wood being suspended in Figure 1b range in weight between 0.7 and 1.9 kg. A wire threaded through the plastic provides a facile way to hold the grippers, as seen in the lower right-hand image of Figure 1b. The lightest and heaviest blocks can be suspended by the grippers for time scales on the order of months and days, respectively, before failing. When optimized, these grippers can withstand >24 000 times their own mass for time spans on the order of minutes or ∼5000 times their own mass for time spans on the order of months. We utilized a tensile testing machine to increase the force applied to the grippers until failure occurs; four modes of gripper failure were identified. One mode of failure is when a gripper is unable to grasp the targeted object; this is classified C
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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ACS Applied Polymer Materials
Figure 4. (a) A load map shows the maximum load values for samples implementing the direct mechanism of curvature with varying panel geometry and number of panels. Regions of high and low load bearing capabilities are shown by the red and white squares, respectively. The ink patterns for samples are superimposed onto the load map. Yield graphs are also plotted showing gripper yields for triangular (b), trapezoidal (c), and rectangular (d) panel geometries. The color of the bars indicates the mode of failure at maximum loading.
desirable failure outcomes. We postulate that this result is due to more uniform deformation and gripping of each panel and represents a limitation on how much repositioning the gripper experiences during loading. Grippers with increased numbers of panels exhibit repositioning atop the grasped object upon applied force, as will be described in detail later. We performed similar strength and repeatability tests for samples implementing the direct mechanism of producing curvature. As seen in the load map (cf. Figure 4a), the maximum load values range from 8 to 48 N; the maximum load values can also be found in Table S2. Samples with fewer panels exhibit higher load capacities. When the repeatability of samples implementing the direct mechanism for generating curvature is studied, a similar trend appears where samples with fewer panels produce a higher yield of successful grips. However, the majority of samples produced with this ink pattern result in grippers failing due to a “bad grip”, as seen in Figure 4b. We postulate that this poor outcome is likely due to the grippers not fully shrinking along the outer corners of the panels; shrinkage along the corners allows the panels to wrap under the targeted object, resulting in a more conformal grip. The designs presented within Figure 4 are therefore considered less effective due to a lack of repeatability and lower load capacity. Toughness values for each gripper are reported as Figure S2 with no apparent trend emerging. To extend the parameter design space, we report the performance of grippers with only three panels; similar load maps and yield plots for three-paneled grippers are seen in Figure S3. Based on Figure S3a, the maximum load capacity ranges from 27 to 47 N. In addition, three-paneled grippers demonstrate more repeatable folding with 69% of samples failing due to “wire shearing” (cf. Figure S3b). These values validate the previously mentioned claim that grippers with
curvature, ink is placed along the entire surface of the material in a gradient fashion. In this case, we place the darkest ink along the tip of the panel, and the ink density decreases linearly toward the base of the panel. Regions of higher ink density absorb more light and thus heat more efficiently than regions that possess lower ink density. This results in a gradient of curvature throughout the panel, while a hinge at the panel base allows the panels to simultaneously fold downward. In this study, we investigated grippers with 4, 6, 8, and 10 panels in rectangular, trapezoidal, and triangular geometries. All gripper designs implementing the indirect mechanism of generating curvature are displayed in Figure 3a as an inset to each figure. For clarity, Figure S1 depicts representative gripper designs with a single panel outlined. To determine the effectiveness of the grippers, we analyzed each design based on the maximum load it can withstand. We tested a minimum of 8 grippers per design by measuring the gripper’s maximum load in an extensometer (Instron) at a strain rate of 10 mm min−1. Figure 3a reports the maximum load values with the ink patterns superimposed onto this load map; the maximum load values can also be found in Table S1. The maximum load capabilities range between 15 and 45 N. Samples with fewer panels exhibit the largest load capabilities, whereas grippers with more panels are weaker. Ideally, the panels of a gripper should simultaneously deform the same amount, which is more difficult to achieve as the number of panels increases. Figures 3b−d plot the yield for each panel geometry implementing the indirect mechanism of producing curvature. These plots demonstrate the prevalent modes of failure for each gripper design. By correlating load maps with their corresponding yield graph, we determine that grippers with fewer panels also exhibit more repeatable folding and more D
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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ACS Applied Polymer Materials
mechanism of generating curvature have a linear gradient of surface heat flux along their surface corresponding with patterns of high ink densities along the outer edge of the panels and low ink densities along the inner panel width, as seen in Figure 4a. As a result of this gradient, the maximum shrinkage occurs along the center of the panel’s outer edge instead of within the corners, as seen experimentally and verified computationally in Figures 5b, d, and f. To further test this hypothesis, we created experimental samples with axisymmetric gradients in ink density along the panels; the outermost corner of each panel has the maximum ink density. Increasing the ink density within these corners resulted in an increase in gripping repeatability and maximum load capacity. For example, when comparing the strength and repeatability of the rectangular designs within Figure 4a with their axisymmetric gradient counterparts as seen in Figure S6, both designs result in a maximum load capacity >40 N. However, samples with an axisymmetric gradient in ink density report no samples failing due to a bad grip, while 40% of samples tested with a linear gradient in ink density fail by this undesirable mechanism. Representative load−displacement curves for the rectangular and triangular paneled samples are seen in Figures 6a and b, respectively. Generally, samples with fewer panels reach higher maximum load values, while samples with more panels reach higher displacement values. We postulate the increased displacement for samples with more panels is a result of gripper repositioning during applied force. While pulling the sample at a rate of 10 mm min−1, the gripper moves on the grasped object in the form of visibly noticeable readjustments. To verify these readjustments, we took images of a gripper under increasing load (cf. Figure 6c) and correlated them to the resulting load−displacement curve in Figure 6d. The two large drops in load are mirrored by noticeable changes in position of the gripper, while smaller drops in load are mirrored by less significant readjustments. The results of Figure 6 quantify the force necessary to physically release an object. Alternatively, the grippers can release the object by uniform heating (which causes the gripper to soften and shrink back to a flat shape). Understanding this relationship between gripper design and the resulting maximum load and displacement values could allow for targeted applications. For example, if a lightweight object needs to be encapsulated, then grippers with more panels would be ideal. Alternatively, targeted objects of larger weight are more aptly suited to grippers with fewer panels. To demonstrate the encapsulation potential of these grippers, Figure S7 depicts the encapsulation of a variety of objects ranging from an acorn to a small screw. To test the endurance of the grippers, the wooden blocks seen in Figure 1b were used; grippers suspended blocks weighing 1.9 and 0.7 kg and were left undisturbed until the gripper mechanically failed due to wire shearing. In both cases, a four-paneled gripper of rectangular geometry was implemented. The block weighing 1.9 kg induced mechanical failure in the gripper after ∼72 h, while the block weighing 0.7 kg has yet to induce mechanical failure in the gripper after more than a year. Throughout the endurance test employing the 0.7 kg wooden block, the wire slowly shears through the polymer sheeting, and we anticipate the gripper will eventually fail due to wire shearing. We postulate this slower failure rate is related to the viscoelastic creep of the PS material.
fewer panels result in an increased maximum load and gripping reproducibility. It should be noted that grippers can be released from any grasped object. To do so, the gripper can be heated uniformly to temperatures >Tg.33 Sample designs shown in Figure 4 exhibit poor performance due to a lack of sufficient shrinkage along the panel’s outer corners. To verify this behavior, a finite element analysis was performed for each panel design where in Figure 5, red and
Figure 5. Finite element modeling is used to determine the shrinkage variations of the rectangular (a and b), trapezoidal (c and d), and triangular (e and f) panel geometries for ink patterns of both indirect and direct mechanisms of generating curvature. Shrinkage is defined as the change in length divided by the initial length prior to heating and is dimensionless. The shrinkage profiles indicate regions of high and low shrinkage as red and blue areas, respectively, according to the color bar in panel a. The images shown are two-dimensional projections of the curved panels depicting the shrinkage profile. The scale bar represents 5 mm.
blue regions indicate areas of high and low shrinkage, respectively.36−38 The computational results display a twodimensional projection of the strain map generated by localized heating. The geometries were based on the dimensions of a four-paneled structure where the ink patterns are seen in Figure S4 and the three-dimensional shapes are seen in Figure S5; the indirect and direct mechanism of producing curvature designs are shown in the left and righthand column of Figure 5, respectively. For designs implementing the indirect mechanism of generating curvature, a surface heat flux was applied around the outer edge of each panel to correspond to the black ink regions as seen in Figure 3a. This ink border results in maximum, and almost complete, shrinkage (∼55%) within these corners, as seen in Figures 5a, c, and e. In comparison, designs implementing the direct E
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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ACS Applied Polymer Materials
Figure 6. Load−displacement curves for both rectangular (a) and triangular (b) gripping devices that employ the indirect mechanism of generating curvature. Generally, grippers with fewer panels reach larger maximum load values, while grippers with more panels reach larger displacement values in comparison. (c) Time-lapse images of a gripper being pulled by the Instron at 10 mm min−1. This 4-panel trapezoidalgripper formed by indirect curvature undergoes several readjustments on the head of the hex bolt until eventually slipping off the bolt. The scale bar represents 2 mm. (d) The load−displacement curve which corresponds to the sample shown in panel c is plotted. Labels indicate how the sample readjustments on the bolt result in minor load drops until sample failure leads to a final and pronounced drop in load. For example, (i) depicts the gripper position when a maximum load is applied while image (ii) shows a new gripper position on the bolt after the load has been redistributed. Images (iii and iv) demonstrate a smaller repositioning of the gripper until complete mechanical failure is seen in image (v).
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CONCLUSIONS
MATERIALS AND METHODS
Experimental Section. The polymer used in all experiments is a prestrained polystyrene material, commercially known as ShrinkyDinks where the strain is imbedded prior to purchase. These substrates are 0.3 mm thick and contain a thin layer of poly(vinyl alcohol) (PVA) on the surface to aid in ink adhesion. All ink patterns are designed in CorelDRAW and are printed onto the material using an Epson Stylus C88+ inkjet printer with the corresponding black, Epson 60 ink. Scissors or a laser cutter (Universal Laser Systems VLS 3.5) were used to remove the samples from the sheet of material based on design intricacy. The sample dimensions range in size; however, the length of the panels for each design was kept constant at 10 mm. This length was chosen to ensure the panels could adequately wrap around the targeted object for a sufficient grip. In addition, the equivalent inked surface area of each panel was kept constant at 50%; this was to ensure that each panel shrinks to the same degree. Previous studies have shown that increasing the amount of inked surface area increases the amount of shrinkage experienced by the material.32 In all cases, a hot plate and a 250W IR lamp were used to activate the material, and the lamp was placed ∼5 cm above the surface of the polymer sheets. The extension tests were performed using an Instron extensometer with a strain rate of 10 mm min−1. For all mechanical tests, the grippers were tested by grasping a hex bolt where the bottom portion of the bolt was held in place by the bottom grip of the Instron. The wire, threaded through the top portion of the gripper, was held by the upper grip of the Instron and pulled at a constant strain rate. No noticeable slippage of the bolt or wire was observed within the Instron grips. Computational. We utilize a coupled, thermo-mechanical finite element framework to investigate the local shrinking behavior of thermally activated SMP sheets. This framework implements a viscoelastic material model based on experimental data obtained using a dynamic mechanical analyzer.36 The finite element framework applies representative thermal and mechanical loads to prestrain the
We report grippers produced from stimuli-responsive thermoplastic sheets which have been evaluated for strength and endurance. Experimental parameters impacting gripping strength and endurance include ink pattern, panel geometry, and the number of panels within each design. Finite element analysis of the investigated patterns indicates that samples implementing the indirect mechanism of producing curvature were able to more effectively grip the targeted object due to increased shrinkage in the corners of the panels. These thermoplastic grippers provide significantly greater strength compared with elastomeric or hydrogel-based stimuli-responsive grippers, although the gripping is not reversible. The grippers are able to withstand >24 000 times their own mass for time scales on the order of minutes and ∼5000 times their own mass for time scales on the order of months before mechanically failing. This increase in strength and endurance allows for more applications previously thought impossible due to the inherent weakness of typical stimuli-responsive gripper materials such as hydrogels or elastomers. The grippers shown here start as flat sheets and actuate into the shape of a gripper in response to light due to the presence of light absorbing black ink on the surface of the sheet. The ability to start from a completely flat sheet provides a unique and compact form factor relative to other grippers. Although the grippers here form in a simple way, it may be possible to form more complex grippers by using different colors of ink and light to control the sequence39 or through the use of patterned light.40 F
DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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ACS Applied Polymer Materials material (referred to as the prestrain sequence). During the prestrain sequence, the polymer sheet, initially at an elevated temperature, is compressed through the sheet thickness. This produces prestrain in the transverse plane. After the material is cooled, the compressive mechanical boundary condition is removed, and the material prestrain remains. The self-folding mechanism is then activated by applying a specified surface heat flux. The magnitude of this heat flux depends spatially on the local ink darkness of the experimental sample and is based on experimental measurements of heat flux produced by the IR light. Results from the computational framework agree well with experimental results.32,36 The shrinkage variations shown in Figure 5 are calculated at each node on the ink-patterned surface. At the instant shown, we determine the shrinkage between each node and other nodes that share an element edge, using the prestrained state as the reference state. Then we compute the average of these values to determine the shrinkage at each node.
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(5) Breger, J. C.; Yoon, C.; Xiao, R.; Kwag, H. R.; Wang, M. O.; Fisher, J. P.; Nguyen, T. D.; Gracias, D. H. Self-Folding ThermoMagnetically Responsive Soft Microgrippers. ACS Appl. Mater. Interfaces 2015, 7, 3398−3405. (6) Yao, S.; Cui, J.; Cui, Z.; Zhu, Y. Soft Electrothermal Actuators Using Silver Nanowire Heaters. Nanoscale 2017, 9, 3797−3805. (7) Lee, T. H.; Jho, J. Y. Temperature-Responsive Actuators Fabricated with PVA/PNIPAAm Interpenetrating Polymer Network Bilayers. Macromol. Res. 2018, 26, 659−664. (8) Chen, L.; Liu, C.; Liu, K.; Meng, C.; Hu, C.; Wang, J.; Fan, S. High-Performance, Low-Voltage, and Easy-Operable Bending Actuator Based on Aligned Carbon Nanotube/Polymer Composites. ACS Nano 2011, 5, 1588−1593. (9) Gultepe, E.; Yamanaka, S.; Laflin, K. E.; Kadam, S.; Shim, Y.; Olaru, A. V.; Khashab, M. A.; Kalloo, A. N.; Gracias, D. H.; Selaru, F. M. Biologic Tissue Sampling with Untethered Microgrippers. Gastroenterology 2013, 144, 691−693. (10) Azam, A.; Laflin, K. E.; Jamal, M.; Fernandes, R.; Gracias, D. H. Self-Folding Micropatterned Polymeric Containers. Biomed. Microdevices 2011, 13, 51−58. (11) Felton, S. M.; Tolley, M. T.; Shin, B.; Onal, C. D.; Demaine, E. D.; Rus, D.; Wood, R. J. Self-Folding with Shape Memory Composites. Soft Matter 2013, 9, 7688−7694. (12) Luo, X.; Mather, P. T. Triple-Shape Polymeric Composites (TSPCs). Adv. Funct. Mater. 2010, 20, 2649−2656. (13) Diller, E.; Sitti, M. Three-Dimensional Programmable Assembly by Untethered Magnetic Robotic Micro-Grippers. Adv. Funct. Mater. 2014, 24, 4397−4404. (14) Ghosh, A.; Yoon, C.; Ongaro, F.; Scheggi, S.; Selaru, F. M.; Misra, S.; Gracias, D. H. Stimuli-Responsive Soft Untethered Grippers for Drug Delivery and Robotic Surgery. Front. Mech. Eng. 2017, 3, 3. (15) Rus, D.; Tolley, M. T. Design, Fabrication and Control of Soft Robots. Nature 2015, 521, 467−475. (16) Bassik, N.; Brafman, A.; Zarafshar, A. M.; Jamal, M.; Luvsanjav, D.; Selaru, F. M.; Gracias, D. H. Enzymatically Triggered Actuation of Miniaturized Tools. J. Am. Chem. Soc. 2010, 132, 16314−16317. (17) Ranzani, T.; Russo, S.; Bartlett, N. W.; Wehner, M.; Wood, R. J. Increasing the Dimensionality of Soft Microstructures through Injection-Induced Self-Folding. Adv. Mater. 2018, 30, 1802739. (18) Morales, D.; Podolsky, I.; Mailen, R. W.; Shay, T.; Dickey, M. D.; Velev, O. D. Ionoprinted Multi-Responsive Hydrogel Actuators. Micromachines 2016, 7, 98. (19) Abdullah, A. M.; Li, X.; Braun, P. V.; Rogers, J. A.; Hsia, K. J. Self-Folded Gripper-Like Architectures from Stimuli-Responsive Bilayers. Adv. Mater. 2018, 30, 1801669. (20) Malachowski, K.; Jamal, M.; Jin, Q.; Polat, B.; Morris, C. J.; Gracias, D. H. Self-Folding Single Cell Grippers. Nano Lett. 2014, 14, 4164−4170. (21) Ilievski, F.; Mazzeo, A. D.; Shepherd, R. F.; Chen, X.; Whitesides, G. M. Soft Robotics for Chemists. Angew. Chem., Int. Ed. 2011, 50, 1890−1895. (22) Taylor, J. M.; Perez-Toralla, K.; Aispuro, R.; Morin, S. A. Covalent Bonding of Thermoplastics to Rubbers for Printable, Reelto-Reel Processing in Soft Robotics and Microfluidics. Adv. Mater. 2018, 30, 1705333. (23) Cafferty, B. J.; Campbell, V. E.; Rothemund, P.; Preston, D. J.; Ainla, A.; Fulleringer, N.; Diaz, A. C.; Fuentes, A. E.; Sameoto, D.; Lewis, J. A.; Whitesides, G. M. Fabricating 3D Structures by Combining 2D Printing and Relaxation of Strain. Adv. Mater. Technol. 2019, 4, 1800299. (24) Habault, D.; Zhang, H.; Zhao, Y. Light-Triggered Self-Healing and Shape-Memory Polymers. Chem. Soc. Rev. 2013, 42, 7244−7256. (25) Shintake, J.; Cacucciolo, V.; Floreano, D.; Shea, H. Soft Robotic Grippers. Adv. Mater. 2018, 30, 1707035. (26) Liu, Y.; Genzer, J.; Dickey, M. D. 2D or Not 2D”: ShapeProgramming Polymer Sheets. Prog. Polym. Sci. 2016, 52, 79−106. (27) Gracias, D. H. Stimuli Responsive Self-Folding Using Thin Polymer Films. Curr. Opin. Chem. Eng. 2013, 2, 112−119.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsapm.9b00106.
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Figures and tables containing representative designs, maximum load values, average toughness values, maximum load maps, yield plots, ink density patterns, finite element modeling, and photos of gripper designs (PDF) Video showing a six-paneled gripper with trapezoidal panels moving downward to grasp the head of a hex bolt (AVI)
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Jan Genzer: 0000-0002-1633-238X Michael D. Dickey: 0000-0003-1251-1871 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank the National Science Foundation (NSF) Emerging Frontiers in Research and Innovation (EFRI) Program (Grant 1240438). In addition, the authors recognize an NSF Graduate Research Fellowship (awarded to A.M.H.) under Grant DGE-1746939 for financial support. A.M.H. also thanks Mr. Taylor Neumann for his aid in developing the paper title.
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REFERENCES
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DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
Article
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DOI: 10.1021/acsapm.9b00106 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
