Name: rod-based fabrication of customizable soft robotic pneumatic gripper devices for delicate tissue manipulation
Uploaded: 2016-08-02T13:00:00
Description: Watch this Scientific Journal Video about Rod-based Fabrication of Customizable Soft Robotic Pneumatic Gripper Devices for Delicate Tissue Manipulation at JoVE.com

The research was supported by R-397-000-204-133 (National University of Singapore Young Investigator Award).

Note: All the soft pneumatic grippers were fabricated by casting silicone-based elastomeric mixtures into customized 3D-printed molds, which followed a fabrication process comprising three steps: molding gripper-arm components with embedded pneumatic channels, molding chamber component connected to the pneumatic channels, and sealing the chamber component filled with air.
1. Preparation of Elastomers
<ol>
	<li>Place a container for mixer on a weighing scale and tare it. Pour parts A and B of the silicone-based e...

<ol>
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We have successfully demonstrated that the soft robotic pneumatic gripper devices allowed compliant gripping of objects, which exerted much lower compressive forces on the gripped object than the elastomer-coated forceps tips and forceps exerted. Forceps is an essential tool for nerves manipulation during peripheral nerve repair surgeries11, 12. However, its metallic structure required extreme caution in usage from the surgeons in order to prevent nerve damage caused by excessive gripping forces and the incide...

Soft robots have sparked great research interest within the robotics community and they have been used in different functional tasks such as undulatory locomotion in unstructured environments1 and gripping2. They are mainly composed of soft elastomeric materials and controlled by different actuation techniques through the use of different materials such as electroactive polymer (EAP), shape memory alloy (SMA), or compressed fluid3. EAPs function based on a differential voltage that induces electrostatic forces to produce active strains and thereby generates actuation. The peculiar shape memory effect of the SMAs is deployed to generate the desired actuation based on the force generation during phase transformations upon the change in temperature. Lastly, compressed fluid actuation technique facilitates a simple design strategy to induce stiffness difference in the soft actuators, such that the more compliant regions will inflate upon pressurization. Soft robots are designed to broaden the applications of traditional hard robots, especially in applications where delicate objects are involved. Particularly, in this paper, we present our unique approach in developing soft robotic grippers for delicate surgical manipulation.
Surgical gripping is an important aspect involved in many surgical procedures such as hepatic, gynecological, urological, and nerve repair surgeries4, 5. It is typically performed by rigid, steel tissue gripping tools such as the forceps and laparoscopic graspers for the purpose of facilitating observation, excision, anastomosis procedures, etc. However, extreme caution is required as the conventional gripping tools are made of metal that may cause high stress concentration areas in the soft tissue at the points of contact6. Depending on the severity of the tissue damages, various complications, such as pain, pathological scar tissue formation, and even permanent disability, may result. A prior study reported that the complication rate in peripheral nerve surgery was 3%7. Therefore, the concept of soft gripping that can provide safe compliant grip can be a promising candidate for delicate surgical manipulation.
Here, we present a combination of 3D-printing and modified soft lithography techniques, which adopted a rod-based approach, to fabricate customizable soft robotic pneumatic grippers. Traditional fabrication technique of soft robots based on compressed fluid actuation requires a mold with pneumatic channels printed on it and a sealing process to seal the channels8. However, it is not feasible for miniaturized soft robots which need small pneumatic channels where occlusion of channels can easily happen in the sealing process. The traditional technique requires the sealing of the pneumatic channels to be done by bonding a coated sealing layer to it. Hence, the layer of elastomeric material which initially serves as a bonding layer may spill into the tiny channels and occlude those channels. It is also not possible to position the pneumatic channels at the middle of the structure and connect to a chamber component using conventional techniques. The proposed approach allows the creation of miniaturized pneumatic channels connected to an air-filled chamber using rods and does not require sealing of the tiny channels. In addition, the chamber connected to the pneumatic channels serve as an air source which does not require external air sources for compressed fluid actuation. It allows both the manual and robotic control modes by facilitating the chamber compression to actuate the gripping component, thereby providing users the option of controlling the amount of force that they are applying through the gripper. This approach is highly customizable and can be used to fabricate various types of soft gripper designs such as grippers with single or multiple actuatable arms.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Weighing Scale</td>
			<td>Severin</td>
			<td>KW3667</td>
			<td>(Step: Preparation of elastomers)</td>
		</tr>
		<tr>
			<td>Ecoflex Supersoft 0030 Elastomer</td>
			<td>Smooth-On</td>
			<td>EF0030</td>
			<td>(Step: Preparation of elastomers)</td>
		</tr>
		<tr>
			<td>Planetary Centrifugal Mixer and Containers</td>
			<td>THINKY USA Inc.</td>
			<td>ARE-310</td>
			<td>(Step: Preparation of elastomers)</td>
		</tr>
		<tr>
			<td>Solidworks CAD</td>
			<td>Dassault Syst&#232;mes&#160;</td>
			<td>Solidworks Research Subscription</td>
			<td>(Step: Soft single/double-actuatable arm pneumatic grippers)</td>
		</tr>
		<tr>
			<td>Objet 3D Printer</td>
			<td>Stratasys</td>
			<td>260 Connex2</td>
			<td>(Step: Soft single/double-actuatable arm pneumatic grippers)</td>
		</tr>
		<tr>
			<td>Titanium Wire Rods</td>
			<td>Titan Engineering</td>
			<td>N/A</td>
			<td>(Step: Soft single/double-actuatable arm pneumatic grippers)</td>
		</tr>
		<tr>
			<td>Natural Convection Oven with Timer</td>
			<td>Thermo Fisher Scientific</td>
			<td>BIN#ED53</td>
			<td>(Step: Soft single/double-actuatable arm pneumatic grippers)</td>
		</tr>
		<tr>
			<td>Linear Actuator</td>
			<td>Firgelli Technologies</td>
			<td>L12</td>
			<td>(Step: Insertion of soft robotic pneumatic gripper device into handling tool)</td>
		</tr>
		<tr>
			<td>Jumper Wire</td>
			<td>sgbotic</td>
			<td>CAB-01146</td>
			<td>(Step: Evaluations and grip compressive test)</td>
		</tr>
		<tr>
			<td>Force Sensing Resistor</td>
			<td>Interlink Electronics</td>
			<td>FSR402</td>
			<td>(Step: Evaluations and grip compressive test)</td>
		</tr>
	</tbody>
</table>

rod-based fabrication of customizable soft robotic pneumatic gripper devices for delicate tissue manipulation

Soft compliant gripping is essential in delicate surgical manipulation for minimizing the risk of tissue grip damage caused by high stress concentrations at the point of contact. It can be achieved by complementing traditional rigid grippers with soft robotic pneumatic gripper devices. This manuscript describes a rod-based approach that combined both 3D-printing and a modified soft lithography technique to fabricate the soft pneumatic gripper. In brief, the pneumatic featureless mold with chamber component is 3D-printed and the rods were used to create the pneumatic channels that connect to the chamber. This protocol eliminates the risk of channels occluding during the sealing process and the need for external air source or related control circuit. The soft gripper consists of a chamber filled with air, and one or more gripper arms with a pneumatic channel in each arm connected to the chamber. The pneumatic channel is positioned close to the outer wall to create different stiffness in the gripper arm. Upon compression of the chamber which generates pressure on the pneumatic channel, the gripper arm will bend inward to form a close grip posture because the outer wall area is more compliant. The soft gripper can be inserted into a 3D-printed handling tool with two different control modes for chamber compression: manual gripper mode with a movable piston, and robotic gripper mode with a linear actuator. The double-arm gripper with two actuatable arms was able to pick up objects of sizes up to 2 mm and yet generate lower compressive forces as compared to elastomer-coated and non-coated rigid grippers. The feasibility of having other designs, such as single-arm or hook gripper, was also demonstrated, which further highlighted the customizability of the soft gripper device, and it's potential to be used in delicate surgical manipulation to reduce the risk of tissue grip damage.

The soft robotic pneumatic gripper devices were capable of picking up objects with dimensions of up to 1.2 mm in diameter (Figure 6). The maximum grip compressive force generated by the single- actuatable-arm, and double- actuatable-arm soft gripper devices were 0.27 &#177; 0.07 N and 0.79 &#177; 0.14 N respectively, as compared to 1.71 &#177; 0.16 N and 2.61 &#177; 0.22 N compressive forces in simulated surgery by the elastomer-coated forceps and by uncoated forceps (<st...

Watch this Scientific Journal Video about Rod-based Fabrication of Customizable Soft Robotic Pneumatic Gripper Devices for Delicate Tissue Manipulation at JoVE.com

Rod-based Fabrication of Customizable Soft Robotic Pneumatic Gripper Devices for Delicate Tissue Manipulation

This protocol describes a rod-based approach, combining 3D-printing and soft lithography techniques for fabricating the soft gripper devices. This approach eliminates the need for an external air source by incorporating a chamber component and reduces the chance of occlusion during the sealing process, particularly for miniaturized pneumatic channels.

Soft compliant gripping is essential in delicate surgical manipulation for minimizing the risk of tissue grip damage caused by high stress concentrations ...

The overall goal of this procedure is to fabricate soft gripper devices using a rod-based approach. Combined with 3-D printing and soft lithography techniques. This method can help answer key issues faced in the fabrication of soft pneumatic grippers such as channel occlusion during the setting process and the incorporation of an air chamber.The main advantage of this technique is that it allows us to build miniaturized pneumatic channels within the soft gripper structures to ensure consistent actuation. The implication of this technique extends to what's nerve anastomosis surgery because the soft robotic gripper permits delicate nerve manipulation without over-gripping damage. We first had the idea for this method when we faced difficulty developing functional soft gripper using conventional casting sealing process and started experimenting with thin rods in the casting phase.Begin with weighing out an equal mass of the two component materials for the elastomer in a mixing vessel. Then, cover the container and load it into a centrifugal mixer along with a balancing mass. Now, run a 30 second mixing cycle with the mixing phase at 2000 RPM and the deaeration phase at 2200 RPM.Expect that the thoroughly mixed components will now cure uniformly when molded. Note that the design and production of the molds is covered in the text protocol and the next section deals with their use. This process begins with molding the gripper-arm components.First, insert the two 3-D printed chamber blocks into the left and right side of the chamber component to generate a sealed chamber with pneumatic channels connected to it. Next, insert one or two 1.5 millimeter diameter titanium wire rods through the chamber, depending on if this is a single-or double-channel model. Leave a distance of two millimeters between the gripper tip and the rod to create the pneumatic channels.Now, fully load the mold with the elastomeric mixture, ensuring no air bubbles are trapped within. Then, cure the mold at 60 degrees Celsius for 10 minutes. The next step is to pull the wire rods and the two chamber blocks out from the mold.Make certain that the connection between the pneumatic channels and the chamber is well-established, as this allows the compression of the chamber to actuate the gripper arms. Now, proceed with placing the 3-D printed gripper-block on top of the gripper component in order to create the chamber. First, insert the wire rods to block the holes in the wall of the mold.Then, fill the mold with the elastomeric mixture and ensure there are no visible air bubbles trapped in the mold. Cure this mold for 10 minutes at 60 degrees Celsius as well. Next, de-mold the cured components to assemble the gripper chamber structure.The final step is to fill the sealed chamber component with air. To do this, make the 2.5 millimeter sealing-layer that completes the assembly. Fill the mold with the elastomeric mixture and cure it at 60 degrees Celsius for 10 minutes.Once cured, brush a layer of elastomeric material on the cured 2.5 millimeter sealing-layer. Then, place the gripper chamber structure on the sealing-layer and let the bond form, making certain the seal is perfect, thus an air-filled chamber is made. Now, cure the entire structure for another 15 minutes at 60 degrees Celsius.Then remove the remaining mold to complete the device. The handling tool is also made from a mold and details are in the text protocol. Insert the gripper into the handling tool and cover the opening area with a removable rectangular cap.Then, insert a movable piston to facilitate chamber compression which completes a manual tool. Alternatively, insert the gripper and a linear actuator into a robotic handling tool. In this case, cover the opening area with a movable rectangular cap.To evaluate the functionality of the soft gripper, test it with a jumper wire. Adjust the gripper so that the wire is in between the two arms. Then, move the piston to compress the chamber which actuates the gripper arms to hold the wire.Hold and move the wire at least 20 centimeters away from the wire's original location. The proposed technique demonstrates how to quickly fabricate low-cost soft pneumatic grippers. Simply changing the mold design and using the same elastomer can make grippers for different applications.The design presented here is capable of picking up objects with dimensions of up to 1.2 millimeters in diameter. In a simulated surgery, the maximum compressive force generated by the single actuatable arm grip was around 0.27 Newtons. The double actuatable arm devices measured around 0.8 Newtons.Comparatively, forceps with and without elastomer had grip forces of about 1.7 and 2.6 Newtons respectively. Once mastered, this technique can be done in an hour if it is performed properly. While attempting this procedure, it's as important to remember to align the rods firmly before casting and perform the final sealing carefully.Following this procedure, the completed soft gripper can be attached onto a piston base or linear actuator base handling tool to allow intuitive control of the gripping. After it's development, this technique paved the way for researchers in the field of soft robotics to explore the design of chamber-gripper devices for delicate object manipulation. Don't forget that silicone-rubber can be an ingestion hazard and precautions such as wearing gloves should always be taken while performing this procedure.

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