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

Summary

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.

Abstract

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.

Introduction

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....

Protocol

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

1. Place a container for mixer on a weighing scale and tare it. Pour parts A and B of the silicone-based elastomer in the container with a 1:1 weight ratio.
2. Cover the container and measure the total weight.
3. Place the container and mater....

Results

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 ± 0.07 N and 0.79 ± 0.14 N respectively, as compared to 1.71 ± 0.16 N and 2.61 ± 0.22 N compressive forces in simulated surgery by the elastomer-coated forceps and by uncoated forceps (Figure 7

Discussion

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 surgeries^{11, 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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Weighing Scale	Severin	KW3667	(Step: Preparation of elastomers)
Ecoflex Supersoft 0030 Elastomer	Smooth-On	EF0030	(Step: Preparation of elastomers)
Planetary Centrifugal Mixer and Containers	THINKY USA Inc.	ARE-310	(Step: Preparation of elastomers)
Solidworks CAD	Dassault Systèmes	Solidworks Research Subscription	(Step: Soft single/double-actuatable arm pneumatic grippers)
Objet 3D Printer	Stratasys	260 Connex2	(Step: Soft single/double-actuatable arm pneumatic grippers)
Titanium Wire Rods	Titan Engineering	N/A	(Step: Soft single/double-actuatable arm pneumatic grippers)
Natural Convection Oven with Timer	Thermo Fisher Scientific	BIN#ED53	(Step: Soft single/double-actuatable arm pneumatic grippers)
Linear Actuator	Firgelli Technologies	L12	(Step: Insertion of soft robotic pneumatic gripper device into handling tool)
Jumper Wire	sgbotic	CAB-01146	(Step: Evaluations and grip compressive test)
Force Sensing Resistor	Interlink Electronics	FSR402	(Step: Evaluations and grip compressive test)