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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

This manuscript describes a 4D printing strategy for fabricating intelligent stimuli-responsive soft robots. This approach can provide the groundwork to facilitate the realization of intelligent shape-transformable soft robotic systems, including smart manipulators, electronics, and healthcare systems.

Abstract

The present protocol describes the creation of four-dimensional (4D), time-dependent, shape-changeable, stimuli-responsive soft robots using a three-dimensional (3D) bio-printing method. Recently, 4D printing techniques have been extensively proposed as innovative new methods for developing shape-transformable soft robots. In particular, 4D time-dependent shape transformation is an essential factor in soft robotics because it allows effective functions to occur at the right time and place when triggered by external cues, such as heat, pH, and light. In line with this perspective, stimuli-responsive materials, including hydrogels, polymers, and hybrids, can be printed to realize smart shape-transformable soft robotic systems. The current protocol can be used to fabricate thermally responsive soft grippers composed of N-isopropylacrylamide (NIPAM)-based hydrogels, with overall sizes ranging from millimeters to centimeters in length. It is expected that this study will provide new directions for realizing intelligent soft robotic systems for various applications in smart manipulators (e.g., grippers, actuators, and pick-and-place machines), healthcare systems (e.g., drug capsules, biopsy tools, and microsurgeries), and electronics (e.g., wearable sensors and fluidics).

Introduction

The development of stimuli-responsive soft robots is important from both technical and intellectual perspectives. The term stimuli-responsive soft robots generally refers to devices/systems composed of hydrogels, polymers, elastomers, or hybrids that exhibit shape changes in response to external cues, such as heat, pH, and light1,2,3,4. Among the many stimuli-responsive soft robots, N-isopropylacrylamide (NIPAM) hydrogel-based soft robots perform the desired tasks or interactions using spontaneous shape transformation

Protocol

The stimuli-responsive soft gripper was composed of three different types of hydrogels: non-stimuli-responsive acrylamide (AAm)-based hydrogel, thermally responsive N-isopropyl acrylamide (NIPAM)-based hydrogel, and magnetic responsive ferrogel (Figure 1). The three hydrogel inks were prepared by modifying previously published methods29,30,31. The data presented in this study are available .......

Representative Results

The NIPAM-based hydrogel was primarily considered when designing the thermally responsive soft gripper owing to its sharp LCST, which causes it to exhibit significant swelling-deswelling properties9,10. In addition, the AAm-based hydrogel was considered as a non-stimuli-responsive system to maximize the shape transformation of the soft hybrid gripper while reducing the delamination of the interface during multiple heating and cooling processes. In addition, ferro.......

Discussion

In terms of material selection for the soft hybrid gripper, a multi-responsive material system composed of a non-stimuli-responsive AAm-based hydrogel, a thermally responsive NIPAM-based hydrogel, and a magnetic-responsive ferrogel was first prepared to allow the soft hybrid gripper to exhibit programmable locomotion and shape transformation. Owing to their thermally responsive swelling-deswelling properties, NIPAM-based hydrogels exhibit bending, folding, or wrinkling when fabricated as bilayer or bi-strip structures wi.......

Acknowledgements

The authors gratefully acknowledge support from the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No.2022R1F1A1074266).

....

Materials

NameCompanyCatalog NumberComments
2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenoneSigma Aldrich410896-50GIrgacure 2959, photoinitiator
3D WOX 2Xsindohn/a3D printer for fabricating a maze
AcrylamideSigma-Aldrich29-007≥99%
Airbrush compressorWilTecAF18-2
Ammonium persulfateSigma AldrichA4418
Auto CADAutodeskn/asoftware for computer-aided-design file
BLX UV crosslinkerBIO-LINKU01-133-565
CartridgeCELLINKCSC010300102
Digital stirring Hot PlatesCorning6798-420D
Fluorescein O-methacrylateSigma Aldrich568864dye of AAm gel
INKREDIBLE+ bioprinterCELLINKn/a
Iron(III) Oxide redDUKSAN general scienceI0231
Laponite RDBYKn/ananoclay
Microcentrifuge tubeSPL60615
Micro stirrer barCowie27-00360-08Φ3×figure-materials-17600 
N, N, N', N'-tetramethylethylenediamineSigma AldrichT7024-100ML
N, N'-methylenebisacrylamideSigma AldrichM7279≥99.5%
N-isopropylacrylamideSigma-Aldrich415324-50G
Poly(N-isopropylacrylamide)Sigma-Aldrich535311
Rhodamine 6GSigma AldrichR4127dye of NIPAM gel
Slic3r software (v1.2.9)Slic3rn/aopen-source software to convert .stl file to gcode
Sodium hydroxide beadsSigma AldrichS5881
Sterile high-precision conical bioprinting nozzlesCELLINKNZ327000500122 G, 25 G
SyringeKorea vaccineK0741538910 CC 21 G (1-1/4 INCH)
Vortex mixerDAIHANDH.WVM00030

References

  1. Gracias, D. H. Stimuli responsive self-folding using thin polymer films. Current Opinion in Chemical Engineering. 2 (1), 112-119 (2013).
  2. Zhang, Y. S., Khademhosseini, A. Advances in engineering hydrogels. Science. 356

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Four dimensional PrintingStimuli responsive HydrogelSoft RobotsBioprintingAcrylamide HydrogelN isopropylacrylamide HydrogelFerrogel3D PrintingG codeDual Print Heads

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