4D Printing: Enabling Technology for Microrobotics Applications

Abstract

This review demonstrates that 4D printing constitutes a key technology to enable significant advances in microrobotics. Unlike traditional microfabrication techniques, 4D printing provides higher versatility, more sophisticated designs, and a wide range of sensing and actuation possibilities, opening wide new avenues for the next generation of microrobots. It brings disruptive solutions in terms of variety of stimuli, workspaces, motion complexities, response time, function execution, and genuinely 3D microrobots. This review brings to light how soft and smart materials directly printed in 3D are particularly well suited for microrobotics requirements. This review gives an overview of 4D printing in microrobotics, highlighting advanced microrobotics requirements, fabrication methods, used smart materials, activation techniques, recent advances in the microrobotics field, and emerging opportunities.

A Tissue Adhesion‐Controllable and Biocompatible Small‐Scale Hydrogel Adhesive Robot

“…[11][12][13][14][15] Efforts have been made to develop and implement such robots, including fabrication of microscale soft robotic devices, and synthesis of biocompatible or biodegradable materials and strategies for locomotion inside the body. [16][17][18][19] However, applying these approaches have many limitations to operate safely and robustly in such complicated environments.Among various limitations, achieving strong adhesion to biological tissues whose surfaces are soft, rough, and wet is critical for the robots to efficiently implement various biomedical functions, including collecting bio-signals, bonding with unwanted derivatives and destroying them, healing wounds, and applying electrical impulses to nerves. [20][21][22][23] Although there are already commercial adhesives for tissues, the lack of long-term durability causes the failure of adhesion on the tissue.…”

“…[11][12][13][14][15] Efforts have been made to develop and implement such robots, including fabrication of microscale soft robotic devices, and synthesis of biocompatible or biodegradable materials and strategies for locomotion inside the body. [16][17][18][19] However, applying these approaches have many limitations to operate safely and robustly in such complicated environments.…”

Temperature‐Responsive 4D Liquid Crystal Microactuators Fabricated by Direct Laser Writing by Two‐Photon Polymerization

“…[ 3,6–14 ] Direct laser writing by two‐photon polymerization (DLW‐TPP), in particular, has proven suitable for inducing locally selective polymerization in various stimuli‐responsive materials. [ 3,6,9,10,15–19 ] This technique offers outstanding resolution and a high degree of freedom in structural design, [ 9,20,21 ] which has been used to generate microactuators which can perform advanced tasks such as walking, grasping, swimming, and delivering drugs among others. [ 6,8,10,15,17,22–24 ] Among the available stimuli‐responsive materials, liquid crystals (LCs) have attracted special attention for the fabrication of microactuators via DLW‐TPP as they can deliver rapid, reversible, pre‐programmed anisotropic shape deformations in both dry and wet environments.…”

NanoRobotic Structures with Embedded Actuation via Ion Induced Folding

“…In the last decade, tridimensional microfabrication has been experiencing rapid growth, and few methods have emerged, such as layer by layer stacking, [ 4–6 ] direct laser writing, [ 7–10 ] template synthesis, [ 11–13 ] and self‐assembly. [ 14–16 ] Among these methods, Focused Ion Beam Stress‐Induced Deformation (FIB‐SID) have shown great promises thanks to its ability to turn planar thin films into sophisticated volumetric structures by folding.…”