Biocompatible hydrogel printing for soft robotic systems made easy

(Nanowerk Spotlight) Hydrogel materials possess intrinsic softness and they also exhibit other favorable properties that make them a perfect fabrication material for biomimetic soft robots: stretchability, biocompatibility, permeability, and stimuli-adaptability.
Currently, the pervasive application of hydrogels for soft robotic constructs is still hampered by two challenges. For one, conventional hydrogels usually show limited mechanical robustness. For another, the building of hydrogel-based robots typically depends on custom-designed molds and laborious post-assembly, which limits the freeform 3D structure design.
In general, there still is a lack of manufacturing schemes that can enable the rapid design of biomimetic soft robots from hydrogels with desired architectural sophistication and mechanical robustness.
Recently, the research group of Ghim Wei Ho, an Associate Professor at National University of Singapore, has developed a facile and versatile strategy to directly print hydrogels into biomimetic soft robots.
"Biocompatible alginate rheological modifier of hydrogel allows straightforward manufacturing into arbitrary 3D topologies using direct-ink-write (DIW) 3D printing," Ho explains. "Notably, the intrinsically hydrophilic alginate preserves the valuable properties of the host hydrogels, accompanied by enhanced mechanical toughness owing to the double polymer network."
Schematic illustration of DIW 3D printing hydrogels into biomimetic soft robots
Figure 1. Schematic illustration of DIW 3D printing hydrogels into biomimetic soft robots. (a) Hydrogel precursor solution photo (AAM as an example here) with the composition diagram and typical water-like rheological behavior. (b) Printable DIW ink photo (AAM DIW ink as an example here) with the composition diagram and typical gel-like rheological behavior after rheological modification. (c) Digital design and print of DIW ink (schematic) and the composition diagram after hydrogel curing. (d) Biomimetic soft robotic systems (schematic) including an artificial tentacle, a bioengineered robotic heart, and an artificial tendril. (Reprinted with permission from American Chemical Society)
Ho's team reported their findings in ACS Nano ("Direct-Ink-Write 3D Printing of Hydrogels into Biomimetic Soft Robots").
Figure 1 schematically shows the design concept of this work.
"The integration of free structures and available functionalities from diversified hydrogel family renders a rich design platform for bio-inspired fluidic and stimulus-activated robotic prototypes," first author Yin Cheng points out.
A series of representative bio-inspired fluidic and stimulus-activated robotic prototypes is shown in Figure 2 below.
Figure 2. A polyacrylamide (PAM) based artificial tentacle with 3D mobility (Figure 2a and 2b), a polyvinyl alcohol (PVA) based bioengineered robotic heart with beating-transporting functions (Figure 2c and 2d), and a poly (N-isopropylacrylamide) (PNIPAM) based artificial tendril with programmable phototropic motion (Figure 2e and 2f). (Image: Ho Research Group)
phototropic bending and anchoring of an artificial tendril
Figure 3. The phototropic bending and anchoring of the artificial tendril. (Image: Ho Research Group)
"In our work, we are targeting low-cost and low-toxicity soft materials," Ho concludes. "We are convinced that the proposed DIW printing technique could empower design freedom towards embedded intelligence soft robots, and possibly extendable to other applications i.e. wearable electronics, sensors, tissue engineering and biomedical therapeutics."
Provided as a Nanowerk exclusive by Yin Cheng and Ghim Wei Ho, Department of Electrical and Computer Engineering, National University of Singapore

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