New research on 3D printing: 3D printing of elastic biogels for omnidirectional and extrinsic soft actuators

Researchers from the Soft Materials Laboratory of the Johann Kepler University Linz University in Austria used fused deposition3D printingwill be completely possible
biology
Degraded gelatin hydrogel (biogel) inks are printed into complex objects with dimensional stability, which can be used in the field of soft robotics.The research has been published in
Science Robotics journal (Impact factor: 23.748)

Soft robots are a new type of soft robots that can adapt to a variety of unstructured environments and interact more safely with humans. But the materials for making soft robots are often non-biodegradable, or come from non-renewable resources, which damages the ecological environment to a certain extent.In addition, traditional manufacturing methods such asmoldCasting is not suitable for reproducing the complexity of nature.Thus, inDevelop new manufacturing processesAt the same time, it is necessary to considersustainable developmentthe concept of.

This study reports a
Fused deposition
of3D printingprocess, which enables the
Fully biodegradable gelatin hydrogel (biogel) ink prints dimensionally stable complex objects
.This process can
Fast, economical and efficient
Prototype elastic soft robots, the gel can
stretched to six times its original length
and the technique has
Zero waste recycling system
. This study fabricated a fast-response (less than one second) pneumatic actuator for omnidirectional motion with a 3D-printed stretchable waveguide (waveguide: a structure used to directionally guide electromagnetic waves) capable of bulk and external perception. With dynamic real-time control, these software devices can automatically detect and clear obstacles. They can be reprinted or treated harmlessly, which has important implications for the sustainable development of soft robotics.

3D printed soft actuators with waveguide sensors. (A) Biodegradable components enable soft robotic “cradle-to-cradle” (sustainable) design (B) Three-chamber pneumatic actuator with fiber reinforcement and integrated optical sensors. Sensors detect obstacles in the actuator’s path and allow objects to move. (C) The gelatin actuator and waveguide swell and dissolve when immersed in water.

Schematic of 3D printing of biogels for soft robotics

3D printing of biogels

In soft robotics, soft and highly stretchable materials must be made. Although silicone elastomers such as polydimethylsiloxane proliferate in abundance, they are not biodegradable and, once cross-linked, cannot be reshaped or reused. Considering resource sustainability and waste reduction, elastic materials derived from biopolymers (such as gelatin), alginates or cellulose and synthetic polyesters (such as polyglycerol sebacate) have become bioavailable for many applications. The material of choice for degradable, renewable or recyclable solutions.

In this study, the researchers usedElastic but fully degradable gelatin hydrogelwhose elastic modulus hasAdjustability (0.3~3 MPa)andHigh elongation (>300%). To extrude these biogels during 3D printing, the researchers used existing extruder equipment and modified it to suit the needs of biogel printing.Contrary to the traditional need to heat the build plateFDMDifferent from fabrication, the most important thing in this experiment is to speed up the gel fabrication process by cooling the printed product to keep the shape of the extruded biogel stable.researchers willAir conditioning system connected to the print chamber for cooling, the system can reduce the print chamber temperature to about 10° to 15°C. Immediately after printing, the sample became soft (Young’s modulus of 0.27 MPa) and stretchable to about 507% of the ultimate strain, but then the sample hardened with a slight change in ductility. After 24 hours, the final strain becomes 470%, which still exceeds the strain performance of Mochiba biogel (about 140%). After 12 days of storage under ambient conditions, the biogel can still stretch to the ultimate strain above 430%, And withstand the ultimate stress of about 2.2 MPa.When comparing the printed and molded biogels, the researchers foundThe 3D printed samples had better properties, reaching higher elongation and ultimate stress.

3D printing of gelatin-based biogels. (A) Extrusion scheme of a two-stage heating system. After extrusion, the gelation is accelerated by a stream of cold air. (B) Printing a solid calibration cube. (C) A twisted bottle with a wall thickness of 0.8 mm was printed. (D) Soft structure and low Young’s modulus allow reversible deformation. (E) Resolution test, (F) The printed part can be recycled by heating and reprinting the material. (G) Changed mechanical properties due to drying at ambient conditions. (H) Young’s modulus of the samples as a function of time (J) Relative changes in mechanical properties due to gelatin degradation upon continuous heating. (K) Hysteresis of the biogel sample at 100% strain during the first two cycles. (L) Peeling energies of biogels directly printed on different substrates.

Printing of stretchable waveguide sensors

With the growing demand for device functionality, soft robots need to have self and external perception issues for controlled navigation and interaction with the environment. Stretchable waveguides can be used to solve the above problems. In particular, lossy waveguides (with or without cladding) exhibit high sensitivity to length changes when stretched. They can be achieved with various materials such as silicone elastomers, UV-curable resins or hydrogels.Among them, the gelatin substrate hasthermoplasticthis property allows it to passmelt extrusionManufacture waveguides at scale, or quickly produce waveguides by 3D printing. In this study, the researchers printed waveguides without cladding directly from the biogel ink.

3D printed omnidirectional actuator

So far, soft actuators have been used inOperationIn this study, the researchers used3D printing technologyprinted a biodegradable pneumatically actuated three-chamber actuator (16.6mm in diameter and 60mm in height. The parallel arrangement of the individual gas-filled chambers allows for omnidirectional actuation using a single pressure source and three electropneumatic pressure regulators.

Performance of multidirectional self-inductive actuators. (A) Waveguide sensors are placed on the actuator and cross each other at the top to detect bending states and touch input. (B) Step response of the bending angle of the actuator when pressurizing one of the three chambers. (C) Bending angle versus pressure characteristics for all three chambers. (D) Inferring the bending direction of the actuator from the intensity map of the waveguide. When the cavity is pressurized, the intensity drop is greatest in the nearest waveguide. (E) When the tip of the actuator (grey area in the figure) is touched, the intensity decreases on all three waveguides.

summary:

The researchers propose a 3D printed omnidirectional soft actuator made of sustainable biomaterials that enables multidirectional sensing through 3D printed soft optical waveguides. Versatile and high-precision sensors are able to sense the bending state of the actuator and its surrounding objects. This allows the soft robot to autonomously locate obstacles in its vicinity and remove them.
The researchers also noted that the waveguide’s signal output may vary. Depending on the manipulation, it is still necessary to differentiate between different stimuli (eg, bending and touching).

The main structure of the robot in this study isfully biodegradableof.Furthermore, due to the water solubility of the biogel, a simple method can be used to separate the robot from its non-biodegradable control portion, allowingReuse of the gel. The researchers also found that the biogel could be reprinted up to five times, maintaining more than 70 percent of its initial performance specification.Restore printability by rehydration of biogels, andMore repeat print cycles can be achieved by increasing the print speed to reduce the print temperature or shorten the heating cycle. In conclusion, this research is of great significance for the sustainable development of soft robots.

Note: The content of this article has been slightly adjusted, if necessary, you can view the original text.

Adapted from the original:Heiden A, Preninger D,Lehner L, et al. 3D printing of resilient biogels for omnidirectional andexteroceptive soft actuators[J]. Science Robotics, 2022, 7(63): eabk2119.

DOI: 10.1126/scirobotics.abk2119

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New research on 3D printing: 3D printing of elastic biogels for omnidirectional and extrinsic soft actuators

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