Researchers at South Korea's Jeju National University have examined the latest research and developments in fabricating soft robots using 3D printing technologies. While 3D printing is well suited to building robots with complex external shapes with an internally porous structure, the field is still new and major challenges must be addressed in order to print multiple materials that readily adhere to each other.
Soft robots are made with highly compliant materials such as fluids, gels and polymers so they can mimic functions present in living organisms. In the last few years, there has been a significant trend toward using 3D printing for manufacturing instead of conventional molding and casting approaches.
These printing technologies convert digital data into 3D objects by adding successive layers of a material until the object is fabricated. Different types of materials are used in each approach, as are different routes for layering them. For example, researchers used 'selective laser sintering' of powdered metals to develop a multi-finger soft robotic hand that can lift, grip, spin and precisely position objects.
Other materials used to 3D print soft robots include dielectric elastomers, which are polymers that change their size and shape when stimulated by an electric field; shape memory polymers, which change their shape in response to heat; and hydrogels that are affected by a variety of stimuli including heat, electricity, acidity, magnetism and light.
Soft robots are being tested for a variety of purposes inside and outside the human body. A 3D-printed soft silicone pump could be used as an artificial heart, and 3D-printed soft "micro-biobots," which can travel through blood vessels or the gut, are being tested for monitoring diseases. Outside the body, soft robots are being developed for prosthetics, for monitoring vital signs and for organ-on-a-chip devices that can replace animals in drug testing.
But many challenges must be overcome to improve these technologies for clinical use. The materials sometimes shrink during the solidification process, and 3D printing is yet too slow for mass production.
The commercial success of these technologies, the researchers conclude, will depend on developing rapid prototypes that can lead to mass-production. Robots must also be inexpensive and satisfy market needs.
The research is published in Science and Technology of Advanced Materials.